The chain transfer-to-monomer dominated regime of the molar mass distribution of low-conversion emulsion copolymers of styrene and methyl acrylate and of styrene and methyl methacrylate of various compositions, prepared with varying initiator concentrations, was analyzed with size exclusion chromatography. By extrapolation of the values of the slope of the natural logarithm of the number molar mass distribution to zero initiator concentration, it was possible to determine the average chain-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 propagation model, the values of the cross-chain transfer rate constants of styrene-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.