Article pubs.acs.org/ac
Sequence Analysis of Styrenic Copolymers by Tandem Mass Spectrometry Aleer M. Yol,†,§ Jonathan Janoski,‡,∥ Roderic P. Quirk,‡ and Chrys Wesdemiotis*,†,‡ †
Department of Chemistry, and ‡Department of Polymer Science, The University of Akron, Akron, Ohio 44325, United States S Supporting Information *
ABSTRACT: Styrene and smaller molar amounts of either mdimethylsilylstyrene (m-DMSS) or p-dimethylsilylstyrene (p-DMSS) were copolymerized under living anionic polymerization conditions, and the compositions, architectures, and sequences of the resulting copolymers were characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and tandem mass spectrometry (MS2). MS analysis revealed that linear copolymer chains containing phenyl−Si(CH3)2H pendants were the major product for both DMSS comonomers. In addition, two-armed architectures with phenyl−Si(CH3)2−benzyl branches were detected as minor products. The comonomer sequence in the linear chains was established by MS2 experiments on lithiated oligomers, based on the DMSS content of fragments generated by backbone C−C bond scissions and with the help of reference MS2 spectra obtained from a polystyrene homopolymer and polystyrene endcapped with a p-DMSS block. The MS2 data provided conclusive evidence that copolymerization of styrene/DMSS mixtures leads to chains with a rather random distribution of the silylated comonomer when m-DMSS is used, but to chains with tapered block structures, with the silylated units near the initiator, when p-DMSS is used. Hence, MS2 fragmentation patterns permit not only differentiation of the sequences generated in the synthesis, but also the determination of specific comonomer locations along the polymer chain.
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polymeric silyl hydrides can serve as macromonomers to synthesize star-branched or comb-type polymers via hydrosilylation.20 Due to the high reactivity of Si−H bonds, the macromonomer synthesis is accompanied by side reactions. As will be shown here, MS methods are ideally suitable for the detection and identification of the byproducts as well as for the characterization of the comonomer composition of the main (desired) products. Further, the utility of MS2 for not only distinguishing copolymer sequences but also determining specific comonomer positions along a chain will be illustrated for the first time.
opolymers are composed of two or more different comonomers. Depending on the type of monomers and synthetic approach used, sequences with block, tapered, alternate, or random architecture may be formed.1 The analysis of such materials by mass spectrometry (MS) presents significant challenges, as the molecular weight and end group distributions are convoluted by comonomer content distributions.2,3 With soft ionization techniques, in particular matrixassisted laser desorption ionization (MALDI)4,5 and electrospray ionization (ESI),6 and a reasonable mass accuracy (
