Ruthenium carborane complexes in the controlled radical polymerization of methyl methacrylate

New initiators based on closo-and exo-nido-ruthenacarboranes with phosphine and diphosphine ligands were proposed as chain growth regulators. They allow conducting the controlled synthesis of poly(methyl methacrylate) under radical initiation conditions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 85–89, January, 2006.     

Photo-living radical polymerization of methyl methacrylate using alkoxyamine as an initiator

The photoradical polymerization of vinyl acetate was performed using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator in the presence of bis(alkylphenyl)iodonium hexafluorophosphate (BAI). The MTEMPO/BAI system using 2,2’-azobis(isobutyronitrile) or 2,2’-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator did not succeed in controlling the molecular weight and produced polymers that showed a bimodal gel permeation chromatography with the broad molecular weight distribution. On the other hand, the polymerization using 1-(cyano-1-methylethoxy)-4-methoxy-2,2,6,6-tetramethylpiperidine and BAI proceeded by the living mechanism based on linear increases in the first order time–conversion and conversion–molecular weight plots. The molecular weight distribution also increased with the increasing conversion due to cloudiness of the solution as the polymerization proceeded. It was found that the polymerization had a photolatency because the propagation stopped by interruption of the irradiation and was restarted by further irradiation.     

Studies on bulk polymerization of methyl methacrylate. I. Thermal polymerization

The thermal bulk polymerization of methyl methacrylate (MMA) in a wide range of temperatures has been studied using a dilatometric reactor. It is shown that, irrespective of the care taken to purify the MMA, the evolution of the time-conversion curve can be explained only if we account for the presence of an impurity associated with the monomer acting as a free radical initiator. The activation energy for the decomposition of this impurity has been estimated as 98 kJ/mol. Having accounted for this impurity, the activation energy for the real thermal polymerization of the MMA has been estimated to be 75 kJ/mol. © 1993 John Wiley & Sons, Inc.     

The effect of mixed solvents pyridine–carbon tetrachloride on the radical polymerization of methyl methacrylate

A study was made of the methyl methacrylate (MMA) solution polymerization in CCl₄-pyridine mixtures as well as in net components at 30, 50, and 70°C. The results obtained show that there are no significant deviations from additivity in the overall chain transfer constants that fit the straight line between the values of Cs for CCl₄ and pyridine. It can be concluded that the EDA interaction between CCl₄ and pyridine does not change the sensitivity of each component for chain transfer from propagation PMMA free radical. The pyridine in the system increases the rate of MMA polymerization as a result of the higher rate of initiation.     

Azobenzene‐based initiator for atom transfer radical polymerization of methyl methacrylate

2‐Bromopropionic acid 2‐(4‐phenylazophenyl)ethyl ester, 2‐bromopropionic acid 6‐(4‐phenylazophenoxy)hexyl ester (BPA₆), 2‐bromopropionic acid‐(4‐phenylazoanilide), and 2‐bromopropionic acid 4‐[4‐(2‐bromopropionyloxy)phenylazo]phenyl ester (BPPE) were used as initiators with monofunctional or difunctional azobenzene for the heterogeneous atom transfer radical polymerization of methyl methacrylate with a copper(I) chloride/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalytic system. The rates of polymerizations exhibited first‐order kinetics with respect to the monomer, and a linear increase in the number‐average molecular weight with increasing monomer conversion was observed for these initiation systems. The polydispersity indices of the polymer were relatively low (1.15–1.44) up to high conversions in all cases. The fastest rate of polymerization and the highest initiation efficiency were achieved with BPA₆, and this could be explained by the longer distance between the halogen and azobenzene groups and the better solubility of the BPA₆ initiator. The redshifting of the UV absorptions of the polymers only occurred for the BPPE‐initiated system. The intensity of the UV absorptions of the polymers were weaker than those of the corresponding initiators in chloroform and decreased with the increasing molecular weights of the polymers in all cases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2358–2367, 2005     

Free radical polymerization of methyl methacrylate initiated by the diphosphine Mo(0) complexes

The polymerization of methyl methacrylate MMA catalyzed by [Mo(CO)₄L₂] [L₂ = diphenylphosphinomethane (dppm), diphenylphosphinoethane (dppe) or diphenylphosphinopropane (dppp)] has been studied. The activity of these single‐component catalysts depends on the length of the (CH₂)_n bridge of diphosphine ligand. Thus, the dppm derivative displays higher activity than dppe or dppp ligands. These complexes, as free radical initiators, afforded the methyl methacrylate polymerization in chlorinated solvents. The mechanism of the polymerization was discussed and a radical mechanism was proposed. Copyright © 2006 John Wiley & Sons, Ltd.     

Novel ionic liquids as reaction medium for atom transfer radical polymerization of methyl methacrylate

Atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) employing ethyl 2-bromoisobutyrate (EBiB)/ CuBr as the initiating system was investigated at 50℃ in the absence of any additional ligand in the three room temperature ionic liquids (RTIL_s), 1-methyl-imidazolium acetate ([mim][CH_3COO]), 1-methylimidazolium propionate ([mim][CH_3CH_2COO]) and 1-methylimidazolium butyrate ([mim][CH_3CH_2CH_2COO]), respectively. All the polymerization in the three RTILs proceeded in a well-controlled manner. The sequence of the apparent polymerization rate constants was kapp([mim][CH_3COO]) > kapp([mim] [CH_3CH_2COO]) > kapp ([mim][CH_3CH_2CH_2COO]).     

