Sequential interpenetrating polymer networks from bisphenol A based cyanate ester and bimaleimide: Properties of the neat resin and composites

Blends of varying composition of a bisphenol A based cyanate ester-viz., 2, 2-bis-(4-cyanatophenyl) propane (BACY)-and a bisphenol A based bismaleimide -viz., 2,2-bis[4-(4-maleimido phenoxy) phenyl] propane (BMIP)-were cured to gether in a sequential manner to derive bismaleimide-triazine network. poly mers. Enhancing the bismaleimide content was conducive for decreasing the t ensile properties and improving both the flexural strength and fracture tou ghness of the cyanate ester-rich neat resin blends. Although DMA analyses o f the cured blend indicated a homogeneous network for the cyanate ester dom inated compositions, microphase separation occurred on enriching the blend with the bismaleimide. Addition of bismaleimide did not result in any enhan cement in T-g of the blend. Interlinking of the two networks and enhancing crosslink density through coreaction with 4-cyanatophenyl maleimide impaire d both the mechanical and fracture properties of the interpenetrating polym er network. (IPN), although the T-g showed an improvement. Presence of the bismaleimide was conducive for enhancing the mechanical properties of the c omposites of the cyanate ester rich blend, whereas a higher concentration o f 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. (C) 1999 John Wiley & Sons, Inc.