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The chain transfer activities of a series of ω-unsaturated methyl methacrylate oligomers (dimer ( 1 ), trimer ( 2 ), tetramer ( 3 ), and a methyl methacrylate macromonomer with average chain length of 24 units ( 4 ) have been evaluated in methyl methacrylate polymerizations over the temperature range 45−100 °C. Transfer constants were determined by analysis of the ln chain length distributions. The dimer ( 1 ) was found to be substantially less effective as a chain transfer agent than the trimer ( 2 ) or the higher macromonomers ( 3, 4 ) C T (60 °C) 1, 0.013; 2, 0.19; 3, 0.31; 4, 0.21. The transfer constants show only a small temperature dependence and no variation with conversion. No discernible retardation was observed in these polymerizations. A reduced yield of polymer observed at conversions >10% in bulk polymerizations of MMA carried out in the presence of 1 − 4 can be attributed to the absence of the gel (Trommsdorff) effect. The results are interpreted in terms of the addition−fragmentation mechanism for chain transfer.
Moad et al. (Mon,) studied this question.