Methyl Methacrylate Free Radical Polymerization. 111.1. Free Radical ..... laboratory for the kinetics experiments; to G. Winner and C. Rottell of the chemistry ...
GRAFT POLYMERIZATION OF METHYL METHACRYLATE ONTO POLYTETRAFLUOROETHYLENE FREE RADICALS
A Thesis Presented to The Faculty of the College of Engineering and Technology Ohio University
In Partial Fulfillment of the Requirement for the Degree Master of Science
by
Karen Ann Donato November, 1985
OHIO UNIVERSITY LIBRARY
TABLE OF CONTENTS
List of Tables •••••••••••••••••••••••••••••••••••••••••••••••••••••••• 4 Li st of Figures ••••••••••••••••••••••••••••••••••••••••••••••••••••••• 5 ~knowledgement
••••••••••••••••••••••••••••••••••••••••••••••••••••••• 9
I.
Introduction •••••••••••••••••••••••••••••••••••••••••••••••••••10
II.
Radiation Effects on Polytetrafluoroethylene
III.
IV.
11.1.
Effects of Radiation on the Structure of Polymers •••••• 12
11.2.
The Structure of Polytetrafluoroethylene ••••••••••••••• 13
11.3.
Effects of Radiation on the Structure of Polytetrafluoroethylene •••••••••••••••••••••••••••••••• 15
Methyl Methacrylate Free Radical Polymerization 111.1.
Free Radical Chain Polymerization •••••••••••••••••••••• 19
111.2.
Methyl Methacrylate Homopolymerization ••••••••••••••••• 21
111.3.
~l
Effect ••••••••••••••••••••••••••••••••••••••••••••• 22
Experimental Apparatus and Procedures IV.l.
Kinetics Experiments ••••••••••••••••••••••••••••••••••• 24
IV.2.
Infrared Transmittance Measurements •••••••••••••••••••• 26
IV.3.
Electron Spin Resonance Measurements ••••••••••••••••••• 28
IV.4.
Differential Scanning Calorimetry •••••••••••••••••••••• 28
2
V.
Results
V.I.
VI.
Kinetics Data•••••••••••••••••••••••••••••••••••••••••• 30
V.I.a.
Effects of Preheating the Monomer ••••••••••••••••• 30
V.I.b.
Effects of PTFE:MMA Ratio ••••••••••••••••••••••••• 31
V.I.c
Effects of Temperature•••••••••••••••••••••••••••• 32
V.I.d
Effects of Hydroquinone ••••••••••••••••••••••••••• 32
V.I.e
Effects of Different Grades of PTFE ••••••••••••••• 33
V.I.f
Extractions ••••••••••••••••••••••••••••••••••••••• 34
V.2.
DSC Scans •••••••••••••••••••••••••••••••••••••••••••••• 34
V.3.
Fourier Transform Infrared Scans••••••••••••••••••••••• 35
V.4.
Electron Spin Resonance •••••••••••••••••••••••••••••••• 35
Discussion of Results
VI.I.
Kinetics Results ••••••••••••••••••••••••••••
e ••••••••••
37
VI.I.a.
Development of Kinetics Equations ••••••••••••••••• 37
VI.I.b.
Temperature Effects ••••••••••••••••••••••••••••••• 43
VI.I.c.
Ratio Effects ••••••••••••••••••••••••••••••••••••• 44
VI.I.d.
Gel Effect at 353K(80°C) •••••••••••••••••••••••••• 45
VI.I.e.
Comparison with Literature Values ••••••••••••••••• 47
VI.2.
DSC Results •••••••••••••••••••••••••••••••••••••••••••• 49
VI.3.
FTIR Results ••••••••••••••••••••••••••••••••••••••••••• 51
VI.4.
Electron Spin Resonance •••••••••••••••••••••••••••••••• 52
3
VII
Properties of the PMMA-PTFE Graft
VII.I.
Physical Appearance •••••••••••••••••••••••••••••••••••• 53
VII.2.
Stability •••••••••••••••••••••••••••••••••••••••••••••• 53
VII.3.
Moldability •••••••••••••••••••••••••••••••••••••••••••• 53
VII.4.
Possible Applications of the Graft Polymer ••••••••••••• 54
VIII Summary
VIII.!. Conclusions •••••••••••••••••••••••••••••••••••••••••••• 57 VIII.2. Recommendations for Future Work •••••••••••••••••••••••• 60
References ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 63
Appendices ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 67
A.
Properties of Methyl Methacrylate •••••••••••••••••••••• 67
B.
Properties of Polytetrafluoroethylene •••••••••••••••••• 68
c.
Summary of Variables ••••••••••••••••••••••••••••••••••• 69
D.
Experiment Codes ••••••••••••••••••••••••••••••••••••••• 70
E.
Sample Codes ••••••••••••••••••••••••••••••••••••••••••• 71
~stract
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 112
4
List of Tables
Table
Page
1.
Experiment 3: Reaction data at 333K(60°C) with 1 gram PTFE(L-169):3 milliliters MMA(DuPont) at room temperature •••••••••••••••••••••••••••••••••••••••••••••• 72
2.
Experiment 4: ~eaction data at 133K(60°C) with 1 gram PTFE(L-169):3 milliliters MMA(DuPont) at the reaction temperature •••••••••••••••••••••••••••••••••••••••••• 7~
3.
Experiment 5: Reaction data at 333K(60°C) with 1 gram PTFE(L-16Q):5 milliliters MMA(DuPont) at the reaction temperature •••••••••••••••••••••••••••••••••••••• 73
4.
Experiment 6: Reaction data at 353K(80°C) with 1 gram 'PTFE(L-169):3 milliliters MMA(DuPont) at the reaction temperature •••••••••••••••••••••••••••••••••••••• 73
5.
Experiment 7: Effects of hydroquinone on postpolymerization:reaction data at 353K(80°C) with 1.5 gram PTFE(L-169):2 milliliters MMA(Fisher) at the reaction temperature •••••••••••••••••••••••••••••••••••••• 74
6.
Experiment 8: Reaction data at 343K(70°C) with 2 grams PTFE(Polymist~ F 5-A):5 milliliters MMA at 273.2K(O.2°C) ••••••••••••••••••••••••••••••••••••••••••••••••• 74
7.
Experiment 9: Reaction data at approximately 353K(80°C) with different ratios of PTFE( L-171) : MMA( Fi sher) ••••••••••••••••••••••••••••••••••••••• 74
8.
Residue after evaporation of the acetone used for extractions ••••••••••••••••••••••••••••••••••••••••••••••• 75
9.
Results of DSC Scans•••••••••••••••••••••••••••••••••••••••••• 75
10.
Mass Ratios of PMMA to PTFE in the graft polymer as determined by FTIR ••••••••••••••••••••••••••••••••••••••••• 76
11.
Kinetics constants and linear correlation coefficents as defined by equation VI.1.19 •••••••••••••••••••• 76
5
List of Figures Figure
Page
1.
Schematic diagram of a crystalline sheet of sintered PTFE(not to scale). The striation length includes amorphous material on the hexagonal faces formed by chain ends, irregular folds, and tie molecules (from Reference 9) •••••••••••••••••••••••••••••••••••••••••••••••••• 77
2.
Models of the PTFE chain above and below the 292K(19°C) transitions(from Reference 8) ••••••••••••••••••••••••••••••••• 77
3.
Experiment 3: Conversion(%) vs. time(min.) at 333K(60°C) with 1 gram PTFE(L-169):3 milliliters MMA(OuPont) at room temperature ••••••••••••••••••••••••••••••• 78
4.
Experiment 4: Conversion(%) vs. time(min.) at 333K(60°C) with 1 gram PTFE(L-169):5 milliliters MMA(OuPont) at the reaction temperature ••••••••••••••••••••••• 79
5.
Experiment 5: Conversion(%) vs. time(min.) at 333K(60°C) with 1 gram PTFE(L-169):5 milliliters . MMA(OuPont) at the reaction temperature •••••••••••••••••••••••80
6.
Experiment 6: Conversion(%) vs. time(min.) at 353K(80°C) with 1 gram PTFE(L-169):3 milliliters MMA(OuPont) at the reaction temperature •••••••••••••••••••••••81
7.
Experiment 7: Effects of hydroquinone on post polymerization: conversion(%) vs. time(min.) at 353K(80°C) with 1.5 gram PTFE(L-169):2 milliliters MMA(Fisher) at room temperature •••••••••••••••••••••••••••••••82
8.
Experiment 8: Conversion(%) vs. time(min.) at 343K(70°C) with 2 grams PTFE(Polymist® F5-A):5 milliliters MMA(OuPont) at 273.2K(O.2°C) ••••••••••••••••••••••83
9.
Experiment 8: Conversion(%) vs. 1n time(min.) at 343K(70°C) with 2 grams PTFE(Polymist® F-5A): 5 milliliters MMA(OuPont) at 273.2K(O.2°C) ••••••••••••••••••••84
10.
FTIR scan of the residue in the acetone after extraction of graft sample 80-145B made at 353K(80°C) for 145 minutes with 1 gram PTFE(L-169):3 milliliters MMA(OuPont) at the reaction temperature ••••••••••••••••••••••• 85
6
List of Figures (continued)
11.
DSC scan of L-169 •••••••••••••••••••••••••••••••••••••••••••••86
12a.
OSC scan of graft sample 80-558 made at 353K(80°C) for 55 minutes with 1 gram PTFE(L-169):3 milliliters MMA(DuPont) at the reaction temperature; first run of melting and recrystallization ••••••••••••••••••••••••••••••87
12b.
OSC scan of 80-558 (same sample as in figure 12a); second run of melting and recrystallization •••••••••••••••••••88
12c.
Duplicate DSC run of the sample 80-558 used in figure 12a ••••••••••••••••••••••••••••••••••••••••••••••••••••89
13a.
DSC scan of graft sample 80-908 made at 353K(80°C) for 90 minutes with 1 gram PTFE(L-169):3 milliliters MMA(OuPont) at the reaction temperature •••••••••••••••••••••••90
13b.
Duplicate DSC run of sample 80-908••••••••••••••••••••••••••••91
14a.
FTIR scan of graft sample 80-1A produced at 353K(80°C) for 1 minute at 1 gram PTFE(L-169):3 milliliters MMA(OuPont) at the reaction temperature ••••••••••••••••••••••• 92
14b.
FTIR scan of graft sample 80-3A produced at 353K(80°C) for 3 minutes at 1 gram PTFE(L-169):3 milliliters MMA(OuPont) at the reaction temperature •••••••••••••••••••••••93
14c.
FTIR scan of graft sample 80-20A produced at 353K(80°C) for 20 minutes at 1 gram PTFE(L-169):3 milliliters MMA(OuPont) at the reaction temperature ••••••••••••••••••••••• 94
14d.
FTIR scan of graft sample 80-55A produced at 353K(80°C) for 55 minutes at 1 gram PTFE(L-169):3 milliliters MMA(OuPont) at the reaction temperature •••••••••••••••••••••••95
14e.
FTIR scan of graft sample 80-145A produced at 353K(80°C) for 145 minutes at 1 gram PTFE(L-169):3 milliliters MMA(DuPont) at the reaction temperature ••••••••••••••••••••••• 96
14f.
FTIR scan of graft sample 80-1458 produced at 353K(80°C) for 145 minutes at 1 gram PTFE(L-169):3 milliliters MMA(DuPont) at the reaction temperature ••••••••••••••••••••••• 97
15.
FTIR scan of L-169 •••••••••••••••••••••••••••••••••••••••••••• 98
7
List of Figures (continued)
103) ••••••••••••••••••••••••••••••••99
16a.
ESR scan of L-169.(Gain
16b.
ESR scan of the same L-169 sample as in figure 16a, taken 2 months later.(Gain = 103) •••••••••••••••••••••••••••••99
17a.
ESR scan of Polymist® F-5A.(Gain
17b.
ESR scan of the same Polymist® F-5A sample as in figure 17a, taken 2 months later.(Gain = 2 x 102) •••••••••••• 100
18.
ESR scan of sample 55A run at 353K(80°C) for 55 minutes with 1 gram PTFE(L-169):3 milliliters MMA(DuPont) at the reaction temperature. Curve 1 corresponds to a scan with DPPH in the reference cavity. Curve 2 corresponds to a scan without the DPPH in the reference cavity. (Gain = 104) •••••••••••••• 101
19.
FTIR scan of sample RT-55A produced at room temperature with 1 gram PTFE(L-169):3 milliliters MMA(DuPont) at room temperature •••••••••••••••••••••••••••••• l02
20.
