Copolymerization of tetrahydrofuran with 1,3-dioxane and telechelic oligomers

Copolymers of tetrahydrofuran (T) with 1,3-dioxane (D) were prepared by cationic copolymerization initiated with benzoylium hexafluoroantimonate or triflic anhydride in order to prepare macromolecules having predominantly hydrolitically stable ether (interunit) bonds with some hydrolitically unstable acetal bonds. Structure of copolymers was determined by H-1 and C-13 NMR. The proportion of the acetal bonds in copolymers was additionally confirmed in studies of the products of hydrolysis (only the acetal bonds hydrolyze). D is unable to homopolymerize for the thermodynamic reasons and therefore, mostly copolymers with long blocks of T separated with one or a few units of D: (-D-x T-y-), x<<y, are formed. Nevertheless, the reshuffling reactions are responsible for the appearance of "wrong" units. These are: the separate oxymethylene (M) and oxy-1,3-propylene units (P), subunits of D, located between two T units. Only the acetal bonds are cleaved in the acidic hydrolysis with dilute HCl. This gives telechelic oligomers of mostly HO-P-T-x-OH structure.