This paper provides a third update to the review of reversible deactivation radical polymerization (RDRP) achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669) and the second in December 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymerization which include reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.

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Living Radical Polymerization by the RAFT Process - A Second Update

Department of Chemistry, Department of Radiology, Washington University in Saint Louis, Saint Louis, Missouri 63130, Department of Chemistry, Texas A&M University, College Station, Texas 77842, Cancer Center Karolinska, Department of Oncology-Pathology CCK, R8:03 Karolinska Hospital and Institute, SE-171 76 Stockholm, Sweden, and Department of Chemistry and Biochemistry, Department of Materials, and Materials Research Laboratory, University of California, Santa Barbara, California 93106

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Applications of Orthogonal “Click” Chemistries in the Synthesis of Functional Soft Materials

Radical addition-fragmentation chemistry in polymer synthesis

Monomers composed of a (meth)acrylate moiety connected to a short poly(ethylene)glycol (PEG) chain are versatile building-blocks for the preparation of “smart” biorelevant materials. Many of these monomers are commercial and can be easily polymerized by either anionic, free-radical, or controlled radical polymerization. The latter approach allows synthesis of well-defined PEG-based macromolecular architectures such as amphiphilic block copolymers, dense polymer brushes, or biohybrids. Furthermore, the resulting polymers exhibit fascinating solution properties in aqueous medium. Depending on the molecular structure of their monomer units, non linear PEG analogues can be either insoluble in water, readily soluble up to 100 °C, or thermoresponsive. Thus, these polymers can be used for building a wide variety of modern materials such as biosensors, artificial tissues, smart gels for chromatography, and drug carriers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3459–3470, 2008

Polymerization of oligo(ethylene glycol) (meth)acrylates: Toward new generations of smart biocompatible materials

Interest in thermoresponsive polymers has steadily grown over many decades, and a great deal of work has been dedicated to developing temperature sensitive macromolecules that can be crafted into new smart materials. However, the overwhelming majority of previously reported temperature-responsive polymers are based on poly(N-isopropylacrylamide) (PNIPAM), despite the fact that a wide range of other thermoresponsive polymers have demonstrated similar promise for the preparation of adaptive materials. Herein, we aim to highlight recent results that involve thermoresponsive systems that have not yet been as fully considered. Many of these (co)polymers represent clear opportunities for advancements in emerging biomedical and materials fields due to their increased biocompatibility and tuneable response. By highlighting recent examples of newly developed thermoresponsive polymer systems, we hope to promote the development of new generations of smart materials.

New directions in thermoresponsive polymers.

Phase diagrams with very flat LCST phase separation line for aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions are theoretically derived on the basis of sequential hydrogen bond formation between polymer chains and water molecules (cooperative hydration) and compared with experimental spinodal curves. The two-phase region systematically changes its shape with the cooperativity parameter σ, and the spinodals turned out to be almost independent of the polymer molecular weight for strongly cooperative hydration (small σ) as observed in PNIPAM solutions. Hydration takes place sharply within a very narrow temperature region. The number of hydrogen-bonded water molecules on a chain is calculated as a function of the temperature and the polymer concentration.

Cooperative Hydration, Chain Collapse, and Flat LCST Behavior in Aqueous Poly(N-isopropylacrylamide) Solutions

We examine the influence of the macromolecule chain length on the cloud point temperature (Tcp) and the temperature of the coil-to-globule transition (TM) in aqueous solutions of hydrophobically modified (HM) telechelic poly(N-isopropylacrylamides) (PNIPAM) ranging in concentration from 0.01 to 35 g L-1 (0.1−310 mmol of NIPAM L-1). The telechelic HM-PNIPAM samples with n-octadecyl termini were obtained by RAFT polymerization of NIPAM in dioxane in the presence of S-1-n-octadecyl-S‘-(α,α‘-dimethyl-α‘ ‘-N-n-octadecylacetamide)trithiocarbonate as a chain transfer agent. Their molar mass (Mn) ranged from 12 000 to 49 000 g mol-1 with a polydispersity index lower than 1.20. The cloud point temperatures, measured by monitoring the temperature-induced changes in scattering intensity, decreased significantly with increasing polymer concentration, this effect being more pronounced with decreasing polymer molar mass. In contrast, the temperature of the PNIPAM chain coil-to-globule collapse (30 ± 1 °C) was only slig...

Impact of end-group association and main-chain hydration on the thermosensitive properties of hydrophobically modified telechelic poly(N-isopropylacrylamides) in water

The authors present a model describing the coexistence of hydrophobic association and phase separation with lower critical solution temperature (LCST) in aqueous solutions of polymers carrying short hydrophobic chains at both chain ends (telechelic associating polymers). The LCST of these solutions is found to decrease along the sol/gel transition curve as a result of both end-chain association (association-induced phase separation) and direct hydrophobic interaction of the end chains with water. The authors relate the magnitude of the LCST decrease to a hydration cooperativity parameter σ. The LCST decreases substantially (∼100K) in the case of random hydration (σ=1), whereas only a small shift (∼5–10K) occurs in the case of cooperative hydration (σ=0.3). The molecular weight dependence of the LCST drop is studied in detail in each case. The results are compared with experimental observations of the cloud points of telechelic poly(ethylene oxide) solutions, in which random hydration predominates, and of ...

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Unified model of association-induced lower critical solution temperature phase separation and its application to solutions of telechelic poly(ethylene oxide) and of telechelic poly(N-isopropylacrylamide) in water.

The effect of vapor pressure on the thermoreversible gelation in polycondensation reactions is theoretically studied on the basis of the lattice theory of polymer solutions combined with the conventional Flory−Stockmayer theory of gelation. In polycondensation systems, concentration of the produced three-dimensional branched polymers in the reaction bath changes as reaction proceeds due to the byproduct of the solvent molecules, such as water, alcohol, etc., and hence it is not a controllable parameter. We calculate the polymer concentration as a function of temperature and vapor pressure of the solvent, and we study how sol/gel transition interferes with macroscopic phase separation in such reactive solutions. We find a new reentrant sol phase at high pressure that is brought by a strong backward reaction. The thermodynamic conditions to reach the gel point without phase separation are found. Gel point can be reached even for reactions in closed vessels where pressure changes under a constant volume. The...

Yukinori Okada

Papers

Cooperative Hydration, Chain Collapse, and Flat LCST Behavior in Aqueous Poly(N-isopropylacrylamide) Solutions

Impact of end-group association and main-chain hydration on the thermosensitive properties of hydrophobically modified telechelic poly(N-isopropylacrylamides) in water

Unified model of association-induced lower critical solution temperature phase separation and its application to solutions of telechelic poly(ethylene oxide) and of telechelic poly(N-isopropylacrylamide) in water.

Pressure-controlled thermoreversible gelation

Theoretical Study on the Phase Diagrams of Associating Polymers