Cobalt-mediated Radical Polymerization Research Articles

Synthesis of poly(vinyl acetate)-b-poly(vinyl chloride) block copolymers by Cobalt-Mediated Radical Polymerization (CMRP)

The synthesis of poly(vinyl acetate)-b-poly(vinyl chloride) (PVAc-b-PVC) block copolymers by Cobalt-Mediated Radical Polymerization (CMRP) is investigated for the first time in this paper. A PVAc–Co(acac)2 macroinitiator is prepared by CMRP using the V-70/Co(acac)2 binary system or a preformed alkylcobalt(III) compound. Then, the block copolymerization occurs in the bulk at 40 °C by the addition of VC. The addition of water to the polymerization medium or the slow generation of alkyl radicals during the whole polymerization is beneficial to the process by consuming part of the excess of deactivator (Co(acac)2) that blocks the polymer chains into the dormant form. Dynamic light scattering (DLS) measurements and AFM analyses evidence that the PVAc-b-PVC forms core–shell micelles in a selective solvent of the PVAc block, i.e. methanol, evidencing the blocky structure of the copolymer. PVAc-b-P(VC-co-VAc) copolymers are also successfully prepared by initiating the radical copolymerization of VC and VAc at 40 °C from a PVAc–Co(acac)2 macroinitiator.

Key Role of Intramolecular Metal Chelation and Hydrogen Bonding in the Cobalt‐Mediated Radical Polymerization of N‐Vinyl Amides

This work reveals the preponderance of an intramolecular metal chelation phenomenon in a controlled radical polymerization system involving the reversible trapping of the radical chains by a cobalt complex bis(acetylacetonato)cobalt(II). The cobalt-mediated radical polymerization (CMRP) of a series of N-vinyl amides was considered with the aim of studying the effect of the cobalt chelation by the amide moiety of the last monomer unit of the chain. The latter reinforces the cobalt-polymer bond in the order N-vinylpyrrolidone<N-vinyl caprolactam<N-methyl-N-vinyl acetamide, and is responsible for the optimal control of the polymerizations observed for the last two monomers. Such a double linkage between the controlling agent and the polymer, through a covalent bond and a dative bond, is unique in the field of controlled radical polymerization and represents a powerful opportunity to fine tune the equilibrium between latent and free radicals. Possible hydrogen bond formation is also taken into account in the case of N-vinyl acetamide and N-vinyl formamide. These results are essential for understanding the factors influencing Co-C bond strength in general, and the CMRP mechanism in particular, but also for developing a powerful platform for the synthesis of new precision poly(N-vinyl amide) materials, which are an important class of polymers that sustain numerous applications today.

Mechanistic investigation and selectivity of the grafting onto C60 of macroradicals prepared by cobalt-mediated radical polymerization

The grafting mechanism of poly(vinyl acetate) macroradicals prepared by cobalt-mediated radical polymerization onto C60 is investigated. The experimental conditions directly impact the nature and stability of the PVAc/C60 adducts. In the presence of residual initiating radicals that can compete with PVAc° macroradicals for addition onto C60, mixtures of PVAc/C60 adducts having between one and eight polymer chains per C60 are formed. PVAc/C60 adducts prepared with low [PVAc]:[C60] ratios may contain weak C60–C60 bonds that further dissociate and account for the instability of the products. The formation of such dimers can be lessened by increasing the temperature from 30 °C to 100 °C. The temperature increase also allows a complete dissociation of the PVAc-Co dormant species into PVAc° macroradicals and an almost quantitative grafting of eight PVAc chains onto C60, leading to well-defined C60(PVAc)8 octa-adducts. These results might shed new light on the grafting onto C60 of macroradicals prepared by other CRP techniques.

Synthesis of poly(vinyl laurate)-b -poly(vinyl stearate) diblock copolymers by cobalt-mediated radical polymerization in solution

