CHAIN TRANSFER ACTIVITY OF OMEGA-UNSATURATED METHYL-METHACRYLATE OLIGOMERS

The chain transfer activities of a series of omega-unsaturated methyl methacrylate oligomers [(dimer (1), trimer (2), tetramer (3), and a me thyl methacrylate macromonomer with average chain length of 24 units ( 4)] have been evaluated in methyl methacrylate polymerizations over th e temperature range 45-100 degrees C. Transfer constants were determin ed by analysis of the In chain length distributions. The dimer (1) was found to be substantially less effective as a chain transfer agent th an the trimer (2) or the higher macromonomers (3, 4) [C-T(60 degrees C ) 1, 0.013; 2, 0.19; 3, 0.31; 4, 0.21]. The transfer constants show on ly a small temperature dependence and no variation with conversion. No discernible retardation was observed in these polymerizations. A redu ced yield of polymer observed at conversions >10% in bulk polymerizati ons of MMA. carried out in the presence of 1-4 can be attributed to th e absence of the gel (Trommsdorff) effect. The results are interpreted in terms of the addition-fragmentation mechanism for chain transfer.