Reversible Polymer-Chain Modification: Ring-Opening and Closing of Polylactone.

A reversible polymer modification involving structural changes of the polymer chains was accomplished for the copolymer of CO2 and butadiene. The bicyclic structures were opened by hydrolysis and aminolysis reactions of the lactone moiety. For the hydrolysis product, the ring-closing of the ring-opened product was achieved by simply heating without any reagents or solvents. Nuclear magnetic resonance and matrix assisted laser desorption/ionization time-of-flight analyses and size-exclusion chromatography measurement of the polymer before ring-opening and after ring-closure suggested the retention of the polymer structure as well as the molecular weight and polydispersity during the reversible processes, proving that the modification can be performed without significant macroscopic changes of the polymer structure.