Information on the Monomer Sequence of Poly(lactic acid) and Random Copolymers of Lactic Acid and Glycolic Acid by Examination of Static Secondary Ion Mass Spectrometry Ion Intensities

Abstract

Static secondary ion mass spectrometry (SSIMS) has been used to analyze a range of poly-(lactic acid)s (PLA) and copolymers of lactic and glycolic acids (PLGA). Ion assignments for the full range of radical cations observed are presented, along with the observation of chain end contribution to the SSIMS spectra in the case of low molecular weight PLA. The ion intensities within different radical cation series in PLGA have been compared with theoretical intensity distributions. In the case of random copolymers, the radical cation intensities are almost identical with the predicted binomial distribution. Dimeric character in some of the polymers is demonstrated using a statistical approach.

Extracting information on the surface monomer unit distribution of PLGA by ToF‐SIMS

“…Our data, however, lie somewhere between the purely monomeric and purely dimeric model, and this was taken as evidence that trans-esterification occurs during synthesis. [11,13] We now extend the previous model to show that it is possible, using SIMS, to determine the degree of trans-esterification. Assuming that the probability of encountering an ester link that has undergone a trans-esterification reaction is independent of the nature of the adjacent repeat units, we can assign a global probability, P T , which represents the ratio of trans-esterified bonds to the total number of ester bonds.…”

“…Positive ion spectra are employed in this study, since SSIMS positive ion spectra are found to be informative with regards to PLGA [13,32] and the ToF-SIMS spectrum of PLGA is given in Ref. [13].…”

“…[32] All existing characteristic PLGA fragments, including glycolide, lactide and mixed fragments in SSIMS spectra are summarised in Table 3 [32] and the possible postulated structures are discussed in Ref. [13]. Fragments with the same unit mass (numbers underlined in Table 3 After normalising the spectra throughout the composition by total ion counts, general increase in the intensity of lactide and mixed characteristic fragments were observed with decrease in the intensity of glycolide-only fragments, with increase in the bulk lactide composition.…”

A comparison of the static SIMS and G‐SIMS spectra of biodegradable homo‐polyesters

“…The SSIMS spectrum was in close agreement with the spectra obtained from the previous studies. [14,15] However stability of the structures given above for m/z 100 and 101 are extremely strained, and therefore, unlikely that the ions possess these structures. This was discussed in the previous paper by Shard et al, where it was proposed that if the cyclic structures are allowed to exist they would exist as intermediate structures, and there should be a 'scrambling' of the isotopically different oxygen atoms, which would be evident in further fragmentation of the ion.…”

“…This was discussed in the previous paper by Shard et al, where it was proposed that if the cyclic structures are allowed to exist they would exist as intermediate structures, and there should be a 'scrambling' of the isotopically different oxygen atoms, which would be evident in further fragmentation of the ion. [15] At m/z 101, there was also another peak present, which was assigned as C 4 H 5 O 3 + with a deviation of 3.8 ppm. For PLA, significant broadening of the mass peaks was observed for m/z > 300.…”