Characterization of Polyesters by Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

A series of aliphatic polyesters, characterized by assymetric oligomer distributions, heteroterminated linear chains, and cyclic oligomers, were studied using MALDI. The results from structural characterization of these materials was compared with those acquired using fast atom bombardment mass spectrometry (FAB-MS), electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR) spectroscopy, and end group titration. Information on the composition of these polymers obtained from MALDI, ESI-MS, and end group titration showed reasonable agreement. However, the MALDI ionization efficiency appeared to be higher for carboxyl-terminated oligomers. MALDI molecular weight determination were contrasted with those from GPC and NMR. Reasons for disparities in the results between the three methods are discussed. The feasibility of using acidolysis for structural characterization of high molecular weight or insoluble materials was explored. Reaction of the polyesters with trifluoroacetic acid (TFA) produced mono- and bis(trifluoroacetate) esters of the starting material. The products were characterized and the progress of the reaction was monitored using MALDI.