STATIC ATOMISTIC MODELING OF THE STRUCTURE AND RING DYNAMICS OF BULK AMORPHOUS POLYSTYRENE

A detailed static atomistic model of dense, glassy polystyrene is simulated using a well established technique that previously proved successful for simple vinyl polymers. Initial chain conformations that are generated using a Monte Carlo technique including periodic continuation conditions are ''relaxed'' by potential energy minimization. In total 24 microstructures at densities of 1,07 g/cm(3) were obtained with a cube-edge length of 18,65 Angstrom. Detailed analysis of the minimized structures indicates that intermolecular packing influences create a large variety of chain conformations different from the purely intramolecular ground states. The systems are amorphous, exhibiting random coil behavior. The described structures have been used for a quasistatic simulation of localized motions. These motions include stepwise rotation and oscillation of the phenyl groups. The frequency distribution for the simulated ring motions covers many orders of magnitude. It is very rare that an energy barrier with a reorientation angle indicating a ring ''flip'' is overcome. Motions with small reorientation of the phenyl rings, and therefore not leading to a ring ''flip'', dominate with an average reorientation angle of 16 degrees (+/-12 degrees). The intermolecular effects of the analyzed processes were found very important and far-reaching, widely influencing the cooperative motions of molecular groups.