MALDI MS quantification of transesterification reactions in β-cyclodextrin-oligolactides systems

Abstract

Over the past decade, metal-free catalysis in the ring-opening polymerization of lactides has gained significant attention. Amine catalysts have enabled precise control over ring-opening processes, but transesterification side reactions, which impact polymer structure and properties, may also occur. Size exclusion chromatography was mainly used to quantify these processes and correlate their occurrence with synthesis parameters. However, mass spectrometry proved highly accurate in identifying transesterifications of polylactides. This study proposes a semiquantitative assessment of transesterification using MALDI MS during β-cyclodextrin-oligolactide synthesis via ring-opening oligomerization of D,L-lactide initiated by β-cyclodextrin. The degree of transesterification (Tr) and the relative rate of transesterification were measured to evaluate the influence of reaction parameters (temperature, solvents, concentration, molar ratios, and organocatalysts) on these side reactions. Parallel analysis of number average molecular mass and Tr evolution provided insights into the role of various organocatalysts (4-dimethylaminopyridine, imidazole, (-)-sparteine, 1,8-diazabicyclo[5.4.0]-undec-7-ene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene) in optimizing the synthesis process.