Thermo-responsive micelles prepared from brush-like block copolymers of proline- and oligo(lactide)-functionalized norbornenes

Thermo-responsive micelles were prepared from brush-like block copolymers of proline-derived norbornene and macromonomers bearing oligo(lactide) groups. The brush-like polymers with moderate molecular weights were synthesized by the ring-opening metathesis block copolymerization of a proline-functionalized norbornene (1) with norbornene macromonomers bearing oligo(lactide) groups using Umicore M31 as a catalyst. The proline-functionalized polynorbornene [poly(1)] exhibited the lower critical solution temperature (LCST) at 18 degrees C. Phase separation was reversible on heating and cooling without hysteresis. Poly(1) featured amphiphilic character, it self-assembled to form micelles in water at temperatures below the LCST, and aggregation of micelles was observed above the LCST. The LCST of the block copolymers increased with increasing percentage of the branched oligo(lactide) component, suggesting that the phase transition temperatures are tunable with respect to the monomer composition. The block copolymers self-assembled into micelles below the LCST, and further aggregated into larger particles, presumably due to dehydration at the corona, at temperatures above the LCST. The block copolymers also showed the potential to self-assemble into a variety of shapes determined by the amphiphilic balance of the block components.