Temperature-Induced Gels from Worms Made by RAFT-Mediated Emulsion Polymerization

A RAFT-mediated emulsion polymerization of styrene using a thermoresponsive macro chain transfer agent (MacroCTA) was used to produce diblock copolymer spherical particles that when cooled, below the lower critical solution temperature of the thermoresponsive block, transformed into long and flexible worm structures. The MacroCTA acted as seed particles for the nucleation and polymer growth, in which the molecular weight and particle size distributions were both narrow. The worms could be cleaved to short rods of 100 nm in length using ultrasound. The temperature-induced gelation of the worms and rods (i.e., the sol-gel transition temperature) was studied as a function of the weight fraction of polymer and the concentration of salt. It was found that the addition of salt (or DPBS buffer) lowered the sol-gel transition temperature, in which less than a 2 wt% of the worm or rod could form gels at or below 37 degrees C. These gels could have interesting applications as scaffolds for tissue regeneration.