Chain Transfer Catalyst Research Articles

Radiation polymerization of methacrylates controlled by a chain transfer catalyst

The effect of γ-radiation dose and chain transfer catalyst on polymerization of methyl methacrylate (MMA) and copolymerization of MMA with hydroxyethyl methacrylate or triethylene glycol dimethacrylate has been investigated. The addition of 5 × 10−4−10−3 mol/L of bis[(difluoroboryl) isopropylpyridine dimethylglyoximato]cobalt(II) (Co(II)) makes it possible to produce macromonomers MM == bearing terminal double bonds and having a degree polymerization of n = 2−40 and a polydispersity index of 1.05−1.15. It has been found that the degree polymerization of the macromonomers increases with the increasing γ-radiation dose and monomer conversion through the mechanism of the reversible β-cleavage of the terminal unit: R ∙ + MM = ↔ MM +1 = + R -1 ∙ followed by the living polymerization of both radicals. This reaction may compete with the catalytic chain transfer reaction and have a significant effect on the evolution of the molecular weight characteristics of the macromonomers during the course of MMA (co)polymerization.

Synthesis of Nanocomposite Hybrids

Controllable synthesis of zinc sulfide (ZnS) nanocrystals (NCs)/polymer transparent nanocomposite hybrids in situ based on the catalytic chain transfer polymerization (CCTP) technique. Firstly, a polymeric ligand PMAA (PMAA = poly(acrylic acid)) with controllable low-molecular-weight and a terminal double bond was synthesized through CCTP Catalytic chain transfer polymerization (CCTP) has emerged as an efficacious method to produce low- molecular weight polymers. In this paper, we reported the first controllable synthesis of nanosilica surface-grafted poly(methyl methacrylate) (PMMA) (SI-PMMA) macromonomers by using bis(aqua)bis((difluoroboryl)- dimethylglyoximato)cobalt(II) (CoBF) as a chain transfer catalyst via CCTP.

Controllable synthesis of nanosilica surface-grafted PMMA macromonomers via catalytic chain transfer polymerization

Catalytic chain transfer polymerization (CCTP) has emerged as an efficacious method to produce low-molecular weight polymers. In this paper, we reported the first controllable synthesis of nanosilica surface-grafted poly(methyl methacrylate) (PMMA) (SI-PMMA) macromonomers by using bis(aqua)bis((difluoroboryl)-dimethylglyoximato)cobalt(II) (CoBF) as a chain transfer catalyst via CCTP. In a typical run, we firstly prepared functionalized nanosilica by using 3-(trimethoxysilyl)propylmethacrylate (MPS) as the coupling agent, allowing naosilica containing unsaturated double bonds in end groups. Subsequently, SI-PMMA macromonomers were prepared by PMMA surface-grafted onto the functionalized nanosilica via CCTP. The as-prepared products were characterized by Fourier transforms infrared (FT-IR) spectrum, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transforms Raman (FT-Raman) spectrum and gel permeation chromatography (GPC). We also investigated the dependence of macromonomers on CoBF concentrations.

Molecular Weight Evolution in the Catalytic Chain Transfer Polymerization of CO2-Expanded Methyl Methacrylate

Molecular weight evolution in catalytic chain transfer polymerization of methyl methacrylate expanded with dense CO2 is reported. Experimental molecular weight and polydispersity index data are presented at 50 °C in the range of conversion from 1 to 25%, and at pressures of 5 and 6 MPa. A cobaloxime complex is used as the chain transfer catalyst. Both molecular weight and polydispersity increase in the range of conversion achieved at conditions below the homogeneous expansion limit. Predici simulations suggest that either irreversible catalyst deactivation or cobalt−carbon bond formation, between the catalyst and the propagating radicals, is the most likely mechanism for the increase in molecular weight with conversion. At conditions above the homogeneous expansion limit, a bimodal molecular weight distribution is observed, indicating two zones of polymerization. These conditions produce relatively high molecular weight macromonomers with broad molecular weight distributions.

Chain-transfer catalysis by vanadium complexes during methyl methacrylate polymerization

A series of V(CO) 4(P–P) or HV(CO) 4(P–P) ((P–P) = bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), and 1,4-bis(diphenylphosphino)butane (dppb)) complexes have been tested as chain-transfer catalysts for methyl methacrylate (MMA) polymerization. The chain transfer constants C s (= k tr/ k p), determined by Mayo plots, suggest that V(CO) 4(dppe) is the most efficient chain-transfer catalyst among the complexes investigated ( C s = 750 at 70 °C).

Synthesis and reactivity of metal-containing monomers 64. Synthesis, structure, polymerization, and catalytic properties of the palladium and cobalt vinylporphyrin complexes

2-Vinylporphyrin and its complexes with PdII and CoII were synthesized and characterized by NMR, IR, and mass spectra. The palladium vinylporphyrin complexes are efficient metal-containing monomers in radical copolymerization with styrene. Palladium(II) in an amount of up to 1 mol.% can thus be introduced into the polymers. The synthesized polymeric Pd complexes perform the photosynthesized activation of dioxygen to the lowest excited singlet state, which is an active oxidizing agent for anthracene producing the 1,4-addition products. The monomeric and macromolecular cobalt complexes are chain-transfer catalysts in radical styrene polymerization.