FTIR scan of sample 40-55A produced at 311K(40°C) with 1 gram PTFE(L-169):3 milliliters MMA(OuPont) at the reaction temperature •••••••••••••••••••••••••••••••••• 103
,21.
Application of equation VI.1.19. to experiment 3; reaction data at 333K(60°C) with 1 gram PTFE(L-169): 3 milliliters MMA(DuPont) at room temperature •••••••••••••••• l04
22.
Application of equation VI.l.19. to experiment 4; reaction data at 333K(60°C) with 1 gram PTFE(L-169): 3 milliliters MMA(DuPont) at the reaction temperature •••••••• 105
23.
Application of equation VI.1.19. to experiment 5; reaction data at 333K(60°C) with 1 gram PTFE(L-169): 5 milliliters MMA(DuPont) at room temperature •••••••••••••••• 106
24.
Application of equation VI.l.19. to exper;~ent 6; reaction data at 353K(80°C) with 1 gram PTFE(L-169): 3 milliliters MMA(DuPont) at the reaction temperature •••••••• 107
=
=
2 x 102) •••••••••••••••••• 100
8
List of Figures (concluded)
25.
Application of equation VI.1.19. to experiment 8; reaction data at 343K(70°C) with 2 gram PTFE(Polymist® F5-A):5 milliliters MMA(DuPont) at 272.2K(O.2°C) ••••••••••••••••••••••••••••••••••••••••••••• 108
26.
Schematic of the grafting of MMA on to the PTFE free radical matrix •••••••••••••••••••••••••••••••••••••••••• 109
27.
~ Hmelting of the graft polymer vs. gram graft/gram PTFE. Data were obtained from DSC scans in figures 11 - 13•••••••••••••••••••••••••••••••••••••••••••••••••••••• 110
28.
~ Hcrystallization of the graft polymer vs. gram graft/ gram PTFE. Data were obtained from DSC scans in figures 11 - 13••••••••••••••••••••••••••••••••••••••••••• 111
9
ACKNOWLEDGEMENT
Special thanks are extended to Carleton A. Sperati for guidance and encouragement throughout the course of this research. Thanks are also due to several members of the Ohio University Chemistry Department: to Professor C. C. Houk, for use of his laboratory for the kinetics experiments; to G. Winner and C. Rottell of the chemistry department staff for helping to arrange and maintain the experimental apparatus; to Professor P. D. Sullivan for running and helping to interpret electron spin resonance scans; and to Professor R. R. Williams for use of his Fourier Transform Infrared Spectrometer and his help in interpreting the IR scans. In addition, acknowledgement is made to those people who supplied experimental materials:
R. G. Alsup, formerly of DuPont, for methyl
methacrylate monomer; A. Matthews of ICI Americas for Fluon® micropowder; and F. Fifoot of Allied for Polymist® micropowder. Most sincere thanks and graditude are extended to my husband, Bruce, for his support and sacrifices throughout the course of this work and for typing, analyzing, and proofreading this manuscript.
10
PART I Introduction
Copolymers are being developed to augment and enhance the favorable properties of each of their constituents.
Among the many
requirements for these new materials are better environmental resistance, easy processability and machinability, low cost, and a quality appearance. Polytetrafluoroethylene (PTFE), a highly crystalline polymer, is a chemically inert material used in such diverse applications as metal coatings, textile fibers, pipe liners, and wire and cable insulation. •
When sintered and then subjected to ionizing radiation, the PTFE degrades to a micropowder that has found extensive use as a lubricant.
This micropowder contains PTFE free radicals that have a
very long lifetime due to being trapped in the crystalline matrix. Poly(methyl methacrylate) (PMMA) and its homologs are easily processed polymers that can be melt extruded or molded under heat and presssure.
PMMA is best known for its optical qualities and is a
primary component of safety glass and lighting covers.
It recently
has found favor as an architectural material for use in kitchens and bathrooms. The purpose of this research was to use the PTFE free radicals in commercially available micropowder to initiate methyl methacrylate (MMA) polymerization.
Since the PTFE free radicals have a high
molecular weight, the material resulting from this research is a graft
11
polymer of PTFE and PMMA.
Because the steady state assumption in the
theory of free radical polymerization does not apply to this system, a kinetics mechanism was developed to explain the production of the block copolymer.
The amount of graft produced was determined
gravimetrically, and data were substantiated by Differential Scanning Calorimetry and Fourier Transform Infared Analysis
The kinetics model
developed fi,t the data well and its assumptions were supported by electron spin resonance scans. Of special interest are the properties of this graft copolymer, including its stability aand appearance.
Samples were molded in a
press to qualify its machinability and strength.
12
PART II Radiation Effects on Polytetrafluoroethylene
Effects of Radiation on the Stucture of Polymers
11.1
When exposed to high energy radiation (Y -rays, x-rays, electron beams, etc.), polymer chains undergo two types of reactions: 1) crosslinking, leading to the formation of an infinite network; or
2) scission, resulting in shorter, lower molecular weight chains(l). For some polymers, both reactions occur simultaneously(l), usually with one predominating due to the effects of temperature(2,3), oxygen(l), or other materials(4). For most polymers which crosslink upon irradiation: •
Each carbon of the main chain carries at least one hydrogen atom, the repeat unit being H :1
-[- CH2- C-]1 R
n
Polymers such as polyethylene, polypropylene, polystyrene and polyesters are in this category. •
The molecular weight of the polymer increases with dose, due to branching.
This results in the formation of a gel which
is insoluble in the polymer1s normal solvents. •
Radicals form at adjacent sites to allow cross-linking to occur(l).
13
For those polymers which degrade after radiation exposure: •
A tetrasubstituted carbon is present in the main chain, the repeat unit being
R' t
-C- CX2- C-JI n R where X = H, F, or OH.
Polymers which have this structure
include poly(methyl methacrylate), polytetrafluoroethylene, cellulose and poly(iso-butylene).
Strain in the molecule due
to steric repulsion weakens the C-C bond, allowing scission to occur(1,3). •
The molecular weight of the polymer decreases with dose as random chain scissions occur.
The molecular weight can
decrease enough that the polymer is degraded to a very viscous liquid(l,3). •
Melting temperatures may decrease due to the lower molecular weight of the material(5).
•
Recombination is dependent upon the mobility of the radicals.
Radicals can recombine if they remain close enough
(cage effect) or diffuse to within a distance that allows termination to occur(6).
11.2.
The Structure of Polytetrafluoroethylene
Polytetrafluoroethylene (PTFE) is a high molecular weight homopolymer of tetrafluoroethylene with a repeat unit of
14
Typical methods of molecular weight determination are not suitable for PTFE since it does not dissolve in common solvents (7,8,9). Radioactive end group counts and a standard specific gravity test (ASTM 01457)(8) set the molecular weight of commerical PTFE at 106 107(7,8,9). PTFE is well known for its resistance to chemical attack.
Only
alkalai metals, fluorine, and strong fluorinating agents at elevated temperature and pressure will cause degradation(9).
This chemical
resistance is due to the high C-F bond strength, which has a dissociation energy of 460 kJ/mole (8). PTFE is believed to be a linear, unbranched, non-crosslinked polymer due to its sharp melting point (608-618 kelvins(335 - 345°C) for virgin resin and 600K for sintered material), high degree of crystallinity (93-98 per cent) as polymerized, and its ability to be oriented (8,9,10).
The molecules assume a helical conformation and
fold back on themselves at regular intervals to form a crystalline structure of hexagonal thin sheets, about 1.0 microns thick, with the molecular segments normal to the sheets (Figure 1)(9).
Chains in the
crystalline region pack tightly and have a higher density of 2.3 Mg/m 3(2.3 g/cm3), compared to the randomly oriented chains in the amorphous phase with a density of 2.0 Mg/m 3(2.3 g/cm3)(8,10).
The crystalline part of the polymer undergoes solid state transitions at 292K(19°C) and 303K(30°C).
The amorphous region is
15
unaffected by these transitions(9).
The two transitions combined
result in about a 1 per cent increase in the density upon heating. At 292K, the helical structure of the PTFE chain changes from 13 to 15 carbon atoms per 1800 twist and from 1.69 nm to 1.95 nm per repeat unit(9) (Figure 2).
Between 292K and 303K, chain segments
become disordered from the perfect hexagonal structure (as shown in Figure 1) by small angular displacements about the longitudinal axis. Above 303K, molecular segments oscillate along the longitudinal axis. Higher temperatures cause the chain to twist and untwist.
Even above
its melting point of 600K(327°C), the sintered polymer retains much of its crystalline structure(8).
Properties of PTFE are summarized in
Appendix A.
11.3.
Effects of Radiation on the Structure of Polytetrafluoroethylene
Despite its chemical stability, PTFE degrades readily upon exposure to ionizing radiation.
This degradation is very rapid in the
presence of oxygen, but occurs at a significantly lower rate in a vacuum(11,12,13).
The degradation is a result of the weakening of the
structure near the scission point, plus the effects of the build-up of internal pressure of various gaseous products(16,21). Using electron spin resonance, Siegel and Hedgpeth note the existence of two radicals formed upon degradation in a vacuum(4):
16
1)
2)
A propagating radical
A chain radical
There are ten times more chain than propagating radicals since the propagating radicals can recombine more easily(10).
Both radicals
will react with oxygen to form peroxide radicals(14). The hypothesized mechanism for the production of the propagating radical and its peroxide derivative is given in reactions 11.3.1. and 11.3.2.;
that for the chain radical is given in 11.3.3. and 11.3.4.
(10,15) •
11.3.1.
11.3.2.
11.3.3.
11.3.4.
17
The symbol
~
by ionizing radiation.
indicates that the reaction is initiated
Other possible reactions are given by Fisher
and Corelli in Reference 10. The number of radicals produced in air is proportional to the dose according to an equation developed by Judeikis et. al.(17):
R = 0.87 x 10- 3 (D)0.88
in which R = Radical concentration (micromole/kg) D = Dose (rads)
For degassed samples the 0.88 becomes 1 within experimental error. Scission of the PTFE chain during irradiation is a random process which results in shorter chains and a broadening of the molecular weight distribution, regardless of the original polydispersity of the sample.
During the irradiation, the PTFE undergoes a steady weight
loss proportional to the dose due to the evolution CF 4, C2 F6' C3Fg, and other volatile fluorocarbons(16). When the bonds in the PTFE are broken by the radiation, pairs of chain ends generated in the crystalline regions are prevented from moving due to their close packing in the matrix; therefore, the pairs may readily recombine.
In the amorphous region, the chains are
loosely packed and may diffuse away before combination can occur; most permanent scission, therefore, must take place in these amorphous
18
regions.
A "cage effect" determines if the scission is permanent.
the chain ends remain in the cage, recombination is possible.
If
If the
ends become separated, scission is completed(18,19). The lower molecular weight PTFE chains created by the scissions, being more mobile, assume the lower free energy conformation of the crystalline phase.
Scissions in the amorphous regions may reduce
hindrances, chain entanglements, and other stresses and grant enough mobility to the chains to promote crystallinity(lO). This increase in crystallinity has been proven by NMR work which shows a broadening of the amorphous component of the spectrum.
This
corresponds to an increase in the hindrance of molecular motion in the amorphous phase, implying that the chains have become more tightly packed.
In addition, Differential Thermal Analysis (DTA) (19) and
Differential Scanning Calorimetry (DSC) (10) work show a peak on the low temperature side of the irradiated PTFE melting endotherm, which may indicate the presence of imperfect crystallites formed in the amorphous region(lO). In this crystalline conformation, the chains with their free radical ends are rigidly packed and recombination of the radicals is unlikely(3,20).
This accounts for the long lifetime of the PTFE free
radical of at least many months to years, compared to milliseconds for most other free radicals(15,2l).
19
PART III Methyl Methacrylate Free Radical Polymerization
I I I .1.
Free Radical Chain Polymerization
Radical chain polymerization consists of a three step sequence: initiation, propagation, and termination(22,23). The initiation step requires two reactions:
the homolytic
dissociation of an initiator, I, to yield a pair of radicals, R·,
I
111.1.1.
and the addition of the first monomer molecule to produce the chain initiating species
Mi ' R. + M
k·1
111.1.2.
in which Mrepresents a monomer molecule and kd and ki are the respective rate constants. Reaction 111.2. is assumed to be so fast that it cannot be rate controlling. In the propagation step, the radical grows
by
successive additions
of monomer molecules:
M. + M - - - ) r .... M· 1 2
111.1.3.
M. + M n
111.1.4.
>-
M·
n+1
20
in which kp is the propagation rate constant.
