Polymerization of bicyclic acetals, 8. Cationic polymerization of 6,8‐dioxabicyclo[3.2.1]oct‐2‐ene

Abstract

AbstractPoly(5,6‐dihydro‐2H‐pyran‐2,6‐diyloxymethylene) (6), a new polyacetal having a dihydropyran ring in its repeating unit was prepared by selective ring‐opening polymerization of 6,8‐dioxabicyclo[3.2.1]oct‐2‐ene (5) at temperatures between −60 and −90°C in dilute methylene chloride or toluene solutions using boron trifluoride etherate as initiator. The resulting polymers, having a number average molecular weight up to 1,5 · 104, melted at 110 – 130°C and decomposed at ≈ 170°C in air. The isotactic dyad content of the polymers, estimated by 13C NMR spectroscopy, was found to be in the range of 70 to 77 mole‐%, somewhat lower than that of its saturated analogue, poly(tetrahydropyran‐2,6‐diyloxymethylene), (2). The preferred formation of the isotactic sequence along the polymer chain is rationalized in terms of the enantiomer selection by the growing chain end control mechanism as previously proposed for the polymerization of 6,8‐dioxabicyclo[3.2.1]octane, (1).