Effect of solvent in radical polymerization of butadiene 1-carboxylic acid

The radical polymerization and copolymerization of butadiene 1-carboxylic acid (Bu-1-Acid) were studied in a variety of the electron-donor solvents such as dimethylformamide (DMF), tetrahydrofuran (THF), methyl ethyl ketone (MEK), acetonitrile (ACN), and benzene (BZ) using AIBN as an initiator at 50°C. Under these conditions, the polymerization rate of Bu-1-Acid increased in the order, DMF < THF < MEK < ACN < BZ in the various solvents. In copolymerization with styrene [M₂] and acrylonitrile [M₂], the monomer reactivity ratio r₁ increased and r₂ decreased in the same order. Moreover, it was found that Alfrey-Price Q-e value of Bu-1-Acid increased depending on solvent in the order DMF < THF < MEK < ACN < BZ. These variations were correlated to the electron-donating power (Δvcm^?) of the solvents used and are discussed on the basis of the solvation of Bu-1-Acid into the solvent. Also, it was found that the microstructures of these polymers were always trans-1,4 and did not change with the solvent used.     

Asymmetric radical polymerization of butadiene 1-carboxylic acid

Optically active S(?)-α-phenethylammonium butadiene 1-carboxylate was prepared and polymerized in methanol, using azobisisobutyronitrile as initiator. The optical rotation, optical rotatory dispersion and circular dichroism spectra of the polymers, before and after removal of chiral amine, have demonstrated that the asymmetric induction occurred in the main chain. An asymmetric inductive polymerization mechanism is discussed.     

Radical polymerization of butadiene-1-carboxylic acid

The homopolymerization and copolymerization of butadiene-1-carboxylic acid (Bu-1-Acid) (M₁) were studied in tetrahydrofuran at 50°C with azobisisobutyronitrile as an initiator. The initial rate of polymerization was proportional to [AIBN]^1/2 and [Bu-1-Acid]¹. The overall activation energy for the polymerization was 22.87 kcal/mole. For copolymerization with styrene (M₂) and acrylonitrile (M₂), the monomer reactivity ratios r₁, r₂ were determined by the Fineman-Ross method, as follows; r₁ = 5.55, r₂ = 0.08 (M₂ = styrene); r₁ = 11.0, r₂ = 0.03 (M₂ = acrylonitrile). Alfrey-Price Q-e values calculated from these values were 6.0 and +0.11, respectively. The Bu-1-Acid unit in the copolymer as well as the homopolymer was found from infrared and NMR spectral analyses to be composed of a trans-1,4 bond. The hydrogen-transfer polymerization of Bu-1-Acid leading to polyester was attempted with triphenylphosphine as initiator, but did not occur.     

Effect of dielectric properties and structure of aqueous solutions of diallylammonium salts on their reactivity in radical polymerization

The complex dielectric permittivity in the frequency range 7.5–25.0 GHz and the low-frequency specific conductivity of aqueous solutions of diallylammonium salts (diallylammonium and diallylmethylammonium trifluoroacetates and diallyldimethylammonium chloride) were measured at 293–308 K over a wide concentration range. On the basis of the results, the parameters of dielectric relaxation were calculated. The number of water molecules in the solvation shell of the salts was estimated. The concentration behavior of the initial rate of radical polymerization of diallylammonium salts and the rate constant of bimolecular chain termination was correlated with the specific features of the structure of aqueous monomer solutions. The role of “free” water in the initial salt solutions was revealed, a species whose presence in the system determines the character of concentration behavior of the rate constants for the elementary steps of polymerization, such as propagation, chain transfer to the monomer, and bimolecular chain termination.     

Effect of surfactants on the polymerization of acrylamide in aqueous solutions

The polymerization of acrylamide in aqueous surfactant solutions, initiated by potassium persulfate, has been investigated, dilatometry being used to follow the conversion. It has been shown that below the critical micellar concentration (CMC), cationic, anionic and non-ionic surfactants have no effect, while above the CMC only cationic soaps have an effect, lowering both the rate of polymerization and the molecular weight of the resultant polymer.     