Growth to high
polymer is almost instantaneous for free radical polymerizations. Termination occurs by a bimolecular reaction between radicals to produce dead polymer.
Combination simply adds two radicals together:
M. + M. ------",-.. Mn+m
n
111.1.5.
m
in which ktc is the rate constant for combination termination. A disproportionation termination results in the formation of one saturated and one unsaturated polymer molecule:
M. + M.
n
m
_ _ _ _)-~
Mn +
fv\n
111.1.6.
in which ktd is the rate constant for disproportionation termination. Coupling is a more likely termination scheme, but a combination of coupling and disproportionation also can occur. To simplify the kinetic equations, several assumptions are made. •
The radical reactivity is independent of radical size.
•
The total rate of reaction of the monomer is equal to the rate of reaction of the monomer in the propagation steps alone, neglecting any consumption of monomer in the initiation or the termination steps.
•
After a "pre-effect
ll
time, a steady state concentration
of free radicals is reached(22). With these assumptions, the kinetics equation for reactions 111.1.1. 111.1.6. can be rearranged to give a useful expression for the rate
21
of propagation, Rp :
111.1.7.
The value "f" is the initiator efficiency, the number of polymer chains formed per initiator fragment, and has a value between
a
and 1, depending on the initiator, solvent, and conditions used. [M] and [IJ refer to the concentrations of monomer and initiator respectively(23).
111.2.
Methyl Methacrylate Homopolymerization
The carbon-carbon double bond in methyl methacrylate polymerizes by a free radical chain mechanism to poly (methyl methacryl ate) :
n
CH3 I CH2=C
l
~00CH3_
CH3
>
I
111.2.1.
- CH2-C
,
COOCH3
n
Methyl methacrylate (MMA) undergoes a very low rate of uninitiated thermal polymerization(22) of 1.94 x 10- 7 mol/l-sec at 273K(OoC). Initators such as benzoyl peroxide and azobisisobutyronitrile have been used to polymerize MMA to a number average molecular weight,
Mn , of up to 105 to 6 x 106(24).
22
In the initial stages of MMA polymerization, the reaction medium increases in viscosity from a mobile liquid to a viscous syrup(25,26). Between about 10 and 50 per cent conversion, the rate of polymerization increases.
The ratio of kp/k t increases rapidily due to a large drop in kt• It is during this stage that the "gel" effect occurs(25,26). In the later stages, the polymer radicals have limited mobility. The number of monomer units has decreased and the diffusion of these units to active propagating sites becomes more difficult.
Termination
becomes, in effect, the cessation of the ability to propagate(25,26). Most termination is by combination, but disproportionation is favored at higher temperatures(27,28,29).
Properties of MMA are summarized in
Appendix B.
111.3.
Ge 1 Effect
Using benzoyl peroxide as an initator for MMA, Norrish and Smith(30) noted a rapid increase in the polymerization rate after a particular conversion was reached.
This deviation from typical
kinetics occurs for vinyl monomers and ;s known as the Norrish-Smith, Trommsdorf, or gel effect(23). The gel effect is due to an increase in the viscosity of the system(31,32) caused by entanglements of high molecular weight propagating radicals and dead polymer(33).
These entanglements
prevent active free radical ends from diffusing close enough together to terminate(31,34).
Propagation and initiation involve small monomer
23
molecules whose mobility is not affected by this increase in the systemls viscositY(31); therefore, the corresponding rapid increase in conversion is attributed to a drop in the termination rate and kt , rather than an increase in the propagation or initiation rates.
24
PART IV Experimental Apparatus and Procedures
IV.I.
Kinetics Experiment
Polytetrafluoroethylene (PTFE) free radicals, as produced by irradiation, were used as initiators for a methyl methacrylate polymerization. Three different commercially available irradiated PTFE grades were used: Al lied.
Fluon~
L-I69 and L-171 from leI and
Polymist~
F-5A from
Two sources of methyl methacrylate were used:
Fisher
laboratory grade (inhibited with 25 ppm hydroquinone) and Dupont1s commercial grade (inhibited with 100 ppm hydroquinone). The methyl methacrylate was washed several times with sodium hydroxide until no color change was apparent.
Afterward, it was
washed repeatedly with distilled water until a clear layer of methyl methacrylate was obtained.
Drierite® was added to the methyl
methacrylate to remove any traces of the distilled water.
For most
reactions, the methyl methacrylate was put in a constant temperature bath at the reaction temperature until added to the PTFE.
For several
runs, the methyl methacrylate was kept in an ice bath or used at room temperature.
The temperature of the methyl methacrylate for each run
is noted in Tables 1 to 7. Samples of irradiated PTFE were weighed in test tubes to grams using a Mettler H-IO balance.
~
0.0001
The samples were placed in a
constant temperature bath and heated to the reaction temperature.
25
Methyl methacrylate was added volumetrically to the weighed irradiated PTFE samples using either a graduated cylinder or a graduated pipette.
The mixture of irradiated PTFE and methyl methacrylate
monomer was returned to the constant temperature bath and the reaction was carried out for a specified amount of time.
At the end of the
time limit, hydroquinone at approximately I weight per cent of the total reacting mixture was added to the test tube to quench the reaction. All reactions were performed in air at atmospheric pressure. Various temperatures and ratios of PTFE to MMA were used. The contents of the test tubes were transferred to dried, preweighed extraction thimbles.
Extractions with acetone were carried
out in a Soxleht extraction column until the thimble and its contents reached a constant weight.
The amount of poly(methyl methacrylate)
grafted onto the polytetrafluoroethylene free radicals was found by using equation IV.I.I.:
Mass Mass Mass Mass
of thimble + contents of thimble of irradiated PTFE used of PMMA graft
IV.I.I.
The definition of conversion is given in equation IV.I.2.:
% conversion
= Mass of PMMA graft x 100. Initial weight of MMA used
A summary of variables is given in Appendix C. Appendix D
IV.l.2.
26
contains the conditions used for each experiment.
IV.2.
Infrared Transmittance Measurements
In reflectance spectroscopy, an infrared beam is directed at some fixed angle onto the sample.
The energy reflected from the sample is
collected, appropriate computer manipulations are made, and the absorbance spectrum is obtained(35). Fourier transform infrared analysis is preferred over conventional infrared studies due to the "multiplex" advantage:
in FTIR, all
spectral elements contribute simultaneously to the interferogram, whereas in IR, spectral increments of particular wavelengths are measured successively.
For this reason, FTIR is considerably faster
in generating the same data as conventional IR(3fi). To substantiate the results of the kinetics experiments, Fourier transform infrared spectra of samples of the graft product were made using a Matteson Instruments Sirus 100.
The samples were ground in a
Wig-L-Bug with a small quantity of potassium chloride to reduce the amount of energy scattered.
Since the samples were in powder form,
the diffuse relectance attachment was used and KUbelka-Monk functions were generated(37). The Kubelka-Monk function is defined as
F( Roo)
in which
=
(I-Roo ) 2/ 2Roo
= k/ s
IV.2.1.
27 F(Roo)
=
Kubelka-Monk function
Roo
=
Reflectance of a layer so thick that further increases in thickness fail to change the reflectance
k
= absorption coefficient
s
=
scattering coefficient
Roo is further defined as
F(Roo)
= R~
sample
=
IV.2.2.
k/s
R'oo standard
in which R~
=
absolute reflectance of the layer.
In this instance, the sample is either the graft polymer or irradiated, unreacted PTFE and the standard is potassium chloride with R~
approximately equal to 1. F(R oo) is also related to the molar concentration, C, according to
equation IV.2.3.:
IV.2.3.
in which k is a constant equal to s/2.303t: with l
extinction coefficient.
E:
defined as the
S;s rendered independent of wavelength by
using scattering particles whose size is large in relation to the wavelength used(37).
If it ; s assumed that k' is constant for a given
28
sample, then a ratio of Kube1ka-Monk functions at different wavelengths will be equal to the molar concentration of those substituents absorbing at the given wavelengths. If the log F(Roo ) is plotted against the wavelength or wave number, the curve obtained corresponds to the real absorption spectrum of the compound determined by transmission measurements, except for a displacement by (- log s) in the ordinate direction(37,38)
IV.3.
Electron Spin Resonance Measurements
Electron spin resonance is based upon the absorption by unpaired electrons of electromagnetic radiation which causes transitions between energy levels.
The spectra recorded are the first derivative
of absorbed power as a function of the applied magnetic field.
The
number of spins, or free radicals, can be determined from the spectra by the application of quantum mechanics(39). In order to determine the presence of free radicals in the PTFE and in the graft product, ESR scans using a Varian E-15 EPR Spectrometer were made.
1,1-dipheny1(-2-picrylhydrazyl) (DPPH) was
used as the reference material.
Since the accuracy of measuring
absolute quantities of free radicals is very low, no better than per cent(39),
IV.4.
~
20
ESR scans were used only for qualitative purposes.
Differential Scanning Calorimetry
Whenever a material undergoes a change in physical state, such as melting, or in chemical composition, such as decompostion, energy is
29
either absorbed or liberated.
Differential Scanning Calorimetry
measures the heat flow required to maintain a sample and a reference system at the same temperature as this temperature is either kept constant or varied linearly at a predetermined rate(40).
When the
sample undergoes a thermal transition, a signal proportional to the power difference between the heater of the sample and that of the reference is plotted on the y-axis of the recorder with time recorded on the x-axis.
The area under the resulting curve is a direct measure
of the heat of transition(41). A Perkin Elmer Model DSC-l Differential Scanning Calorimeter was used to study the heats of melting/fusion of the unreacted irradiated PTFE and the PTFE-PMMA graft polymer.
A continuous heating rate of
10 kelvins/minute over a temperature range of about 580-620K (307-347°C) was used for the analysis.
30
PART V Results
V.I.
Kinetics Data Tables I - 5 give the data for the kinetics experiments.
Included
in these tables are the quantities of PTFE and MMA used, the amount of graft formed, the per cent conversion of MMA to graft, and the ratio of the graft to the initial quantity of PTFE. Figures 3 - 9 are graphs of conversion versus time at the various temperatures and conditions studied.
No weight increase was noted in samples run in experiment I at oC) 293K(20 or in experiment 2 at 313K(40oC). Sam~les run at 333K(60oC)-353K(80oC) showed an increase in weight, i.e., the production of a poly(methyl methacrylate) graft, at all the time allowed for polymerization, the ratios of the PTFE to MMA, the initial temperature of the MMA, or the grade of irradiated PTFE used.
V.I.a.
Effects of Preheating the Monomer
Tables 1 - 3 and Figures 3 and 4 give the data for the reactions at 333K(60oC). Table I and Figure 3 show the data for experiment 3 for PTFE (L-169) and MMA (DuPont) in a ratio of 1 gram of PTFE to 3 milliliters MMA at room temperature.
Table 2 and Figure 4 give the
data for experiment 4 for PTFE (L-169) and MMA (DuPont) in the same ratio with the MMA volumetrically measured at the reaction temperature.
The average conversion expected at each time interval is
31
approximately the same for both experiments; however, experiment 4 gave more consistent results, with a linear correlation coefficient(42), r, of 0.88 versus r=O.76 for the run using unheated MMA.
Since prior heating of the MMA gave better results, this step
was repeated for most runs.
V.1.b.
Effects of PTFE:MMA Ratio
Tables 2 and 3 and Figures 4 and 5 describe the effects of the ratio of the irradiated PTFE (L-169) to methyl methacrylate monomer (DuPont) on the conversion to graft polymer. reaction temperature is 333K(60°C).
In both instances, the
Table 2 and Figure 4 give
information for experiment 4 for 1 part by weight PTFE to 3 parts by volume MMA; Table 3 and Figure 5 are for experiment 5 using 1 gram of PTFE to 5 milliliters MMA.
About three times more conversion at
shorter times and twice as much conversion at the longer times was noted for the 1:3 ratio as compared to the 1 to 5 ratio. Reaction data for experiment 9 run at 353K(80°C) with a different grade of PTFE (L-171) at two different ratios of irradiated PTFE to MMA is given in Table 7.
Both runs lasted 60 minuntes.
Using three
times more PTFE to a constant amount of MMA resulted in three times more conversion of MMA to graft.
The ratio of grams of graft to grams
of PTFE remained constant despite the change in the PTFE:MMA ratio and is only a function of time.
A higher value of grams of graft to grams
of PTFE is obtained using L-171 versus L-169 (Table 4), probably due to a larger number of free radicals in L-171 (see section VI.1.).
32
V.l.c.
