This paper presents a review of living radical polymerization achieved with thiocarbonylthio compounds [ZC(=S)SR] by a mechanism of reversible addition–fragmentation chain transfer (RAFT). Since we first introduced the technique in 1998, the number of papers and patents on the RAFT process has increased exponentially as the technique has proved to be one of the most versatile for the provision of polymers of well defined architecture. The factors influencing the effectiveness of RAFT agents and outcome of RAFT polymerization are detailed. With this insight, guidelines are presented on how to conduct RAFT and choose RAFT agents to achieve particular structures. A survey is provided of the current scope and applications of the RAFT process in the synthesis of well defined homo-, gradient, diblock, triblock, and star polymers, as well as more complex architectures including microgels and polymer brushes.

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Living radical polymerization by the RAFT process

We developed nanosized, reduced graphene oxide (nano-rGO) sheets with high near-infrared (NIR) light absorbance and biocompatibility for potential photothermal therapy. The single-layered nano-rGO sheets were ∼20 nm in average lateral dimension, functionalized noncovalently by amphiphilic PEGylated polymer chains to render stability in biological solutions and exhibited 6-fold higher NIR absorption than nonreduced, covalently PEGylated nano-GO. Attaching a targeting peptide bearing the Arg-Gly-Asp (RGD) motif to nano-rGO afforded selective cellular uptake in U87MG cancer cells and highly effective photoablation of cells in vitro. In the absence of any NIR irradiation, nano-rGO exhibited little toxicity in vitro at concentrations well above the doses needed for photothermal heating. This work established nano-rGO as a novel photothermal agent due to its small size, high photothermal efficiency, and low cost as compared to other NIR photothermal agents including gold nanomaterials and carbon nanotubes.

https://web.stanford.edu/group/dailab/Reprint/185.%20Ultrasmall%20Reduced%20Graphene%20Oxide%20with%20High%20Near-Infrared%20Absorbance%20for%20Photothermal%20Therapy.pdf

Ultrasmall Reduced Graphene Oxide with High Near-Infrared Absorbance for Photothermal Therapy

Radical addition-fragmentation chemistry in polymer synthesis

Among the living radical polymerization techniques, reversible addition–fragmentation chain transfer (RAFT) and macromolecular design via the interchange of xanthates (MADIX) polymerizations appear to be the most versatile processes in terms of the reaction conditions, the variety of monomers for which polymerization can be controlled, tolerance to functionalities, and the range of polymeric architectures that can be produced. This review highlights the progress made in RAFT/MADIX polymerization since the first report in 1998. It addresses, in turn, the mechanism and kinetics of the process, examines the various components of the system, including the synthesis paths of the thiocarbonyl-thio compounds used as chain-transfer agents, and the conditions of polymerization, and gives an account of the wide range of monomers that have been successfully polymerized to date, as well as the various polymeric architectures that have been produced. In the last section, this review describes the future challenges that the process will face and shows its opening to a wider scientific community as a synthetic tool for the production of functional macromolecules and materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43:5347–5393, 2005

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/pola.20986

Macromolecular design via réversible addition-fragmentation chain transfer (RAFT)/Xanthates (MADIX) polymerization

Tethered polymer chains refers to macromolecular chains that are attached into microstructures by their ends. Highly branched polymers, polymer micelles and end-grafted chains on surfaces are a few examples. This review brings out the common features of these seemingly widely disparate microstructures. Tethering can be reversible or irreversible and is frequently sufficiently dense that the chains are crowded. Densely tethered chains stretch to alleviate the interactions caused by crowding. They thus exhibit deformed configurations at equilibrium. These effects of tethering on the structure of the polymer chains are reflected in distinctive behavior and properties of microstructures containing tethered chains.

