CHAIN TRANSFER TO SOLVENT IN 2-STATE ANIONIC-POLYMERIZATION .1. FAST EXCHANGE BETWEEN PROPAGATING SPECIES

A theoretical consideration of molecular weights and molecular weight distribution (MWD) of polymers formed in anionic polymerization procee ding via active centres of two different types under conditions of cha in transfer to solvent with a fast exchange between propagating specie s is presented. Analytical expressions for number- and weight-average degrees of polymerization are obtained. Expressions for ($) over bar P -n and ($) over bar P-w are shown to be the same as in a one-centre pr ocess with the apparent intensity of chain transfer proportional to th e weight fraction of the polymer formed via ''transferring'' centres. The polymers formed possess a moderately wide unimodal MWD. The depend ence of the polydispersity index on the effective intensity of chain t ransfer goes through a maximum; for M(0)/I-0 = 10(3) the maximum value of ($) over bar P-w/($) over bar P-n is ca. 4,6. The method is sugges ted for the estimation of the relative reactivity in chain propagation of two active centres from the dependence of molecular weight on init iator mixture composition. The effects of association of active centre s on the average molecular weights are analyzed. The case when one of the centres is dormant is also considered.