Synthesis of new polyethers derived from isoidide under phase-transfer catalysis: Reactivity and selectivity under microwaves and classical heating

Abstract

Microwave irradiation was applied to the synthesis of polyethers from 1,8-dibromo- and 1,8-dimesyl-octane under solid-liquid phase-transfer catalytic conditions. To evaluate the influence of microwaves on the reaction rates and polyether properties, we carried out the polymerization reactions under similar conventional conditions (oil bath) with the same temperature profiles. First, the microwave-assisted syntheses proceeded more rapidly in comparison with conventional heating, and the reaction time was reduced from 24 h to 30 min with higher yields of polyethers. Second, the structure of the polymers strictly depended on the activation mode. Under microwave conditions, the polyethers were characterized by higher molecular weights with better homogeneity. Third, the mechanism of chain termination was different under microwave and conventional conditions. The polyethers prepared with conventional heating possessed shorter chains with mainly hydroxylated ends, whereas under microwave irradiation, the polymer chains were longer with mainly ethylenic group ends. In fact, under microwave irradiation, ethylenic group ends were formed rather rapidly and set up a hindrance to further polymer growth. In contrast, under conventional conditions terminations were essentially constituted by hydroxyl functions; however, further polymerization was terminated as well.