Analysis of Structurally Complex Polymers by Time-Lag Focusing Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry

The analytical utility of matrix-assisted laser desorption ionization (MALDI) mass spectrometry for the characterization of structurally complex polymers is demonstrated. The advantages and limitations of the MALDI method are discussed through the analysis of several low molecular weight copolymers. Oligomer resolution is achieved by using a MALDI time-of-flight mass spectrometer equipped with pulsed ion extraction for time-lag focusing. Accurate mass analysis of the oligomers provides data sufficient for the confirmation of the repeat unit and end group structures for alternating copolymers. It is shown that for alternating copolymers poly[(o-cresyl glycidyl ether)-co-formaldehyde] and glycidyl end-capped poly[(bisphenol A)-co-epichlorohydrin], the molecular weight as well as detailed structural and compositional information can be obtained from a single spectrum of each. It is found to be more difficult to obtain compositional information on block copolymers or random copolymers. Through the analysis of poly[(propylene glycol)-b-(ethylene glycol)-b-(propylene glycol)]bis(2-aminopropyl ether) and Dow polyol A and polyol B, it is shown that prior knowledge of the end group and monomer masses is required to determine information on the monomer composition. Loss of unit mass resolution complicates the analysis for monomer composition. The issue of obtaining the necessary quantitative information for complete characterization of the above polymer systems is also addressed.