Bismaleimides (BMIs) are key cross-linked polymers that are used in advanced structural composites due to their high service temperature, great moisture resistance, and good processibility. However, in contrast to extensive molecular modelling of epoxy crosslinking and the prediction of their structure-property relationships, no concerted effort has been invested in modelling BMIs, in part because of the complex curing chemistry of the latter. Unlike epoxies which often requires modelling a single amine-epoxy reaction, curing of BMI-5292 resin involves five separate reactions (ene reaction, maleimide homo-polymerization, alternating maleimide-adduct copolymerization, ene-adduct homo-polymerization via propenyl groups, and dehydration/etherification reaction). The objectives of this study are to develop molecular models of cross-linked Matrimid-5292, a BMI polymeric resin, based on AMBER force-field and analyze the thermo-physical and mechanical properties using molecular dynamics simulations to elucidate how the molecular structure and degree of curing affect structure property relationships. In order to capture the complex curing chemistry of BMI, a unique, flexible cross-linking framework is developed to implement five distinct aforementioned reactions. The framework is written in python as a LAMMPS MD package wrapper which utilizes an existing molecular modeling file format for storing new topology parameters and implements an algorithm to automatically determine what new bonds, angles, and dihedrals need to be created or deleted. This framework allows for reactions to be introduced efficiently when using a fixed-bond force field with minimal external intervention. The cross-linked models at different degrees of curing are annealed and subjected to uniaxial tensile loading for characterization of thermo-physical and mechanical properties, respectively. The developed cross-linking model is observed to correctly predict experimentally-observed trends for BMI such as density, glass transition temperature, coefficient of thermal expansion, thermal conductivity, Young’s modulus, as well as an unintutive experimental observation of decreasing density with increasing curing extent.

Molecular modeling of crosslinking reactions in high-temperature bismaleimide resins: Matrimid-5292

251st National Meeting (2016)

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