Poly(vinyl laurate) (PVL) and poly(vinyl stearate) (PVS) were synthesized by means of cobalt-mediated radical polymerization (CMRP). Cobalt(II) diacetylacetonate (Co(acac)2) was demonstrated to control the radical polymerization of these monomers in solution. Molecular weights up to 15,000 g·mol−1 were obtained with reasonably low polydispersity indices (PDI < 1.3). The efficiency of the redox initiator [lauroyle peroxide (LPO)/citric acid (CA)] was found to be low (around 10%) as already reported for vinyl acetate. The solvent and temperature were found to have a very weak influence on the initiator efficiency. It appeared that CA played no role in the initiation process that only involved a redox reaction between LPO and Co(acac)2. PVL-b-PVS diblock copolymers could be synthesized using two strategies: (1) Sequential addition, that is, addition of the second monomer (VS) at high conversion of the first one (VL). (2) Macroinitiator technique, that is, isolation of a PVL macroinitiator then polymerization of VS from this cobalt functionalized macroinitiator. Both techniques allowed the synthesis of diblock copolymers with molar masses around 25,000 g·mol−1 and PDI lower than 1.4. The resulting materials were characterized by DSC, revealing that both blocks exhibit side-chain crystallinity and phase segregate in the bulk. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Synthesis of poly(vinyl acetate)-b-poly(4-vinylpyridine) block copolymers by a combination of cobalt-mediated radical polymerization and RAFT polymerization and their use in dispersion polymerization under UV radiation

Well-defined poly(vinyl acetate)-block-poly(4-vinylpyridine) (PVAc-b-P4VP) block copolymers were synthesized for the first time by a combination of cobalt-mediated radical polymerization (CMRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization, and were used to prepare PVAc-b-P4VP hairy polystyrene (PSt) particles. PVAc end-capped by a cobalt(II) acetylacetonate complex was first synthesized by the CMRP of vinyl acetate, after which the cobalt complex was modified into a dithiobenzoate group for the RAFT polymerization of 4-vinylpyridine. The hairy PSt particles were synthesized by the dispersion polymerization of St using the PVAc-b-P4VP as both a macro-initiator and a colloidal stabilizer under UV radiation. The average size of PSt particles synthesized with 20 wt.% of PVAc-b-P4VP (Mn = 39,500 g/mol) was 136 nm (CV = 19.2%). Very small Au nanoparticles were successfully immobilized on the surface of the PSt particles.

Cobalt-mediated radical (co)polymerization of vinyl chloride and vinyl acetate

Download options Please wait... Article information DOI https://doi.org/10.1039/C2PY20413D Article type Paper Submitted 13 Jun 2012 Accepted 17 Jul 2012 First published 18 Jul 2012 Download Citation Polym. Chem., 2012,3, 2880-2891 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Cobalt-mediated radical (co)polymerization of vinyl chloride and vinyl acetate Y. Piette, A. Debuigne, C. Jérôme, V. Bodart, R. Poli and C. Detrembleur, Polym. Chem., 2012, 3, 2880 DOI: 10.1039/C2PY20413D To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Yasmine Piette Antoine Debuigne Christine Jérôme Vincent Bodart Rinaldo Poli Christophe Detrembleur

Synthesis of star and H-shape polymersvia a combination of cobalt-mediated radical polymerization and nitrone-mediated radical coupling reactions

Via the combination of nitrone-mediated radical coupling and cobalt-mediated radical polymerization, mid-chain functionalized polymers are obtained that can be assembled into H-shaped polymers.

Synthesis of thermo‐responsive poly(N‐vinylcaprolactam)‐containing block copolymers by cobalt‐mediated radical polymerization

AbstractThermo‐responsive block copolymers based on poly(N‐vinylcaprolactam) (PNVCL) have been prepared by cobalt‐mediated radical polymerization (CMRP) for the first time. The homopolymerization of NVCL was controlled by bis(acetylacetonato)cobalt(II) and a molecular weight as high as 46,000 g/mol could be reached with a low polydispersity. The polymerization of NVCL was also initiated from a poly(vinyl acetate)‐Co(acac)2 (PVAc‐Co(acac)2) macroinitiator to yield well‐defined PVAc‐b‐PNVCL block copolymers with a low polydispersity (Mw/Mn = 1.1) up to high molecular weights (Mn = 87,000 g/mol), which constitutes a significant improvement over other techniques. The amphiphilic PVAc‐b‐PNVCL copolymers were hydrolyzed into unprecedented double hydrophilic poly(vinyl alcohol)‐b‐PNVCL (PVOH‐b‐PNVCL) copolymers and their temperature‐dependent solution behavior was studied by turbidimetry and dynamic light scattering. Finally, the so‐called cobalt‐mediated radical coupling (CMRC) reaction was implemented to PVAc‐b‐PNVCL‐Co(acac)2 precursors to yield novel PVAc‐b‐PNVCL‐b‐PVAc symmetrical triblock copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Preparation of polyacrylonitrile nanoparticles via dispersion polymerization of acrylonitrile using a poly(N-vinyl pyrrolidone)-cobalt complex in an aqueous system

