Controlled synthesis and solution behavior of macrocyclic poly[(styrene)-b-(ethylene oxide)] copolymers

A series of cyclic poly[(styrene)-b-(ethylene oxide)] diblock copolymers 4 (1.5 kg/mol < <(M)over bar>(n) < 1.1 kg/mol) with narrow molecular weight distributions (I <less than or equal to> 1.12) have been synthesized. They were obtained by intramolecular cyclization of linear a-diethyl acetal-omega -styrenyl poly(styrene ethylene oxide) 3, under high dilution conditions. The use of well-defined linear precursors in association with a cyclization process based on an unimolecular end-to-end coupling reaction allows the formation of macrocyclic diblocks in high yield (more than 90%). The structural characterization and the solution behavior of both the linear and cyclic amphipathic diblock copolymers have been investigated by means of NMR, size exclusion chromatography, and viscosimetry.