Kinetics and mechanism of radical polymerization of weak unsaturated acids in aqueous solutions

The behaviour of weak unsaturated acids (such as acrylic and methacrylic) and their salts in radical polymerization in aqueous solutions was studied. A characteristic of these reactions was attributed to change of the effective reactivity of the propagating radicals with the nature of the reaction mixture. The data suggest that the formation of ion pairs may be responsible for a considerable increase in the propagation rate and, in consequence, in the overall polymerization rate. For alkaline values of pH, chain propagation involves only radicals having ion pairs at their ends; the participation of the ion pairs in the propagation can influence the microstructure of the polymer chains. Due to stereochemical control effected by the ion pairs, practically stereospecific polyacids may, in certain cases, be formed. Investigations on the temperature dependence of microtacticity have given values of activation enthalpy and entropy differences greatly exceeding those known up to now for isotactic and syndiotactic radical additions.     

Radiation polymerization of 2-acrylamido-2-methylpropanesulfonic acid in aqueous solutions

The dependence of the yield of polymer and its molecular mass on the absorbed dose of γ-irradiation of a 0.8 M 2-acrylamido-2-methylpropanesulfonic acid aqueous solution was determined, as well as the gel fraction of the polymer produced. The feasibility of obtaining a crosslinked polymer via radiation polymerization of 2-acrylamido-2-methylpropanesulfonic acid in the presence of N,N′-methylenebisacrylamide admixtures was shown. It was found that the maximal degree of crosslinking is reached at a dose on the order of 20 kGy and the maximal water uptake (1150 g/g) is achieved at a dose of 1.25 kGy.     

Controlled/living radical polymerization of isoprene and butadiene in emulsion

A process for RAFT-controlled radical polymerization in emulsion [36] has been applied to the polymerizations of isoprene and of butadiene in emulsion systems, with the goal of producing latex particles containing block copolymers of acrylic acid (stabilizer and starting polymer), styrene (second polymer) and isoprene or butadiene (third polymer). The microstructure of the polymer chains was examined using dual-detection size-exclusion chromatography, and the nanostructure of the materials was investigated by differential scanning calorimetry and solid-state nuclear magnetic resonance. Reactions were always slow (although faster than the corresponding processes in solution), and exhibited limited reinitiation by isoprene when in emulsion. The materials containing isoprene exhibit a nanostructure with a phase separation into high-T_g polystyrene-rich domains and low-T_g polyisoprene-rich domains, revealed by DSC and NMR. This has the potential to lead to barrier materials with novel physical properties.     

Effect of pH on one-electron oxidation chemistry of organoselenium compounds in aqueous solutions

Pulse radiolysis coupled with absorption detection has been employed to study one-electron oxidation of selenomethionine (SeM), selenocystine (SeCys), methyl selenocysteine (MeSeCys), and selenourea (SeU) in aqueous solutions. Hydroxyl radicals (*OH) in the pH range from 1 to 7 and specific one-electron oxidants Cl2*- (pH 1) and Br2*- (pH 7) have been used to carry out the oxidation reactions. The bimolecular rate constants for these reactions were reported to be in the range of 2 x 10(9) to 10 x 10(9) M(-1) s(-1). Reactions of oxidizing radicals with all these compounds produced selenium-centered radical cations. The structure and stability of the radical cation were found to depend mainly on the substituent and pH. SeM, at pH 7, produced a monomer radical cation (lambdamax approximately 380 nm), while at pH 1, a dimer radical cation was formed by the interaction between oxidized and parent SeM (lambdamax approximately 480 nm). Similarly, SeCys, at pH 7, on one-electron oxidation, produced a monomer radical cation (lambdamax approximately 460 nm), while at pH 1, the reaction produced a transient species with (lambdamax approximately 560 nm), which is also a monomer radical cation. MeSeCys on one-electron oxidation in the pH range from 1 to 7 produced monomer radical cations (lambdamax approximately 350 nm), while at pH < 0, the reaction produced dimer radical cations (lambdamax approximately 460 nm). SeU at all the pH ranges produced dimer radical cations (lambdamax approximately 410 nm). The association constants of the dimer radical cations of SeM, MeSeCys, and SeU were determined by following absorption changes at lambdamax as a function of concentration. From these studies it is concluded that formation of monomer and dimer radical cations mainly depends on the substitution, pH, and the heteroatoms like N and O. The availability of a lone pair on an N or O atom at the beta or gamma position results in monomer radical cations having intramolecular stabilization. When such a lone pair is not available, the monomer radical cation is converted into a dimer radical cation which acquires intermolecular stabilization by the other selenium atom. The pH dependency confirms the role of protonation on stabilization. The oxidation chemistry of these selenium compounds is compared with that of their sulfur analogues.     

