Hydrogel formation by the 'topological conversion' of cyclic PLA-PEO block copolymers

Abstract

An amphiphilic cyclic block copolymer consisting of poly(L- or D-lactide) and poly(ethylene oxide), that is, PLLA-PEO or PDLA-PEO, was synthesized from its corresponding linear triblock precursor, PLLA-PEO-PLLA or PDLA-PEO-PDLA, respectively, with alkenyl end groups. A mixture of the micellar dispersions of linear PLLA-PEO-PLLA and linear PDLA-PEO-PDLA formed a gel upon heating, whereas a mixture of the cyclic counterparts did not undergo this phase transition. These results suggest that the gelation behavior is directed by the topology of the polymer components. Furthermore, cyclic PLLA-PEO and cyclic PDLA-PEO block copolymers incorporating photocleavable o-nitrobenzyl units were synthesized. A mixture of the micellar dispersions of these block copolymers formed a gel upon ultraviolet irradiation via the 'topological conversion'.