Cyclic diperoxides as sources of radicals for the initiation of the radical polymerization of methyl methacrylate

Thermolysis of cyclic diperoxides gave radicals. When solution polymerization of MMA was initiated by acetone cyclic diperoxide transfer to solvent was the dominant feature of the initiation process. However, transfer in the bulk polymerization of MMA was not a significant feature. Initiation of polymerization of MMA in solution by dibenzyl ketone cyclic diperoxide occurred at lower temperatures, and also aromatic end groups, derived from initiation by benzyl radicals, could be detected by ¹H NMR.     

Effects of chlorophosphines on the radical polymerization of methyl methacrylate

The effect of chlorophosphines (phosphorus trichloride, dichlorophenylphosphine, chlorodiphenylphosphine) on the radical polymerization of methyl methacrylate was investigated in benzene solution. The polymerization was carried out at 50°C by the standard solution method, α,α′-azobisisobutyronitrile being used as an initiator. These chlorophosphines accelerated the polymerization of methyl methacrylate but did not affect the rate of decomposition of α,α′-azobisisobutyronitrile. Ultraviolet and infrared spectral data suggested that the acceleration effect was due to the complex formation of methyl methacrylate with each chlorophosphine. From the result of a copolymerization with styrene, it was found that the reactivity of methyl methacrylate monomer increased in the presence of dichlorophenylphosphine.     

Specifics of radical polymerization of styrene and methyl methacrylate in the presence of ruthenium carborane complexes

The specifics of the radical polymerization of styrene and methyl methacrylate in the presence of ruthenium closo- and exo-nido-carborane complexes with phosphine and diphosphine ligands were investigated. It was shown that, depending on a coinitiator, the polymerization proceeds through the atom transfer radical mechanism or the reverse atom transfer radical mechanism to high conversions without gelation to yield macromolecules with a low polydispersity. The influence of the ligand environment, the oxidation state of ruthenium atoms in the carborane complexes, and the temperature conditions on the specific features of the polymer synthesis was established.     

New efficient boron-containing initiators of methyl methacrylate radical polymerization

An efficient method for methyl methacrylate radical polymerization by tri-n-propyl-, triisopropyl-, and triisobutylborane ammonia complexes, including the addition of a boron-containing initiating agent into the monomer in air, was developed. An advantage of this method is that the reaction occurs at room temperature, requires no peroxide components, and leads to polymers with enhanced thermal stability.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2120–2125, October, 2004.     

Nitroxide-mediated photo-living radical polymerization of methyl methacrylate in solution

The photoradical polymerization of methyl methacrylate (MMA) was performed in an acetonitrile solution at room temperature using (2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator, 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator, and (4-tert-butylphenyl)diphenylsulfonium triflate as the photo-acid generator. This solution polymerization showed a non-steady-state during the very early stage followed by a steady-state. The polymerization produced oligomers with several thousand molecular weights at a very low conversion under the non-steady-state. It was confirmed that the polymerization proceeded in accordance with a living mechanism under the steady-state based on the linear correlations for both the first-order time-conversion plots and the conversion–molecular weight plots. The molecular weight distributions of the polymers obtained in the steady-state were approximately 1.8. The block copolymerization with isopropyl methacrylate ( ⁱ PMA) demonstrated that the growing polymer chain ends of the MMA prepolymer were stabilized even at a high conversion and efficiently initiated the ⁱ PMA polymerization.     

Atom‐transfer radical polymerization of methyl methacrylate (MMA) using CuSCN as the catalyst

The effect of CuSCN as a catalyst in atom‐transfer radical polymerization (ATRP) was investigated. CuSCN can successfully be used for the ATRP of MMA. Substituted bipyridines as well as imines can be used to stabilize the copper complex in solution. CuSCN induces faster polymerization compared to CuBr and CuCl when tosylchloride is used as the initiator. However, the polydispersity is larger than that obtained in the cases of CuCl and CuBr.     

High-conversion polymerization. I. Theory and application to methyl methacrylate

The concept of polymer entanglements has been applied in conjunction with classical free-radical kinetics to describe vinyl polymerizations carried to high conversion. A kinetic model has been developed on the assumption that two populations of radicals exist in a high-conversion polymerization system: those radicals whose chain lengths are long enough to become entangled with neighboring molecules and have, therefore, a restricted mobility; and those shorter radicals whose mobilities are not strongly affected by diffusional effects. It has also been assumed that the kinetic rate constant for the termination step between entangled radicals is inversely proportional to the mean entanglement density. The model contains only two parameters in addition to the kinetic rate constants required to describe low-conversion polymerizations. One of these parameters can be determined, at least in principle, from measurements of solution properties of the polymer-monomer mixtures. The model so developed has been tested against experimental data obtained from the literature on the bulk polymerization of methyl methacrylate. The agreement between predicted and experimental monomer conversions and molecular weight averages is found to be satisfactory.     

The cupric sulfate–hydrazine system as an initiator of vinyl polymerization. I. The polymerization of methyl methacrylate in aqueous solution in the presence of oxygen

The cupric sulfate–hydrazine system has been used to initiate the aqueous solution polymerization of methyl methacrylate at pH 9.25 in the presence of oxygen. At cupric sulfate concentrations greater than the saturation solubility of cupric hydroxide, hydrazine is adsorbed on, and decomposes on, the surface of the hydroxide. The kinetics of the decomposition are zero-order both in the absence and the presence of monomer. The initiation of the polymerization occurs both at the surface of the cupric hydroxide on to which some monomer is adsorbed and also in solution. Below the saturation solubility of cupric hydroxide, the initiation reaction between cupric ions and hydrazine occurs in solution.