Bob W. J. Pirok

End-group-selective size-exclusion chromatography (esSEC) coupled with mass spectrometry (MS) is presented as an analytical approach for the separation and characterization of acid-terminated and non-acid-terminated poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA). The method employs a gradient normal-phase liquid chromatography system with basic (triethylamine) and acidic (formic acid) additives in ethyl acetate-based mobile phases, enabling selective retention of acid-terminated polymers, while non-acid-terminated species elute according to hydrodynamic volume, i.e., their effective size in solution. Following their release from the stationary phase, the acid-terminated polymers also undergo separation according to hydrodynamic volume.The separation involves adsorption of acid-terminated polymers under basic conditions, followed by their release upon introduction of an acidic mobile phase and subsequent size-based separation. Gradient steepness strongly influenced the elution behavior of acid-terminated polymers. Shallow gradients resulted in broader elution profiles reflecting prolonged adsorption–desorption, whereas steeper gradients produced sharper, more symmetrical peaks.The method can be directly coupled to MS, enabling molecular-level characterization of end-group structures and chemical composition across the chromatographic separation.The proposed esSEC–MS method provides a novel strategy for end-group-resolved polymer analysis. Its applicability is demonstrated by monitoring the formation of cyclic structures by intramolecular transesterification and the degradation of an ester-terminated PLGA copolymer over time.

End-group-selective size-exclusion chromatography (esSEC) coupled with mass spectrometry (MS) is presented as an analytical approach for the separation and characterization of acid-terminated and non-acid-terminated poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA). The method employs a gradient normal-phase liquid chromatography system with basic (triethylamine) and acidic (formic acid) additives in ethyl acetate-based mobile phases, enabling selective retention of acid-terminated polymers, while non-acid-terminated species elute according to hydrodynamic volume, i.e., their effective size in solution. Following their release from the stationary phase, the acid-terminated polymers also undergo separation according to hydrodynamic volume. The separation involves adsorption of acid-terminated polymers under basic conditions, followed by their release upon introduction of an acidic mobile phase and subsequent size-based separation. Gradient steepness strongly influenced the elution behavior of acid-terminated polymers. Shallow gradients resulted in broader elution profiles reflecting prolonged adsorption–desorption, whereas steeper gradients produced sharper, more symmetrical peaks. The method can be directly coupled to MS, enabling molecular-level characterization of end-group structures and chemical composition across the chromatographic separation. The proposed esSEC–MS method provides a novel strategy for end-group-resolved polymer analysis. Its applicability is demonstrated by monitoring the formation of cyclic structures by intramolecular transesterification and the degradation of an ester-terminated PLGA copolymer over time.

We introduce a novel analytical strategy for characterizing PLGA's monomer sequence and block-length distribution (BLD). Our approach couples controlled chemical degradation with RPLC-HRMS analysis. By employing two degradation strategies (0.5 vs 3 hrs), we characterize the microstructure of the PLGA co-polymer in terms of the dimer alternating structures (0.5 hr) and the BLD (3 hrs). This method allows for precise monitoring of the randomization caused by transesterification reactions. The BLD, characterized using a specialized algorithm, accurately reflects the polymer's blockiness without underestimation due to dimer-alternating structures, which is a common limitation of other methods like 13C NMR. We demonstrate the method's utility by showing that heterogeneities in block structure significantly influence PLGA's solubility. This new strategy provides critical insights into the relationship between monomer sequence and polymer properties, supporting the development of sequence-controlled PLGA for a wide range of applications.