MORPHOLOGY AND PROPERTIES OF SEMI-IPNS OF POLYETHERIMIDE AND BISPHENOL A DICYANATE

Semi-interpenetrating polymer networks (semi-IPNs) were synthesized from mixtures of polyetherimide (PEI) and bisphenol A dicyanate (BPACY) at different compositions and different cure temperatures. The phase separation behavior during cure was analyzed in terms of glass transition temperature (T-g) behavior of fully cured semi-IPNs and the morphology-property relationship was also studied. The mixtures of PEI and BPACY monomer showed upper critical solution temperature behavior and their semi-IPNs showed sea-island morphology in 1-14 wt% PEI composition, dual-phase morphology in 15-19 wt% PEI composition and nodular morphology in 20-60 wt% PEI composition, respectively. The sea-island morphology was formed via nucleation and growth, while the other morphologies were predominantly formed via spinodal decomposition. Cure temperature did not influence the macroscopic morphology, but the domain size changed with temperature. As cure temperature was increased, the PEI domain size in the sea-island morphology decreased, while the BPACY nodule size increased in the nodular morphology. Mechanical and thermal properties were so strongly dependent upon the morphology that they changed dramatically near the phase inversion point.