Simultaneous interpenetrating polymer networks of epoxy resin/bismaleimide-allylester copolymer. I. Dynamic mechanical properties

Abstract

Simultaneous interpenetrating polymer networks (SINs) were prepared from nadic methyl anhydride-cured epoxy resin and bismaleimide (BMI) coreacted with triallyltrimellitate (TAT), triallylisocyanurate (TAIC), and diallylisophthalate (DAP), under the same gelling conditions for both the epoxide resin and BMI-allylester comonomer. Dynamic mechanical properties of the SINs were measured over the temperature range from room temperature to about 300°C. The rubbery modulus and glass transition temperature (T_g) due to the cured epoxy resin considerably increased with loading of BMI-allylester copolymer. The value of T_g exhibited an asymptotic behavior at high loading, the value increasing in the order of BMI-TAT, -TAIC, and -DAP. The relative modulus in the rubber state shows that phase inversion occurs in the SINs at the concentration of 30–40 wt% BMI-allylester. The increase in T_g with loading can be explained in terms of the contributions of both an increase in crosslink density and an interaction between the epoxy resin and BMI-allylester copolymer. The increments in T_g with loading can be correlated to the logarithm of a nominal crosslink density in the loading polymer, and the difference among the asymptotic values of T_g for each series is discussed based on polar-nonpolar solubilities of the components. The increase in T_g with loading can also be corre-lated to the percent densification, which exhibits a maximum at a composition of about 50%, resulting from interpenetration.