Monte Carlo Simulation of the Topology and Conformational Behavior of Hyperbranched Molecules: Pd-Diimine-Catalyzed Polyethylene

Abstract

A kinetic Monte Carlo model was developed to simulate the polymerization of ethylene with palladium-α-diimine catalyst wherein hyperbranched molecules are formed through a chain-walking mechanism. The total degree of branching and the distribution of short branches obtained with the model agree well with reported 13 C NMR experimental results. Different chain topologies were generated by varying the probability of chain walking, P n , which controls the competition between chain-walking and monomer insertion. Molecular Monte Carlo simulations were subsequently conducted to study the conformations of isolated molecules (created by the kinetic Monte Carlo scheme) to relate molecular shape and topology, Our results provide evidence that the topology varies from predominantly linear with many short branches at low P w to a densely branched,globular structure at high P w . In contrast to experimental observations, our results for the molecular weight (N) dependence of the radius of gyration (R g N') indicate that the branching topology has an effect on this relation, i.e., high-P w molecules have a smaller scaling exponent v. The simulated N-dependence of the second virial coefficient exhibits a similar behavior. We also discnss the unusual conformational behavior of highly branched polymers obtained when P w → 1.