Complementary Characterization of End Groups in Radically Polymerized Poly(methyl methacrylate) by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry and Pyrolysis-Gas Chromatography-Mass Spectrometry.

The end groups in radically polymerized poly(methyl methacrylate) samples with tert-butyl peroxy-2-ethylhexanoate as an aliphatic peroxide initiator and 1-octanethiol as a chain transfer reagent were complementarily characterized by high-resolution matrix assisted laser desorption/ionization (MALDI) spiral time-of-flight mass spectrometry (MS) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). The end groups comprised of three types of the initiator fragments and octylthio group originating from the chain transfer agent were confirmed by MALDI-MS measurements. In addition, their quantitative information was obtained by Py-GC-MS. Furthermore, combined with size exclusion chromatographic fractionation, the molar mass dependence of the end groups in the PMMA samples was also examined. It was suggested that the relative content of the octylthio end groups might increase with increase in the molar mass of the fractions. The observed results were interpreted in terms of the polymerization reactions of the PMMA samples.