Oxygen promoted radical polymerization of acrylonitrile in aqueous nitric acid. A kinetic study

The polymerization of acrylonitrile (AN) initiated by oxygen-ascorbic acid (AA)-ferric ion system was studied in dil. HNO₃ at 40°. The rate of polymerization, R_p, was found gravimetrically. In the [Fe³⁺] range, (2–5 × 10^?5 M, R_p was proportional to [AN]^{1.5 ± 0.05}, [O₂]^{0.5 ± 0.02} [AA]⁰ and [Fe³⁺]⁰; for [Fe³⁺] = (5–30) × 10^?5 M, it was proportional to [AN]^{1.8 ± 0.05}, [O₂]^{0.6 ± 0.02}, [AA]⁰ and [Fe³⁺]^{?0.9 ± 0.05}. A plausible reaction scheme is proposed and rate law presented to explain these results. R_p increased with ionic strength and [HNO₃] (up to ～0.25 M). An initial rate increase with temperature followed by a decrease was noticed. Chain lengths of the polymers were determined viscometrically.     

Free radical reactions of bromoform (BF) in air free and air saturated aqueous solutions. Effect of pH

G(Br̄) and G(H₂O₂) have been reported in Ar, N₂O and air saturated bromoform, containing 0.1 M t-butanol at various pHs. The results demonstrate an increase in G(Br̄) with increasing bromoform concentration and increasing pH. e^-_aq and Ḣ atoms react with bromoform to give Br̄, whereas ȮH radicals produce the t-butanol radical which interacts with bromoform and generates Br̄. This reaction is catalysed at acidic and alkaline pH. The results suggest that the reactivity of the primary radicals and t-butanol radical appear to be in the order e^-_aq > ḢȮH > ĊH₂(CH₃)₂COH. Ḃr radicals formed as a result of reactions of dibromomethyl radical with bromoform, further react with bromoform to give Br̄.G(Br̄) values at high pH are attributed to the formation of a reactive intermediate BrOḢ^- (Ḃr + OH^-), which decays to Br̄ and ȮH at higher pH. G(Br̄) values are considerably higher in the presence of oxygen. This is because of the formation of peroxy radicals CHBr₂Ȯ and CBr₃Ȯ which decompose to Br̄ and CO, and Br̄ and CO₂, respectively. High G(Br̄) values are found in the presence of isopropanol, ethanol and methanol suggesting a chain reaction. Rate constants for the reaction of ċHBr₂ radical with isopropanol, ethanol and methanol have been measured as 553, 136 and 56 mol^-1dm³s^-1 respectively. G(H₂O₂) ∼ 0.6 in Ar and N₂O saturated solution, and G(H₂O₂) ∼ 1.0 in air saturated solutions.     

Atom transfer radical polymerization in aqueous dispersed media

During the last decade, atom transfer radical polymerization (ATRP) received significant attention due to its exceptional capability of synthesizing polymers with pre-determined molecular weight, well-defined molecular architectures and various functionalities. It is economically and environmentally attractive to adopt ATRP to aqueous dispersed media, although the process is challenging. This review summarizes recent developments of conducting ATRP in aqueous dispersed media. The issues related to retaining “controlled/living” character as well as colloidal stability during the polymerization have to be considered. Better understanding the ATRP mechanism and development of new initiation techniques, such as activators generated by electron transfer (AGET) significantly facilitated ATRP in aqueous systems. This review covers the most important progress of ATRP in dispersed media from 1998 to 2009, including miniemulsion, microemulsion, emulsion, suspension and dispersed polymerization.      

Free radical polymerization of acrylonitrile in dimethylsulphoxide solutions

The gamma-ray initiated polymerization of acrylonitrile in DMSO solutions was investigated at various monomer concentrations and temperatures. In a narrow range of monomer concentrations (70–80%), the “auto-acceleration index” of the reaction is higher than in the bulk polymerization. Some auto-acceleration persists at high DMSO contents when the reaction proceeds in a homogeneous medium. The results are interpreted by a “matrix effect” which is enhanced in those mixtures in which the precipitated polymer particles are swollen to a larger extent by the reacting mixture.     

