Kinetic Studies of Elementary Reactions in SET-LRP / SARA ATRP

Abstract

A kinetic scheme for controlled radical polymerization in the presence of copper is developed, first neglecting comproportionation or disproportionation reactions, then taking them into account. Experimental results on the kinetics of the elementary reactions of comproportionation, activation by copper(0) and biradical termination are presented, showing solvent effects on activation and comproportionation reactions and chain length dependence of activation and termination. Unusually high rates of termination are observed in controlled radical polymerizations in the presence of copper; around an order of magnitude faster than in conventional or RAFT polymerizations.

Copper-Mediated Living Radical Polymerization (Atom Transfer Radical Polymerization and Copper(0) Mediated Polymerization): From Fundamentals to Bioapplications

“…Because of the significantly higher reactivity of Cu­(I) in comparison with Cu(0), SET-LRP postulates that Cu­(I) disproportionates quantitatively and rapidly (or “instantaneously”) into Cu(0) and Cu­(II) in DMSO and other polar solvents, such as water. ,,, This is an important assumption for the SET-LRP mechanism, as the presence of very low amounts of Cu­(I) should dictate the polymerization kinetics. Several studies have measured and simulated the disproportionation and comproportionation equilibria . Haddleton, Anastasaki, and co-workers measured the disproportionation and comproportionation equilibria in various solvents.…”

“…Several studies have measured and simulated the disproportionation and comproportionation equilibria. 218 Haddleton, Anastasaki, and co-workers 216 measured the disproportionation and comproportionation equilibria in various solvents. These equilibria are strongly affected by the nature of the solvent and monomer, and the concentration of ligand.…”

“…More importantly, in the presence of monomer, such as MA, disproportionation was further suppressed. These results support the previous experimental and simulation works from Matyjasweski's group 47,125,212,219 and Harrison and co-workers, 218 which tend to support the SARA ATRP mechanism, while contradicting the SET-LRP mechanism. However, copper(0)-mediated polymerization is a complex system, with several components, which include monomer, ligand, solvent, initiator, and copper at different oxidation states, in addition to several equilibrium reactions (including disproportionation and comproportionation).…”