GENERATION OF GLASS STRUCTURES FOR MOLECULAR SIMULATIONS OF POLYMERS CONTAINING LARGE MONOMER UNITS - APPLICATION TO POLYSTYRENE

We describe a method for generating glass structures of polymers conta ining large monomer units for use in molecular simulations. This metho d is an extension of the technique proposed by Rigby and Roe (Rigby, D .; Roe, R. J. Chem. Phys. 1987,87,7285) for short-chain alkanes and in volves a ''polymerization'' of randomly placed monomers in the simulat ion box. An optimum polymerization sequence is found by the technique of simulated annealing, and a well relaxed glass structure is generate d from this sequence by a combination of molecular mechanics and molec ular dynamics simulations. We have used the technique to prepare 10 gl ass structure of polystyrene, for which we have calculated average str uctural properties. The amorphous nature of these structures is demons trated by the absence of long-range orientational correlations for the chain backbone. The phenyl rings also show a preference to pack at a distance of 5-6 angstrom and to align at right angles to one another.