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The initiator-derived residues in polystyrene prepared by using azobis(isobutyronitrile-a-13C) as the initiator have been identified and quantified by 13C NMR. For low-conversion polymers the only initiator fragments present are those incorporated during the initiation step (i.e., by tail addition to monomer). Contrary to some recent reports, primary radical termination and transfer to initiator were found to be of little importance in AIBN-initiated styrene polymerization. These processes account for less than 2% of end groups in low-conversion (8%) polymers prepared in bulk with initiator concentrations in the range 0.01-0.2 M. In high-conversion (85%) polymers prepared with a high (0.2 M) initiator concentration the copolymerization of methacrylonitrile formed from the initiator can be detected.

The relative mobility is here defined using the mobility of the "tracking dye" bromophenol blue as a reference.

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