Studies on controlled radical polymerisation using 5-membered cyclic PROXYL nitroxides and corresponding alkoxyamines

Autor: Piet Span, Alistair Reid, Neil R. Cameron, J. J. G. Steven van Es, Anton L. German, Stefan Antonius Franciscus Bon
Rok vydání: 2000
Předmět:
Zdroj: Macromolecular Chemistry and Physics. 201:2510-2518
ISSN: 1521-3935
1022-1352
DOI: 10.1002/1521-3935(20001101)201:17<2510::aid-macp2510>3.0.co;2-s
Popis: 2,2',5,5'-tetramethylpyyridine-N-oxyl (PROXYL) and derivatives bearing one α-aryl substituent (Ph, p-CF 3 Ph, p-Me 2 NPb) were prepared and converted to alkoxyamines by reaction with di-tert-butyl peroxalate (DTBPO) and excess styrene. Both the nitroxides (plus DTBPO as is radical source) and alkoxyamines were investigated in the controlled radical polymerisation (CRP) of styrene, and their behaviour was compared to that of TEMPO. Polymerization mediated by each nitroxide displayed a linear relationship between molecular weight and conversion, producing material of low polydispersity indicating a controlled process. However, a comparison of kinetic behaviour was complicated by the unknown concentration of active species present. Polymerisation with preformed alkoxyamines at a known concentration also displayed controlled behaviour (polydispersities 1.25-1.5), and an influence of nitroxide substituent on the overall rate of polymerisation could be determined. PROXYL and the dimethylanilino-substituted nitroxide gave smillar CRP rates to TEMPO, whereas a Ph or to a lesser extent p-CF 3 Ph substituent resulted in significantly faster reactions. These results are discussed in terms of the likely steric and electronic influence of substituents on the nitroxide radical centre, and the resulting influence on polymerization rate. It is concluded that the steric bulk of the Ph substituent is the most likely cause of the rate enhancement displayed by the corresponding mediator.
Databáze: OpenAIRE
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