Fate of the initiator in the azobisisobutyronitrile-initiated polymerization of styrene

Abstract

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.

Radical Chain Polymerization

“…3-2a). This expectation is generally verified in the few systems which have been experimentally examined [Bevington, 1988;Moad et al, 1982Moad et al, , 1984Solomon and Moad, 1987]. Tail addition occurs exclusively in the AIBN and tbutyl peroxide initiated polymerizations of styrene and the AIBN-initiated polymerization of vinyl chloride; there is no detectable head addition.…”

“…A minor reaction of 2-cyano-2-propyl radicals is disproportionation to methacrylonitrile and isobutyronitrile [Moad et al, 1984;Starnes et al, 1984]. This presents a complication for polymerizations carried out to high conversions where the methacrylonitrile concentration is significant since methacrylonitrile undergoes copolymerization with many monomers.…”

A novel approach to the characterization of end groups in styrene-methyl methacrylate copolymers by pyrolysis-gas chromatography

“…12 The NEW END-GROUP ANALYSIS OF ST-MMA COPOLYMERS 1, although the former structure might be mostly formed by the recombination termination between a propagating PMMA chain and an isobutyronitrile radical rather than by the initiation reaction. 17 Among these, 2,3-dicyano-2,3-dimethylbutane (Peak 5) might be attributed to a recombination product of isobutyronitrile radicals formed from the remaining AIBN in the polymer sample because it was also observed on the pyrogram of AIBN alone with a fairly strong intensity. The fact that its relative intensity on the pyrogram significantly decreased by repeated purification of the sample also supports its origin from the remaining AIBN rather than from the endgroup AIBN residues.…”

On the Origins of Nitroxide Mediated Polymerization (NMP) and Reversible Addition–Fragmentation Chain Transfer (RAFT)

“…[34,35] The other disproportionation product, methacrylonitrile (3 in Scheme 11), is a potential comonomer. [36,37] Furthermore, the formation of the ketenimine (2 in Scheme 11) can complicate the analysis.…”