Functionality, Molecular Weight, and Architectural Analysis of Water-Soluble Polymers by Multidimensional Mass Spectrometry

Abstract Poly(ethylene glycol) (PEG) is an industrial polymer, employed widely in biomedical, pharmaceutical, and materials applications due to its biocompatibility, water solubility, and stability. However, its end group and architectural diversity and susceptibility to oxidative and environmental degradation complicate precise molecular characterization. This study employed a multidimensional mass spectrometric approach, combining matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) with high-resolution mass spectrometry (MS), trapped ion mobility (IM) separation, and tandem mass spectrometry (MS/MS) fragmentation for the comprehensive compositional, structural, and architectural analysis of a degraded sample of methoxy poly(ethylene glycol) methacrylate (mPEG-methacrylate), a hydrophilic polymer used for the preparation of hydrogels and antifouling surfaces. MALDI-MS provided molecular-level resolution of the major degradation products, which included a small amount of surviving mPEG-methacrylate and significant quantities of new products, generated by modification or oligomerization of the methacrylate functionality. Comb-shaped copolymers with double bond and/or oxidized polymethacrylate chain ends were the predominant degradants. ESI-IM-MS added a rapid gas-phase separation dimension, resolving PEG chains according to both charge state and molecular shape and rendering ion mobilities (collision cross-sections) indicative of the architectural diversity produced during degradation. Products invisible by MALDI-MS could be identified, inter alia, as mPEG from ester hydrolysis and poly(mPEG-methacrylate)s with high degrees of polymerization. Charge-dependent mobility trends confirmed variations in polymer compactness depending on the number of PEG side chains, while MS/MS analysis validated the formation of comb architectures and revealed remarkable robustness for methoxy-capped polyether chains. This multidimensional MS strategy offers an advanced framework for the detailed structural elucidation of complex materials and formulations, capturing both the intact polymeric architecture and degradation-derived chemical diversity reflecting the sample’s age and usage. The integration of MALDI-MS and ESI-IM-MS enables simultaneous analysis of molecular weight, primary structure, architecture, and functional heterogeneity, thus providing critical insights into the synthesis, stability, and reactivity of industrial polymers.