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).

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Classical initiation induces polymerization through cyclic tertiary oxonium ions which are responsible for the formation of an important quantity of cyclic oligomers. The activated monomer mechanism, i.e. polymerization in the presence of a diol, has been successful in the case of some substituted oxiranes such as epichlorohydrine and propylene oxide. It has also been used in the case of cyclic acetals [1,3‐dioxolane (DXL) and 1,3‐dioxepane (DXP)] and allows the preparation of dihydroxylated homopolymers as well as that of triblock copolymers. It was nevertheless shown that transacetalization leads to complications at the onset of the reaction. In order to shed some light on the reactions involved, we used a monoalcohol ‐ methanol ‐ instead of a diol. The products were separated and characterized: a monoadduct (methanol‐DXL) was observed, confirming the occurence of the active monomer mechanism, but dimethoxymethane was also observed, evidence of transacetalization between methanol and DXL. It was shown that fast equilibration takes place between the following compounds: (methanol + DXL), (monoadduct of methanol and DXL), (dimethoxymethane + ethyleneglycol). When p‐isopropenylbenzyl alcohol was used, it was possible to prepare macromonomers, i.e. poly(DXL) chains carrying polymerizable double bonds at their ends. Nevertheless because of the transacetalization reaction described above, a mixture of products was obtained.

1,3-Dioxolane was polymerized in the presence of ethylene glycol in order t o prepare awdihydroxylated polymers which, upon reaction with pluriisocyanates yielded networks swellable in water. The crosslinks were made of urethane groups, which are bulky and hydrophobic. In order to expand the scope of the networks that can be envisioned, we have studied the replacement of the two end-standing hydroxylic groups by unsaturated polymerizable groups. Several methods are presented which allow successfully the quantitative endowment of the polymer endings with methacryloyl-or styryl-or vinylether-type groups.am-dihydroxylated poly( 1,3-dioxolane) was also metallated and used as a macroinitiator for the polymerization of ethylene oxide: the a,w-dihydroxylated triblock copolymer obtained is made of a central poly( 1,3-dioxolane) block flanked by two poly(ethy1ene oxide) ones.Several methods are also shown t o be efficient in the characterization of the hydroxylic end-standing functions of the polymer.