Effects of Temperature
The results of experiment 6 at 353K(80°C) with PTFE (L-169) to MMA (DuPont) at a 1 gram: 3 milliliters ratio are given in Table 4 and Figure 6.
Average conversion at this temperature is higher than at
333K(60°C) at the same conditions:
8.5 per cent at 353K(80°C) versus
6.4 per cent at 333K(60°C) for the 55 minute runs. conversion continues to increase with time:
The amount of
about 13 per cent
conversion of MMA to graft polymer is obtained at 90 minutes and about 21 per cent conversion at 145 minutes.
The conversion at 145 minutes
corresponds to a ratio of 0.52 grams of graft to 1.0 gram of PTFE, or about 60 per cent graft by volume.
V.l.d.
Effects of Hydroquinone
Hydroquinone is a common inhibitor for methyl methacrylate polymerizations.
Table 5 and Figure 7 show the effects of
hydroquinone addition on the reacting samples.
This was used to
determine if it was necessary to inhibit the samples chemically to prevent any post-polymerization once the samples were removed from the constant temperature bath.
In experiment 7, irradiated PTFE (L-169)
and MMA (Fisher) were used in a ratio of 1.5 gram to 2 milliliters with the reaction carried out at 353K(80°C).
Inconsistent results
were obtained for the shorter reaction times, but for longer periods, a slightly higher conversion was obtained for those samples to which no hydroquinone was added.
To avoid complicating the kinetics results
by post-polymerization grafting that might occur as the sample cooled
33
or was heated in the extraction column, hydroquinone inhibition at about 1 part per 100 parts monomer was used in all other runs. As noted in the 333K(60°C) runs, the higher ratio of PTFE to MMA results in a greater conversion of MMA to graft.
For experiment 7
using 1.5 grams of PTFE to 2 milliliters MMA (Table 5 and Figure 7), conversion was about 19 per cent at 50 minutes compared to R.5 per cent conversion at 55 minutes for experiment 4 for 1 gram of PTFE to 3 milliliters MMA (Table 4 and Figure 6), both at 353K(80°C).
V.1.e.
Effects of Different Grades of PTFE
Several manufacturers produce irradiated polytetrafluoroethylene. Since these materials are used in different applications, radiation doses are varied to produce a micropowder of the appropriate size. Given in Table 6 and Figure 8 are results of experiment 8 run at 343K(70°C) using Allied's Polymist® F-5A instead of ICI's L-169 or L-171.
The Polymist@ to MMA ratio was 2 grams: 5 milliliters.
Even
though the methyl methacrylate was kept in an ice bath prior to reaction, higher average conversions are noted for this run than for experiment 6 using L-169 at 353K(80°C) (Table 4 and Figure 6) at 1 gram of PTFE to 3 milliliters of MMA.
Using the Polymist® resulted in
46 per cent conversion of MMA to graft at 55 minutes. L-169, conversion was 8.5 per cent for 55 minutes. PTFE to graft is obtained.
Using the
About 1:1 ratio of
This corresponds to approximately 74 per
cent graft by volume. Figure 8 gives the percent conversion versus time with r
=
0.77.
34
for Unlike the other runs which gave linea r corre lation s, the data a this experiment imply a logar ithmi c relati onshi p. Figure 9 shows the graph of per cent conversion versu s the natur al logarithm of time; linea r corre lation coeff icent for this relati onshi p is 0.93.
V.I.f .
Extra ction s
cted Samples of PTFE as received were weighed in thimbles and extra noted under the same condi tons as polymerized samples. No change was . in the PTFE weigh t. The acetone used for extra cting the two graft samples run at 6) was 353K(80°C) for 145 minutes in experiment 6 (Table 4 and Figure evaporated and the residu e was weighed.
For comparison, the
experiment was repeated for pure acetone and acetone to which nder hydroquinone was added. Resul ts are given in Table 8. The remai of the residu e for the polymerized samples after the amount of of hydroquinone is subtr acted has a value equal to about 10 per cent the quant ity of graft formed and is due to any impu rities in the the aceto ne, hydroquinon~, methyl metha cryla te, or PTFE, or due to r. production of a small amount of methyl metha crylat e homopolyme A Fouri er transf orm infrar ed scan (FTIR) (Figu re 10) of this and residu e from sample B shows a small amount of PTFE carry over (1200 2400 em-I) , C-O groups (1400 - 1600 em-I) , C=O groups (1600-1800 em-I) , and OH groups (above 2800 em-I) .
35
V.2.
DSC Scans DSC scans were run on unreacted irradiated PTFE L-169 and graft
polymer made in experiment 6 at 353K(80°C) using a 1 gram: 3 milliliters ratio of PTFE:MMA for both 55 minutes and 90 minutes. The melting peak for PTFE was assumed to correspond to a melting
= 75.3
Joules/gram.
H
~
Areas of the other melting and fussion
peaks were measured relative to the L-169 melting peak, with
~
H
proportional to the relative areas. DSC scans are given in Figures 11 - 13. of melting and fusion are given in Table 9.
A summary of the heats The sample 80-558 was
melted and crystallized twice; all other samples were scanned once.
V.3.
Fourier Transform Infrared Scans Samples from experiment 6 at 353K(80°C) were scanned by infrared
analysis.
These scans are given in Figures 14a - 14f.
designation are given in Appendix E.
Sample
A FTIR scan of unreacted L-169
is given in Figure 15. The peak at approximately 1200 cm- 1(8.333 ~ ) corresponds to the C-F bond in PTFE(41), while the peak at about 1700 cm-1(5.882~ corresponds to the C=O bond in the methyl methacrylate (42).
) Relative
areas under the peaks at 1200 cm- 1 and 1700 cm- 1 were taken to be proportional to the molar concentration of C-F to C=O. ratios are given in Table 10.
These molar
36
V.4.
Electron Spin Resonance ESR scans of L-169, Polymist® F-5A, and the graft polymer made at
353K(80°C) for 145 minutes with 1 gram L-169 : 3 milliliters MMA are given in Figures 16 - 18.
The scans were made relative to diphenyl
1,1-diphenyl(-2-picrylhydrazyl) (DDPH).
The shape of these curves
coresponds well with the results of Siegel and Hedgpeth(14). The L-169 sample was run on a sensitivity (gain) one order of magnitude higher than the Polymist®.
Still, the area under the
Polymist® curve is larger; therefore, there is at least one order of magnitude more free radicals in the Polymist® than in the L-169.
The
slight blip in the PTFE curve near the DPPH curve is believed to be a shadow of the signal from the DPPH. The graft polymer was run at a sensitivity one order of magnitude higher than the L-169.
Curve 1 corresponds to a scan with DPPH in the
reference cavity; for curve 2 the DPPH was removed.
The loss of the
"blip" substantiates the likelihood of a DPPH shadow in other scans. Running at this higher sensitivity results in more noise in the scan. The area under the resulting PTFE peaks is much lower than for the unreacted L-169 sample, suggesting that there are significantly fewer free radicals present in the graft polymer. The stability of the PTFE free radical is sUbstantiated by comparing Figure 16a to Figure 16b and Figure 17a to Figure 17b. a and b scans were made 2 months
The
apart and show only a small decrease
in the areas under the curves, signifying only a small drop in the number of free radicals present in the samples.
37
PART VI Discussion of Results
VI.I.
Kinetics Results
vr.i.s.
Development of Kinetic Equations
Theory for free radical chain polymerization uses the steady state assumption to simplify the kinetics equations:
the rate of initiation
is equal to the rate of termination, which means that the the number of free radicals quickly reaches a steady state concentration at which it remains constant for the course of the polymerization(23). Production of free radicals involves the dissociation of the initiator to yield a pair of free radicals (111.1.1), which in turn react with the momomer molecules to produce the polymer chain (111.1.2). In the irradiated PTFE-MMA graft polymerization system, the PTFE free radicals are already present and no more can be produced.
The
concentration of these radicals starts at a set amount and decreases as the PTFE free radicals are used up; steady state assumptions do not apply.
For this reason, the kinetic equations must be modified to
model this system.
The resulting kinetic steps are given as follow:
Initiation:
R· + M
Propagation:
M. n
+
M
---'7-~
M·
VI.l.I.
M· n+l
VI.l.2.
38
dead or ______----~~ occluded m polymer
Termination:
M. + M.
in which:
R·
=
M
= Methyl methacrylate monomer
n
VI.I.3.
PTFE free radicals
M· = PTFE-MMA growing graft radical. Several assumptions are made. (A)
Step VI.I.I. is very fast.
This step is assumed to be so
fast in free radical polymerization kinetics that it cannot be rate controlling, and therefore, does not affect the development of the kinetics.
In this system, this step is
assumed to be so fast that all initiator (PTFE free radical s) is used up almost immediately; this is substantiated by ESR results (Figure 18).
The initial
number of M· radicals is then equal to the initial number of PTFE free radicals.
A certain activation energy barrier
must also be crossed, as is shown
by
the dependence of
conversion on temperature. (B)
Equal reactivity of all free radicals is assumed for steps
VI.I.2. and VI.I.3. (C)
Steady state conditions do not apply.
(D)
Average rate constants, which are not functions of time, are determined from the kinetics.
A derivation of appropriate kinetics is similar to that found in Qdian(23) •
39
The rate of disappearance of monomer (-d[MJ/dt) is equal to the rate of initiation (R i) plus the rate of propagation (R p): -d[M]/dt
=
Ri + Rp
VI.l.4.
in which the brackets signify concentration. The rates of initiation and propagation are defined from steps
VI.I.I. and VI.l.2. as
R.1 =
VI.I.S.
VI.l_6.
in which ki and kp are the respective rate constants for initiation and propagation_ Substituting into equation VI.l.4. gives
VI.I.7.
Dividing this equation by [M] and multiplying by dt gives
-d[M]/[M]
=
(ki[RO] + kp[MO])dt
Assumption (A) says that for time greater than zero, [R·]
VI.I.B.
=
0;
therefore, [M-J o = [R-J o ' in which the [R·]o ;s the initial concentration of free radicals and the sUbscript zero
40
signifies the condition at time
[R·]
=
=
O.
For any time greater than zero,
0 and
-d[M]/[M]
=
kp[MO]dt
VI.I.9.
From the termination step VI.I.3. and assumption (B),
VI.I.IO.
in which k t is the rate constant for termination. From this equation, the concentration M· can be determined as a function of time:
VI.I.II.
Integration gives
by assuming that the constant of integration is zero. states that [R·]o
=
Assumption (A)
[M-J o' and when this is substituted in
VI.l.12., the expression for [M·J becomes
VI.l.13.
41
gi ve s uation V I. I. 9. eq to in e lu va is S u b st it u ti n g th V I. l. 14 .
le s( 45 ) show Integration ta b
~1/(aX
x + b) + c +b))dx = I/ a In(a
V I. I. IS .
gr at io n constant of in te e th g in tt se d lv e V I. l. 1 4 . an Using th is to so ve s equal to zero gi V I. 1. 16 .
the at io n and [M] is tr en nc co er om on th e in ti al m at io n in in which [M]o is eting the in te gr ation at monomer concentr . gi ve s equation V I. l. 16
time t.
Compl
V I. I. 17 .
than 1; ·] o much greater R t[ k t se 6) (2 es L it er at u re valu dropped from the be n ca 1 e th n io fi rs t approximat th er ef or e, as a ss io n is re su lt in g ex p re e Th t. gh ri e on th lo ga ri th m ic term V I. I. 18 .
42
Expanding the logarithmic term on the right side,of VI.I.18. gives
In([M]O/[M])
=
VI.I.19.
(kp/kt)ln(t) + (kp/kt)ln(kt[RO]o)
When In([MJo/[M]) is graphed versus In(t), equation VI.l.19. defines a straight line with a slope of kp/k t and a y-intercept of
(kp/kt)ln(kt[Ro])o Since the exact concentration of PTFE free radicals is difficult to measure, it will be assumed that the number of free radicals in an irradiated PTFE sample is homogenous throughout the sample; therefore, the total mass of the PTFE sample can be used for the kinetics equations since it is directly proportional to the number of free radicals in the sample.
All concentrations in VI.I.19. can be changed
to a mass basis, relative to the initial mass of MMA, with the resulting kinetic constants having units of grams MMA/grams PTFE-minutes, rather than the typical moles/liter-minutes.
The term
[R·]o has the units of grams of PTFE/initial gra~s of MMA. Equation VI.I.19. predicts that for longer periods of time or for larger concentrations of irradiated PTFE initiator relative to MMA monomer, more conversion of MMA to graft will occur. Application of equation VI.I.19. to the data of the PTFE-MMA system is given in Figures 21-25.