Effect of hydroacoustic treatment on chitosan dissolution in aqueous acetic acid solutions

Effect of a hydroacoustic treatment in a rotary-pulsatory apparatus on the dissolution rate and the achievable limiting solubility of chitosan in aqueous acetic acid solutions of various concentrations was studied. The rheological properties of solutions produced by the conventional method and with mechanical activation were compared     

Photoinitiated free radical polymerization of vinyl compounds in aqueous solution

A new method for the photochemical initiation of polymerization of vinyl compounds in aqueous solution is described. The photochemically active species is an ion pair complex of the formula Fe³⁺X⁻(X⁻ = OH⁻, CI⁻, N⁻₃, etc.). The light absorption by the ion pair leads to an electron transfer causing reduction of the cation and oxidation of the anion to an atom or free radical X. The latter leads to the initiation of polymerization in accordance with X + CH₂CHR→XCH₂ CHR . The kinetics of the reaction were studied by the measurement of: (a) ferrous ion formed (colorimetrically), (b) monomer disappearance (by titration and by weighting the polymer), (c) the chain length of the polymer (in the case of methyl methacrylate). The dependence of the quantum yield on the light intensity, light absorption fraction, and the concentration of vinyl monomer and ferrous ion added initially was investigated. A complete mechanism, both with regard to the formation of free radicals and the polymerization reaction, was put forward involving: (1) light absorption, (2) a primary dark back reaction, (3) dissociation of the primary product, (4) a secondary dark back reaction, (5) initiation of polymerization by free radicals, (6) propagation of polymerization, and (7) termination by recombination of active polymer endings. The mechanism was verified by the experimental results and some constant ratios were estimated quantitatively.     

The properties of aqueous solutions of some short chain cosurfactants used for radical polymerization of vinyl acetate

 The refractive index and excess molar volume, of the following short hydrocarbon chain co-surfactants were studied: ethylene glycol, ethylene glycol monomethyl ether, ethanol, n-, i-propanol, acrylic acid, ethyl monomethylmaleate and acrylamide. The refractive indexes of the aqueous solutions of these compounds vary nonlinearly with composition. The maximum variation of refractive indexes occurs up to a cosurfactant/water molar ratio equal to 1 5. The fluorescence probe method was successfully used to evidence the structure modifications of the alcohol–water mixtures. The intensity ratio of pyrene fluorescence vibrational bands varies nonlinearly with the composition of the systems; in case of 1-propanol, the sudden decrease of the ratio is similar to that of micellar solutions, so that a critical concentration of association can be determined at a 0.88 water mole fraction. It was shown, in good agreement with data in literature, that the compounds mentioned penetrate into the cluster structure of water and associate. At concentrations higher than critical, restructuring of aqueous solutions continues and structures of bicontinuous or w/o type may arise. The excess volume of the first six compounds is negative owing to the restructuring just mentioned. Vinyl acetate may penetrate in the struc-tures of binary systems to form homogeneous systems. The number of homogeneous systems decreases in the sequence: ethanol, i-propanol, acrylic acid, n-propanol, the mono-methylether of ethyleneglycol, methyl monomaleate. The vinyl acetate over cosurfactant molar ratio of limiting homogeneous systems varies in inverse sequence at the same monomer/water ratio. After radical polymerization of VAc in homogeneous samples transparent systems were obtained only when the polymer was solubilized in cosurfactant water mixtures. Received: 16 July 1996 Accepted: 14 January 1997     

Radiation induced depolymerization of hyaluronic acid (HA) in aqueous solutions at pH 7.4

The separation of the trivalent metal ions Am(III) and Eu(III) by extraction chromatography employing TBP impregnated macroporous XAD-4 resin as the stationary phase was examined; some parameters affecting the distribution ratio (K_d) and the column resolution (R_s) of Am(III) and Eu(III) were investigated. These parameters are the effect of TBP loading, aqueous nitrate concentrations, and flow rate. Both K_d andR_s increase with the TBP loading.