OH-functional polyesters based on malic acid: Influence of the OH-groups onto the thermal properties

Linear aliphatic polyesters having pendant hydroxyl groups were successfully synthesised by polycondensation using scandium triflate as catalyst. A first set of samples was prepared starting with hexane-, octane-, decane-, and dodecanediol and l-malic acid as hydroxyl functional dicarboxylic acid, on the one hand, and succinic acid as non-functional analogue, on the other. A second set of samples was prepared starting with different hydroxytelechelic oligo(ε-caprolactone)s, synthesised in a ring opening polymerisation (ROP) initiated by hexanediol using the same catalyst, and reacted with l-malic acid or succinic acid, respectively. The successful reaction was confirmed by nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS). The thermal properties of both types of polyesters – with and without pendant hydroxyl groups – were analysed by differential scanning calorimetry (DSC). While all polyesters based on succinic acid are highly crystalline, for the polyesters based on l-malic acid the crystallinity depends on the concentration of pendant hydroxyl groups and on the microstructure. Hence, the influence of the hydroxyl group enables to tailor the crystallinity.