Cobalt-mediated Radical Polymerization Research Articles

Controlled Radical Polymerization of Acrylates and Isocyanides Installs Degradable Functionality into Novel Copolymers.

Installing ketones into a polymer backbone is a known method for introducing photodegradability into polymers; however, most current methods are limited to ethylene-carbon monoxide copolymerization. Here we use isocyanides in place of carbon monoxide in a copolymerization strategy to access degradable nonalternating poly(ketones) that either maintain or enhance the thermal properties. A cobalt-mediated radical polymerization of acrylates and isocyanides synthesizes nonalternating poly(acrylate-co-isocyanide) copolymers with tunable incorporation using monomer feed ratios. The kinetic product of the polymerization is a dynamic β-imine ester that tautomerizes to the β-enamine ester. Hydrolysis of this copolymer affords a third copolymer microstructure─the elusive nonalternating poly(ketone)─from a single copolymerization strategy. Analysis of the copolymer properties demonstrates tunable thermal properties with the degree of incorporation. Finally, we show that poly(acrylate-co-isocyanide) and poly(acrylate-co-ketone) are photodegradable with 390 nm light, enabling chain cleavage.

Cyanocobalamin (VB12) Bionic Enzyme-Assisted Photocatalytic Chain-Growth Polymerization for Detection of Lung Cancer Biomarkers.

Cobalt-mediated radical polymerization is noted for its great level of control over the polymerization of acrylic and vinyl esters monomers, even at high molar mass. Vitamin B12, a natural bionic enzyme cobalt complex, involves the conversion of organic halides to olefins through chain-growth polymerization. In this work, the notion of R-Co(III) free radical persistent free radical effect and vitamin B12 circulation were first reported for the perception of ultralow abundance of microRNA-21, a lung cancer biomarker. Indeed, most Co-containing catalytic reactions can occur under mild conditions due to their minimal bond dissociation of the C-Co bond, with blue light irradiation. Based on the intrinsic stability of the vitamin B12 framework and recycling of the catalyst, it is evident that this natural catalytic scheme has potential applications in medicinal chemistry and biomaterials. In addition, this strategy, combined with highly specific recognition probes and vitamin B12 circulation-mediated chain-growth polymerization, has a detection limit as low as 910 aM. Furthermore, it is sensitive for sensing in serum samples containing biomarkers and shows great potential for RNA selection and amplification sensing in clinical samples.

Synthesis of block copolymer of vinyl acetate and methyl acrylate by cobalt-mediated radical polymerization in a packed column system: simultaneous control of molecular weight, separation, and purification

Synthesis of block copolymer of vinyl acetate and methyl acrylate by cobalt-mediated radical polymerization in a packed column system: simultaneous control of molecular weight, separation, and purification

A Hydrometalation Initiation Mechanism via a Discrete Cobalt-Hydride for a Rapid and Controlled Radical Polymerization.

Cobalt-mediated radical polymerization (CMRP) is a versatile technique for controlling the polymerization of vinyl monomers via reversible termination using CoII complexes as persistent radical deactivators. Here, we report a facile approach for the in situ generation of Co-H as a discrete initiator and mediator for CMRP of acrylate and acrylamide monomers, overcoming the limitations of existing initiation strategies. In situ oxidation of a CoII complex followed by transmetalation with silane generates a Co-H species, which initiates polymerization via hydrometalation of the monomer. This method precludes an induction period with excellent control over targeted molecular weight and dispersity. Strikingly, our approach allows complete polymerization when the induction period ends for conventional CMRP. A broad scope of monomers is amenable to this protocol, including acrylates and acrylamides. Tunable catalyst electronics afford tailored dispersity while maintaining agreement in molecular weight in stark contrast to conventional methods. Elimination of this induction period imbues polymerization behavior entirely to the catalyst electronic effects on reversible deactivation/activation rates.

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

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

Polymer End Group Control through a Decarboxylative Cobalt-Mediated Radical Polymerization: New Avenues for Synthesizing Peptide, Protein, and Nanomaterial Conjugates.

Cobalt-mediated radical polymerizations (CMRPs) have been initiated by the radical decarboxylation of tetrachlorophthalimide activated esters. This allows for the controlled radical polymerization of activated monomers across a broad temperature range with a single cobalt species, with the incorporation of polymer end groups derived from simple carboxylic acid derivatives and termination with an organozinc reagent. This method has been applied to the synthesis of a polymer/graphene conjugate and a water-soluble protein/polymer conjugate, demonstrating the first examples of CMRP in graphene and protein conjugation.

