Preparation of Thermoresponsive Polymers Bearing Amino Acid Diamide Derivatives via RAFT Polymerization

We report here the synthesis of well-defined homopolymer bearing amino acid diamide, poly(N-acryloyl-L-valine N'-methylamide), via reversible addition fragmentation chain transfer (RAFT) polymerization using alkynyl-functionalized 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl-propionic acid propargyl alcohol ester as chain transfer agent (CTA) and 2,2'-azobis(isobutyronitrile) as initiator. The effects of a variety of parameters, such as temperature and solvent, on RAFT polymerization were examined to determine the optimal control of the polymerization. The controlled nature of RAFT polymerization was evidenced by the controllable molecular weight and low-molecular-weight polydispersity index (M-w/M-n) of resulting homopolymers and further demonstrated to have retained end-group functionality by the fact of the successful formation of block copolymers from further RAFT polymerization by using the resultant polymer as macro-CTA, as well as from "click" chemistry. Thermoresponsive property of the prepared polymer was evaluated in terms of the lower critical solution temperature in aqueous solution by measuring the transmittance variation at 500 nm from UV/vis spectroscopy. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3573-3586, 2010