Polymeric Composites Based on Alicyclic Polyimide

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 12, pp. 2151–2154. © Pleiades Publishing, Ltd., 2008. Original Russian Text © B.A. Zhubanov, V.D. Kravtsova, R.M. Iskakov, A.A. Matnishyan, G.E. Nurumbetov, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 12, pp. 2040–2044.

MACROMOLECULAR CHEMISTRY AND POLYMERIC MATERIALS

Polymeric Composites Based on Alicyclic Polyimide and Polyaniline B. A. Zhubanov, V. D. Kravtsova, R. M. Iskakov, A. A. Matnishyan, and G. E. Nurumbetov Bekturov Institute of Chemical Sciences, Ministry of Education and Science of the Republic of Kazakhstan, Almaty, Kazakhstan Yerevan Research Institute of Optical and Physical Measurements, Yerevan, Armenia Kazakh–British Technical University, Almaty, Kazakhstan Received June 23, 2008

Abstract—Specific features of modification of an alicyclic polyimide with polyaniline were examined. The thus obtained new polymeric composites exhibit better capability for silver plating. DOI: 10.1134/S1070427208120215

Polymeric materials, both individual polymers and multicomponent systems, attract growing researchers’ interest. Modification of polymers with various low- and high-molecular-weight additives allows preparation of composites with valuable properties, making them suitable for application in microelectronics, radio engineering, and space industry [1, 2]. Of particular interest are composites of nanosize polyaniline, polypyrrole, and polythiophene, which, thanks to the high electrical conductivity and stability in redox processes have found use in high-capacity batteries; supercapacitors; corrosion-protecting, reflecting, and absorbing coatings; and power-converting and power-saving devices [3, 4]. Among conducting polymers, the most widely used are polyaniline (PANi) and its derivatives [5, 6]. Homogeneous defect-free composites with high electrical conductivity and good mechanical properties, prepared by forming PANi layers on the surface of aliphatic polymers (polyethylene, polypropylene), have been described [6–8]. It was of interest to evaluate the effect of electroactive polymers on heat-resistant polymers and, in particular, polyimides. In this study, we examined specific features of formation and the main properties of composites based on a nanosize polyaniline and an alicyclic polyimide derived from tricyclodecenetetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether:

EXPERIMENTAL The starting compounds and solvents were purified by standard procedures. N,N'-Dimethylacetamide (DMAA) was additionally dried over 4-Å molecular sieves. Acetone, methanol, and 4,4'-diaminodiphenyl ether (DADPE), all of chemically pure grade, were used without additional purification. Polyimide (PI) was prepared in the presence of catalytic amounts of triphenyl phosphate in a DMAA solution. The polyimide was prepared in an inert atmosphere by the following procedure: A three-necked flask was charged with 13.70 g (0.05 mol) of the dianhydride, 10.00 g (0.05 mol) of DADPE, and 1.18 g (5 wt % relative to the sum of the monomers) of triphenyl phosphate, after which 70.0 ml of DMAA was added. The mixture was heated for 20 min at 70°C, after which the temperature was raised to 120°C, and the mixture was stirred for additional 4.0 h. From the resulting solution, in which, according to the IR spectra, the degree of imidization of the polymer was 94–96%, we cast films or precipitated the polymer into acetone. The products obtained were washed with two portions of acetone and dried in a vacuum oven at 80–90°C to constant weight. The polyimide films were prepared by casting the reaction solutions or a 25% solution of the precipitated polyimide in DMAA onto glass surfaces. To remove the solvent, the films were dried at 80°C for 0.3 h, after which they were additionally heat-treated in the temperature range 80–250°C in air for 1.0 h. Silver plat-

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Table 1. Some properties of alicyclic polyimide in the presence of polyaniline Property red

of 0.5% solution, dl g–1, DMF,

Polymer PI

PANi

1.52

25° 370 Decomposition onset temperature in air, °C Temperature of 50% weight loss, °C 540 140 Tensile strength, MPa 32 Elongation, % 4200 Elastic modulus, MPa

PI + PANi, wt %

0.56* 360 487 Brittle – –

0.10 1.55

0.25 1.57

0.5

1.0

1.67

1.74

1.5

2.0 1.81

1.80

370

367

365

360

360

360

540 135 30 4200

536 135 28 4230

522 130 25 4270

530 125 23 4340

532 128 20 4380

525 127 18 4570

* In concentrated H2SO4.

