Sequence analysis of cyclic polyester copolymers using ion mobility tandem mass spectrometry

Abstract

Tandem mass spectrometry (MS2) via collisionally activated dissociation (CAD), coupled with ion mobility (IM) separation, has been employed to determine the sequence of macrocyclic polyester copolymers with thermoresponsive properties. The polyesters were synthesized by polyesterification of succinic acid with two diols functionalized with different, bioinspired amide pendants. MS analysis confirmed the formation of cyclic and linear chains composed of two different polyester repeat units, N and P. MS2 experiments on the sodiated macrocyclic trimer P3 showed that fragmentation encompasses ring opening by 1,5-H rearrangement over an ester group and consecutive dissociation of the ring-opened species via the same mechanism. Investigation of the macrocyclic trimers N1P2 and N2P3 revealed that ring opening occurs randomly at any of the ester groups of the macrocycle. Armed with these data, the sequence of the macrocyclic tetramer N2P2 was elucidated based on the dimeric NN, NP (or PN), and PP fragments generated by CAD of the sodiated ion. The observed fragment distribution provided evidence that the tetramer had predominantly a block architecture, viz. cyclo-NNPP. Preference for the block arrangement of the monomers was also found for a linear oligomer with four diol units. The IM dimension enabled the examination of singly sodiated cyclic or linear chains that overlapped with higher charge states of larger oligomers. The described sequencing strategy should be generally applicable to polymers with ester groups in the backbone. The architectural information deduced by such sequencing would significantly facilitate structure/property correlations and the design of copolymers with the desired physical properties.