Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry investigations of polystyrene and poly(methyl methacrylate) produced by monoacylphosphine oxide photoinitiation

Abstract

AbstractThe chain‐end‐group composition was determined by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) analyses of low‐molecular‐weight polystyrene (PS) and poly(methyl methacrylate) (PMMA) produced by free‐radical polymerization with a monoacylphosphine oxide, (2,4,6‐trimethylbenzoyl) diphenylphosphine oxide (TPO), as a photoinitiator. Gel permeation chromatography (GPC) fractionation of the PS and PMMA samples with initial polydispersities of 1.81 and 2.81, respectively, yielded improved MALDI‐TOF MS spectra. Spectral analyses of the PS fractions showed distributions attributable to PS having two diphenylphosphinyl ends and PS having one diphenylphosphinyl end and/or one 2,4,6‐trimethylbenzoyl end, indicating that a combination of PS radicals with the highly reactive diphenylphosphine oxide group at one end of the chains was the predominant mode of termination. MALDI‐TOF MS results for PMMA fractions provided evidence for termination primarily by disproportionation, but structure determination was confounded by the presence of isobaric peaks. Discernible peaks were obtained by MALDI‐TOF MS analyses of GPC fractions of TPO‐initiated poly(methyl‐d3 methacrylate‐d5), in which the major product was PMMA with a diphenylphosphinyl end group and an abstracted deuterium end group, whereas the minor combination product had two diphenylphosphinyl chain ends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2161–2171, 2007