Monodisperse spherical polyacrylonitrile (PAN) nanoparticles were successfully prepared for the first time by dispersion polymerization of acrylonitrile (AN) in water using well-defined poly(N-vinyl pyrrolidone) (PVP) that was end-capped by a cobalt(II) acetylacetonate (Co(acac)2) complex (PVP-Co(acac)2) as both a macroinitiator and a colloidal stabilizer. The well-defined PVP-Co(acac)2 (Mn = 14,000 g/mol, PDI = 1.25) was synthesized by the bulk cobalt-mediated radical polymerization of N-vinyl pyrrolidone at 20 °C using 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) as an initiator and Co(acac)2 as a regulating agent. The PVP macroradicals generated at 30 °C by the homolytic cleavage of the C–Co bonds in PVP-Co(acac)2 initiated the dispersion polymerization of AN, as well as successfully stabilized the growing PAN particles. The average diameters of PAN nanoparticles synthesized with 20, 30, 40, and 50 wt% of PVP-Co(acac)2 at 30 °C for 24 h were 263.5, 163.1, 157.3, and 143.5 nm, respectively. The PAN nanoparticles had a slightly crumpled spherical appearance, and the degree of crystallinity of the PAN nanoparticles prepared using 30 wt% of PVP-Co(acac)2 was 31.2%. The mol% of VP units in the PAN nanoparticles was about 6 mol%, and the PVP chains were present on the surface of the PAN nanoparticles as a stabilizing layer. The PVP hairy chains could successfully stabilize very small Ag nanoparticles on the surface of the PAN nanoparticles.

Synthesis of 1-Vinyl-3-ethylimidazolium-Based Ionic Liquid (Co)polymers by Cobalt-Mediated Radical Polymerization

The cobalt-mediated radical polymerization (CMRP) of 1-vinyl-3-ethylimidazolium bromide (VEtImBr) is described. Polymerizations were performed at 30 °C in solution either in dimethylformamide (DMF) or in methanol (MeOH) or in a mixture of both solvents, using a preformed alkyl–cobalt(III) adduct, CH3OC(CH3)2CH2–C(CH3)(CN)–(CH2–CHOAc)<4–Co(acac)2, as the mediating agent. Excellent control over molecular weights and dispersities (Mw/Mn ∼ 1.05–1.06) was achieved in MeOH, with a linear increase of experimental molecular weights with the monomer conversion. Substituting methanol for DMF induced much faster polymerization process, even under quite high diluted conditions: for instance, about 80% monomer conversion was reached in 30 min in DMF, compared to 10 h in MeOH. However, size exclusion chromatography (SEC) traces of PVEtImBr samples synthesized in DMF revealed a side population in the high molecular weight region, presumably due to the occurrence of irreversible coupling reactions of a small proportion of growing chains. Well-defined diblock copolymers featuring both a poly(vinyl acetate) (PVAc) block and a PVEtImBr-based poly(ionic liquid) block, PVAc-b-PVEtImBr, were next obtained by sequential CMRP of VAc and VEtImBr. To this end, a PVAc-Co(acac)2 was first prepared by CMRP and employed as a macroinitiator for the polymerization of VEtImBr either in methanol or in a mixture of DMF and MeOH (2/1: v/v) at 30 °C. Finally, cobalt-mediated radical coupling (CMRC) of the aforementioned PVAc-b-PVEtImBr diblock copolymers, using isoprene as a simple coupling agent, led to unprecedented and structurally well-defined PVAc-b-PVEtImBr-b-PVAc triblock copolymers.

New functional poly(N-vinylpyrrolidone) based (co)polymers via photoinitiated cobalt-mediated radical polymerization

The photoinitiated cobalt-mediated radical polymerization enables the synthesis of novel α-functional and α,ω-telechelic polymers. In combination with ring-opening polymerization, it also produces new amphiphilic copolymers which self-assemble into flower-like vesicles in water.

Cobalt-mediated radical polymerization routes to poly(vinyl ester) block copolymers

Cobalt-mediated radical polymerizations (CMRPs) utilizing redox initiation are demonstrated to produce poly(vinyl ester) homopolymers derived from vinyl pivalate (VPv) and vinyl benzoate (VBz), and their block copolymers with vinyl acetate (VAc). Combining anhydrous Co(acac)2, lauroyl peroxide, citric acid trisodium salt, and VPv at 30 °C results in controlled polymerizations that yield homopolymers with Mn = 2.5–27 kg/mol with Mw/Mn = 1.20–1.30. Homopolymerizations of scrupulously purified VBz proceed with lower levels of control as evidenced by broader polydispersities over a range of molecular weights (Mn = 4–16 kg/mol; Mw/Mn = 1.34–1.65), which may be interpreted in terms of the decreased nucleophilicity of these less electron donating propagating polymer chain ends. Based on these results, we demonstrate that sequential CMRP reactions present a viable route to microphase separated poly(vinyl ester) block copolymers as shown by small-angle X-ray scattering analyses. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

New cobalt-mediated radical polymerization (CMRP) of methyl methacrylate initiated by two single-component dinuclear β-diketone cobalt (II) catalysts.

