Determination of polyglycerol substructures and their connectivity by multidimensional and quantitative NMR spectroscopy

Artikel i vetenskaplig tidskrift, 2026

Polyglycerol (PG) is a versatile polyether whose properties strongly depend on its molecular weight and constitutional architecture. However, detailed characterization of its molecular constitution remains challenging due to its inherent heterogeneity and the resulting spectral overlap in NMR experiments. In this work, we present an approach for the assignment and quantitative analysis of PG substructures using NMR spectroscopy. A detailed assignment of ¹³C NMR signals was achieved, enabling identification of glycerol units based on both connectivity (terminal, linear, dendritic) and linkage type (via primary or secondary carbons). The assignments further reveal the identities of connected glycerol units, enabling characterization of local constitutional environments in addition to individual glycerol substructures. This provides a more comprehensive description than conventional methods. Based on these assignments, a user-friendly protocol was established to quantify the relative abundance of PG substructures. Applying this methodology to four oligomeric PG samples (PG2–PG6) reveals an increasing proportion of linear units with molecular size and a predominance of primary linkages, consistent with mostly linear molecules. The results also reveal an increasing diversity of constitutional substructures with increasing molecular size. A simplified ¹H NMR approach is further introduced for rapid estimation of terminal and linear content. This work provides a broadly applicable framework for quantitative constitutional characterization of polyglycerol, enabling improved understanding of its structure and supporting future studies of structure–property relationships.