Macrocycles, 7 Cyclization of oligo- and poly(ethylene glycol)s with dibutyltin dimethoxide - a new approach to (super)macrocycles

When commercial oligo- or poly(ethylene glycol)s and dibutyltin dimethoxide were condensed in bulk with elimination of methanol, no linear polycondens ates were obtained and tin-containing macrocycles were the only reaction pr oducts. In order to improve the hydrolytic stability, stoichiometric amount s of gamma-thiobutyrolactone were inserted into thp macrocyclic oligoethers , so that the Sn-O bends were transformed into Sn-S bonds. The formation of monomeric (containing one Bu2Sn group) macrocycles was confirmed. The tin- containing macrocyclic polyethers were used as macrocyclic initiators for t he ring-expansion polymerization of epsilon-caprolactone. The resulting mac rocyclic poly(ether-ester)s were isolated in the form of telechelic A-B-A b lock copolymers after precipitation into methanol.