Two dinuclear cobalt complexes based on bis-diketonate ligands (ligand 1: 3,3′-(1,3-phenylene)bis(1-phenylpropane-1,3-dione); ligand 2: 3,3′-(1,4-phenylene)bis(1-phenylpropane-1,3-dione)) were successfully synthesized. The two neutral catalysts all showed satisfactory activities in the cobalt-mediated radical polymerization (CMRP) of methyl methacrylate (MMA) with the common initiator of azodiisobutyronitrile (AIBN). The resulting polymerizations have all of the characteristics of a living polymerization and displayed linear semilogarithmic kinetic plots, a linear correlation between the number-average molecular weight and the monomer conversion, and low polydispersities. Mono- or dicomponent low polydispersity polymers could be obtained by using the two dinuclear catalysts under proper reaction conditions. All these improvements facilitate the implementation of the acrylate CMRP and open the door to the scale-up of the syntheses and applications of the multicomponent low polydispersity polymers.

Synthesis of water-soluble poly(vinyl alcohol)-grafted multi-walled carbon nanotubes

A facile method for preparing waster-soluble poly(vinyl alcohol)-grafted multi-walled carbon nanotubes (PVA-grafted MWNTs) was developed. Well-defined poly(vinyl acetate) chains end-capped by a cobalt(II) acetylacetonate (Co(acac)2) complex [PVAc-Co(acac)2] were synthesized by the cobalt-mediated radical polymerization (CMRP) of vinyl acetate. PVAc macroradicals generated by the homolytic cleavage of the carbon-cobalt (C-Co) bonds of PVAc-Co(acac)2 chains were then grafted directly to the MWNTs via radical addition reactions in dimethyl sulfoxide (DMSO) at 50 °C. The amount of the PVAc grafted onto the surface of the MWNTs decreased with increasing molecular weight of PVAc-Co(acac)2. Hydrolysis of the grafted PVAc finally yielded PVA-grafted MWNTs, which showed good solubility in water. Surface functionalization of the MWNTs was confirmed by 1H NMR spectroscopy, FTIR spectroscopy and TEM.

Synthesis of Poly(vinyl alcohol)/C60 and Poly(N‐vinylpyrrolidone)/C60 Nanohybrids as Potential Photodynamic Cancer Therapy Agents

Well-defined poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone)-co-poly(vinyl acetate) (PNVP-co-PVAc) chains end-capped by Co(acac)(2) (acac=acetylacetonate) and prepared by cobalt-mediated radical polymerization (CMRP) are grafted onto a fullerene. Homolytic Co-C bond cleavage of the polymer chain ends at 30 degrees C releases the polymeric radicals that add onto C(60), thereby leading to the corresponding PVAc/C(60) and PNVP-co-PVAc/C(60) nanohybrids. The [polymer-Co(acac)(2)]/[C(60)] molar ratio was varied to adjust the structure of the nanohybrids, and more particularly the number of grafted arms. Finally, the potential of the hydrosoluble PVOH/C(60) nanohybrids, which result from the methanolysis of the ester groups of PVAc/C(60), and of the PNVP-co-PVAc/C(60) nanohybrids as photosensitizers for photodynamic therapy (PDT), was approached. First, photobleaching tests demonstrated the ability of these nanohybrids to produce singlet oxygen upon irradiation, which can play a role in cell damage. Second, cell viability assays demonstrated that both types of nanohybrids are deprived of intrinsic cytotoxicity in the dark, whereas they promoted significant cell mortality when subjected to light treatment. The selective response of these materials to irradiation makes them promising compounds for PDT.