Rate constants and linear
correlation coefficients are summarized in Table 11.
43
VI.I.b.
Temperature Effects
Temperature plays a significant role in the production of the PTFE-MMA graft.
Although no weight gain was noted in samples
polymerized with 1 gram L-169 : 3 milliliters MMA at either room temperature or at 313K(40°C) (experiments 1 and 2), the FTIR scans for these conditions (Figures 19 and 20) are slightly different than the scan for unreacted irradiated L-169 (Figure 15).
The scan of RT-55A
(Figure 19) shows a broad peak at about 1700 cm-l(5.882~), which may be due to the presence of poly(methyl methacrylate).
The scan of
40-55A (Figure 20) shows a peak around 900 cm-l(ll.111~ ) which does not appear in the PTFE scan, but does show up in FTIR scans at higher temperatures. A small amount of polymer may have been formed at these lower temperatures, but a more sensitive test than a weight gain would be required to detect its amount. The higher temperatures used for other runs result in higher conversion and, therefore, more grafting (Figure 14a - 14f). The data at the higher temperatures give a good fit to equation VI.l.19(Table 11).
Higher temperatures result in a higher conversion;
these samples have a larger weight gain that is more easily measured. The nature of the experiment will result in more error at the lower temperatures, and therefore lower conversions, since only a smaller quantity of graft will be produced.
44
VI.I.c.
Ratio Effects
The presence of more free radicals results in higher conversion of MMA to graft.
These can be seen in figures 4 and 5 of experiments 4
and 5 with PTFE:MMA at ratios of 1 gram: 3 milliliters and 1 gram milliliters.
5
This is also noted by the high conversion using
Polymist® F 5A at a reaction temperature of 343K(70°C) in experiment 8 (Figure 8), which was shown by ESR scans (Figure 17a and 17b) to contain significantly more free radicals than L-169:
the more free
radicals, the more sites available for MMA to add on to the PTFE. The data at 333K(60°C) from experiments 3-5 show a better fit to VI.l.19. when the ratio of PTFE:MMA is higher. initiator available, there can be more grafting.
With more PTFE As stated above, a
larger amount of graft to measure will reduce experimental error of the measurement.
The conversion versus time data for experiment 8
using Polymist® F 5-A as given in Table 6 and Figure 25 substantiates that given the same quantity of MMA, the amount of graft depends upon the amount of PTFE free radicals available.
ESR scans show a larger
amount of free radicals in the Polymist@ compared to the L-169 (Figures 7a and 7b), resulting in a higher conversion. Dropping the 1 from equation VI.I.17. has little effect on the calculated rate constants.
For shorter times, ktt[RoJ is
approximately equal to 1, but since most data are for longer times than 1 minute and linear regression techniques favor the data at the upper end of the range, this will have little effect on the results.
45
vr.r.a,
Gel Effect at 353 kelvins (80°C)
The data in experiment 6 at 353K(80°C) imply the onset of a gel effect after about 10 per cent conversion.
According to the work of
Norrish and Smith(30), this is a reasonable point for the gel effect to occur.
The data show a sharp break and linear regression
statistics for VI.l.19 for each side of the break result in significant error when used to predict the conversion for the opposite side (Figure 24).
Using VI.l.19., the ratio of kt/k p for time less than about one hour is 41.1; for time greater than about one hour, the ratio is 4.9(Table 11).
The lower ratio for the higher
times implies that the termination is much less likely than for the shorter times.
The mechanics of this possible gel effect can be
explained by the schematic in Figure 25.
As the PMMA chains grow away
from the the PTFE matrix, they can terminate by bridging over from one chain to the other, provided that there are no obstacles to sterically hinder them and that there is a near enough neighbor to allow a ready termination to occur.
As the chains become longer with the higher
conversion, more movement must occur for the chains to be in a favorable orientation to terminate(31,33).
More entanglements can
occur around the IIbridges" that have already terminated
and among the
longer chains that are not in a favorable position to terminate.
In
order to get over the bridges and other obstacles, these longer chains must grow still longer to find another chain, since many of its nearest neighbors have already terminated.
This schematic mechanism
can explain the decrease in the termination rate constant by a factor
46
of 34, as determined by the y-intercept in equation VI.l.19., at the break in the data in Figure 24. During the gel effect, the propagation rate is not expected to change since the mobility of small monomer molecules is unaffected by the increase in the system's viscosity due to entanglements and conversion.
The data collected at 353K(80°C), however, show a
decrease hy a factor of four in the propagation rate, as determined from equation VI.l.19.
This may be due to a slight shielding of the
free radical end in the growing PTFE - graft matrix which would prevent the monomer from easily finding an active propagating site. It is unlikely that the decrease in propagation is caused by decrease in the amount of monomer available, since approximately only 10 per cent conversion has occurred, and therefore, there is still a large amount of MMA available for reaction. Overall, the 34-fold decrease in termination rate shows a tendency toward a gel effect at these conditions, despite the slight decrease in the propagation rate. Even though the higher conversion occurred using the Polymist® F 5-A in experiment 8, no tendency toward a gel effect is noted in the data.
This may be due to the presence of more free radicals in the
Polymist® F 5-A which allows for the formation of a larger number of shorter chains.
In general, a higher quantity of initiator results in
Shorter, low molecular weight chains since more active sites are competing for a set amount of monomer(23).
The larger number of
shorter chains in the Polymist@ - PMMA graft have more near neighbors
47
with which they can terminate before any obstacles sterically prevent their movement; therefore, a gel effect is much less likely in the Polymist® system.
VI.1.e.
Comparison with Literature Values
Literature values for methyl methacrylate homopolymerization constants at 333K(60°C) are given(23).
kP = 0.515 x 1031/mol-sec
Ep
=
Ap kt
= =
Et
=
At
=
26.4 kJ/mol 0.087 x 107 l/mol-sec 2.55 x 107 l/mol-sec 11.9 kJ/mol 0.11 x 109 l/mol-sec
The subscript p denotes propagation constants, while t is used for termination.
A is the frequency or collision factor and E is the
activation energy as defined by
k
= A exp(-E/RT)
VI.1.21
in which R is the gas law constant and T is the absolute temperature. Values for the rate constants for grafting of MMA on to PTFE at 333K(60°C) are taken from Table 11.
Application of equation VI.l.19.
using data for 55 minutes from experiment 4 at 333K(60°C) and from experiment 5 at 353K(80°C) provides the values of the collision
48
constant and activation energy.
kp
= 0.0272 gram MMA/ gram PTFE-min Ep = 31.3 kJ/mol
Ap = 2201 gram MMA/ gram PTFE-min kt Et
= 2.0457 gram MMA/ gram PTFE-min = 1.7 kJ/mol
At
=
3.9 gram MMA/ gram PTFE-min
Literature values are for MMA polymerization in a solvent; whereas, the experimental data for the grafting are for a bulk system.
In addition, the experimental values of the rate constants
cannot be easily converted to a mole basis since the molecular weight of the PTFE is difficult to measure.
It is important to note that
these values will be applicable only for the L-169 : MMA system, since different grades of PTFE will have different amounts of free radicals per gram. Useful unformation, however, can be gained by comparing various ratios of the literature and experimental values.
The literature
value of kp/k t is 2.02 x 10- 5; the experimental value of kp/k t for the graft is 1.33 x 10- 2• The lower value for the literature ratio shows that termination· is much more likely in the solvent system that in the grafting system (Figure 25).
The solvent
may improve the mobility of the chains, making termination easier. This assumes that the propagation of the MMA graft proceeds according
49
to a typical MMA homopolymerization. The ratio of Ap/At gives the relative frequency of propagation versus termination. The literature values gives Ap/At = 7.91 x 10- 3; the experimental value for grafting gives 568.73 as this ratio.
These values also show that termination is much more likely in
a solvent rather than in the PTFE-MMA grafting system where more obstacles must be overcome. Once the chain has grown away from the PTFE matrix, it would be expected that the addition of more MMA monomer molecules would proceed at about the same rate and activation energy as in a homopolymeriztion.
The literature values of 26.4 kJ/mol for Ep compares favorably with the experimental value of 31.3 kJ/mol. The experimental value may be slightly higher to account for any steric hindrances that would allow propagation to occur from only particular orientations. The values for Et are not in good agreement: 11.9 kJ/mol for the literature value versus 1.8 kJ/mol for the graft polymer. The lower experimental value may be a result of obstacles and entanglements.
Although termination seems to be less likely in the
grafting system, once the chains have oriented themselves favorably for termination to occur, other hindrances prevent these chains from easily moving away from each other, and· termination results.
VI.2. ~
DSC Results H values determined from DSC scans are summarized in Table 9.
50
If the average
~
H values of duplicate runs along with the
H for
unreacted L-169 are graphed versus gram of graft/ gram of PTFE in the sample, regression lines are obtained (Figure 26 and 27).
~Hmelt;ng(J/g) = -31.98(gram graft/gram PTFE) + 76.27
~Hcrystall;zt;on(J/g)= -44.99(gram graft/gram PTFE) + 74.16
VI.2.1.
VI.2.2.
The values of the y-intercepts in both equations compare favorably with a value of 75.31 Joules/gram for unreacted PTFE. Addition of the PMMA graft to the PTFE matrix results in a decrease in the enthalphies of melting and crystallization since less PTFE is present per gram of polymer.
Temperatures at which these
transitions occurred remained approximately constant, despite the amount of graft.
Since the major portion of the polymer by weight is
PTFE, transitions occur at conditions similar to those for PTFE.
In
addition, the ratio of the heights of melting to crystallization peaks remained constant. Sample 80-55B was DSC scanned twice.
The increase in disorder
caused by melting and recrystallization is shown by a slight decrease in the enthalpies and transition temperatures for subsequent scans. The increase in the ratio of the heights of the melting to crystallization peaks is related to the increased disorder in the system that would cause a broadening of the crystallization peak. With enough data to establish a better linear regression, DSC
51
scans could be used to determine the amount of graft in a sample given the enthalpies of transition.
VI.3.
FTIR Scans
FTIR scans of several samples agre given in Figures 14a - 14b.
Ratios of
-CF 2CF 2- in the PTFE to C=O in the poly(methyl
methacryalate) graft are given in Table 10.
Concentrations as
determined by the relative heights of the peaks at 1200cm-1(8.33~) and 1700 cm-1(5.88~ ) are given in the first column. The second column gives the relative concentrations based on the area under the scans at these wavelengths.
The results of either method do not
correspond well with the data collected gravimetrically for the ratio of PMMA graft to PTFE as shown in the third column. These discrepancies may be a result of the high molecular weight of the polymeric materials:
given a set number of moles of PTFE, a molar
quantity of MMA will graft.
With high molecular weights, increases on
a mass basis will show as only slight increases in molar quantities. Kube1ka-Monk functions may not be appropriate to use with high molecular weight materials.
Further FTIR work would be required to
substantiate this. Despite the methods used for calculations, the value of the ratio for sample 80-1A is much smaller than those for the other polymerization times because only a very small amount of conversion has occurred at this point. FTIR can be used as a qualitative tool to determine if significant
52
conversion of MMA monomer to graft has occured; however, its usefulness as a quantitative tool is limited unless the molecular weight of the graft and PTFE can be measured accurately.
VI.4.
Electron Spin Resonance
Electron spin resonance scans demonstrate the presence of free radicals in irradiated PTFE(14) (Figures 16 and 17). significantly more free radicals in
Polymist~
The scans show
F 5-A (Figure 17a and
17b) than in L-169 (Figure 16a and 16b).
This results in a much
higher conversion of MMA to graft for the
Polymist~
sample since more
active sites are available for reaction in this material (Figures 8 and 9).
Graft material made in experiment 6 with L-169 and polymerized for 55 minutes at 353K(80°C) still showed the presence of a slight amount of free radicals, approximately 5 per cent of the quantity seen in as received L-l69 (Figure 18).
This substantiates assumption A in
section VI.l.a., that the majority of PTFE active sites are used up in the initial stages of the polymerization (less than 10 per cent conversion).
53
PART VII Properties of the PMMA-PTFE graft polymer
VII.I.
Physical Appearance
The graft polymer, as produced, is white and slightly translucent.
At low conversions it has the consistency of a fine
powder similar to the irradiated PTFE.
At higher conversions, the
graft polymer is hard due to the presence of a higher amount of PMMA and assumes the shape of the inside of its reacting vessel.
VII.2.
Stability
When heated on a McQuinne block, the graft polymer softens at 483K(165°C).
At 493 - 498K(220-225°C), the material flattens more
easily and shows some elasticity by springing back when sliced with a spatula.
