Analysis of All-Aromatic Polyesters by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Abstract

Vectra, a commercial copolymer of 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA), is highly intractable, and its analysis has always been problematic. Lower molecular weight polymer and an analogue have been synthesized and analyzed by MALDI−TOF mass spectrometry. Our sample preparation uses pentafluorophenol and hexafluoro-2-propanol as solvents and parafilm on the MALDI plate. In the MALDI−TOF spectra a characteristic difference was found between the copolymers synthesized using HNA with either 3-HBA or 4-HBA: the 3-HBA copolymer resulted in one main series of ions indicating no significant degradation during the polymerization, while the 4-HBA copolymer showed evidence of several depolymerization via a quinomethide mechanism. The MALDI−TOF spectra demonstrated that the distribution of the oxybenzoyl (B) and oxynaphthoyl (N) monomer units was close to the stoichiometric ratio, indicating that the reactivities of these units are very similar.