In order to develop a material having combined properties of the toughness of thermoplastic and the heat resistance of thermoset, semi-IPN's of bisphenol A dicyanate (BPACY) and polyarylate (PAR)was synthesized and the cure kinetics and the properties were studied.
The semi-IPN was synthesized by polymerizing the mixture of BPACY monomer and polyarylate obtained by solution blending the two components and removing the solvent.
The cure kinetics of BPACY could be well described by the autocatalytic reaction mechanism. Parameters of kinetic equation were determined from the isothermal DSC experimental data through the Marquardt's multivariable nonlinear regression method. During curing reaction, vitrification occurred, so curing reaction became diffusion controlled. Modified WLF equation was introduced to the rate constant, therefore vitrification effect during cure was successfully described.
Semi-IPN synthesized were transparent in all the composition, but scanning electron microscope (SEM) results of the semi-IPN's showed the phase separated morphology. Sea and island morphology of continuous poly(dicyanate) and dispersed polyarylate above 85wt% of BPACY, while interconnected nodular morphology was observed when the composition was below 80wt% of BPACY. For the semi-IPN of BPACY 80wt%, sea and island morphology and interconnected nodular morphology co-existed and this implied that the phase inversion occurred at this composition. It was observed that the morphology of the semi-IPN was influenced by the reaction temperature. When BPACY formed a continuous phase, the size of PAR domain decreased with increasing temperature. In contrast, when PAR formed a continuous phase, the nodule size of BPACY increased with increasing temperature.
In the dynamic mechanical analysis(DMA), two $T_g$ s were observed in IPN's having 50wt% or more poly(dicyanate), and single $T_g$ was observed when the composition was below 50wt% of poly(dicyanate).
It was observed that tensile strength, elongation at break, flexural strength, flexural modulus, and hardness increased with increasing poly(dicyanate) content, while impact strength decreased with increasing poly(dicyanate) content.
Heat resistance of the semi-IPN was measured by the Vicat softening temperature. Vicat softening temperature increased with increasing poly(dicyanate) content.
Addition of catalyst had an effect on the morphology and mechanical properties as well as reaction kinetics. Phase separation was suppressed due to the increased reaction rate, so mechanical property such as the impact strength decreased compared to that of uncatalyzed system.
