mechanism involves Reversible Addition-Fragmentation chain Transfer, and we have designated the process the RAFT polymerization. What distinguishes RAFT polymerization from all other methods of controlled/living free-radical polymerization is that it can be used with a wide range of monomers and reaction conditions and in each case it provides controlled molecular weight polymers with very narrow polydispersities (usually <1.2; sometimes <1.1). Living polymerization processes offer many benefits. These include the ability to control molecular weight and polydispersity and to prepare block copolymers and other polymers of complex architecturesmaterials which are not readily synthesized using other methodologies. Therefore, one can understand the current drive to develop a truly effective process which would combine the virtues of living polymerization with versatility and convenience of free-radical polymerization.2-4 However, existing processes described under the banner “living free-radical polymerization” suffer from a number of disadvantages. In particular, they may be applicable to only a limited range of monomers, require reagents that are expensive or difficult to remove, require special polymerization conditions (e.g. high reaction temperatures), and/or show sensitivity to acid or protic monomers. These factors have provided the impetus to search for new and better methods. There are three principal mechanisms that have been put forward to achieve living free-radical polymerization.2,5 The first is polymerization with reversible termination by coupling. Currently, the best example in this class is alkoxyamine-initiated or nitroxidemediated polymerization as first described by Rizzardo et al.6,7 and recently exploited by a number of groups in syntheses of narrow polydispersity polystyrene and related materials.4,8 The second mechanism is radical polymerization with reversible termination by ligand transfer to a metal complex (usually abbreviated as ATRP).9,10 This method has been successfully applied to the polymerization of various acrylic and styrenic monomers. The third mechanism for achieving living character is free-radical polymerization with reversible chain transfer (also termed degenerative chain transfer2). A simplified mechanism for this process is shown in

/pdf/living-free-radical-polymerization-by-reversible-addition-i0mf46u2rt.pdf

Living free-radical polymerization by reversible addition - Fragmentation chain transfer: The RAFT process

Metal-catalyzed living radical polymerization.

Controlled/living radical polymerization: Features, developments, and perspectives

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.

/pdf/living-radical-polymerization-by-the-raft-process-qf42rfce4m.pdf

Living radical polymerization by the RAFT process

http://wwwcourses.sens.buffalo.edu/ce435/Riess03.pdf

Micellization of block copolymers

The invention provides in one aspect a process for preparing a microgel by RAFT polymerizing in the presence of a RAFT chain transfer agent, one or more solvophobic monomers and one or more solvophilic monomers to form one or more block copolymers comprising one or more solvophobic blocks and one or more solvophilic blocks wherein the solvophobic block is insoluble in a dispersing medium and the solvophilic block is soluble in the dispersing medium. The block copolymer is dispersed in the dispersing medium to form micelles, which is then stabilized to form the microgel. The dispersing medium can be aqueous or lipophilic. The method of the present invention also permits one to encapsulate a wide variety of materials, such as pigments, dye molecules, and aluminum flakes used in metallized paints.

Process of microgel synthesis and products produced therefrom

A new method for determining transfer constants based on an analysis of the ln chain length (or molecular weight) distributions has recently been reported. In this paper, the basis of this method i...

Use of Chain Length Distributions in Determining Chain Transfer Constants and Termination Mechanisms

The kinetics and mechanism of the initiation and reinitiation of free radical polymerization is reviewed. The importance of understanding the kinetics, specificity and efficiency of initiation and chain transfer when predicting polymerization kinetics and polymer composition is highlighted. These factors are particularly important when making low molecular weight polymers and in living or controlled polymerization processes. Examples of RAFT polymerization and catalytic chain transfer are provided.

Initiating free radical polymerization

Chain transfer constants have been determined for an unsaturated methyl methacrylate trimer, CH2C(CO2Me)CH2[C(CO2CH3)(CH3)CH2]2H (MMA3), in polymerizations of methacrylate esters (ethyl, EMA; n-butyl, BMA; tert-butyl, tBMA; 2-ethylhexyl, EHMA) and for the analogous trimers of butyl methacrylate (BMA3) and methacrylic acid (MAA3), a hydroxyethyl methacrylate dimer (HEMA2), a hydroxyethyl methacrylate−methyl methacrylate−hydroxyethyl methacrylate trimer (HEMA−MMA−HEMA), and a HEMA macromonomer in methyl methacrylate (MMA) polymerization. These data have been assessed with reference to our previously reported data on chain transfer of MMA macromonomers in MMA polymerizations. The transfer constants (Ctr) for MMA3 in polymerizations of methyl, ethyl, n-butyl, tert-butyl, and 2-ethylhexyl methacrylate at 60 °C are similar (∼0.18). The Ctr of MAA3 (0.28 at 60 °C in 2-butanone solvent) in MMA polymerization is ca. 50% higher than that of MMA3 under similar conditions. Other trimers (BMA3, HEMA−MMA−HEMA) and a lo...

Chain transfer activity of ω-unsaturated methacrylic oligomers in polymerizations of methacrylic monomers

A method for the solution or emulsion polymerization of ethylenically unsaturated monomers, styrene, and other free radical polymerizable monomers in aqueous media in which a cobalt chain transfer agent is used which has both hydrolytic stability and solubility in water and in the organic phase with preferential solubility in the organic phase.

Catherine Louise Moad

Papers

Process of microgel synthesis and products produced therefrom

Use of Chain Length Distributions in Determining Chain Transfer Constants and Termination Mechanisms

Initiating free radical polymerization

Chain transfer activity of ω-unsaturated methacrylic oligomers in polymerizations of methacrylic monomers

Polymerization in aqueous media