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

This invention relates to a process for controlling the architecture of copolymers of at least two unsaturated monomers, made by free-radical polymerization in the presence of a cobalt-containing chain transfer agent, including the control of molecular weight, degree of branching and vinyl end group termination, by varying at least one of the variables of molar ratio of monomers, their relative chain transfer constants, polymerization temperature and degree of conversion and amount of cobalt chain transfer agent; and polymers made thereby

Catalytic polymerization process and polymers made thereby

Controlled growth free radical polymerization of methacrylate esters - Reversible chain transfer vs. reversible termination

L'invention concerne un procede permettant de modifier l'architecture de copolymeres d'au moins deux monomeres insatures, ces copolymeres etant obtenus par polymerisation par radicaux libres en presence d'un agent de transfert de chaines contenant du cobalt. On peut modifier le poids moleculaire, le degre de ramification et l'arret de la polymerisation au niveau des groupes vinyliques terminaux, en faisant varier au moins une des variables suivantes: rapport molaire des monomeres, les constantes de transfert de chaine relatives de ceux-ci, la temperature de polymerisation, le degre de conversion et la quantite d'agent de transfert (cobalt). L'invention concerne, egalement, les polymeres obtenus par ce procede.

Procede de polymerisation catalysee

L'invention porte sur un procede de polymerisation en emulsion ou en solution de monomeres non satures en ethylene, de styrene et d'autres monomeres susceptibles de polymerisation radicalaire dans un milieu aqueux. On utilise, pour ce procede, un agent de transfert de chaine de cobalt, stable a l'hydrolyse et soluble dans l'eau et dans la phase organique avec une solubilite preferentielle dans la phase organique.

Catherine Louise Moad

Papers

Catalytic polymerization process and polymers made thereby

Controlled growth free radical polymerization of methacrylate esters - Reversible chain transfer vs. reversible termination

Procede de polymerisation catalysee

Polymerisation en milieu aqueux