Tethered chains in polymer microstructures

Preparation, characterization and biodegradation studies on cellulose acetates with varying degrees of substitution

Radical copolymerization of maleic anhydride and substituted styrenes by reversible addition-fragmentation chain transfer (RAFT) polymerization

Nonaqueous poly(methyl methacrylate) dispersions: radical dispersion polymerization in the presence of AB block copolymers of polystyrene and poly(dimethyl siloxane)

Chromatographic Characteristics of polymer-based high-performance liquid chromatography packings

For separations performed with crosslinked polystyrene gels, an interpretation is proposed for the displacement to high retention volume of plots of log hydrodynamic volume versus retention volume for polystyrene (PS) in poor and theta solvents, e.g. cyclohexane, trans-decalin, and N,N-dimethylformamide, with respect to plots for other polymers for which these same eluents are good solvents. PS separates by steric exclusion and by solute-gel interaction effects giving rise to partition and adsorption mechanisms. The retention volume VR is given by 






where V0 is the interstitial volume, Vi is the solvent volume within the gel, KD is the distribution coefficient for steric exclusion, and Kp is the distribution coefficient for solute-gel interaction effects. For polymers in good solvent media separating solely by steric exclusion, Kp is unity. For PS in poor and theta solvents, network-limited partition and network-limited adsorption mechanisms are proposed in which Kp is greater than unity. The hydrodynamic volume universal calibration method is applicable when Kp is greater than unity, provided the retention parameter is changed from VR to (VR–V0)/Kp. From the network-limited adsorption mechanism, a plot of log[(VR–V0)/Kp] versus polymer hydrodynamic radius yields the average pore size of the crosslinked polystyrene gel. Experiments are reported showing the dependence of Kp on gel porosity and on solvent power by varying the temperature of the eluent.



Fur die mit vernetzten Polystyrol-Gelen ausgefuhrten Trennungen wird eine Interpretation der Verschiebung zu hoheren Elutionsvolumina bei der graphischen Darstellung des Logarithmus des hydrodynamischen Volumens gegen das Elutionsvolumen vorgeschlagen, die fur Polystyrol (PS) in schlechten und Theta-Losungsmitteln z. B. Cyclohexan, trans-Decalin und N,N-Dimethylformamid gefunden wird, in Bezug auf die Eichkurve fur andere Polymere, fur die die gleichen Elutionsmittel gute Losungsmittel sind. PS wird in diesen Fallen durch sterischen Ausschlus und durch Solut-Gel Wechselwirkungen, die Verteilungs- und Adsorptions-Effekte verursachen, getrennt. Das Elutionsvolumen VR wird durch 






beschrieben, in dem V0 das Zwischenraumvolumen, Vi das Losungsmittelvolumen innerhalb des Gels, KD der Verteilungskoeffizient fur den sterischen Ausschlus und Kp der Verteilungskoeffizient fur die Solut-Gel Wechselwirkungen ist. Fur Polymere in guten Losungsmitteln, die dann nur durch sterischen Ausschlus getrennt werden, ist Kp = 1. Fur PS in schlechten und Theta-Losungsmitteln werden Netzwerk-limitierte Verteilungsund Netzwerk-limitierte Adsorptions-Mechanismen vorgeschlagen; in diesen Fallen ist Kp > 1. Die universelle Kalibrierung uber das hydrodynamische Volumen ist anwendbar, wenn Kp > 1, vorausgesetzt, das der Elutions-Parameter VR in (VR − V0)/Kp, geandert wird. Nach dem Netzwerk-limitierten Adsorptions-Mechanismus ergibt eine Auftragung des Logarithmus [(VR − V0)/Kp] gegen den hydrodynamischen Radius des Polymeren die durchschnittliche Porengrose des vernetzten Polystyrol-Gels. Einige Untersuchungen werden beschrieben, die die Abhangigkeit des Verteilungskoeffizienten Kp von der Gelporositat und des durch Temperaturanderung des Elutionsmittels beeinflusten Losevermogens zeigen.

John V. Dawkins

Papers

Preparation, characterization and biodegradation studies on cellulose acetates with varying degrees of substitution

Radical copolymerization of maleic anhydride and substituted styrenes by reversible addition-fragmentation chain transfer (RAFT) polymerization

Nonaqueous poly(methyl methacrylate) dispersions: radical dispersion polymerization in the presence of AB block copolymers of polystyrene and poly(dimethyl siloxane)

Chromatographic Characteristics of polymer-based high-performance liquid chromatography packings

Gel permeation chromatography with crosslinked polystyrene gels and poor and theta solvents for polystyrene, 2. Separation mechanism