Simultaneous interpenetrating polymer networks of epoxy resin/bismaleimide-allylester copolymer. II. Influence of gelling conditions on mechanical properties

Simultaneous interpenetrating polymer networks (SINs) were prepared from nadic methyl anhydride-cured epoxy resin and bismaleimide (BMI) coreacted with one of three different allylesters under different gelling conditions for both the epoxide resin and BMI-allylester comonomer. Dynamic mechanical and tensile properties were measured for these SINs. The rubbery modulus increased monotonically with increasing gel time ratio of the epoxide resin to that of the comonomer. On the other hand, the glass transition temperature (T g) and tensile strength ([sgrave] b ) exhibited maxima when the two gelations were most nearly simultaneous. This behavior was observed in all series of the SINs. irrespective of the kinds of the allylesters. The behavior of the rubbery modulus can be explained by the hypothesis that the BMI-allylester copolymer networks become more continuous as the comonomer reacts faster than the epoxide resin does. In addition, the maxima in T g and [sgrave] b can be explained in terms of the greater extent of molecular mixing attained in a truely simultaneous gelation.