Synthetic resins typically contain a range of polymeric structures comprised of various ratios of the monomeric components. When analysed by ESI, mostly singly-charged ions are produced predominantly and the oligomeric species of the polyesters can be clearly identified. The ESI spectra enabled identification of: the range of chemical structures present in each sample; the distribution of acid versus alcohol "end groups" (important in the stability of cross linked resins) and; the degree of branching, transesterification and cyclisation. The identities of the peaks in the ESI mass spectra have been confirmed by tandem mass spectrometry. The results of ESI analyses will also be compared to MALDI mass spectra of the same resins. In general the spectra obtained by the two techniqes are very similar, however, there were some differences in the relative intensities of minor species present in these resins (e.g. branched and cyclic) which probably reflect the different mechanisms operative with these techniques.
Finally, ESI and MALDI analyses have been performed on fractions of the polyesters isolated by size exclusion chromatography (SEC) and the implications of these results for the molecular weight determination of polymers will be discussed.