Molecular architecture of poly[(R,S)-3-hydroxybutyrate-co-6-hydroxyhexanoate] and poly[(R,S)-3-hydroxybutyrate-co-(R,S)-2-hydroxyhexanoate] oligomers investigated by electrospray ionization ion-trap multistage mass spectrometry

A series of aliph. copolyesters was obtained from (R,S)-ß-butyrolactone and two isomeric hydroxy acids, 6-hydroxyhexanoic and (R,S)-2-hydroxyhexanoic acids. The reactions were conducted in bulk without catalyst. Electrospray ionization tandem mass spectrometry (ESI-MSn) was used for mol. characterization of these copolyester oligomers. The mass spectra of the copolyesters studied have enabled identification of their mol. structures including chem. nature of the end groups (hydroxyl and carboxylate). The compns. of the oligocopolyesters and their sequence distributions were detd. based on measurement of the relative intensities of the individual oligocopolyester peaks in the ESI mass spectra. The mass spectra (MS1) provided information on compn. and sequence distribution, and small deviations from Bernoulli statistics were detected. The arrangement of co-monomer structural units along the oligopolyester chains was verified by MS/MS expts. and investigation of the fragmentation pathways.