Characterizing chain-end structures formed during initiation reactions of radical polymerization for MMA-St-BA terpolymer using pyrolysis-gas chromatography/atmospheric pressure chemical ionization high-resolution time-of-flight mass spectrometry.

Abstract

Analyzing polymer end groups using pyrolysis (Py) gas chromatography/mass spectrometry (GC/MS) in multi-component polymer samples is not an easy task because of the insufficient sensitivity, selectivity, and mass resolution of conventional Py-GC/MS systems. A new Py-GC/MS system using an atmospheric pressure chemical ionization (APCI) source combined with high-resolution time-of-flight mass spectrometry (TOFMS) was used for end-group analysis of a methyl methacrylate (MMA)-styrene (St)-butyl acrylate (BA) terpolymer (P (MMA-St-BA)), which was radically polymerized using 2,2'-azobis(2-methylbutyronitrile) (AMBN) as an initiator. Five possible pyrolyzates, comprising an AMBN fragment and a monomer unit, formed during the initiation reactions from one of the three types of end groups, were selectively detected and exclusively identified in their respective extracted ion chromatograms for molecule-related ions, such as M+ and [M + H]+ , with a narrow mass window of ±2 milli m/z units. It was demonstrated that Py-APCI-TOFMS is a powerful technique to characterize in detail the complex end groups in multi-component polymer samples, because of the soft ionization nature of APCI and the high mass resolution of TOFMS.