Hyperbranched polymers via RAFT copolymerization of an acryloyl trithiocarbonate

Hyperbranched copolymers of N-isopropylacrylamide (NIPAM) and styrene were prepared by reversible addition-fragmentation chain transfer ( RAFT) polymerization in the presence of a novel acryloyl trithiocarbonate, namely 1-[3-(2-methyl- 2-dodecylsulfanylthiocarbonylsulfanylpropionyloxy) propyl]-1H-[ 1,2,3] triazol-4-ylmethyl acrylate. By employing an example of 'click chemistry', we were able to prepare the vinyl RAFT chain transfer agent (CTA) by copper-catalyzed 1,3- dipolar cycloaddition of an azido-functionalized trithiocarbonate and propargyl acrylate. The resulting CTA facilitated the preparation of highly branched poly( N-isopropylacrylamide) ( PNIPAM) and polystyrene. Interestingly, the branched PNIPAM demonstrated a reduced lower critical solution temperature (LCST) of 25 degrees C as opposed to the conventional value of 32 degrees C expected for linear PNIPAM, an effect attributed to increased contribution of hydrophobic dodecyl trithiocarbonate end groups.