Bimodal molecular mass distribution upon polymerization by the action of dilithium initiators: A refined model for the two-phase process: Comparison of calculations to experiment

A refined model is proposed for the formation of bimodal molecular mass dis tribution upon polymerization of hydrocarbon monomers by the action of dili thium initiators, which accounts for the separation of the reaction mixture into two phases (sol-fraction solution and swollen gel fraction) during po lymerization. The model includes the dependence of the propagation rate par ameters and the crosslinking efficiency in the precipitate phase on the pol ymer chain length, as well as the dependence of the entropy term of the fre e energy for the tetrameric and dimeric association of living chains on the concentration of elastically active chains in the precipitate phase. The c alculation results are compared with experimental data on a change in molec ular mass distribution parameters in the course of 1,4-dilithiumpentane-ini tiated butadiene polymerization in heptane.