Addition-fragmentation chain transfer:: Molecular weight distributions and retardation in the system methyl methacrylate/methyl α-(bromomethyl)acrylate

A detailed investigation of addition-fragmentation chain transfer (AFCT) in the free-radical polymerization of methyl methacrylate (MMA) in the presence of methyl alpha-(bromomethyl)acrylate (MBMA) was carried out to elucidate mechanistic details with efficient macromonomer synthesis as an underlying goal. Advanced modeling techniques were used in connection with the experimental work. Curve fitting of simulated and experimental molecular weight distributions with respect to the rate coefficient for addition of propagating radicals to MBMA (k(add)) over 60-120 degreesC resulted in E-add = 21.7 kJ mol(-1) and A(add) = 2.18 x 10(6) M-1 s(-1) and a very weak temperature adds dependence of the chain-transfer constant (E-add approximate to E-p). The rate coefficient for fragmentation of adduct radicals at 60 degreesC was estimated as k(f) approximate to 39 s(-1) on the basis of experimental data of the MMA conversion and the concentration of 2-carbomethoxy-2propenyl end groups. The approach developed is generic and can be applied to any AFCT system in which copolymerization does not occur and in which the resulting unsaturated end groups do not undergo further reactions. (C) 2004 Wiley Periodicals, Inc.