CONCENTRATION AND TEMPERATURE-DEPENDENCE OF DILUENT DYNAMICS STUDIED BY LINE-SHAPE EXPERIMENTS ON A PHOSPHATE ESTER IN POLYCARBONATE

P-31 Hahn spin echo line shape and proton line shape experiments are r eported on bisphenol A polycarbonate (BPAPC)-tris(2-ethylhexyl)phospha te (TOP) systems to study the concentration and temperature dependence of the local dynamics. In an earlier P-31 line shape study a lattice model was presented as a framework to interpret the plasticization and antiplasticization behavior of the diluent based on a fractional popu lation given by the type of nearest neighbor contacts in the mixed pol ymer-diluent glass. In this study, P-31 spin echo line shapes of BPAPC , with 5%, 10% and 15% TOP, which monitor the diluent dynamics, at dif ferent temperatures and echo delay times are simulated in terms of fas t- and slow-moving components, and the resulting fractional population s are compared with that predicted by the lattice model. Comparisons w ith the lattice model calculations are also made in the simulation of the H-1 line shapes on BPAPC with 5% and 10% TOP, which probes both th e polymer and diluent dynamics, and on BPAPC with 5% and 10% perdeuter ated trioctylphosphate (DTOP), which detects only the polymer motion. Fairly good line shape simulations and agreement between the lattice m odel and the fitting results at low diluent concentrations are obtaine d in all cases. Restricted cone motion best describes the slow-moving component in the P-31 line shape fittings. For the fast component, rot ational Brownian diffusion with a distribution of correlation times co rresponding to a stretched exponential function is used. An activation energy E(a) Of 56 kJ/mol and an exponent alpha of 0.7 for the fractio nal exponential correlation function are obtained and used to calculat e the mechanical loss peak which was compared with the experimental lo ss data. The plateau character of the fractional population as a funct ion of temperature can also be interpreted and understood in terms of the lattice model.