ing of the polyimide films was performed as described in [9]. Polyaniline was prepared by oxidative polycondensation of a solution of aniline in 1 M HCl with potassium persulfate [10]. The product obtained as an emeraldin salt was additionally purified by successive extraction with methanol and acetone for 24 h and treated with a 10% solution of ammonium hydroxide, after which it was dried in a vacuum oven at 50°C for 5 h. The bulk electrical conductivity of emeraldin and the emeraldin salt was 10–10 and 0.45 –1 cm–1, respectively. The molecular weight of the emeraldin form of PANi in concentrated sulfuric acid was 35-000. The fibril size, according to an electron-microscopic examination, was 150–220 nm [11]. The reduced viscosity was measured in an Ubbelohde viscometer at 25°C for 0.5% solutions of the polyimide in DMF and for solutions of PANi in concentrated 2S 4. The thermal gravimetric analysis of PI and composites was performed with a Mettler Toledo GA SDTA device at a heating rate of 8 deg min–1. The temperatures of the decomposition onset, d.o, and 50% weight loss for the polymers were calculated from the TG curves. The tensile strength t, relative elongation l, elastic modulus , dielectric loss tangent tan , relative permittivity , and bulk and surface resistivities v and s of 40–45- m-thick films were measured under standard conditions [12, 13]. The electrical properties of the metal-modified films were measured in the dc mode at a field istrength of 20 mV cm–1, using sputtered silver electrodes. The temperature dependence of the surface resistivity was studied in the range 25–200° . The reflection coefficient R( ) was determined in the wavelength range 400–750 nm for samples with a surface area of 2.2 cm2 on an SF-1201 spectrophotometer. The determination error was ±0.05%

for v and s, and ±1% for R. The IR spectra of 3–5m-thick films were measured on an IR-25 device. Polymer blends with nanosize polyaniline were prepared by homogenization of 0.1–2.0 wt % PANi in a polyimide solution at 20–25° . After settling, films were cast and dried in air for 1.0 h at 80–250°C. The surface morphology of the composite systems was studied with a Jeol JSM-1800 scanning electron microscope (Japan) equipped with an Oxford MathScan attachment. The first step in studying the specific features of modification of the alicyclic polyimide with the conducting polymer was to examine the effect of PANi samples of the general formula

x = y = 0.5

on the PI viscosity. In contrast to the known PE–PANi composite systems prepared by successive deposition of PANi layers on the surface of polyethylene films [6], composites of alicyclic polyimide and polyaniline were prepared by mechanical mixing of the starting polymers. The experimental results obtained show that the systems remain homogeneous and transparent at a PANi content of up to 2.0 wt %, and above this concentration the solution becomes turbid, the system undergoes phase separation, and high-quality films are not obtained. In the presence of conducting polymer additives, the viscosity of the PI solution somewhat increases: from 1.54 to 1.80 dl g–1. The viscosity reaches a maximum in the presence of 1.5 wt % PANi and then does not change noticeably (Table 1). This fact can be attributed to the plasticizing effect of PANi, apparently leading to loosening of the structure of the initial polyimide.

RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 12 2008

POLYMERIC COMPOSITES BASED ON ALICYCLIC POLYIMIDE AND POLYANILINE

As can be seen from Table 1, the thermal stability of the polyimide–polyaniline systems is relatively high and, at the PANi content examined, it is determined, on the whole, by the structure of the polyimide. Analysis of the spectral characteristics of the polymeric system with PANi shows that the IR spectra do not change noticeably in the presence of relatively low amounts of the conducting polymer. We only observe an increase in the intensity of the absorption bands of the aromatic rings at 1500 cm–1 and a shift of the imide ring band from 1375 to 1385 cm–1. The positions and intensities of the other bands remain essentially unchanged. To evaluate the stability of mechanical properties of films with different PANi contents, we measured their tensile strength and elongation. As can be seen from Table 1 for unmodified PI, the mean values of t and l are 140 MPa and 32%, respectively, and the elastic modulus is 4200 MPa. For the samples with PANi, these characteristics vary as follows: the tensile strength remains nearly unchanged, and the elasticity decreases (e.g., for the sample with 2% PANi, by a factor of 1.8 relative to the initial sample); the elastic modulus increases practically to 400 MPa, i.e., the system becomes appreciably more rigid. This fact, which is on the whole expected, can be attributed to structurization of the polyimide chains with a rigid PANi framework (according to [6–8], PANi is cross-linked in the temperature range 160–200° ). The optical and electrical properties change in the presence of PANi more significantly. As can be seen from Fig. 1, as the polyaniline concentration is raised from 0.1 to 1.5 wt %, the optical reflection coefficient of the metal-plated composites increases. An evaluation of the residual silver content by TGA showed that an increase in the PANi content leads to a rise in the sorption capacity of the composite for silver ions by a factor of 1.1–1.5. It is also seen from Fig. 1 that the shape of the curve of the optical reflection coefficient of the metal-plated PI vs. wavelength (curve 1) differs from the corresponding curves for the systems with PANi, characterized by stabilization of this parameter at = 550–600 nm. On the whole, it can be noted that, as the polyaniline content of the composite is raised (within the examined range), the metal content also increases. A similar trend has been observed previously for alicyclic polyimide–poly(ethylene terephthalate) composites [14], but for the composites with the electroactive component the effect is more significant.

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Fig. 1. Influence of the polyaniline concentration on the optical reflection coefficient R of (1) PI, (2–4) PI + PANi, and (5) Ag films. ( ) Wavelength. PANi concentration, wt %: (2) 0.1, (3) 0.5, and (4) 1.5.

Fig. 2. Temperature dependence of the surface electrical resistivity s of (1) PI and (2, 3) PI + PANi films. PANi concentration, wt %: (2) 0.5 and (3) 1.5.

