Chain transfer activity of ω-unsaturated methyl methacrylate oligomers

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 In 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.