ISSN 20751133, Inorganic Materials: Applied Research, 2013, Vol. 4, No. 2, pp. 131–137. © Pleiades Publishing, Ltd., 2013. Original Russian Text © V.M. Buznik, Yu.E. Vopilov, V.K. Ivanov, A.S. Sigachev, V.S. Polyakov, M.A. Smirnov, T.P. Kulagina, Yu.V. Sorokin, V.P. Tarasov, E.P. Kharitonova, G.Yu. Yurkov, 2012, published in Perspektivnye Materialy, 2012, No. 4, pp. 44–52.
MATERIALS FOR GENERAL PURPOSE
Structure of Polytetrafluoroethylene Powders Obtained by Photochemical Polymerization of Gaseous Monomer V. M. Buznika, Yu. E. Vopilovb, V. K. Ivanovc, A. S. Sigachevd, V. S. Polyakovd, M. A. Smirnove, T. P. Kulaginae, Yu. V. Sorokind, V. P. Tarasove, E. P. Kharitonovab, and G. Yu. Yurkova a
Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Moscow, 117334 Russia b Department of Physics, Moscow State University, Moscow, 119992 Russia c Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russia d Research Institute of Elastomeric Materials and Products, Moscow, Russia e Institute of Problems of Chemical Physics, Chernogolovka, Russia email:
[email protected],
[email protected] Received December 15, 2011
Abstract—A set of physical methods is used to study the molecular, supramolecular, and topologic structure of polytetrafluoroethylene (PTFE) powders obtained from the gaseous phase of a monomer, tetrafluoroeth ylene (TFE) (C2F4), under ultraviolet irradiation in the presence of different initiators. Morphological diver sity of particles forming powders is found; the effect of technological modes on the regularities of the mor phological powder structure is established. The method of nuclear magnetic resonance (19F NMR) of broad lines allowed detecting the difference in the rotational dynamics of fragments of macromolecular chains in samples synthesized under different conditions. Keywords: polytetrafluoroethylene, photochemical polymerization, structure, NMR, SEM, XRD, IR spec troscopy, DTA/TGA. DOI: 10.1134/S2075113313020044
INTRODUCTION PTFE powders find application in a number of industries as materials for antifriction, antiwear, hydrophobic, protective, and biocompatible coatings. The area and effectiveness of their application are largely determined by the powder particle size and morphology, which, in turn, depend on the method of their synthesis and the applied processing methods [1–3]. In most cases, powders are obtained by synthesis from the monomer (TFE–C2F4) used in industrial production [3] or thermal processing of PTFE [1, 2]. As shown by the studies [1], powdered PTFE products have a considerably different molecular, supramolecu lar, and morphological structure. The aim of the work was to study the structure of PTFE powders obtained by UV photopolymerization of gaseous TFE using the scanning and transmission electron microscopy (SEM and TEM) techniques, laser scattering, Xray diffractometry, derivatographic techniques, and IR and NMR spectroscopy. SAMPLE SYNTHESIS TECHNIQUES AND STUDY METHODS The highly dispersed PTFE powder was synthe sized using the earlier developed and patented tech
nique [4]. Its originality consists in photochemical polymerization of gaseous PTFE using tetrachlo romethane as the main initiator. The UV irradiation source was a quartz–mercury lamp. Tetrachlo romethane is decomposed forming radicals under UV irradiation: hν fast
CCl 4
•
CCl 3 + Cl
•
•
•
slow
CCl 2 + 2Cl .
Radicals take part in the growth of a polymer chain without impairing its chemical and physicochemical properties. The amount of tetrachloromethane is 4– 10 wt % of loaded TFE. This reaction can be schemat ically represented as follows: F
F hν CCl4
n
F
F
Cl Cl Cl
F
F n
F
Cl
.
F
The photochemical polymerization reaction was carried out in a stainless steel reactor equipped with a quartz lantern with a quartz–mercury lamp. Samples of T495MN and T495ChN powders were obtained for studies using different manufactur ing methods. The process was carried out in three stages: (1) photochemical polymerization yielding raw polymer using different initiators; (2) sieving and
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Results of studies of sample no. 1 using the Xray diffraction technique 2θ
I/I0
d/n, Å
hkl
18.0 31.51 36.58 49.04 56.17 65.70 68.90 72.58
100.0 1.0
