Effect of a Dwell Stage in the Cure Cycle on the Interphase Formation in a Poly(ether imide)/High <i>T</i>_g Epoxy System

Epoxies are inherently brittle materials and to overcome this brittleness, a second microphase (i.e., thermoplastic) is typically added. This modification of epoxy resin using thermoplastics results in reaction-induced phase separating morphologies the micrometer range. In study, influence curing history, beyond separation, on interphase formation final morphology PEI high Tg system investigated. Several cure cycles were examined, each with first dwell temperature ranging from 120 180 °C for given time up onset separation (OPS) or 80% degree (80% DOC) then at 200 20 min complete cycle. Hot-stage microscopy experiments carried out several temperatures before conversion dwell. The resulting droplet size distribution interphase, after cure, analyzed through scanning electron microscopy. Results showed that diffusion distance was significantly higher case OPS as compared DOC case, particularly lower temperatures. behavior attributed fact that, OPS, polymeric chains still mobile state diffused further during stage, while DOC, completely bound but diffuse due non-stoichiometric curing. restricted mobility resulted larger number smaller droplets case.