Chain transfer to solvent in two‐state anionic polymerization, 2. Slow exchange between propagating species

Abstract

AbstractThe effect of slow exchange between growing chains on the average degree of polymerization (DP) and the molecular weight distribution (MWD) of polymers formed in a two‐state polymerization accompanied by chain transfer to solvent is considered. For the case when centres of only one type are capable of chain transfer it is shown that the exchange can be regarded as fast or slow, depending on the ratio of characteristic times of exchange (τex) and chain transfer (τtr) for these centres. The conditions for fast exchange, when the MWD of the polymer becomes independent of the rate of exchange, are derived. Under otherwise the same conditions, polymer of the narrowest MWD is formed if the exchange is fast, the number‐average DP being independent of the exchange rate. With increasing ratio τex/τtr, the weight‐average DP of the polymer increases and the MWD changes from unimodal to bimodal. For the case when “non‐transferring” centres are dormant, it was also found that at slow exchange the number‐average DP is greater and the MWD is less broadened than at fast exchange.