The combination of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF-MS) and size exclusion chromatography (SEC) combined with pulsed laser polymerization has been used to evaluate propagation rate coefficients (kp) in bulk free-radical polymerization for the systems methyl methacrylate and styrene. By varying laser frequencies, the relation between polymer chain length and observed propagation rate coefficient (k p obs ) has been investigated in detail. It has been found that deviations between MALDI-ToF-MS and SEC at higher molecular weights are the result of instrumental effects in SEC. Moreover, using a model and taking into account experimental studies on the propagation of oligomeric species, it has been inferred that the relationship between k p obs and polymer chain length is the result of chain-length-dependent behavior of the true kp in the oligomeric range, therewith excluding any chain-length-dependent behavior at higher molecular weights.

The catalytic chain transfer polymerization of styrene is only truly effective when the reaction mixture is exposed to (UV‐)light. The apparent chain transfer constant depends inversely on radical concentration and can be increased up to 8000. These results can be explained by combining aspects of both catalytic chain transfer and the formation of cobalt‐carbon bonds. For the catalytic chain transfer polymerization of n‐butyl acrylate a chain transfer constant of 650 was found. The resulting transfer coefficient has the same order of magnitude as the one for n‐butyl methacrylate. This means that the absence of an α‐methyl group hardly influences the transfer step itself. Furthermore, the effect of possible impurities on the catalytic chain transfer polymerization of methyl methacrylate is investigated.

The chain transfer-to-monomer dominated regime of the molar mass distribution of lowconversion 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 chaintransfer coefficient as a function of composition. By calculation of the ratio of the concentrations of styreneterminated 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.

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In this work it is shown that catalytic chain transfer is a very efficient way of controlling molecular weight in the copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA). The experimental data are compared to a previously developed model based on copolymerization kinetics and the mechanisms for catalytic chain transfer and for cobalt‐mediated living radical polymerization that can describe the observed transfer constants. Secondly, it is shown that the presence of a catalytic chain transfer agent does not affect the reactivity ratios within the concentration range studied. Finally, the effect of conversion and therewith composition drift on the catalytic chain transfer polymerization of MMA and BA is investigated and it is shown that under the conditions employed in the experiments a certain degree of macromer copolymerization is present at high partial conversions of MMA.