Direct, Controlled Synthesis of the Nonimmunogenic, Hydrophilic Polymer, Poly(N-(2-hydroxypropyl)methacrylamide) via RAFT in Aqueous Media

Poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA) is a nonimmunogenic, neutral-hydrophilic polymer currently employed in the delivery of anticancer drugs. Herein, we report conditions that facilitate the direct, controlled RAFT polymerization of HPMA in aqueous media. We demonstrate that the use of 4-cyanopentanoic acid dithiobenzoate and 4,4'-azobis(4-cyanopentanoic acid) as the chain transfer agent (CTA) and initiating species, respectively, in the presence of an acetic acid buffer solution at 70 degrees C is a suitable condition leading to controlled polymerization. The "living" nature of these polymerizations is demonstrated via chain-extension of an HPMA macroCTA to yield the corresponding poly(HPMA-b-HPMA) "homopolymer".

Facile, Controlled, Room-Temperature RAFT Polymerization of N-Isopropylacrylamide

Poly(N-isopropyl acrylamide) is a thermoresponsive polymer that has been widely investigated for drug delivery. Herein, we report conditions facilitating the controlled, room-temperature RAFT polymerization of N-isopropylacrylamide (NIPAM). The key to success is the appropriate choice of both a suitable RAFT chain transfer agent (CTA) and initiating species. We show that the use of 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid, a trithiocarbonate RAFT CTA, in conjunction with the room-temperature azo initiator 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), in DMF, at 25 degrees C, yields conditions leading to NIPAM homopolymerizations which bear all of the characteristics of a controlled/"living" polymerization. We also demonstrate facile size exclusion chromatographic analysis of PNIPAM samples in DMF at 60 degrees C, directly on aliquots withdrawn during the polymerizations, which avoids the problems previously reported in the literature.

Aqueous RAFT polymerization: recent developments in synthesis of functional water-soluble (co)polymers with controlled structures

Reversible addition-fragmentation chain transfer (RAFT) polymerization has been the focus of intensive research over the past few years since this methodology allows the synthetic tailoring of macromolecules with complex architectures including block, graft, comb, and star structures with predetermined molecular weight, terminal functionality, and narrow molecular weight distribution. In this paper we recount significant milestones in achieving controlled free radical homopolymerization and block copolymerization of water-soluble and amphiphilic monomers including nonionic, cationic, anionic, and zwitterionic species. It is shown that under aqueous conditions, control of homopolymerization and further blocking to extend the molecular weight or to produce precisely structured block copolymers require not only careful selection of reagents (initiator, chain transfer agent, and monomer) but also regulation or elimination of hydrolysis of the omega-terminal thiocarbonylthio functionality. The technological potential of such systems is illustrated for the stimuli (pH) reversible micellization of amphiphilic block copolymers and for stabilization and stimuli responsive aggregation of gold nanoparticles bearing covalently tethered co(polymers). Given the advantages of RAFT over other controlled free radical techniques for preparation of water-soluble architectures, it may be anticipated that this technology will be at the forefront of nano- and microscale self-assembly in electronics and biotechnology.