The effect of zeolite L content on dielectric behavior and thermal stability of polyimide thin films
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Zeolite L, with the ratio Si/Al = 4, was prepared by hydrothermal method and used to obtain composite films based on a polyimide matrix having pendant carboxylic groups. The effect of zeolite L content on dielectric behavior and thermal stability of polyimide thin films was studied. The films were prepared by casting a suspension resulting from direct mixing of a poly(amic acid) (PAA) solution and zeolite L particles onto glass plates, followed by thermal imidization under controlled temperature conditions. The PAA was synthesized by solution polycondensation of a mixture of two diamines, 3,5-diaminobenzoic acid and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (molar ratio 1:3), with 4,4′-oxydiphthalic anhydride, using N-methyl-2-pyrrolidone as solvent. To improve the compatibility between organic and inorganic phases, the surface of zeolite particles was modified by treating with 3-aminopropyltriethoxysilane. The surface morphology of the composite films investigated by scanning electron microscopy showed good compatibility between filler and polymer matrix. The films were flexible, tough, and exhibited high-thermal stability, having the initial decomposition temperature above 450 °C. Dynamic mechanical analysis and dielectric spectroscopy revealed sub-glass transitions, γ and β, and an α relaxation corresponding to the segmental motions above the glass transition temperature. The values of the dielectric constant at 10 kHz and 200 °C were in the range of 3.3–4.2.
KeywordsZeolite Polyimide Composite Film Dynamic Mechanical Analysis Initial Decomposition Temperature
We thank Dr. M. Cristea at “Petru Poni” Institute of Macromolecular Chemistry, Iasi, Romania, for DMA analyses. Yu. Kalvachev gratefully acknowledges the financial support by the National Science Fund, Bulgaria (Grant DTK02-47).
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