We have studied the reaction of 1,3‐dioxolane with trifluoromethanesulfonic acid in the presence of α,ω‐dihydroxypolytetrahydrofurane and α,ω ‐ dihydroxypolystyrene. Besides polymerization of 1,3‐dioxolane we have observed the occurence of a fast coupling reaction between the initial oligodiols. The mechanism has been studied using a monohydroxylated polystyrene and a model compound, 3‐phenyl‐1‐butanol. We have shown that coupling takes places through transacetalization even under the mild conditions used Ethylene glycol is produced and an acetal bridge is formed between oligodiols. Conditions have been found where high‐molecular‐weight polymer is formed through this polycondensation, in the absence of homopoly(1,3‐dioxolane).

The polymerization of 1,3‐dioxolane was carried out using trifluoromethanesulfonic acid (triflic acid) as catalyst, in the presence of an oligomeric diol, α‐hydro‐ω‐hydroxypoly(oxyethylene) (PEOG) or α‐hydro‐ω‐hydroxypoly(oxytetramethylene) (poly‐THF‐diol). When PEOG was used, a linear increase of the number average molecular weight versus conversion was observed. A triblock copolymer was obtained as well as small cycles in their usual equilibrium concentration. When poly‐THF‐diol was used, fast transacetalization provoked the “polycondensation” of the diol through acetal linkages at the very onset of the reaction, leading to a very inhomogeneous mixture. After equilibrium was reached, through reactions involving all the various species present, a triblock copolymer was also obtained. In conclusion, this method is well suited to prepare α,ω‐diol block copolymers in which the initial oligomeric diol constitutes the center block, while the outside blocks are made of polyacetal.