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.