Applications of Mass Spectrometry to Synthetic Copolymers

Over the last decade, application of mass spectrometry has grown immensely especially in polymer characterization. The focus of this thesis is to assess and extend the applicability of matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) and electrospray ionization mass spectrometry (ESI MS) in the analysis of synthetic copolymers.

Characterization of a non-ionic copolymer was attempted. The copolymer was styrene-co-maleic anhydride, which is in a class of copolymers that are used for commercial applications where low viscosity, high polarity and/or high reactivity are needed. MALDI-TOF MS was employed to obtain weight and number average molecular weight values (M_w and M_n), polydispersity index (PDI), monomer ratio, and endgroup identity. Results closer to the manufacturer’s specifications were obtained for M_w, M_n and PDI using this instrument. However, suitable internal standards were not found to enable distinction between isobaric endgroup possibilities by assessment of accurate mass.

Important information about polymers can be obtained using ESI MS. In conducting studies of in-source depolymerization for copolymer analysis by ESI MS, the limit of detection of monomers in the absence and presence of polymers was determined. In doing so, differences in fragmentation were observed when comparing pure monomer and monomer derived from depolymerization. The hypothesis was then made that monomer contamination could be determined in polymers based on these differences. To validate this method, a homopolymer of styrene sulfonic acid (SSA) was used. It was shown that the monomer-to-fragment ratio could selectively determine the amount of SSA monomer present. It was then of interest to assess whether determination was possible in a copolymer. The copolymer used to test this was poly(styrene sulfonic acid- co-maleic acid) (PSSA-MA). SSA monomer concentrations were assessed in a 1:1 mole ratio PSSA-MA copolymer. Unknown monomer concentrations were calculated from ESI-MS data using matrix algebra. It was then assessed whether monomer ratios could be obtained simultaneously with contamination. Both a 3:1 and 1:1 mole ratio PSSA-MA copolymer were analyzed. It was found that both characteristics (contamination and monomer ratio) could be determined.