Organo‐Cobalt Complexes in Reversible‐Deactivation Radical Polymerization

Abstract

Cobalt complexes have played an essential role in different chemical reactions. One of them that has attracted substantial attention in polymer science is cobalt mediated radical polymerization (CMRP), which is famous for its remarkable efficiency in controlling the radical polymerization of vinyl acetate (VAc) and other less active monomers (LAMs). Two pathways, reversible termination (RT) and degenerative transfer (DT), were recognized to control the polymerization in CMRP and could be further used to rationalize the mechanism of other RDRP methods. These control mechanisms were then found to be correlated to the redox potential of cobalt complexes and thus could be judged more quantitatively. The control of polymer composition and tacticity could also be achieved by using CMRP. The hybridization of CMRP and atom transfer radical polymerization (ATRP) could directly synthesize the vinyl acetate/methyl methacrylate and vinyl acetate/styrene block copolymers in one pot. The copolymer of acrylates and 1‐octene could be obtained by visible‐light‐induced CMRP. With the addition of bulky Lewis acid, CMRP of N,N‐dimethylacrylamide (DMA) showed high isotacticities with the contents of meso dyads (m) and meso triads (mm) up to 94 % and 87 %, respectively, and generated the crystalline PDMA with Tm as high as 276 °C. This personal account reviewed the development of CMRP with the mechanistic understanding, the control of composition and stereoselectivity of the polymeric products, and its perspective.

Coordination of Azobisisobutyronitrile with Cobalt Complexes in Cobalt-Mediated Radical Polymerization Disclosed by Linear Correlation between the Equilibrium Constant and Half-Wave Potential

“…The energy profile from this thermodynamic model indicates the potential to expand the monomer types applicable in CMRP. Because the failure to control polymerization of styrene and methyl methacrylate through CMRP was attributed to inefficiency in the formation of organocobalt­(III) from cobalt­(II) complexes and the radicals of styrene or methyl methacrylate, stabilizing the organocobalt­(III) species shown in this simulation could enhance the formation of organocobalt­(III). Several reports have indicated that the properties of axial ligands, such as p K a and their electronic structure, affect the reactivity of cobalt complexes.…”

Combinations (Є) among controlled/living polymerizations and utilizations of efficient chemical reactions for the synthesis of novel polymeric materials

“…Another combination from CMRP to ATRP was reported by Peng et al [148][149][150] They first conducted CMRP of VAc and subsequently added MMA and CuBr 2 to PVAc-Co(acac) 2 macrocomplex. When MMA is inserted into the end of PVAc, the equilibrium between corresponding dormant and chain-end radicals shifts to the latter.…”

Photo‐induced organo‐manganese‐mediated radical polymerization of acrylates under LED irradiation

“…Depending on the metal/ligand combination, initiation strategy, and monomer used during the reactions, either reversible deactivation (RD) or degenerative transfer (DT) mechanisms can occur in OMRP. 21 In RD, a low concentration of active radicals is maintained, and control over the polymerization reaction is achieved by avoiding termination and side-breaking reactions. The dormant species (M III -C) can generate radicals, and the concentration of radicals should be regulated by the equilibrium between active and dormant species.…”

“…OMRP operates on the principle of reversibly trapping the active radical chain by a metal complex, leading to the direct formation of a metal‐carbon bond. Depending on the metal/ligand combination, initiation strategy, and monomer used during the reactions, either reversible deactivation (RD) or degenerative transfer (DT) mechanisms can occur in OMRP 21 . In RD, a low concentration of active radicals is maintained, and control over the polymerization reaction is achieved by avoiding termination and side‐breaking reactions.…”