Cobalt-Mediated Radical Polymerization of Vinyl Acetate and Acrylonitrile in Supercritical Carbon Dioxide

Abstract

Cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) is successfully achieved in supercritical carbon dioxide (scCO2). CMRP of VAc is conducted using an alkyl-cobalt(III) adduct that is soluble in scCO2. Kinetics studies coupled to visual observations of the polymerization medium highlight that the melt viscosity and PVAc molar mass (Mn) are key parameters that affect the CMRP in scCO2. It is noticed that CMRP is controlled for Mn up to 10 000 g mol(-1), but loss of control is progressively observed for higher molar masses when PVAc precipitates in the polymerization medium. Low molar mass PVAc macroinitiator, prepared by CMRP in scCO2, is then successfully used to initiate the acrylonitrile polymerization. PVAc-b-PAN block copolymer is collected as a free flowing powder at the end of the process although the dispersity of the copolymer increases with the reaction time. Although optimization is required to decrease the dispersity of the polymer formed, this CMRP process opens new perspectives for macromolecular engineering in scCO2 without the utilization of fluorinated comonomers or organic solvents.

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.…”

“…In this regard, in 2013 the market volume of the polymer was more than 1 million tons . A special application of the PVAc as adhesive emulsions as a portative coating and facial conversion to poly(vinyl alcohol), as a water‐soluble biocompatible polymer material, and other derivatives such as poly(vinyl acetate phthalate), have made the controlled synthesis of these polymer an economically valuable issue . Radical polymerization is the only approach for producing PVAc from VAc monomers.…”

“…VAc and all vinyl esters fall in LAM category. Atom transfer radical polymerization (ATRP) and most of the important CPR techniques such as nitroxide‐mediated polymerization, single‐electron transfer living radical polymerization, and organotellurium mediated are inefficient in VAc polymerization . The absence of stabilizing groups in the monomer structure, production of the high reactivity of the propagating radicals, and possibly induced irreversible band formation after trapping of the growing poly(vinyl ester) radicals are the main reasons for the inefficiency of these methods.…”

“…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 . Co(acac) 2 addition to being successful as controlling agent to mediate the radical polymerization of the non‐conjugated vinyl monomers, its high versatility proven to control the polymerization of conjugated monomers such as acrylates and acrylonitrile (AN) and production of well‐defined copolymers of ethylene with polar monomers such as VAc or AN .…”

Block copolymer synthesis by controlled/living radical polymerisation in heterogeneous systems

“…ScCO2 has also been exploited as a medium for cobalt-mediated radical polymerisation (CMRP) to synthesise poly(vinyl acetate)-block-poly(acrylonitrile) (PVAc-b-PAN) in a dispersion polymerisation. 129 Control over PVAc synthesis was maintained until 10 kg mol -1 , above which precipitation occurred, and bimolecular termination led to an increase in dispersity. AN was added after removing unreacted VAc from the reactor by vacuum, and the scCO2-soluble PVAc block stabilised the growing block copolymer particles.…”