Organo-Cobalt Complexes in Reversible-Deactivation Radical Polymerization.

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.

Nitroxide TEMPO-containing PILs: Kinetics study and electrochemical characterizations

The cobalt-mediated radical polymerization (CMRP) of new ionic liquid monomers (ILMs), vinyl imidazolium functionalized with redox-active free radical 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)VIm and its CMR copolymerization with vinyl imidazolium units functionalized with triethylene oxide (TEG)VIm produced a well-defined PILs (co)polymers. The controlled nature of (co)polymerization can be seen from the linear first-order kinetic plot, linear evolutions of the molar mass with total monomer conversion and the low polydispersity of the resulting (co)polymers. By combining the redox activity of (TEMPO)PVIm and remarkable ionic conductivity of (TEG)PVIm, outstanding rate capability performance was achieved with a remarkable capacity of 69 mAh g−1 at 60C. The obtained organic electrode can serve as sustainable electrodes in lithium ion batteries.

Computation-Assisted Investigation of Polymer Kinetics: Mechanism of the Hybridization of Cobalt-Mediated Radical Polymerization and Atom Transfer Radical Polymerization

In this study, we combined the kinetic measurement and the computational simulation to build a kinetic model for the hybridization of cobalt-mediated radical polymerization (CMRP) and atom transfer radical polymerization (ATRP), which is a novel method for the one-pot synthesis of block copolymers of less activated monomers and more activated monomers, such as PVAc-b-PMMA and PVAc-b-PSty. The rate constants of the two most important reactions for PVAc radical, the dissociation of PVAc-Coᴵᴵᴵ(acac)₂ and the deactivation with Cuᴵᴵ(PMDETA)Br₂, have been evaluated at 40 °C as 4.99 × 10–³ s–¹ and 4.19 × 10⁶ M–¹ s–¹, respectively. These two kinetic parameters associated with other rate constants allowed us to build a quantitative model that can simulate the polymerization behavior observed in the hybridization of CMRP and ATRP and thus rationalize the mechanism more precisely.

Cobalt(II) complexes of α-diimine derived from cycloalkylamines as controlling agents for organometallic mediated radical polymerization of vinyl acetate

A series of cobalt(II)-α-diimine complexes derived from cycloalkylamines (cycloalkyl = cyclopentyl (1a), cyclohexyl (1b), cycloheptyl (1c), and cyclooctyl (1d)) were synthesized: [CoCl2(Pent-DAB)] (2a), [CoCl2(Hex-DAB)] (2b), [CoCl2(Hept-DAB)] (2c), and [CoCl2(Oct-DAB)] (2d). The α-diimines 1a-d were characterized by FTIR, UV–Vis, and 1H- and 13C NMR spectroscopy, while their respective cobalt(II) complexes (2a-d) were characterized by elemental analysis, FTIR, UV–Vis, EPR, and computational studies. The ability of complexes 2a-d to mediate the vinyl acetate (VAc) polymerization initiated by AIBN, according to a cobalt-mediated radical polymerization (CMRP) mechanism, was explored. A mechanistic investigation of radical trapping based on the combination of theoretical and experimental results for CMRP using 2a-d was conducted. This study shows that the activation/deactivation equilibrium exerted by 2a-d occurs by only one of the faces of the complexes via reversible-termination mechanism. The molecular weight increased in direct proportion to the monomer conversion in the early stages of polymerization for complexes 2a and 2b, while uncontrolled polymerization was observed for 2c and 2d. The molecular weights indicate that the steric effect operated by the cycloalkyl substituents plays an important role in the polymerization control, and that a greater steric hindrance disfavors the dormant state for CMRP equilibrium.

Straightforward Synthesis of Well-Defined Poly(vinylidene fluoride) and Its Block Copolymers by Cobalt-Mediated Radical Polymerization

The organometallic-mediated radical polymerization (OMRP) of vinylidene fluoride (VDF) using an alkyl cobalt(III) compound as initiator was recently proven successful for the controlled synthesis o...

Precision design of vinyl amine and vinyl alcohol-based copolymers via cobalt-mediated radical polymerization

Controlling the amount and the distribution of vinyl amine and vinyl alcohol units within a copolymer is attractive to modulate the properties of the parent major industrial homopolymers, i.e. poly(vinyl amine) and poly(vinyl alcohol).

