Identification, Composition, and Asymmetric Formation Mechanism of Glycidyl Methacrylate/Butyl Methacrylate Copolymers up to 7000 Da from Electrospray Ionization Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

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Abstract
Glycidyl methacrylate (GMA) and butyl methacrylate (BMA) have the same nominal mass (142 Da) but differ in exact mass by 0.036 Da (CH4 vs O). Therefore, copolymers formed from the two isobaric monomers exhibit a characteristic isobaric distribution due to different monomer compositions. Here, we show that electrospray ionization FT-ICR mass spectrometry at 9.4 T resolves the isobaric components of copolymers as large as 7000 Da with a resolving power (m/Δm50%) of ∼500 000 in a gel permeation chromatography fractionated polymer sample. That resolution provides for complete and unequivocal component analysis of such copolymers of the size used for high solid content automobile coatings. All five possible copolymer products predicted by the polymerization mechanism are resolved and identified in the mass spectrum. Two of those polymer series (each with saturated end group) were previously unresolved by mass spectrometry because they differ in mass from the two other unsaturated products by only 0.0089 Da. Finally, analysis of the asymmetrical isobaric distribution for the copolymer n-mers, (GMA)m(BMA)n-m, 0≤ m ≤ n, in which species with adjacent values of m differ from each other in mass by 36 mDa (i.e., the mass difference, CH4 vs O, between GMA and BMA) proves that GMA is less reactive than BMA in the polymerization process.

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