Experimental study of polystyrene thermolysis to moderate conversion

A general model for polymer degradation by concurrent random and chain-end processes was developed using continuous distribution kinetics. Population balance equations based on fundamental, mechanistic free radical reactions were solved analytically by the moment method. The model, applicable to any molecular weight distribution (MWD), reduces to the cases of independent r andom or chain-end scission. Polystyrene degradation experiments in mineral oil solution at 275-350 degreesC supported the model and determined reacti on rate parameters. The degradation proceeded to moderate extents requiring a MW-dependent random scission rate coefficient. Throughout the experiment s, the polymer MWD, which was measured by GPC, maintained the exponential f orm, so that the logarithm of MWD varies linearly with MW, with slope direc tly related to the number-average MW. Polystyrene random scission activatio n energy was 7.0 kcal/mol, which agrees well with other thermolysis investi gations but is lower than that found by pyrolysis due to fundamental differ ences between the processes. Magnesium oxide, added as a heterogeneous cata lyst in solution, was found to have no effect on polystyrene degradation ra te. (C) 2001 Elsevier Science Ltd. All rights reserved.