Semiquantitative Approach for Polyester Characterization Using Matrix-Assisted Laser Desorption...

Matrix-assisted laser desorption ionization/time-of-flight (MALDI/ToF) mass spectrometry and ¹H NMR were used for the structural investigation of isophthalic and maleic acid copolyesters with neopentyl glycol. Since both methods provided information on the ratio of incorporated acid components and terminating groups, results were compared and linear correlations (R² = 0.96-0.98) could be found. This suggests that MALDI/ToF MS is a suitable tool for the semiquantitative characterization of polyester systems. For the isophthalic/maleic acid ratio, MALDI results yielded constantly lower values than ¹H NMR, which was attributed to varying ionization efficiencies of homo- and copolyesters. Ratios of carboxylic and hydroxylic terminating groups, which are conventionally still measured by time consuming complex titrations, were measured with MALDI and ¹H NMR and were in good agreement. Both methods either excluded or distinguished unreacted monomers in the polyester bulk in contrast to acid-base titrations where those monomers severely distort the results. Additional structural information could be gained including the observation of cyclic structures (MALDI), E/Z isomerism from maleic to fumaric acid, and the statistical distribution of the acid components within the polyester chain (¹H NMR). While ¹H NMR peak assignments have to be verified by ¹³C NMR and multidimensional techniques, MALDI/ToF MS provides a straightforward technique that can be applied to other polyester systems without major alterations.