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Cationic polymerization of 2,3-dihydrofuran. Study on the relationship between glass transition temperature and tacticity of the polymer

The cationic polymerization behavior of 2,3-dihydrofuran (DHF) was investigated. Polymerization of DHF was carried out in the presence of boron trifluoride (BF 3 ) or ethylaluminum dichloride (EADC). The glass transition temperature (T g ) of the polymer depended upon the polymerization conditions. The T g of the polymer obtained in the polymerization with BF 3 at -78 °C was 150 °C. On the other hand, the T g of the polymer obtained in the polymerization above -60 °C was ca. 130 °C. In the polymerization with EADC, addition of ethyl acetate increased the molecular weight of the polymer compared to that of polymerization in toluene only. In the 13 C-NMR spectra of the polymer, splits of signals of main chain carbon atoms which corresponded to erythro and threo isomers were observed. A linear relationship between the ratio of isomers and T g was confirmed. The all-trans conformer of the threo-diisotactic isomer was concluded to be the most stable one from MM2' calculation. 13 C-NMR and molecular mechanics studies suggested that the difference in T g of the polymers was derived from the difference in tacticity of the polymers.