CROSS-CHAIN TRANSFER RATE CONSTANTS OF STYRENE-TERMINATED RADICALS TOMETHYL ACRYLATE AND METHYL-METHACRYLATE

The chain transfer-to-monomer dominated regime of the molar mass distr ibution of low-conversion emulsion copolymers of styrene and methyl ac rylate and of styrene and methyl methacrylate of various compositions, prepared with varying initiator concentrations, was analyzed with siz e exclusion chromatography. By extrapolation of the values of the slop e of the natural logarithm of the number molar mass distribution to ze ro initiator concentration, it was possible to determine the average c hain-transfer coefficient as a function of composition. By calculation of the ratio of the concentrations of styrene-terminated radicals and methyl (meth)acrylate-terminated radicals with an appropriate propaga tion model, the values of the cross-chain transfer rate constants of s tyrene-terminated radicals to methyl acrylate and methyl methacrylate could be deduced. These Values were interpreted in the light of newly gained insights into radical propagation and transfer reactions.