Analysis of non-polar polymers and copolymers by laser mass spectrometry.

摘要

A variety of non-polar polymers and copolymers were structurally characterized using two laser mass spectrometric methods, matrix-assisted laser desorption/ionization (MALDI), and pyrolysis-photoionization with vacuum ultraviolet radiation. Ethylene-methyl acrylate copolymers were compositionally analyzed using pyrolysis-photoionization MS. Comonomer content compared favorably to that obtained by NMR when analyzed using a partial least squares chemometric model based on seven samples of 2.8 mol % to 20.5 mol % methyl acrylate. Methyl acrylate homopolymer and copolymer blends were distinguished from pure copolymer by additional peaks in the spectra.; Isobutylene-para methylstyrene copolymer composition was found directly from MALDI mass spectra, but was higher in methylstyrene content by a factor of three compared to that obtained by NMR. MALDI-MS mass bias effects also caused an apparent composition drift. Compared to a Bernoullian statistical model, oligomers with greater methylstyrene content were overrepresented in the mass spectrum, likely due to preferential ionization. By multiplying the model intensities of the oligomers by an ionization efficiency term, the mole fraction of methylstyrene to the third power, good agreement was reached between the model and experimental intensities.; The microstructure of isobaric oligomers of ethylene-carbon monoxide copolymers unable to be resolved by MALDI-TOF was determined by MALDI-FTMS, which had sufficient resolving power to distinguish the small monomer mass difference (0.036 Da). Derivatization of the carbon monoxide monomers to hydroxyls was attempted to permit MALDI-TOF analysis but resulted in decreased ionization efficiency. Using a first-order Markovian statistical model of the FTMS data, the number average length of carbon monoxide was found to be 1, and that of ethylene, 3.6. Composition determined both by modeling and directly from the mass spectra agreed well with NMR data.; MALDI-MS relative ionization efficiencies were found for end-functionalized polystyrenes. Functionalization with a quaternary amine resulted in a ten-fold increase in signal relative to hydrogen and hydroxyl end groups, with a two-fold increase for a tertiary amine. The relative amount of tertiary amine oligomers cationized by silver was observed to increase with greater oligomer length. Although functionality did not have an effect on average molecular weight measurements, ionization efficiency values did change with molecular weight.