Quantifying Poly(lactide- <i>co</i> -glycolide) Residual Dimer-Alternating Structure and Block-Length Distribution Using Controlled Chemical Degradation and Reverse-Phase Liquid Chromatography–Mass Spectrometry Analysis

The sequence and block-length distribution (BLD) of poly(lactic- co -glycolic acid) (PLGA) strongly influence solubility, degradation, and drug release. Here we present an analytical method combining controlled chemical degradation with reversed-phase liquid chromatography–high-resolution mass spectrometry (RPLC-HRMS) to achieve repeat-unit–resolved characterization of PLGA microstructures. Two complementary degradation pathways reveal dimer-alternating sequences and BLD, while a computational workflow (SWAMP-MS) reconstructs molecule-resolved block-length distributions, capturing features that ensemble-averaged techniques such as 13 C NMR can complement but do not fully resolve. The application of this approach to acetone-soluble and acetone-insoluble PLGA fractions demonstrates how subtle variations in blockiness affect solubility, highlighting the practical impact of sequence heterogeneity on polymer processing and performance. This integrated approach links polymerization chemistry to sequence-dependent properties, providing a robust framework for the rational design of sequence-controlled PLGA for drug delivery and other advanced applications.