Probing the reactivity of photoinitiators for free radical polymerization: Time-resolved infrared spectroscopic study of benzoyl radicals

Christopher S. Colley, David Grills, Nicholas A. Besley, Steffen Jockusch, Pavel Matousek, Anthony W. Parker, Michael Towrie, Nicholas J. Turro, Peter M W Gill, Michael W. George

Research output: Contribution to journalArticle

101 Citations (Scopus)

Abstract

A series of substituted benzoyl radicals has been generated by laser flash photolysis of α-hydroxy ketones, α-amino ketones, and acyl and bis(acyl)phosphine oxides, all of which are used commercially as photoinitiators in free radical polymerizations. The benzoyl radicals have been studied by fast time-resolved infrared spectroscopy. The absolute rate constants for their reaction with n-butylacrylate, thiophenol, bromotrichloromethane and oxygen were measured in acetonitrile solution. The rate constants of benzoyl radical addition to n-butylacrylate range from 1.3 x 105 to 5.5 x 105 M-1 s-1 and are about 2 orders of magnitude lower than for the n-butylacrylate addition to the counterradicals that are produced by α-cleavage of the investigated ketones. Density functional theoretical calculations have been performed in order to rationalize the observed reactivities of the initiating radicals. Calculations of the phosphorus-centered radicals generated by photolysis of an acyl and bis(acyl)phosphine oxide suggest that P atom Mulliken spin populations are an indicator of the relative reactivities of the phosphorus-centered radicals. The α-cleavage of (2,4,6-trimethylbenzoyl)phosphine oxide was studied by picosecond pump-probe and nanosecond step-scan time-resolved infrared spectroscopy. The results support a mechanism in which the α-cleavage occurs from the triplet excited state that has a lifetime less than or equal to the singlet excited state.

Original languageEnglish
Pages (from-to)14952-14958
Number of pages7
JournalJournal of the American Chemical Society
Volume124
Issue number50
DOIs
Publication statusPublished - Dec 18 2002

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phosphine
Free radical polymerization
Ketones
Polymerization
Oxides
Free Radicals
Photolysis
Infrared radiation
Excited states
Phosphorus
Bromotrichloromethane
Infrared spectroscopy
Rate constants
Spectrum Analysis
Acetonitrile
Density functional theory
Lasers
Pumps
Oxygen
Atoms

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Probing the reactivity of photoinitiators for free radical polymerization : Time-resolved infrared spectroscopic study of benzoyl radicals. / Colley, Christopher S.; Grills, David; Besley, Nicholas A.; Jockusch, Steffen; Matousek, Pavel; Parker, Anthony W.; Towrie, Michael; Turro, Nicholas J.; Gill, Peter M W; George, Michael W.

In: Journal of the American Chemical Society, Vol. 124, No. 50, 18.12.2002, p. 14952-14958.

Research output: Contribution to journalArticle

Colley, CS, Grills, D, Besley, NA, Jockusch, S, Matousek, P, Parker, AW, Towrie, M, Turro, NJ, Gill, PMW & George, MW 2002, 'Probing the reactivity of photoinitiators for free radical polymerization: Time-resolved infrared spectroscopic study of benzoyl radicals', Journal of the American Chemical Society, vol. 124, no. 50, pp. 14952-14958. https://doi.org/10.1021/ja026099m
Colley, Christopher S. ; Grills, David ; Besley, Nicholas A. ; Jockusch, Steffen ; Matousek, Pavel ; Parker, Anthony W. ; Towrie, Michael ; Turro, Nicholas J. ; Gill, Peter M W ; George, Michael W. / Probing the reactivity of photoinitiators for free radical polymerization : Time-resolved infrared spectroscopic study of benzoyl radicals. In: Journal of the American Chemical Society. 2002 ; Vol. 124, No. 50. pp. 14952-14958.
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