Organometallic-mediated radical polymerization using well-defined Schiff base cobalt(II) complexes

A series of new cobalt(II) complexes of Schiff base derived from salicylaldehyde and different cycloalkylamines (cycloalkyl = cyclopentyl-1a, cyclohexyl-1b, and cycloheptyl-1c) was synthesized: [Co(CyPen-Salicyl)2] (2a), [Co(CyHex-Salicyl)2] (2b), and [Co(CyHep-Salicyl)2] (2c). The bis(phenoxyiminato)Co(II) complexes (2a-2c) have been fully characterized by FTIR and UV–vis spectroscopy, elemental analysis, cyclic voltammetry, computational methods, and two of the complexes were further studied by single crystal X-ray crystallography. The X-ray structure analysis of 2a-b shows that the geometry around the metal atom is a distorted tetrahedron, confirming the spectroscopic data. Electrochemical studies suggest that the redox potential of 2a-2c are sensitive to the substituent group, decreasing in order cyclopentyl > cyclohexyl > cycloheptyl. Complexes 2a-2c were used as controlling agents for the polymerization of vinyl acetate (VAc) initiated by AIBN, according to a cobalt-mediated radical polymerization (CMRP) mechanism. The VAc polymerization mediated by 2a-2c suggests that the level of control can be slightly tuned by the substitution of the cycloalkyl group on the Schiff base ligand. Complex 2b showed the smaller discrepancy between observed and calculated molecular weight, and narrower molecular weight distribution.

Merging CO2-Based Building Blocks with Cobalt-Mediated Radical Polymerization for the Synthesis of Functional Poly(vinyl alcohol)s

The use of CO2-based α-alkylidene cyclic carbonates in controlled radical polymerization has so far not been exploited, despite the fact that the cyclic carbonate ring offers a multitude of possible modifications. Herein, the synthesis of well-defined copolymers of vinyl acetate (VAc) and 4,4-dimethyl-5-methylene-1,3-dioxolan-2-one (DMMDO) using cobalt-mediated radical polymerization (CMRP) at 40 °C is reported. The controlled nature of the polymerization was confirmed while molecular weights of up to 25 000 g mol–1 and narrow dispersities (<1.4) were obtained. The copolymer structure was elucidated combining NMR, FT-IR, and MALDI-TOF analyses and consists of a polymer backbone with pendant carbonate rings. Further insights into the copolymer structure were gained through the monomers’ reactivity ratios, and a homogeneous distribution of the DMMDO monomer along the polymer chain was observed. A highly water-soluble poly(vinyl alcohol)-based copolymer was obtained by basic hydrolysis, whereas the chemoselective acidic hydrolysis of the acetate groups left the cyclic carbonate rings untouched, which were then exploited for further postmodification with amines. The precise copolymerization of VAc with CO2-sourced five-membered cyclic carbonates bearing an exomethylene moiety is therefore a powerful tool for the synthesis of new variants of poly(vinyl alcohol)-based copolymers.

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

ABSTRACTAn alumina support system for cobalt(II) acetylacetonate (Co(acac)2) catalyst was studied for the cobalt‐mediated radical polymerization (CMRP) of vinyl acetate (VAc). We report a simple but efficient technique to produce this supported catalysts through the adsorption of Co(acac)2 on the surface of alumina particles. Moreover, kinetic and thermodynamic study of Co(acac)2 adsorption on the alumina support were conducted and the influence of effective parameters were investigated. It was found that using alumina‐supported Co(acac)2 for radical polymerization of VAc yields polymers with controlled molecular weight, narrow molecular weight distribution, and high purity. For the alumina‐supported CMRP, changing the polymerization mechanism and domination of termination pathway compared to degenerate transfer pathway resulted in a 2.5 times increase in polymerization rate (kap) and a drop in induction time while maintaining a good control of the VAc polymerization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46057.

Synthesis of cobalt(II)-α-diimines complexes and their activity as mediators in organometallic mediated radical polymerization of vinyl acetate

This study describes the synthesis and characterization of three α-diimine-cobalt complexes of the type [CoCl2(R-DAB)] (R-DAB = RNCHCHNR; R = Mes, Dipp and Dipp∗) and their application as mediators for the cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) using 2,2′-Azobis(2-methylpropionitrile) (AIBN) as initiator. The complexes were characterised by elemental analyses, FTIR, UV–Vis, electron paramagnetic resonance spectroscopy, cyclic voltammetry, and computational methods. The systematic variation of the reaction conditions, such as [initiator]/[Co] and [monomer]/[Co] molar ratios at 65 °C, affected the polymerization rates and the molecular weights, reaching a certain level of control. The VAc polymerization was initiated by AIBN in the presence of DMSO using the α-diimine-cobalt complexes as mediators with [DMSO]/[Co] = 1 at 65 °C. The control over the polymer produced was not improved after the addition of DMSO. Kinetics studies and computational investigations support a tailorable cobalt complex reactivity mainly altered by steric factors of the α-diimine ligands.