Synthesis of Poly(vinyl acetate)-b-polystyrene and Poly(vinyl alcohol)-b-polystyrene Copolymers by a Combination of Cobalt-Mediated Radical Polymerization and RAFT Polymerization

Well-defined poly(vinyl acetate)-block-polystyrene (PVAc-b-PSt) block copolymers were successfully synthesized by a combination of cobalt-mediated radical polymerization (CMRP) and reversible addition−fragmentation chain transfer (RAFT) polymerization. PVAc and PVAc-b-PSt (with an average PSt repeating unit of 2 or 6) were first synthesized via CMRP with cobalt(II) acetylacetonate as a regulating agent. The cobalt complexes attached to their ω chain ends were modified into a phenyl dithioester group by reacting with bis(thiobenzoyl) disulfide, producing PVAc and PVAc-b-PSt macro-chain-transfer agents (PVAc-CTA and PVAc-PSt-CTA), respectively. The RAFT polymerization of styrene with PVAc-CTA or PVAc-PSt-CTA was conducted in N,N-dimethylformamide at 80 °C. PVAc-b-PSt block copolymers synthesized with PVAc-PSt6-CTA (with an average PSt repeating unit of 6) exhibited narrowest molecular weight distributions (Mw/Mn = 1.28−1.30) even at high conversions. The PVAc-b-PSt block copolymer (Mn(GPC) = 21 000 g/mol, M...

Cobalt‐Mediated Radical Coupling (CMRC): An Unusual Route to Midchain‐Functionalized Symmetrical Macromolecules

Cobalt-mediated radical coupling (CMRC) is a straightforward approach to the synthesis of symmetrical macromolecules that relies on the addition of 1,3-diene compounds onto polymer precursors preformed by cobalt-mediated radical polymerization (CMRP). Mechanistic features that make this process so efficient for radical polymer coupling are reported here. The mechanism was established on the basis of NMR spectroscopy and MALDI-MS analyses of the coupling product and corroborated by DFT calculations. A key feature of CMRC is the preferential insertion of two diene units in the middle of the chain of the coupling product mainly according to a trans-1,4-addition pathway. The large tolerance of CMRC towards the diene structure is demonstrated and the impact of this new coupling method on macromolecular engineering is discussed, especially for midchain functionalization of polymers. It is worth noting that the interest in CMRC goes beyond the field of polymer chemistry, since it constitutes a novel carbon-carbon bond formation method that could be applied to small organic molecules.

Solving the Problem of Bis(acetylacetonato)cobalt(II)-Mediated Radical Polymerization (CMRP) of Acrylic Esters

Recent developments in cobalt-mediated radical polymerization (CMRP) and progress in the mechanistic understanding enabled to optimize the copolymerization of n-butyl acrylate (nBA) with vinyl acetate (VAc), as well as to control the homopolymerization of nBA by means of bis(acetylacetonato)cobalt(II) (Co(acac)2). Critical experimental parameters such as the initiating system, the temperature, and the presence of additives were varied and discussed. Under optimized conditions, an alkylcobalt(III) adduct R0−(CH2−CHOAc)<4−Co(acac)2 (R0 = primary radical from the V-70 decomposition) allowed a better control of the nBA/VAc copolymerization than the previously studied V-70/Co(acac)2 pair regarding the molecular weight control and the polydispersities. Importantly, the homopolymerization of nBA was controlled by Co(acac)2 for the first time using the alkylcobalt(III) adduct or the lauroyl peroxide (LPO)/Co(acac)2 redox pair as initiating system. Typically, poly(n-butyl acrylate) with polydispersity around 1.2 a...

Antibacterial activity of poly(vinyl alcohol)-b-poly(acrylonitrile) based micelles loaded with silver nanoparticles

A new amphiphilic poly(vinyl alcohol)-b-poly(acrylonitrile) (PVOH-b-PAN) copolymer obtained by selective hydrolysis of well-defined poly(vinyl acetate)-b-poly(acrylonitrile) copolymer synthesized by cobalt mediated radical polymerization was used for the preparation of PVOH-b-PAN based micelles with embedded silver nanoparticles. The successful formation of silver loaded micelles has been confirmed by UV–vis, DLS and TEM analysis and their antibacterial activity against Escherichia coli ( E. coli), Staphylococcus aureus ( S. aureus), Pseudomonas aeruginosa ( P. aeruginosa) and spore solution of Bacillus subtilis ( B. subtilis) has been studied. PVOH-b-PAN based micelles with embedded silver nanoparticles showed a strong bactericidal effect against E. coli, S. aureus and P. aeruginosa and the minimum bactericidal concentration for each system (MBC) has been determined.

Joining Efforts of Nitroxide-Mediated Polymerization (NMP) and Cobalt-Mediated Radical Polymerization (CMRP) for the Preparation of Novel ABC Triblock Copolymers

Joining Efforts of Nitroxide-Mediated Polymerization (NMP) and Cobalt-Mediated Radical Polymerization (CMRP) for the Preparation of Novel ABC Triblock Copolymers