Abstract
Ring-opening polymerization of 6,8-dioxabicyclo[3.2.1]octane derivatives possessing, as a common substituent, an equatorial benzyloxy group in position 3 was investigated to clarify an important role of the substituent in the formation of structurally regular polyacetals composed of cis-2,6-linked tetrahydropyran rings. Polymerization of 3(e)-benzyloxy-4(a)-methoxy-6,8-dioxabicyclo[3.2.1]octane (1) was undertaken in dichloromethane and toluene with phosphorus pentafluoride as initiator at −60°C. 13C NMR analysis disclosed that the polymer predominantly consisted of the cis-2,6-linked tetrahydropyran rings 4β The proportions of the cis units in the polymers increased with decreasing initial monomer concentration. Polymerization of 3(e)-benzyloxy-6,8-dioxabicyclo[3.2.1]octane (2) was carried out in dichloromethane with phosphorus pentafluoride as initiator at −60 and −90°C. The polymers prepared at −60°C were enriched in the cis units 5β as well, whereas the polymer entirely composed of the trans-2,6-linked tetrahydropyran rings 5α was obtained at −90°C. These results were reasonably interpreted in terms of a previously proposed propagation mechanism involving oxonium exchange at the penultimate unit.
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Hirasawa, T., Okada, M. & Sumitomo, H. Polymerization of Bicyclic Acetals XVI. Substituent Effect of an Equatorially Oriented Benzyloxy Group in Position 3 on the Stereochemical Course of the Cationic Ring-Opening Polymerization of 6,8-Dioxabicyclo[3.2.1]octane Derivatives. Polym J 20, 587–596 (1988). https://doi.org/10.1295/polymj.20.587
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DOI: https://doi.org/10.1295/polymj.20.587