Matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight collision-induced dissociation study of poly(p-phenylenediamine terephthalamide) fragmentation reactions.

MALDI-TOF/TOF collision-induced dissociation (CID) experiments are reported on model poly(p-phenylenediamine terephthalamide) (PPD-T) polymers, revealing a variety of synthesis reaction products. Diamine-terminated oligomers were the major product of synthesis using excess amine, and di-carboxylic acid oligomers were the major product for excess acid. Structures of major reaction products were confirmed by CID fragmentation studies, along with detailed studies of MS/MS decomposition pathways. Apparent fracture of the phenylcarbonyl bond was the major fragmentation pathway (independent of end groups), resulting from initial NHCO bond cleavage with subsequent CO loss. Hydrogen-transfer reactions play an important role in fragmentation, involving both cross-chain abstraction of NH hydrogen and long-range H-transfer. End-group and main-chain modifications produce fingerprint CID fragmentation patterns that can be used to identify end groups and branching patterns; the structure of an unanticipated synthesis product was established using CID. The effect of synthesis conditions on polymer composition was studied using the analysis of variance, specifically, the amine-to-acid ratio used and post-synthesis addition of CaO. Of particular interest is oligomer end-group modification by the solvent (N-methyl pyrrolidone) induced by addition of CaO.