Solvent Choice Differentiates SET-LRP and Cu-Mediated Radical Polymerization with Non-First-Order Kinetics

Abstract

In order to assess the role of the solvent mediating the disproportionation of Cu(I)X into Cu(0) and Cu(II)X 2 during SET-LRP, a series of polymerizations of methyl acrylate initiated with methyl 2-bromopropionate and catalyzed by Cu(0)/Me 6 -TREN at 25 °C in DMSO, MeCN, and their mixtures were investigated. These polymerizations proceed in a dissimilar manner. SET-LRP of MA in DMSO, a solvent that mediates disproportionation, was exemplary of "ultrafast living radical polymerization" with complete conversion in 45 min following the expected first-order kinetics and providing perfect fidelity of the structure of the polymer chain ends. When the polymerization was performed in MeCN, a solvent in which Cu(I)X species do not disproportionate, it displayed nonlinear first-order kinetics with a poor retention of the bromine chain end functionality. The lack of first-order kinetics and decrease of chain end functionality with conversion indicate a nonliving polymerization in MeCN. Increasing the concentration of DMSO in DMSO/MeCN mixtures provided a continuous transition from a nonliving to a living polymerization. The incompatibility of MeCN with SET-LRP lends support that disproportionation of Cu(I)X/N ligand to Cu(0) and Cu(II)X 2 /N ligand is the key step in SET-LRP.

Aqueous SET-LRP catalyzed with “in situ” generated Cu(0) demonstrates surface mediated activation and bimolecular termination

“…1,2,26,37,38,47 It is important to mention that from many LRP methods that provide polymers with narrow molecular weight distribution, only SET-LRP generates polymers with both narrow molecular weight distribution and quantitative or near quantitative chain-end functionality. 6,7,[48][49][50][51]57,[71][72][73][74][75][76][77] Narrow molecular weight distribution is an important feature of the polymers prepared by LRP but the most significant structural parameter of these polymers is the quantitative or near quantitative chain-end functionality combined with narrow molecular weight distribution. Chain-end functionality is the major parameter of a polymer that allows the construction of complex architectures such as multiple block copolymers, 64,73,[76][77][78][79] and dendrimers by iterative synthesis.…”

Surface-initiated SET living radical polymerisation for the synthesis of silica–polymer core–shell nanoparticles

“…As the SET-LRP of methyl acrylate (MA) is a well-studied and understood system, [40][41][42][43][44][45][46] the initiator-fixed silica nanoparticles were used to mediate the growth of poly(methyl acrylate) brushes from the particle surface. All polymerisations were carried out in DMSO at 30 °C using a Cu(0)/Me 6 TREN catalytic system in the presence of a free (sacrificial) initiator, ethyl 2-bromoisobutyrate (EBiB), unless specified otherwise.…”

“…SET-LRP offers a unique opportunity to prepare ultrahigh molecular weight polymers with high chain-end retention under ambient conditions. [38][39][40][41][42] SET-LRP also affords products with lower levels of cytotoxic copper salts compared to traditional ATRP techniques in common use due to the heterogeneous catalyst used. The catalyst can be easily removed and recycled, making this technique more viable for industrial use.…”

Recent developments in metal-catalyzed living radical polymerization

“…17,61,62 More recently, Percec and co-workers proposed that the Cu(0)-based living radical polymerization proceeds via a single-electron transfer mechanism under certain conditions and that their systems are highly effective for the very fast living radical polymerization of various monomers, leading to well-controlled high-molecular weight polymers with narrow MWDs. [63][64][65][66] In contrast, the Cu(I)-based systems in the presence of reducing agents, such as tin(II) 2-ethylhexanoate, ascorbic acid, Cu(0) and radical initiators, also induced an efficient living radical polymerization, in which the accumulated Cu(II) species changed into the active Cu(I) species via the reduction by these additives. [67][68][69][70] Although the working mechanisms of Cu(0) are still controversial and may depend on the conditions, it is clear that the use of lower oxidation metal species is important for constructing highly catalytic systems.…”