Abstract
Propylene carbonate (PC) was used as an alternative to the hazardous propylene oxide (PO) for the oxypropylation of condensed tannins from Acacia mearnsii. The influence of the catalyst, temperature and stoichiometry was evaluated in detail. All the synthesized polymers were characterized by 1H and 31P NMR, FTIR, and size exclusion chromatography. Polyether chains were successfully grafted on all hydroxyl groups. In addition to the ether linkages, some carbonate linkages were also formed. This can cause some chain coupling reactions, through condensation and/or transesterification reactions, which ultimately increase the molar mass and reduce the OH content of the final products. The use of K2CO3 as catalyst rather than hydroxides (KOH or NaOH) and a high temperature of reaction (170 °C) were found to strongly reduce this phenomenon. Using 10–40 equiv of PC per OH in tannins, polyether/polycarbonate chains of 2–6 units in average were grafted, containing less than 25% of carbonate units. The synthesized p...
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