Distribution kinetics of thermolytic macromolecular reactions

Essential elements of thermolytic reaction kinetics for distributions of po lymers are reviewed. Bond scission, occurring randomly along a chain backbo ne or at the chain end, is the major reaction process in polymer thermolysi s. Underlying this bond scission are free radical mechanisms, including ini tiation and termination, hydrogen abstraction, and beta scission. Populatio n-balance equations for the molecular-weight distributions of macromolecule s or their radicals describe the dynamics of the reactions. The governing i ntegrodifferential equations for continuous distributions can be solved by moment methods, similarity techniques, other analytical procedures, or nume rical methods. The approach has been applied to analytical thermolysis and pyrolysis, polymer degradation for stability characterization or plastics r ecycling, and coal thermolysis to produce fuels and feedstocks. Experiments have demonstrated the usefulness of the continuous distribution kinetics a pproach for polymer thermolysis with additives, including hydrogen donors, peroxides, and other polymers. Molecular-weight distributions and their mom ents can be measured by size exclusion chromatography. Experimental data ca n be interpreted by evaluating rate parameters, which may be composites of rate coefficients for elementary steps in complex reaction mechanisms.