For the metal-free polymeric composites, the bulk resistivity increases by two orders of magnitude (Table 2). Introduction of PANi into the polyimide also leads to appreciable changes in the surface resistivity of metal-plated films. Figure 2 shows that, with an increase in the polyaniline content, the surface resistivity s decreases. Thus, active properties of polyaniline are manifested not only on the surface, as noted Table 2. Electrical properties of polymeric composites based on alicyclic polyimide and PANi Polymer PI PI + PANi, %: 0.5 1.0 1.5 2.0 2.5 PANi

tan

ε

m

0.001

2.82

(1–3) × 1015

0.003 0.009 0.020 0.024 0.030 0.25–12*

1.30 1.33 1.32 1.28 1.30 1.40

(2–4) × 1015 (2–3) × 1014 (2–3) × 1014 (2–4) × 1013 (2–4) × 1013 222

* Depends on temperature and doping level.


ρv,

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Fig. 3. Electron-microscopic images of the surface of films of (a) nonmetallized and (b, c) sliver-plated samples. (a) PI, (b) PI + Ag, and (c) PI + PANi + Ag.

in [7, 8], but also in the bulk of the polymer, i.e., these composites can be characterized by both bulk and surface conductivity. Analysis of the properties of alicyclic polyimide + polyaniline composites shows that PANi enhances the capability of the composites for metal plating by favoring formation of larger silver clusters, compared to metal particles in the polyaniline-free polyimide (Fig. 3). It should also be noted that the thus obtained metallic layer is tightly impregnated in the polymer base, with the formation of a more uniform metal layer in the surface layer of the polyimide as compared to the individual polymer. CONCLUSIONS (1) Specific features of modification of the polyimide derived from tricyclodecenetetracarboxylic dianhydride and an aromatic diamine with polyaniline were examined. The components are well compatible at conducting polymer concentrations of up to 2.0 wt %. (2) Introduction of small amounts of polyaniline leads to formation of polymeric composites with a more rigid structure, compared to the initial polyimide, and improved capability for metallization, which is reflected in the optical and electrical properties of the composites: for silver-plated films, the optical reflection coefficient increases and the surface electrical resistivity decreases. (3) In the presence of a conducting polymer, silver clusters of larger size, compared to metal particles in the polyaniline-free polyimide, are formed. ACKNOWLEDGMENTS The study was financially supported by the International Science and Technology Center (project K-1117)

and Program F.0354-06 of Basic Research of the Bekturov Institute of Chemical Sciences, Ministry of Education and Science of the Republic of Kazakhstan, project “Scientific Principles of the Development of New Polymer Systems and Microstructures for Medicine, Agriculture, and Electronics” (2006–2008). REFERENCES 1. Wessling, B. and Skotheim, L., Handbook of Conducting Polymers, New York: Marcel Dekker, 1998. 2. Satheesh Kumar, K.K., Geetha, S., and Trivedi, D.C., urr. Appl. Phys., 2006, vol. 5, no. 6, pp. 603–608. 3. MacDiarmid, A.G., Synth. Met., 2002, vol. 125, pp. 11–12. 4. Handbook of Organic Molecules and Polymers, Nalwa, H.S., Ed., Chichester: Wiley, 1997, vol. 2. 5. Genies, E.M., Boyle, A., Lapkowski, M., and Tsintavis, C., Polyaniline: A Historical Survey, Synth. Met., 1990, vol. 36, pp. 139–145. 6. Kuryndin, I.S., Mokreva, P., Terlemezyan, L., et al., Zh. Prikl. Khim., 2005, vol. 78, no. 3, pp. 484–489. 7. Rozova, E.Yu., Kuryndin, I.S., Bobrova, N.V., and Elyashevich, G.K., Vysokomol. Soedin., Ser. B, 2004, vol. 46, no. 5, pp. 923–927. 8. Hsun-Tsing Lee, Chien-Shiun Liao, and Show-An Chen, Makromol. Chem., 1993, vol. 194, pp. 2443–2452. 9. Vecherkina, E.L., Kudaikulova, S.K., Iskakov, R.M., et al., Vysokomol. Soedin., Ser. A, 2007, vol. 49, no. 2, pp. 246–253. 10. Matnishian, H.A. and Beylerian, N.M., Oxid. Com., 2005, vol. 28, no. 1, pp. 67–80. 11. Matnishyan, A.A. and Akhnazaryan, T.L., Khim. Zh. Arm., 2007, vol. 60, no. 5, pp. 801–831. 12. Gurova, T.A., Tekhnicheskii analiz i kontrol’ proizvodstva plastmass (Technical Analysis and Monitoring of Plastics Production), Moscow: Vysshaya Shkola, 1980. 13. Metz, S., Jiguet, S., Bertsch, A., and Renaud, Ph., Lab. Chip., 2004, vol. 4, pp. 114–120. 14. Kudaikulova, S., Musapirova, S., Sarieva, R., et al., Eur. Chem.-Technol. J., 2004, vol. 6, no. 1, pp. 11–16.