Reversible Chain Transfer between Organoyttrium Cations and Aluminum: Synthesis of Aluminum‐Terminated Polyethylene with Extremely Narrow Molecular‐Weight Distribution

Aminopyridinato-ligand-stabilized organoyttrium cations are accessible in very good yield through alkane elimination from trialkyl yttrium complexes with sterically demanding aminopyridines, followed by abstraction of one of the two alkyl functions using ammonium borates. At 80 degrees C and in the presence of small amounts of aluminum alkyl compounds, very high ethylene polymerization activities are observed if very bulky aminopyridinato ligands are used. During these polymerizations a reversible polyethylene chain transfer is observed between the organoyttrium cations and aluminum alkyls. The chain-transfer catalyst system described here is able to produce relatively long-chain (up to 4000 g mol-1) Al-terminated polyethylene with a molecular-weight distribution<1.1. In the synthesis of higher molecular PE a slight increase in polydispersity with increasing chain length (15,600 g mol-1, approximately 1.4) is observed owing to reduced reversibility caused by higher viscosity and precipitation of polymer chains (temperature of 80-100 degrees C).

Effect of Bulk Viscosity on the Catalytic Chain Transfer Polymerization of CO2-Expanded Butyl Methacrylate and Styrene

The catalytic chain transfer polymerization of CO2-expanded butyl methacrylate and styrene is reported. Experimentally determined values of the chain transfer constant for CO2-expanded butyl methacrylate are presented at 50 and 60 °C and in the range of pressure from 0.1 to 6 MPa, using a cobaloxime complex as the chain transfer catalyst. Similar data are reported for CO2-expanded styrene at 50 °C. The chain transfer constants for both expanded monomers are significantly higher than those obtained in the bulk monomers. It is demonstrated that a linear relationship exists between the chain transfer rate coefficient and the inverse of viscosity. These results provide significant evidence that the rate-determining step in the chain transfer process is diffusion-controlled.

Catalytic chain transfer polymerisation of CO 2-expanded methyl methacrylate

The catalytic chain transfer polymerisation of methyl methacrylate expanded with dense CO 2 is reported. Experimental values of the chain transfer constant ( C s) are presented at 50 °C and in the range of pressure from 0.1 to 6 MPa, using a cobaloxime complex as the chain transfer catalyst. The effect of small quantities of poly(methyl methacrylate) on the volumetric expansion of the monomer with CO 2 is considered. Experimental data are presented on the pressure limit for homogeneous expansion as a function of the molecular weight of the polymer. It is shown that the values of C s in CO 2-expanded methyl methacrylate are significantly higher than that in bulk monomer. This effect is mainly attributed to the enhancement of the chain transfer rate coefficient, arising from the reduction in the viscosity of the medium, and is consistent with a diffusion-controlled rate-determining step in the chain transfer process.

Binary Copolymerization with Catalytic Chain Transfer. A Method for Synthesizing Macromonomers Based on Monosubstituted Monomers

With appropriate choice of conditions, copolymerization of monosubstituted monomers [CH2CHX: e.g., styrene, butyl acrylate (BA)] in the presence of small amounts of an α-methylvinyl monomer [CH2C(CH3)Y: e.g., α-methylstyrene (AMS), methyl methacrylate (MMA), methacrylonitrile (MAN)] and a cobaloxime as chain transfer catalyst provides a route to macromonomers that are composed largely of the monosubstituted monomer and yet have a chain end derived from the α-methylvinyl monomer (−CH2−C(CH2)Y). The various factors (temperature, concentrations, type of cobaloxime, types of monomer) that influence molecular weight and end group purity and the importance of the various side reactions that may complicate the process are described. Macromonomer purity is enhanced by increasing the concentration of the α-methylvinyl monomer and reducing the cobaloxime concentration. It also depends on the structure of the cobaloxime, increasing in the series where the ligands are derived from dimethyl glyoxime < diethyl glyoxi...

Effect of Steric Congestion on the Activity of Chromium and Molybdenum Metalloradicals as Chain Transfer Catalysts during MMA Polymerization

Effect of Steric Congestion on the Activity of Chromium and Molybdenum Metalloradicals as Chain Transfer Catalysts during MMA Polymerization

Macromonomer Chain Growth in the Radical Polymerization of MMA by Cobalt(II) Catalyzed Chain Transfer

AbstractProperties of the radical polymerization of methyl methacrylate in the presence of cobalt(II) tetraphenylporphyrin ((TPP)CoII•) as a chain transfer catalyst are reported. Reversible addition of (L)Co‐H to macromonomers gives living character to the oligomer olefins that grow to higher molecular weight without altering the primary polymer structural features. Incorporation of reversible termination of oligomer radicals in the mechanistic model for chain transfer catalysis by (L)CoII• complexes is an essential feature of the catalytic chain transfer process. Average degree of polymerization as a function of monomer conversion for the (TPP)CoII• mediated CCT polymerization of MMA in C6D6 initiated by AIBN at different concentrations of (TPP)CoII•.magnified imageAverage degree of polymerization as a function of monomer conversion for the (TPP)CoII• mediated CCT polymerization of MMA in C6D6 initiated by AIBN at different concentrations of (TPP)CoII•.

