Search

Density functional theory calculations are used to determine the kinetics and reactivity indices of the first propagation steps of the polyethylene and poly(vinyl chloride) polymerization. Transition state theory is applied to evaluate the rate coefficient from the microscopically determined energies and partition functions. A comparison with the experimental Arrhenius plots validates the level of theory. The ability of reactivity indices to predict certain aspects of the studied propagation reactions is tested. Global softnesses of the reactants give an indication of the relative energy barriers of subsequent monomer additions. The correlation between energy and hardness profiles along the reaction path confirm the principle of maximum hardness. Local indices predict the regioselectivity of the attack of the growing radical to vinyl chloride. [ABSTRACT FROM AUTHOR]

Abstract: Composite binary trees are introduced for an improved kinetic Monte Carlo (kMC) calculation of chemical composition-chain length distributions (CC-CLDs) in polymerization processes, such as the bivariate copolymer composition-CLD (CoC-CLD). For the calculation of the CC-CLD, each leaf node of the main tree, which reflects the number of macromolecules with a given chain length, serves as a root node for a sub-tree containing information on the CC distribution for the macromolecules with the selected chain length. For low maximum chain lengths of 1000, the improvement consists already in a reduction of the kMC operations by a factor between 103 and 106. The approach is illustrated for the calculation of the CoC-CLD in free and atom transfer radical copolymerization of methyl methacrylate and styrene while accounting for potential diffusional limitations. Main focus is on the capability of the algorithm to ensure an accurate calculation of the average copolymer composition including high chain lengths. [Copyright &y& Elsevier]