At 523 - 533K(250-260°C), the material becomes more
malleable, smears, and large pieces can be broken apart easily. Heating to 553K(280°C) resulted in no change of color, no signs of any liquid, and no decrease in weight after extraction, showing that the graft is stable up to this temperature.
VII.3.
Moldability
When the graft polymer is molded in· a Pasedna Platen Press without heating of the plates, a smooth, waxy-film is produced. retains the slippery properties for which PTFE is known. brittle and cleaves easily.
This film The film ;s
It will crumble if enough force is applied.
54
Sample 20A produced with 1 gram L-169 : 3 milliliters-MMA: at 353K(80°C) was molded at 1.15 x 10- 1 pascals(795 psi) for five minutes with the bottom plate of the press at 463K(190°C) and the top plate at 380K(107°C).
A brittle, slightly translucent film was made.
This film was put back into the press at 1.73 x 10- 1 pascals(1,192 psi) for 20 minutes.
The resulting material was slightly less
brittle, but more translucent. this film.
Water readily beaded on the surface of
Two piece of this film were put at right angles to each
other and remolded at 5.23 x 106 pascals for 10 minutes with the top plate at 500K(227°C) and the bottom plate at 388K(115°C).
The pieces
fused well, showing that the graft polymer also had some adhesive properties. Overall, the graft polymer retains the slippery surface of the PTFE and the light transmittance and adhesive nature of the PMMA.
VII.4.
Possible Applications of the Graft Polymer
The polytetrafluoroethylene-poly(methyl methacrylate) graft may prove useful in several diverse applications due to the strength and durability of the PMMA and the non-stick properties of the PTFE.
Paints and Finishes:
Poly(methyl methacrylate) and its homologs are
used extensively in paints and finishes due to their durability and pigment uptake.
Addition of a PTFE-PMMA graft polymer could enhance
these properties by providing a non-stick surface.
This should prove
useful in household paints that must withstand scrubbing, automobile finishes that must bead water to help maintain a strong shine, and
55
marine paints that must prevent the attachment of barnacles and other sea debris.
Textile Uses:
Spinning of the PTFE-PMMA graft into filaments and
yarns could increase their wearability and resistance to soiling.
The
graft polymer would be an integral part of the yarn or filament, rather than an applied film, such as Scotchguard-, that could be worn away.
The non-stick surface of the fabric should prevent staining and
reduce the friction that causes wear.
Outdoor Applications: weatherablility.
PTFE and PMMA are both known for their superior
The graft polymer may be especially suitable for
greenhouse applications that require translucent, rather than transparent, windows.
The graft polymer may also lend itself well to
reflectors; the non-stick surface would increase the efficiency of the reflector by preventing a build-up of dirt.
Household Applications:
PMMA is useful in many indoor applications,
such as countertops and bathtubs.
Incorporation of the PTFE-PMMA
graft into these products should reduce staining and the build-up of soapy residues, thus reducing both the time and frequency of cleaning.
Moldings:
PMMA is very easy to mold; PTFE must be ram extruded since
it does not melt under ordinary processing conditions.
A graft with a
high enough'PMMA content may result in melted PMMA "carrying the PTFE ll
56
matrix along with it and allow for easier moldability.
Internally
lubricated parts, that, in addition, would release from the mold easily, could be produced.
Since the graft polymers made to date do
not have high strength, additives or a higher molecular weight of the PMMA graft may be required to produce parts with adequate dimensional stability.
57
PART VIII Summary
VIII.I.
Conclusions
Several researchers are studying graft polymers produced by irradiating a fluoropolymer film in the presence of reactive monomers(46,47).
In the research, presented here, temperature, rather
than irradiation, was used to drive the reaction to make a graft polymer of polytetrafluoroethylene and methyl methacrylate.
The PTFE
free radicals in commercially available PTFE micropowders, as formed by irradiation, were used to initiate the reaction.
The amount of
graft was set equal to the increase in mass of a PTFE sample after being mixed with a given amount of MMA at a certain temperature for a specified time.
The amount of conversion of MMA to PMMA graft was a
function of concentration, time, and temperature. Given a set amount of MMA, more conversion to PMMA graft occured if more PTFE free radicals were available to initiate the polymerization.
These chains, however, were expected to be of a lower
molecular weight than those that would result if fewer free radicals were available. Various grades of PTFE will result· in different conversions since they do not have the same amount of PTFE free radicals.
For example,
Polymist® F 5-A used for a 343K(70°C) reaction resulted in a higher conversion of MMA to graft than did Fluon® L-I69 used at 353K(80°C),
58
since the Polymist® was irradiated at a higher dosage and, therefore, contained more free radicals. Higher reaction temperatures will result in more conversion. Although gravimetric analysis did not show any gain in mass for samples run at lower temperatures (293 and 313K), Fourier transform infrared scans were different for these samples than for unreacted irradiated PTFE.
A slight amount of conversion or some type of
rearrangement may have taken place at these lower temperatures. Conversion at 353K(80°C) was higher than at 333K(60°C) using the same grade of PTFE. Higher conversion is seen for greater times than for shorter ones. More consistent conversion data were obtained by preheating the MMA to the reaction temperature before adding it to the PTFE.
This
eliminated a lag time required for heating the reaction system that would have affected the results at shorter times more significantly. Adding hydroquinone after the reaction time also improved the consistency of the data by preventing any post-polymerization that might have occured as the polymer cooled down or was extracted. Initiation in this system is very fast, and the PTFE free radicals are used up almost immediately.
Steady-state assumptions do not apply
to this initiation system since no more PTFE free radical initiators can be produced.
The energy of propagation for this system agrees
well with data derived for solvent systems, implying that the propagation of the PMMA graft follows a mechanism similar to that for MMA homopolymerization.
Termination in this system is different
59
compared to a solvent system.
The ratio of kp/k t for a solvent system is much lower than for the MMA graft polymerization, implying
that termination is much more likely in a solvent system than in this one.
The graft chains must grow far enough away from the PTFE matrix
in order to find each other to bridge over other obstacles and terminate.
In a solvent system, mobility is much easier, and
termination more favorable. A gel effect was seen in the PTFE - PMMA graft system for those grades of PTFE that have fewer free radicals, and therefore, produce longer chains for a given conversion.
The reasons for this gel effect
are identical to those for a typical MMA homopolymerization:
the
system's viscosity was increased so greatly by the presence of high molecular weight polymer and growing polymer free radicals, that mobility was restricted and chains ends could not diffuse easily to favorable termination orientations. In order to satisfy the kinetics of this system, a series of equations was derived that explained the relationship of conversion, time, and concentration at a given temperature.
This relationship is
defined by the straight line given by equation VI.l.19.
All
concentrations were set relative to the initial amount of MMA.
Since
the number of free radicals in the PTFE is dificult to determine, but is homogeneous throughout the sample, the initial weight of the PTFE was used instead of the number of free radicals.
Rate constants then
have units of grams MMA/ grams PTFE - minutes. Although
conv~rsion
data were obtained gravimetrically,
60
differential scanning calorimetry gave a good correlation for versus conversion.
~H
It would be necessary, however, to generate more
data to define this relationship. Kubelka-Monk functions generated by FTIR did not prove useful on a quantitative basis for this system, probably due to the relatively few end groups for this high of a molecular weight system.
Qualitatively,
however, the FTIR scans did support the presence of a PMMA graft. ESR scans proved the presence of PTFE free radicals in the micropowder and confirmed the assumption of a very fast initiation that used up the PTFE free radicals almost immediately. The graft polymer made was white and had an appearance ranging from the micropowder to a hard plug, depending on the concentration of the PMMMA.
The polymer showed no change in color or formation of
liquid up to 453K(280°C); however, it did become more malleable at higher temperatures.
When molded, the block copolymer had a smooth,
slippery finish that was not wetted by water.
Layers of molded
polymer adhered to each other with the application pressure and temperature.
VIII.2.
•
Recommendations for Future Work The feasibility and usefulness of the PTFE-PMMA graft copolymer would need to be demonstrated.
Appropriate
testing, such as molding, extrusion, weatherability, etc., would be necessary before applications could be proposed.
•
Production of a greater quantity of the graft copolymer
61
would be necessary before this testing could occur. •
A graft polymer composed of a block of any fluoropolymer and a block of any vinyl polymer could be useful in many applications.
By using the most suitable fluoropolymer
free radical and vinyl monomer, a custom-made block polymer can be produced.
To do this would require a study of the
kinetics involved for each combination. •
In order to determine the usefulness of the kinetics derived for this system to described other non-steadY state cases or those systems for which the steady state assumption is assumed to hold true, appropriate experimentation with other materials would be necessary.
•
To improve the kinetics equations of the system, a relationship between the dose of irradiation to the fluoropolymer was subjected and the conversion of the vinyl monomer to graft polymer would need to be developed.
This
relationship would have to account for the decay of the free radicals with time, if the free radicals were to be used immediately after irradiation. •
DSC scans could be correlated with conversion to define a better relationship between the heats of the transitions and the amount of graft present.
A large amount of time
could be saved using DSC since it is much faster than the gravimetric technique used with extractions to constant weight.
62
•
If IR analysis is to be used, absorption and transmission scans may prove more useful than Kubelka-Monk functions.
63
References
64
References (continued)
14. )
S. Siegel and H. Hedgpeth, J. Chern. Phys.,
15. )
N. R. Lerner, J. Chern. Phys., .E.Q., 2902 (1969).
16.)
J. H. Golden, J. Po 1ym • Sc i ., 45, 146 (lg60).
17.)
H. S. Judeikis, H. Hedgpeth, and S.Siegel, Radiation Research,
~,
3904 (1967).
65 References (continued)
30. )
R. G• W• No r r ish and R. R. Sm i t h, Na t ure , 150 , 336 (1942) •
31.}
J. N. Cardenas and K. F. OIDriscoll, J. Polym. Sci., Polym. Chern. Ed.,..!i, 883 (1976).
32•)
T. Ma1avsic, V. 0sred kar, I. An zur , and I. Viz 0 visek, J. Macrornol. Sci. - Chern., A19(7), 987 (1983).
33.)
E. Abuin and E. A. Lissi, J. Macromol. Sci. - Chern., A13(8),
1147 (1979). 34.)
E. Abuin and E. A. Lissi, J. Macromol. Sci. - Chern., Al1(5), 967 (1977).
35.)
H. A. Szymanski, The Theory and Practice of Infrared Spectroscopy, Plenum Press, N. Y. (1964).
36.)
H. W.Siesler and K. Holland-Moritz, Infrared and Raman Spectroscopy of Polymers, Marcel Dekker, Inc., N. Y. (1980).
37.}
R. W. Frei and J. D. Mac Neil, Diffuse Reflectance Spectroscopy in Environmental Problem Solving, CRC Press, Cleveland, Ohio
(1973) • 38.)
W. W. Wendlandt and H. G. Hecht, Reflectance Spectroscopy, Interscience Publishers, N. Y. (1966).
39.)
M. Symons, Chemical and Biochemical Aspects of Electron Spin Resonance Spectroscopy, John Wiley and Sons, N. Y. (1978).
40.)
"Perkin-Elmer Model DSC-l Di fferential Scanning Calorimeter", Perkin-Elmer Instrument Division, Norwalk, Connecticut.
41.)
W. K. Fisher, Ph.D. Dissertation, Rensselaer Polytechnical Institute, Troy, N. Y. (1981).
66
References (concluded)
42.)
W. L. Gore, Statistical Methods for Chemical ExperiMentation, Interscience Publishers, Inc., N. Y. (1952).
43.)
R. E. Moynihan, J. Amer. Chern. Soc.,
44.)
R. T. Morrison and R. N. Boyd, Organic Chemistry, Allyn and
~,
1045 (1959).
Bacon, Inc., Boston, Mass. (1973). 45.)
G. B. Thomas Jr., Calcul us and Analytical Geometry,
Addison-Wesley PUblishing Company, Reading Mass. (1968). 46.)
T. Nenner and A. Fahrasmove, Int. J. Hydrogen Energy,
~,
309
(1984). 47.)
E. A. Hegazy, J. Polym. Sci., Polym. Chern. tu., .?l, 493 (1984).
48.)
C. A. Sperati, "Fl uoropl ast t c s", Modern Plastics Encyclodedia, ~,
49.)
lOA (1982).
J. Brandrupt and E. H. Immergut, Eds., with W. McDowell, Polymer Handbook, 2nd Ed., Wiley Interscience, N. Y. (1975).
50.)
H. Krenz, "Ac ryl t c'", Modern Plastics
Encyclopedia,~,
IDA, 1982.
