Aqueous RAFT Polymerization:  Recent Developments in Synthesis of Functional Water-Soluble (Co)polymers with Controlled Structures

Abstract

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.

Living Radical Polymerization by the RAFT Process

“…The RAFT process is compatible with a wide range of reaction media including protic solvents such as alcohols and water [13,14,164,165] and less conventional solvents such as ionic liquids [166] and supercritical carbon dioxide. [167] RAFT polymerization has been successfully carried out in aqueous media.…”

“…The potential of this chemistry to cleave end groups and decolourize polymers and produce polymers with thiol end groups was cited in our initial communication on RAFT polymerization. [13] Examples of end-group cleavage with nucleophiles such as amines, [15,96,198,199] hydroxide, [93] and borohydride [164,200] can be found in recent publications. Radical induced reduction with, for example, tri-n-butylstannane [15,201,202] can be used to replace the thiocarbonylthio group with hydrogen.…”

Thermolysis of RAFT-Synthesized Poly(Methyl Methacrylate)

“…[2] Thiocarbonylthio groups undergo reaction with nucleophiles and ionic reducing agents (e.g. amines, [8][9][10][11][12][13][14][15] hydroxide, [16,17] borohydride [18,19] ) to provide thiols. They also react with various oxidizing agents (including NaOCl, H 2 O 2 , Bu t OOH, peracids, ozone) [2,[20][21][22] and are sensitive to UV irradiation.…”

Biological–synthetic hybrid block copolymers: Combining the best from two worlds

“…In addition, over the past years, a number of controlled ATRP and reversible addition-fragmentation chain transfer based polymerization processes have been developed that can be carried out in aqueous solutions. 30,31 It will be exciting to see whether in the near future these developments can be combined and allow the grafting of synthetic polymer segments from posttranslationally modified protein macroinitiators.…”