| Abstract: | 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. |