67
Appendix A
Properties of Polytetrafluoroethylene
Molecular Weight(8) (commercial material) Melting Point(48) (fabricated material)
600K(327°C)
Density(8,lO)
2.0 Mg/m 3 - 2.3 Mg/m 3 (2.0 g/cm 3 -2.3 g/cm3 )
Coefficient of friction(48)
0.01
68
Appendix B Properties of Methyl Methacrylate CH3 Structure(44)
I
H2 C=C
~OOCH3 Density of Monomer(49) 291K( 18°C) 29 3K( 20°C)
0.9558 Mg/m 3(0.9958 g/cm 3) 0.9535 Mg/m 3(0.9535 g/cm 3)
Density of Polymer(23) 298K( 25°C)
1.179 Mg/m 3(1.1790 g/cm 3)
Volume change upon Polymerization(23)
-20.6%
Molecular Weight of Po 1ym er ( 23)
50,000 - 100,000
White Light Optical Transmi 55ion(50)
92%
WeatherabilitY(50)
very hi9h
69
Appendix C
Variables Studied
Variable
Range
Temperature
293 - 353K(20 - 80°C)
Time
1 - 145 minutes
Ratio of grams PTFE to milliliters MMA
1:3, 1:5, 1.5:2, 2:5, 1:27, 1:10
PTFE grades
Fluon® L-169 and L-171, Polymist® F 5-A
MMA grades
Fisher laboratory grade with 25 ppm HQ DuPont commercial grade with 100ppm HQ
70
Appendix D:
Experiment No.
Reaction Temperature, kelvins,(OC)
Experimental Code
PTFE
MMA
grams PTFE: mil liters
MMA
Temperature of MMA kelvins(OC)
1
293 (20)
L-169
Dupont
1
3
room temp.
2
313 (40)
L-169
Dupont
1
3
313 (40)
3
333 (60)
L-169
Dupont
1
3
room temp.
4
333 ( 60)
L-169
Dupont
1
3
333 (60)
5
333 (60)
L-169
Dupont
1
5
333 (60)
6
353 (80)
L-169
Dupont
1
3
353 (80)
7
353 (80)
L-169
Fisher
1.5:2
353 (80)
8
343 (70)
Polymi st~ F 5-A
Dupont
2
5
273.2(0.2)
9
353 (80)
L-171
Fisher
1 1
27
room temp.
10
71
Appendix E:
Sample Code
Sample
Experiment
Reaction Time
RT-55A
1
55
40-55A
2
55
80-lA
6
1
80-3A
6
3
80-20A
6
20
80-55A
6
55
80-55B
6
55
80-90B
6
90
80-145A
6
145
80-145B
6
145
72
Tab 1e 1 Reaction Data at 333K(60°C) with 1 gram PTFE(L-169} : 3 milliliters MMA (DuPont) at room temperature
Time (min) 1 1 1 1 3 3 3 3 7 7 7 7 20 20 20 20 55 55 55 55
PTFE (g) 4.0119 2.8401 3.0195 3.0656 3.0164 3.2570 2.9771 2.9805 3.0890 2.9369 3.1959 ~.9735
2.9175 3.1769 3.0120 2.9461 2.9707 2.9999 2.9452 3.0006
MMA (ml )
9.0 9.1 8.9 8.9 9.0 8.8 9.0 9.0 9.1 9.1 9.1 9.1 8.9 9.1 9.1 9.0 9.0 9.0 8.9 9.0
(temp K) 303 303 298.5 29A.5 303 303 298.5 299 302 303 298.25 298 303 302 299.25 299 303 303 299 300
(g)
Graft (g)
8.4780 8.5722 8.4299
0.0565 0.0773 0.0036
0.6664 0.9018 0.0427
0.0141 0.0272 0.0012
0.0107 0.0008
0.1~56
0.0093 3.4542
0.0036 0.0003 0.1008
0.0732
0.1936 8.7550 2.6786 0.8500
0.0056 0.2516 0.0724 0.0243
0.4411 0.4648 0.5533 O.1i711
5.2029 5.4824 6.5676 . 6.7116
0.1485 0.1549 0.1879 0.1901
Conversion (~)
8.4~q9
8.4780 8.2896 8.5246 8.5194 8.5827 8.5722 8.6219 8.6245 8.3838 8.5827 8.6114 8.5194 8.4780 8.4780 8.4247 8.5091
0.291;1
0.0167 0.7340 0.2~9q
Graft PTFE
Table 2
Experiment 4: temperature
Reaction Data at 333K(600C) w1tB 1 gram PTFE(L-169)
Time (min)
PTFE ( g)
(m 1)
1 1 1 3 3 3 3 7 7 7 7 20 20 20 20 55
3.1130 3.4062 2.8508 3.1630 3.1914 2.7378 3.0710 3.5109 3.4612 2.7063 3.2588 3.1975 3.5393 2.7364 3.0906 3.1169 3.0776
9.0 9.0 9.1 9.0 9.0 9.1 9.1 9.0 9.0 7.4 9.1 9.0 9.0 9.1 9.1 9.1 9.0
55
MMA (temp K) 333.5 333.5 334.5 333.75 333.5 334.5 334.5 333.5 333.5 332 334 333 333.5 334.5 334.5 333 334
Graft (g)
8.1623 8.1623 8.2426 8.1597 8.1623 8.2426 8.2426 8.1623 8.1623 6.7240 8.2478 8.1675 8.1623 8.2426 8.2426 8.2583 8.1572
(g)
..
3 milliliters HMA at the reaction
Conversion
(I)
Graft ---rnt
0.0770 0.0898 0.0732 0.0350 0.0993 0.0282 0.0388
0.9434 1.1002 0.8881 0.4289 1.2166 0.3421 0.4707
0.0247 0.0264 0.0257 0.0111 0.0311 0.0103 0.0126
0.0374 0.0552 0.0383 0.0703 0.1324 0.1486 0.4035 0.4353 0.6212
0.4582 0.8209 0.4644 0.8607 1.6221 4.2292 4.8953 5.2723 7.6154
0.0108 0.0204 0.0118 0.9220 0.0374 0.1274 0.1306 0.1397 0.2018
73 Table 3
Experiment 5: Reaction Data at 333K(60°C) with 1 gram PTFE(L-169) reaction temperature
Time (min)
PTFE (g)
(ml)
MMA (temp K)
1 1 1 1 1 1 3 3 3 3 3 3 7 7 7 7 7 7 20 20 20 20 20 20 55 55 55 55 55 55
2.0886 2.0010 2.2952 2.1866 2.1221 2.0158 2.0998 1.9173 2.1427 1.9406 2.0367 1.9292 1.9406 2.0848 1.9858 2.1845 1.8220 1.8859 1.9855 1.9924 2.1770 1.9467 1.9421 1.9281 1.9903 1.9415 1.9462 1.9952 1.9855 1.9079
10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
333 333 333.5 334.5 334 333.5 334 332.5 334 334.5 334 334 336.5 335 333.5 333.5 334 334 334 335 335 333 333.5 333 332.5 333.5 332.5 333 333 333
Graft (g)
(g) 9.0750 9.0750 9.0693 9.057R 9.0635 9.0693 9.0635 9.0808 9.0635 9.0578 9.0635 9.0635 9.0348 9.0520 9.0693 9.0693 9.0635
5 milliliters MMA (DuPont) at the
Conversion (%)
Graft
PTFt
0.0274 0.0230
0.3019 0.2534
0.0131 0.0115
0.0484
0.5337
0.0240
0.1151 0.0040 0.0017
1.~699
0.0443 0.0188
0.0597 0.0021 0.0008
0.0511 0.0776
0.5645 0.8551
0.0235 0.0399
0.3866 0.3335 0.3486 0.1874 0.1214
4.2573 3.6772 3.8389 2.01\50 1.3377
0.1942 0.171R 0.1791
9.063~
9.0635 9.0520 9.0520 9.0750 9.0693 9.0750 9.0808 9.0693 9.0808 9.0750 9.0750 9.0750
0.09~9
0.0611
Tab 1e 4
Experiment 6: Reaction Data at 353K(80°C) with 1 gram PTFE(L-169) reaction temperature
Time ("'Ii n)
PTFE (g)
1 1 1 1 3 3 3 3 7 7 20 20 55 55 90 90 145 145
2.8464 2.9903 2.9859 2.8569 2.8508 3.0767 3.0606 3.0936 2.9769 2.9333 3.1614 2.987? 3.0604 3.0634 9.2067 9.5245 9.4655 10.6757
MMA (ml) 9 9 9 9 9 9 9 9 9
9 9 9 9 9 31.5 30 30 30
(temp K) 353 354 353 355 353 353 353.75 354.5 352.5 353 352.5 352.5 352.5 353 338 337 353 353.5
(g)
7.9605 7.9502 7.9605 7.9398 7.9605 7.9605 7.9527
Graft (g)
3 milliliters MMA (DuPont) at the
Conversion (~)
Graft
PTFt
0.0370 0.0332
0.4648 0.41R1
0.0124 0.0116
0.0284
0.3571 0.4091 2.5961 5.7597 5.6530 8.8542 8.3521 8.8851 12.9832 13.6194 20.7492 21.9845
0.0093 0.0105 0.0695 0.1563 0.1424 0.?361 0.2174 0.?309 0.4006 0.3873 0.5817 0.5461
7.94~
0.O~25
7.9657 7.9"05 7.9651 7.9657 7.9657 7.9605 28.4051 27.0870 26.5350 26.5178
0.2068 0.4585 0.4503 0.70~3
0.6653 0.7073 3.6879 3.6891 5.5058 5.8298
74 Table 5
Experiment 7: Effects of Hydroquinone on Post-Polymerization: reaction data at 353K(80°C) with 1.5 grams PTFE(L-l~9) : 2 milliliters MHA(Fisher) at the reaction temperature
Time (min) 1 1
3 3 5 5 10 10 25 25 50 50
PTFE (g)
(ml)
1.7846 1.6677 1.5922 1.6300 1.5068 1.5609 1.3320 1.6271 1.4372 1.5087 1.5224 1.5690
HQ*
HMA (temp K)
(9)
1.8840 1.8840 1.8840 1.8840 1.8840 1.8840 1.8840 1.8840 1.8840 1.8840 I.A840 1.8840
303 303 303 303 303 303 303 303 303 303 303 303
2 2 2 2 2 2 2 2 2 2 2 2
Conversion
Graft (g)
(9)
0.065 0.000 0.078 0.000 0.087 0.000 O.OQl 0.000 0.074 0.000 0.092 0.000
Graft
--pm
(I)
0.307
16.2q51
0.3295 0.1463 0.1761 0.1763 0.1674 0.1967 O.34Q9 0.3825
17.4894 7.7654 9.3471 9.3577 8.A854 10.4406
0.1720
0.~187
0.0937 0.1322 0.1084 0.11fi5 0.1304 0.?298 0.2438
1~.5722
20.3025
*Measured on a Mettler P-160 Balance
Table 6
Experiment 8:
Reaction Data at 343K(70°C) with 2 grams PTFE(Polymiste F-5A)
Time (min)
PTFE (g)
(ml)
(temp K)
1 1 3 3 7 7 20 20 55 55
5.9401 5.8Q51 6.1659 5.9942 5.7898 4.5060 , 6.6620 6.2509 6.0352 6.5761
15 15 15 15 15 15 15 15 15 15
273.2 273.2 273.2 273.2 273.2 273.2 273.2 273.2 273.2 273.2
Conversion (%)
Graft (g)
tt4A
(g)
14.6441 14.6441 14.6441 14.6441 14.6441 14.1;441 14.6441 14.6441 14.6441 14.6441
5 milliliters MMA (DuPont) at 273.2K(0.2°C)
11.9550 15.0716 19.6R16 31.3430 34.4296 46.1831 38.7945 52.8445 39.8461
1.7507 2.2071 2.8822 4.5899 5.0419 6.7631 5.6811 7.7386 5.8351
Graft PTFt 0.2970 0.3580 0.4808 0.7928 1.1189 1.0152 0.Q088 1.2822 0.8873
Table 7
Experiment 9: Time (min) 60 60
Reaction Data at approximately 353K(800C) with different ratios of PTFE(L-171)
PTFE (g)
(ml )
HMA (temp K)
1.4980 4.5?53
40 46
303 303
(g)
37.6800 43.3320
Graft (g)
0.6024 I.R122
Conversion (%) 1.5987 4.1821
MMA (Fisher)
Graft
PTFt 0.4021 0.4005
75
Table 8 Residue after evaporation of the acetone used for extrations Acetone used to extract 80-14SA
Acetone used to extract
80';'1458'
.
