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

摘要

When commercial oligo- or poly(ethylene glycol)s and dibutyltin dimethoxide were condensed in bulk with elimination of methanol, no linear polycondensates were obtained and tin-containing macrocycles were the only reaction products. In order to improve the hydrolytic stability, stoichiometric amounts of #gamma#-thiobutyrolactone were inserted into the macrocyclic oligoethers, so that the Sn--O bonds were transformed into Sn--S bonds. The formation of monomeric (containing one Bu_2Sn group) macrocycles was confirmed. The tin-containing macrocyclic polyethers were used as macrocyclic initiators for the ring-expansion polymerization of #epsilon#-caprolactone. The resulting macrocyclic poly(ether-ester)s were isolated in the form of telechelic A-B-A block copolymers after precipitation into methanol.