END-GROUPS IN POLYMERS MADE USING DIMETHYL 2,2'-AZOBISISOBUTYRATE AS A SOURCE OF RADICALS

Azobisisobutyronitrile, enriched in its methyl groups with carbon-13, has been converted to dimethyl 2,2'-azobisisobutyrate. The isotopicall y enriched azoester has been used to initiate polymerizations of vario us monomers. The resulting polymers have been examined by C-13-NMR. Th e signals arising from the enriched methyl groups in the incorporated initiator fragments have been identified; they are strongly dependent on the nature of the attached monomeric unit. It is shown that the iso topically enriched azoester is likely to be useful for comparisons of the reactivities of monomers towards the 1-methyl-1-(methoxycarbonyl)e thyl radical which may serve as a model for the poly(methyl methacryla te) radical.