Ab initio calculation of the rate coefficient for short-chain branching in free-radical polymerizations

摘要

Short-chain branching in polyethylene, which involves a six-centre transition state, is studied by ab initio quantum mechanics up to the QCISD(T) level. The calculation gives a (low-pressure) activation energy of 73 kJ mol-1 and a frequency factor of 4.8 × 1012 s-1. The frequency factor for this six-centre transition state is expected to be of acceptable accuracy and also applicable to homologous systems, such as short-chain branching to polymer in acrylates. These results overestimate the amount of ethylene short-chain branching observed in experiment, but the discrepancy is within the uncertainties of both experiment and calculation. © 2000 Elsevier Science Ltd. All rights reserved.