Matrix-assisted laser desorption/ionization mass spectrometry of synthetic polymers: 2. Analysis of poly(methyl methacrylate)

Matrix-assisted laser desorption/ionization mass spectrometry (m.a.l.d.i.-m.s.) is shown to be a unique method for the determination of the functional heterogeneity of poly(methyl methacrylate)s. In group-transfer polymerization of methyl methacrylate, oligomers with cyclic end-groups are formed in addition to the expected linear oligomers. The cyclics are identified via preparative separation of the cyclic trimer by high-performance size exclusion chromatography. Using m.a.l.d.i.-m.s. the different homologous series are identified and their molar-mass distributions are calculated. In addition, high-performance size exclusion chromatography with dual refractive-index and ultra-violet detection provides information on the molar-mass distribution of the cyclic fraction. For technical products, it is shown that oligomers with cyclic end-groups may be formed in significant amounts and, therefore, have to be accounted for in structural characterization.