Capacitors with an Al–polyimide–Al sandwich film structure have been fabricated: the top and the bottom aluminium electrodes were deposited by vacuum evaporation and the polyimide film was deposited by an isothermal immersion method. An X‐ray diffractogram of the film indicates the amorphous nature of the polyimide film. Dielectric and ac conduction properties of polyimide capacitors in the frequency range 10 kHz to 10 MHz at various temperatures (303–423 K) are reported; the dc conduction at different voltages and at various temperatures (303–423 K) is given. The capacitance of the film decreases with increasing frequency but increases with increasing temperature. The ac conduction studies suggest that electron hopping is responsible for conduction while the dc conduction studies reveal that Poole–Frenkel conduction is predominant at high fields. The activation and zero field activation energies are also calculated. © 2001 Society of Chemical Industry

Blends of varying composition of a bisphenol A based cyanate ester-viz., 2,2-bis-(4-cyanatophenyl) propane (BACY)-and a bisphenol A based bismaleimideviz., 2,2-bis[4-(4-maleimido phenoxy) phenyl] propane (BMIP)-were cured together in a sequential manner to derive bismaleimide-triazine network polymers. Enhancing the bismaleimide content was conducive for decreasing the tensile properties and improving both the flexural strength and fracture toughness of the cyanate ester-rich neat resin blends. Although DMA analyses of the cured blend indicated a homogeneous network for the cyanate ester dominated compositions, microphase separation occurred on enriching the blend with the bismaleimide. Addition of bismaleimide did not result in any enhancement in T g of the blend. Interlinking of the two networks and enhancing crosslink density through coreaction with 4-cyanatophenyl maleimide impaired both the mechanical and fracture properties of the interpenetrating polymer network (IPN), although the T g showed an improvement. Presence of the bismaleimide was conducive for enhancing the mechanical properties of the composites of the cyanate ester rich blend, whereas a higher concentration of it led to poorer mechanical properties due to the formation of a brittle interphase. The IPNs showed reduced moisture absorption and low dielectric constant and dissipation factor, the latter properties being independent of the blend composition.

Epoxy-imide resins were obtained by curing the epoxy resin Araldite GY 250 (DGEBA; difunctional) and Araldite EPN 1138 (Novolac epoxy; polyfunctional) with the diimide-diacid, 2,2-bis[4-(4-trimellitimidophenoxy)phenyl]propane. The adhesive lap shear strength of epoxy-imide resins at room temperature and at 100 and 150°C was determined on a stainless-steel substrate. The effect of solvent on the adhesive strength of epoxy-imide resins was studied, and tetrahydrofuran was found to give the best results for improving the wetting behavior of epoxy resins. It is observed that with the increase in imide content the adhesive strength at room temperature as well as at elevated temperature increases when tetrahydrofuran is used as a solvent in the adhesive formulation. The room temperature adhesive strength for GY 250-based systems is in the range of 20.8 -23.5 MPa and 45-58% of this strength is retained at 150°C. For EPN 1138-based systems, the room temperature adhesive strength is in the range of 14.3-20.3 MPa, and in fact, an increase in adhesive strength by 1-26% is observed at 150°C. All these systems are stable up to 370°C, and char residues of GY 250-and EPN 1138-based systems at 800°C are in the range of 27-31 and 33-41%, respectively, in nitrogen atmosphere. The overall thermal stability and retention of room temperature adhesive strength at elevated temperature are higher for EPN 1138-based systems when compared to those of GY 250-based systems, and this observation has been attributed to the higher crosslinking possible for EPN-based systems when compared to GY 250-based systems.

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