A doubly responsive AB diblock copolymer:: RAFT synthesis and aqueous solution properties of poly (N-isopropylacrylamide-block-4-vinylbenzoic acid)

We describe herein the synthesis and self-assembly characteristics of a doubly responsive AB diblock copolymer comprised of N-isopropylacrylamide (NIPAM) and 4-vinylbenzoic acid (VBZ). The AB diblock copolymer was prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization in DMF employing a trithiocarbonate-based RAFT agent. PolyNIPAM was employed as the macroRAFT agent. The NIPAM homopolymerization was shown to possess all the characteristics of a controlled process, and the blocking with VBZ was judged, by size exclusion chromatography, to be essentially quantitative. The NIPAM-VBZ block copolymer was subsequently demonstrated to be able to form normal and inverse micelles in the same aqueous solution by taking advantage of the stimuli responsive characteristics of both building blocks. Specifically, and as judged by NMR spectroscopy and dynamic light scattering, raising the temperature to 40 degrees C (above the lower critical solution temperature of the NIPAM block), while at pH 12 results in supramolecular self-assembly to yield nanosized species that are composed of a hydrophobic NIPAM core stabilized by a hydrophilic VBZ corona. Conversely, lowering the solution pH to 2.0 at ambient temperature results in the formation of aggregates in which the VBZ block is now hydrophobic and in the core, stabilized by the hydrophilic NIPAM block. (c) 2007 Wiley Periodicals, Inc.