Silica gel supported co(acac)2 catalyst in the controlled radical polymerization of vinyl acetate: an easy and practical method to make crystallized poly(vinyl acetate) in a one step process

Cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) has been suggested as one of the major methods to reduced some of the problems in the synthesis of Poly(vinyl acetate) (PVAc), but the color impurities have been the major disadvantage of this method. An easy and practical method to make a crystallized PVAc in a one step process is to use silica gel particles. The particles have been used as a catalyst support of cobalt(II) acetylacetonate (Co(acac)2). It was found that using silica gel supported-Co(acac)2 in VAc polymerization yields polymers with controlled molecular weight, narrow molecular weight distribution, and high purity. For the silica gel supported CMRP (SS-CMRP) changing the polymerization mechanism resulted in a 2.5 times increase in polymerization rate (kapp) and a drop in the induction time while maintaining the control of the VAc polymerization. In addition PVAc synthesized through SS-CMRP method compared to the one synthesized using unsupported-CMRP has a higher crystallinity.

Highly Stretchable Free-Standing Poly(acrylic acid)-block-poly(vinyl alcohol) Films Obtained from Cobalt-Mediated Radical Polymerization

The block copolymers of poly(acrylic acid)-b-poly(vinyl alcohol) (PAA-b-PVA) were obtained from the hydrolysis of poly(methyl acrylate)-b-poly(vinyl acetate) (PMA-b-PVAc), which was synthesized by cobalt-mediated radical polymerization (CMRP) using the cobalt(II) porphyrin complex (CoII(TMP)) as the mediator. The mechanical properties of the PAA-b-PVA free-standing films could be tuned by the pH of the aqueous solution used to cast the films. The block copolymer films showed a much higher tensile strain and fractural tensile strength than the films prepared from the blends of PAA and PVA homopolymers. FTIR and morphological characterizations suggested that the tensile properties of the films were governed by both the hydrogen bonding between PVA and PAA that led to interpolymer complexation and the phase-separated morphology. For a given type of material, the greater extent of interpolymer complexation attained at lower solution pH led to the film with better tensile properties. The difference in the leng...

Photocontrolled Living Polymerization Systems with Reversible Deactivations through Electron and Energy Transfer.

Recently, visible-light-regulated polymerization has been gaining popularity, as it opens a range of new opportunities for the synthesis of functional polymers and materials. Here, the most recent developments in this field are summarized, which is the use of photocatalysts and catalyst-free approaches to mediate polymerization upon photoexcitation. These catalysts can transfer an electron or energy to activate an initiator. The recent achievements in light-regulated atom-transfer radical polymerization, reversible addition-fragmentation chain-transfer polymerization, ring-opening metathesis polymerization, cobalt-mediated radical polymerization, iodine-mediated radical polymerization, and living cationic polymerization are reviewed. Recent development in these fields have solved important challenges in polymer chemistry, such as the development of oxygen-tolerant polymerization, polymerization mediated by near-infrared, metal-free polymerization, and spatial-, temporal-, and sequence-controlled polymerization. Some applications of these techniques will be discussed, such as adapting the current photocatalytic systems to synthesize heterogeneous photocatalysts that act as recyclable photocatalysts and novel light-mediated approaches for surface functionalization of hybrid materials and living cells. Finally, the existing challenges in polymer chemistry that could be overcome by further development of light-mediated polymerization techniques are highlighted along with the future directions of this field.

Controlled Synthesis of Fluorinated Copolymers via Cobalt-Mediated Radical Copolymerization of Perfluorohexylethylene and Vinyl Acetate

Designing novel polyfluoropolymer architectures is attractive for the development of new applications, such as advanced coatings, purification membranes, or materials for energy. Nevertheless, controlling the radical polymerization of fluoroalkenes is very challenging due to the high reactivity of the propagating fluorinated macroradicals. This study aims at exploring the controlled copolymerization of perfluorohexylethylene (PFHE) and vinyl acetate (VAc) in order to prepare a range of well-defined statistical poly(PFHE-stat-VAc) copolymers with different compositions. Cobalt-mediated radical polymerization demonstrated to be active at 40 °C starting from an alkylcobalt(III) initiator, and copolymers with a fluorinated monomer content as high as ca. 80 wt % were successfully prepared. Reactivity ratios were determined to be rVAc = 0.18 and rPFHE = 0 at 40 °C and emphasized a clear tendency for alternation. Unprecedented PFHE/VAc containing block copolymers were also prepared via a single-step approach or ...