Control of polymer topology through transition-metal catalysis: synthesis of hyperbranched polymers by cobalt-mediated free radical polymerization.

A novel approach was demonstrated for the synthesis of hyperbranched polymers by direct free radical polymerization of divinyl monomers controlled by a cobalt chain transfer catalyst (1). By controlling the competition between propagation and chain transfer with 1, the free radical polymerization of ethylene glycol dimethacrylate (3) afforded soluble hyperbranched polymers in one pot. The structure of the hyperbranched polymers was confirmed by (1)H and (13)C NMR. The molecular weight and intrinsic viscosity of the hyperbranched polymers were measured by matrix-assisted laser desorption ionization (MALDI) mass spectrometry and size exclusion chromatography (SEC) equipped with triple detectors. The intrinsic viscosities of the hyperbranched polymers are much lower than those of their linear analogues and do not show molecular weight dependence. The unique structure and properties of these hyperbranched polymers combined with the commercial availability of many divinyl monomers and the robustness of free radical polymerization make this new approach attractive for the preparation of new functional materials.

Vibrational spectroscopic characterization of cobalt dimethylglyoxime boron difluoride ag

The Fourier-transform Raman and IR spectra of cobalt dimethylglyoxime boron difluoride (cobaloxime boron difluoride) have been obtained, and vibrational assignments made. The assignments were consistent with the symmetry group D2h for the molecular skeleton, although some variation from the vibrational activity of this point group for the methyl group vibrations was ascribed to the local symmetry group, C3ν, and non-planarity about the nitrogen atoms. Raman and IR spectra of nickel dimethylglyoxime were recorded and used for comparison purposes to aid the assignment of the cobaloxime boron difluoride bands. Cobalt dimethylglyoxime boron difluoride and other cobaloxime-based structures have been proposed for use as chain-transfer catalysts in free-radical polymerization chemistry.

Catalytic inhibition of the radical polymerization of methyl methacrylate

In the polymerization of methyl methacrylate in the presence of chain transfer catalysts, i.e. cobalt complexes of macroheterocyclic compounds of the tetramethyl ester of hematoporphyrin (CoPo) and phthalocyanine (CoPh) and a CoPh + quinoline mixture polymerization retardation is observed, which increases in the series CoPo < CoPh < CoPh + quinoline. Not all the additives are used up, and the unused material can be separated unchanged at the end of the process. The stoichiometric inhibition factor determined from the kinetic data is much greater than 2, and in the case of the CoPh + quinoline system exceed 10 2. Chain termination catalysis on the cobalt complexes of the macroheterocyclic compounds is the most likely retardation mechanism.

Kinetic mechanisms of polymerization of butyl acrylate in the presence of porphyrin cobalt during induction

1. The kinetic parameters of polymerization (PM) of butyl acrylate (BA) in the presence of porphyrin cobalts (CoP) fit into the general scheme of radical polymerization in the presence of chain-transfer catalysts. 2. The study of the kinetic mechanisms of PM of BA in the induction period showed that accumulation of macroradicals takes place more rapidly than in the case of irreversible inhibition. This is in agreement with the hypothesis that the process of inhibition of PM of BA by CoP is “reversible.” 3. Some kinetic parameters of this process were estimated based on the proposed kinetic scheme.

Polymerization of acrylonitrile by electron transfer catalysts

AbstractThe heterogeneous polymerization of acrylonitrile in tetrahydrofuran by chain transfer catalysts: monosodium anthracene, disodium anthracene, sodium naphthalene, monolithium anthracene, and lithium naphthalene was investigated. The free radical formed in the initiation was found to participate in the polymerization process only in the case of lithium naphthalene at low catalyst concentrations. Also, block copolymerization with styrene, which is more reactive in free radical polymerization than acrylonitrile and less in anionic, succeeded only with lithium naphthalene. The absence of dimerization of the free radicals is mainly due to their occlusion caused by the high rate of the anionic polymerization of acrylonitrile and the low polymerization temperature, and in the case of the anthracene catalysts also due to inhibition of the free radical dimerization by the liberated anthracene. The mechanism of the termination of the polymerization was found to depend on the catalyst concentration and the ratio [MI]/[C]. At high catalyst concentrations and relatively low [M]/[C] values, termination was by chain transfer to the monomer, as can be seen from the independence of the molecular weights on both monomer and catalyst concentrations. At low catalyst concentrations and relatively high [M]/[C] values, the molecular weights were found to increase with monomer concentration and decrease with catalyst concentration. This was found to be due to the anionic mechanism of the polymerization, and the results are similar to those obtained in a typical anionic polymerization of acrylonitrile with butyllithium.