Plasticization and antiplasticization in polycarbonates : The role of diluent motion

A phosphorus-31 solid echo chemical shift anisotropy line shape study of tris(2-ethylhexyl) phosphate in tetramethyl polycarbonate determined the rate and amplitude of diluent motion in this mixed glass as a function of temperature and concentration. The dynamics of the diluent are observed to be bimodal with diluent in contact with other diluent on a random basis, displaying much greater mobility than diluent surrounded by polymer. A lattice model adequately accounts for the population of each type of diluent. The diluent in contact with other diluent considered to be a microcluster undergoes isotropic Brownian rotational diffusion with an apparent activation energy of 56 kJ/mol. The isolated diluent molecules undergo Brownian rotation restricted to a cone, and the rate and amplitude of this motion increase slowly with temperature. The temperature and breadth of the mechanical loss peak at a frequency of 1 Hz associated with rotation of the diluent in microclusters can be calculated from the interpretati...