Initiation mechanisms for radical polymerization of styrene and methyl methacrylate with highly substituted peroxypivalate initiators

Tomoyuki Nakamura, Shuji Suyama, W. Ken Busfield, Ian D. Jenkins, Ezio Rizzardo, San H. Thang

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17 Citations (Scopus)


The initiation mechanisms of 1,1,2-trimethylpropyl peroxypivalate 1a and 1,1,2,2-tetramethylpropyl peroxypivalate 1b in the radical polymerization of styrene and methyl methacrylate (MMA) have been studied using the nitroxide trapping technique. Thermolysis of 1 generated t-butyl and the corresponding t-alkoxyl radicals, i.e. 1,1,2-trimethylpropoxyl 2a and 1,1,2,2-tetramethylpropoxyl radicals 2b. Both t-alkoxyl radicals underwent very fast unimolecular processes (β-scission) essentially to the exclusion of intermolecular processes (addition and H-abstraction), in contrast to other t-alkoxyl radicals such as t-butoxyl radicals. The extent of β-scission of 2a and 2b to form alkyl radicals R· were 97.6 and 99.7% in styrene and 98.4 and 99.7% in MMA, respectively. Alkyl radicals formed in the reaction then underwent selective tail addition to monomers or were trapped by the nitroxide. From the relative yields of products arising from the competitive addition/trapping reactions of alkyl radicals, the absolute rate constants for the addition of isopropyl radicals to the two monomers at 60°C are estimated to be 4.7 × 105l mol-1 s-1 to styrene and 1.3 × 106l mol-1 s-1 to MMA, respectively.

Original languageEnglish
Pages (from-to)1395-1401
Number of pages7
Issue number6
Publication statusPublished - 1 Jan 1999


  • Initiation mechanism
  • Nitroxide trapping
  • Radical polymerization

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