Moisture absorption-network structure correlations in BMPM/DABPA bismaleimide composite matrices

Systematic studies of the thermoset bismaleimide (BMI) resin matrix network structure controlled by cure time-temperature history and initial monomer composition are reported in terms of density, glass transition temperature, and moisture absorption characteristics for the BMPM/DABPA (Matrimid(TM) 5 292, Ciba-Geigy) systems. The moisture transport behavior was monitored at 50 degrees C and 70 degrees C and correlated to the glass transition temper ature (T-g) and density of alternative BMI network structures derived fr-om systematically varying the initial monomer ratio and time-temperature cure conditions. Equilibrium moisture content and diffusivity increased with in creasing BMPM monomer concentration and degree of cure, but primary depende nce was on the latter: Density decreased with increasing cure and increased with BMPM concentration while T-g increased with cure, and final T-g after equivalent postcuring for 6h at 300 degrees C proved to be independent of the initial monomer stoichiometry The results recorded here are consistent with our previous understanding of the chemical and physical mechanisms inv olved in network structure-BMI resin property modifications by way of dehyd ration-influenced ether crosslink formation and subsequent rearrangement at high temperatures to stiffer crosslinks.