Telechelic polyacetals have been synthesized by endcapping of bifunctionally living polyacetals with tertiary amines. Bifunctionally living poly‐(1, 3‐dioxolane) (poly‐DXL) was obtained by polymerization of the cyclic acetal initiated with terephthaloyl‐bis‐triflate. Attempts to prepare well defined bifunctionally growing poly‐DXL with trifluoro‐methane sulfonic acid anhydride failed. Low molecular weight dialkyl formals containing functional groups were used as transfer agents for the polymerization of cyclic acetals to control the molecular weight of the polymer and to introduce functional endgroups. Polytelechelic hydroxy‐terminated poly‐DXL was synthesized by copolymerization of DXL and glycidol. The latter monomer reacts as comonomer through its epoxy ring and as transfer agent by its hydroxyl group.

: Telechelic polyacetals, obtained by cationic ring-opening polymerization of 1,3-dioxolane (DXL) and 1,3-dioxepane (DXP), have been used as building blocks for polymer materials. In the first part of this paper, the synthesis and the properties of networks based on polyDXL a,w-bis(methacry1ates)ai-e discussed. The second part deals with the synthesis and the properties of polyacetal polyurethanes. A thermoplastic polyurethane was prepared with poly(DXL-co-DXP) a,o-diol as soft segment and the combination butane-1,4-dioI and hexamethylene diisocyanate as hard segment. Polyurethane networks were obtained from polyacetal polyols and diphenylmethane diisocyanate (MDI). Some physical properties of these new materials are reported.

Two methods for the synthesis of branched (co)polymers by cationic ring‐opening polymerization are presented. The first method is based on the spontaneous intermolecular termination that is observed in the polymerization of the four‐membered cyclic sulfides (thietanes). The branching points in these polymers are sulfonium ions. This method has been extended to polyether ‐ polysulfide block copolymers obtained by sequential polymerization of THF and a thietane. In the thus obtained AB block polymers, the branching points are concentrated in the sulfide segments only. By similar techniques, ABA types of block copolymer networks have been obtained making use of bifunctional initiators. The second method consists of copolymerizing a cyclic acetal such as 1,3‐dioxolane (DXL), with a “monofer”, which is a monomer that contains also a chain‐transfer function. As monofers for the DXL polymerization glycidol and glycerol formal were used. The end products are polyacetal‐polyols which contain a hydroxyl group at each of the chain ends. Reaction of these polyols with di‐isocyanates leads to the corresponding polyacetal polyurethanes.

Four different routes for the production of polyacetal containing networks are described : (1) free radical copolymerization of α,ω‐(meth)acrylate terminated polyacetals, (2) hydrosilylation reactions of α,ω‐allyl terminated poly‐ (1,3‐dioxolane) with a multifunctional silane, (3) modification of α,ω‐hydroxy terminated poly(1,3‐dioxepane) through reaction with 3‐isocyanatopropyl‐triethoxysilane and subsequent cross‐linking under influence of H2O and (4) cross‐linking of multifunctional hydroxy‐terminated polyacetals by reaction with a diisocyanate.