In situ bidentate to tetradentate ligand exchange reaction in cobalt-mediated radical polymerization

Abstract

a b s t r a c tOrganometallic-mediated radical polymerization (OMRP) has seen a significant growth in the last years notably due to the development of new metal complexes, especially cobalt derivatives. Despite of this, none of the reported complexes offers optimal control for monomers with very different reactivity, which somewhat limits the synthesis of copolymers. In order to expand the scope of cobalt-mediated radical polymerization (CMRP), we investigated an in situ ligand exchange reaction for modulating the properties of the cobalt complex at the polymer chain-end and adjusting the CACo bond strength involved in the control process. With the aim of improving the synthesis of poly(vinyl acetate)-b-poly (n-butyl acrylate) copolymers, bidentate acetylacetonate ligands, which impart high level of control to the polymerization of vinyl acetate (VAc), were replaced in situ at the PVAcAcobalt chain-end by tetradentate Salen type ligands that are more suited to acrylates.

Highly effective organometallic‐mediated radical polymerization of vinyl acetate using alumina‐supported Co(acac)2 catalyst: A case study of adsorption and polymerization

“…Semi‐logarithmic kinetic plots (ln[ M ] 0 /[ M ] vs. time) are linear, indicating the presence of first‐order kinetics with respect to monomer and the constant free‐radical concentrations throughout the polymerization . This behavior confirms that both the VAc polymerization proceeds without detectable termination . In Figure , the induction time of reaction in the presence of alumina particle as a catalyst support is compared with the reference experiment.…”

“…The use of controlled radical polymerization (CRP) techniques for the synthesis of polymers with well‐defined compositions, dimensions, uniformity, and architectures has revolutionized the macromolecular engineering . One of the most important challenges of CRP is to control the radical polymerization of less activated monomers (LAM) which generate more reactive radicals .…”

“…In this regard, organometallic‐mediated radical polymerization (OMRP) techniques and more particularly cobalt‐mediated radical polymerization (CMRP) can be successfully applied to the control polymerization of vinyl acetate using cobalt complexes as the controlling agent. Depending on the reaction conditions, CMRP process follows a reversible termination pathway or a degenerate chain transfer pathway, which, in simplified form is shown in Scheme . In suggested mechanisms, the role of the cobalt center includes the reversible formation of Co–carbon covalent bond .…”

“…Depending on the reaction conditions, CMRP process follows a reversible termination pathway or a degenerate chain transfer pathway, which, in simplified form is shown in Scheme . In suggested mechanisms, the role of the cobalt center includes the reversible formation of Co–carbon covalent bond . Among various complexes of cobalt used in CMPR of VAc, Co(acac) 2 showed the highest efficiency in the synthesis of well‐defined PVAc of high‐molecular weight polymer .…”

“…Another challenge involved in PVAc synthesis through CMPR method using Co(acac) 2 catalyst is about the long induction time at the beginning of the polymerization . Therefore, several attempts have been recently made to reduce the induction time and accelerate the polymerization.…”