"
Acetone as recei ved
grams of Residue
0.8272
0.9367
1.0484
grams of Hydroqui none
0.1605
0.1885
1.0459
grams of Remainder
0.6667
0.7482
0.0025
Acetone as received +
~droqu1none
0.0018
0.0018
Table 9
Results of DSC Scans MASS
MELTING PEAK TEMP.
CRYSTALLIZATION PEAK TEMP.
SAMPLE
ir!!9l
Hmelting ~
PTFE l-169
11.8
75.31
608.5
75.37
590.5
0.75
80-5581-1 80-5581-2
8.9 8.9
72.08 63.17
607 603
63.17 61.87
588 587
0.79 1.02
80-5582
8.9
70.47
608.5
58.41
590.5
0.75
80-90B1
9.4
61.57
606
61.21
588
0.77
80-90B2
9.2
63.36
607
55.82
588
0.78
sample 558 at 0.2309 g graft/g PTFE Sample 90B at 0.3873 9 graft/g PTFE $ample 5581 was scanned twice
H CRYSTALLIZATION
J&...
~
ill-.
RATIO OF HEIGHTS OF MELTING/CRYST. PEAKS
76
Table 10
Mass ratios of PMMA to PTFE in the graft polymer as detenmined by FTIR. sampl e
Based on peak heights
Based on area under peaks
Based on gravimetric ~
80-1A
0.0040
0.0105
0.0224
80-20A
0.0877
0.0332
0.1424
80-55A
0.1014
0.0289
0.2174
80-145A
0.1037
0.0349
0.5817
80-145B
0.1573
0.0387
0.4445
Table 11
Kinetic Constants and linear Correlation coefficients as Defined by equation VI.l.19.
Experiment
Temp. K(OC)
PTFE:MMA g:ml
3 4
333{ 60) 333{ 60)
1:3
3&4
333(60)
1:3
5
333(60)
1:5
6
353(80)
6
""'A Temp. K(OC)
s ~A 9 PTFE-mi n
g ~~A 9 PTFE-mi n
r
Conwnents
0.0275 0.02fi9
2.1509
0.81 0.73
0.0272
2.0457
0.77
333(60)
0.264
4.0343
0.70
1:3
353(80)
0.0546
1.3369
0.89
All data at 353K
353(80)
1:3
353(80)
0.0516
2.1209
0.92
Data at 353K up to 71 min
6
353(80)
1:3.2
353(80)
0.0129
0.0632
0.99
Data at 353K from 77 min
8
343(70)
2:5
273.2(0.2)
0.6891
4.8990
0.92
PTFE = Poymi stF-5-A
1:3
303(30) 333(60)
1.q858
All data at 333K PTFE:MMA: : 19:3ml
~ ~
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78
Figure 3: Conversion(%) vs. time(min.) at 333K(60°C) with 1 gram PTFE (L-169) : 3 milliliters MMA (DuPont) at room temperature
9
D
8 7
z
B
6
0
~
~
5
~
Z 0 0
~
4
D
3 2 D
0
0
~
~
20 nME(m~)
Linear Regression Line:
y = 0.IOD8x + r = 0.70
0.7637
79
Figure 4: Experiment 4: Conversion(%) vs. time(min.) at 333K(60°C) with 1 gram PTFE(L-lfi9) : 3 milliliters MMA (DuPont) at the reaction temperature.
8 D
7 6
z
0
5
a
iii I[
D
~
0
0
~
3 2
a D
0
0
40
20
60
TIME (min)
Linear regression line:
y = 0.113x + r = 0.88
0.4050
80
Figure 5: Experiment 5: with 1 gram PTFE(L-169) temperature.
Conversion(%) vs. time(min.) at 333K(60°C) 5 milliliters MMA (DuPont) at the reaction
4.5 D
4 D D
3.~
z
3
0
iii
II:
2.5
l&I
> z
0
0
~
D
2 1.5
0
D
0.5 D
a
O.....--a.......- - - . . . , . - . - - . . . . . - - - - . . - - - - - w - - - - - - I o 60 20 TIME (min)
Linear Regression Equation:
y
= 0.0511x
r = 0.84
+ 0.1458
81
Figure 6: Experiment 6: with 1 gram PTFE(L-169) temperature.
Conversion(%) vs. time(min.) at 353K(80°C) 3 milliliters MMA (DuPont) at the reaction
22 20 18
16
z 0 Ii
14
I:
12
~ 0
10
~
8
III
U
D
6
D
D
D
4 2 0 0
20
40
80
60
100
120
140
TIME (min)
Linear Regression Equation:
= O.1341x + 1.7870 r = 0.97
y
82
Figure 7: Experiment 7: Effects of Hydroquinone on post-polymerization: conversion(%) vs. time(min.) at 353K(80°C) with 1.5 grams PTFE(L-169) : 2 milliliters MMA(Fisher) at room temperature.
21 . . , . . - - - - - - - - - - - - - - - - - - - - 20 19 18 D
17 16
z o
15
I:
~o
14
•
12
Ii
o
a
13
11
•
10 9
8 7
6-+-----....----.......- - - . . . - - - - - - - - - - - . . .
o
20 D
No HQ
nME (min) + HQ:f.tMA::1 :4
.=ffi
Linear Regression Equations:
= 0.1308x + 10.5310
No Hydroquinone
y
HQ:MMA::l:4;
y = r =
r = 0.50
0.0397x + 13.3962 0.17
R3
Figure 8: Experiment 8: Conversion(%) vs. time(min.) at 343K(70°C) with 2 grams PTFE(Polymist® F 5-A) : 5 milliliters MMA (DuPont) at 273.2K(O.2°C).
55 D
50 0
45
40
iii
I:
35
D
bJ
> z 0 0
~
D
a
Z 0
30
25 20
D
15
D
D
10
0
20
40
nME (min)
Linear Regression Equation:
O.5006x + 22.7269
y
=
r
= 0.77
60
84
Figure 9: Experiment 8: Conversion(%) vs. time(min.) at 343K(70°C) with 2 grams PTFE(Polymist~ F 5-A) : 5 milliliters MMA (DuPont) at 273.2K(O.2°C).
55 D
50 D
45
z
40
0
iii
3S
~0
30
~
0
"
25 20
D
15
a
10
0
3
2
4
LH nME (min)
Linear Regression Equation:
= 9.5053x + 11.0154 r = 0.93
y
85
Figure 10: FTIR scan of the residue in the acetone after extraction of graft sample 80-1458 made at 353K(80°C) for 145 minutes with 1 gra~ PTFE(L-169) : 3 milliliters MMA(DuPont) at the reaction temperature (experiment 6).
I
I
-
----
~:::;-t-I
I
!
• .a• L
I
~
i> e
I
I :
~
~
I
I
~
~
~
..~
~
~
.
~
~
I
I
;
~
•
86
Figure 11:
DSC scan of L-169
590.5
608.5
600
610
620
610
600
590
Temperature(kelvins)
580
570
87
Figure 12a: DSC scan of graft sample 80-558 made at 353K(80°C) for 55 minutes with 1 gram PTFE(L-169) : 3 milliliters MMA(DuPont) at the reaction temperature; first run of melting and recrystallization.
607 588
600
610
620
610
600
Temperature(kelv;ns)
590
580
88
Figure 12b: Same sample as in Figure 12a; second run of melting and recrystallization.
587
603
590
600
610
600
Temperature(kelvins)
590
580
89
Figure 12c:
Duplicate OSC scan of the sample used in Figure 12a.
608.5
590.5
590
600
610
620
600
590
Temperature(kelvins)
580
570
90
Figure 13a: DSC scan of graft sample 80-90B made at 353K(80°C) for 90 minutes with 1 gram PTFE(L-169) : 3 milliliters MMA(OuPont) at the reaction temperature (experiment 6).
588
600
610
600
620
Temperature(kelvins)
590
580
91
Figure 13b:
Duplicate DSC scan of sample 80-90B (experiment 6).
588
607
590
600
610
600
620
Temperature(kelvins)
590
580
92
Figure 14a: FTIR scan of graft sample 80-1A produced at 353K(80°C) for 1 minute with 1 gram PTFE(L-169) : 3 milliliters MMA(OuPont) at the reaction temperature (experiment 6).
I I... I...
I
! I I I ~
..... I
•.
II
. , •.
1ft
I
.
fit
~
. .... ....
N
1ft
I II
•
.!
;
~ »
93
Figure 14b: FTIR scan of graft sample 80-3A produced at 353K( 80°C) for 3 minutes with 1 gram PTFE(L-ln9) : 3 milli liters MMA(DuPont ) at the reacti on temperature (experiment 6).
I I
-
I...
I I
N°
• L
I I I
..
N
N
N
N
•... •. •. . -
-
N
-
•. •.
..
.
N
I
t• e > a
•
94
Figure 14c: FTIR scan of graft sample 80-20A produced at 353K(80°C) for 20 minutes with 1 gram PTFE(L-169) : 3 milliliters MMA(DuPont) at the reaction temperature (experiment 6).
I I... I...
I I N
• • .a I• a> • L
I I I .......
•. •.
.....
•.
.
1ft
...
..,.
N
. ....
I
95
Figure 14d: FTIR scan of graft sample 80-55A produced at 353K(80°C) for 55 minutes with 1 gram PTFE(L-169) : 3 milliliters MMA(DuPont) at the reaction temperature (experiment 6).
I
-
I
I-
I
! I I
I • •~ •~ •~
N ~
~
•N •N •N
N
N
~
.
•. •. •. . - . •. •. N.
- -- N
I
•~
~
I ~
•
96
Figure 14e: FTIR scan of graft sample 80-145A produced at 353K( for 145 minutes with 1 gram PTFE(L-169) : 3 milli liter s MMA(O 80°C) uPont) at the reaction temperature (experiment 6).
~
•
.
•
. . . . . . . . ~
•
~
•
~
N
~
97
Figure 14f: FTIR scan of graft sample 80-1458 produced at 353K( 80°C) for 145 minutes with 1 gram PTFE(L-169) : 3 milli liters MMA( OuPont ) at the reacti on temperature (experiment 6).
I I
-
I
-
I
!
I
•Ii
1 •~
-. In
98
Figure 15:
FTIR scan of L-169.
I I...
I..
I I
N
I
• •
}
~
>
0
I I
. .... •... ..
N
,.; ,.;
til
• • ..
N
N tV tV N
~z
N
•.... •.... ...... .... N
LL..:)cu.,,·...
•. •. ... . N
Oc:
I
•
99
Figure 16a: ESR scan of L-169.
(Gain
= 103).
DPPH Gain
=
1.25 x 10
0
Figure 16b: ESR scan of the same L-169 sample as in Figure 16a, taken 2 months later.
(Gain = 103).
\
~
DPPH
100
Figure 17a:
ESR scan of
Polymist~
F 5-A. (Gain
=
2 x 102).
Gain = 1.25 x 10
Figure 17b: ESR scan of the same 17a, taken 2 months later. (Gain
Polymist~
=
o
F 5-A sample as in Figure 2 x 102).
DPPH
101
Figure 18: ESR scan of sample 80-55A run at 353(80°C) for 55 minutes with 1 gram PTFE(l-169) : 3 milliliters MMA(DuPont) at the reaction temperature (experiment 6). Curve 1 corresponds to a scan with DPPH in the reference cavity. Curve 2 corresponds to a scan without DPPH in the reference cavity. (Gain = 104).
Curve 2
Gain
= 1.25
x 100
102
Figure 19: FTIR scan of sample RT-55A produced at room temperature for 55 minutes with 1 gram PTFE : 3 milliliters MMA(DuPont) at room temperature (experiment 1).
I
!
•
L
G
I
~
~
G
> a
I I • •~ M• ~•
N
M
~
•N •N •N
N
N
N
•. •. •. N. ~
~
~
~
- .. •. •.
.
N
I
~
103
Figure 20: FTIR scan of sample 40-55A produced at 313K(40°C) for 55 minutes with 1 gram PTFE(L-169) : 3 milliliters MMA(DuPont) at the reaction temperature (experiment 2).
•L i• ~>
a
~
•
~
~
~
N
~
~
~
~
~
~
~
~
•
.... •
~
•
n
..
~
~
N
.
~
104
Figure 21: Application of equation VI.1.19. to experiment 3; reaction data at 333K(60°C) with 1 gram PTFE(L-169) : 3 milliliters MMA(OuPont) at room temperature.
0.07 - - - - - - - - - - - - - - - - - - - . . , , - - - ,
0.06 D
D
O.OS
"~
