Kinetic and ESR studies on the radical polymerization. radical-initiated copolymerization of the diethyl itaconate-SnCl4 complex and styrene

The copolymerization of diethyl itaconate (1) (M₁) and styrene (2) (M₂) with dimethyl 2,2′-azoisobutyrate ( 3 ) was performed in benzene at 50°C, and the following copolymerization parameters were obtained: r₁ = 0,34, r₂ = 0,35, Q₁ = 0,93 and e_l = +0,66. The copolymerization system was found to involve ESR 1

1 Electron spin resonance.

-observed propagating polymer radicals at low monomer feed composition (f₂) of 2 . The apparent rate constant of termination increased rapidly with f₂. The ESR-determined values of the apparent propagation rate constant of the copolymerization were lower than those calculated on the basis of the Mayo-Lewis model, suggesting a significant penultimate effect in the copolymerization. On the other hand, the copolymerization of the 1 -SnCl₄ complex (M₁) and 2 (M₂) at 50°C yielded a nearly alternating copolymer independently of the monomer feed composition. The propagating polymer radicals were ESR-observable even up to f₂ = 0,8. The ESR-determined apparent rate constant (k_p) of propagation showed a maximum near f₂ = 0,5. From the relationship between k_p and f₂, the rate constants of cross-propagations of the present alternating copolymerization were evaluated as k₁₂ = 483 and k₂₁ = 510 L. mol^?1 · s^?1. Comparison of the k₂₁ value and the reported propagation rate constant (209 L · mol^?1 · s^?1) of homopolymerization of 2 leads to the conclusion that the alternating copolymerization via free-monomer propagation mechanism originates from a pronounced penultimate effect suppressing homopropagation of 2 , but not from enhanced cross-propagation.     

Kinetic and ESR studies on radical polymerization. ESR and kinetic evidences for the penultimate effect in the radical-initiated copolymerization of N-cyclohexylmaleimide and bis(2-ethylhexyl) itaconate in benzene

The copolymerization of N-cyclohexylmaleimide ( 1 ) (M₁) and bis(2-ethylhexyl) itaconate ( 2 ) (M₂) with dimethyl 2,2′-azoisobutyrate ( 3 ) as an initiator was carried out at 50°C in benzene. Monomer reactivity ratios were estimated as r₁ = 0,34 and r₂ = 0,38. The copolymerization rate (R_p) and the molecular weight of the resulting copolymer increased with increasing concentration of 1 when the total concentration of comonomers was fixed at 1,00 mol. L^?1. R_p was proportional to [ 3 ]^0,5, indicating a usual bimolecular termination in the copolymerization. An electron spin resonance (ESR) spectrum of the propagating polymer radicals was observable in the actual copolymerization system at 50°C. The spectrum of the copolymerization system is inexplicable in terms of any superposition of spectra observed in the corresponding homopolymerization systems, revealing that some penultimate monomeric unit causes a change in the ESR spectrum, that is, the structure of propagating polymer radical. The apparent rate constant of propagation (k_p) and termination (k_t) were estimated by ESR. The k_p values (1,5–50 L · mol^?1 · s^?1) are fairly higher than those estimated on the basis of the terminal model, affording another piece of evidence for the penultimate effect. The k_t value (1,8–5,4·10³ L · mol^?1 · s^?1) shows a behaviour similar to that of the intrinsic viscosity of the resulting copolymer on varying the monomer feed composition, which seems to reflect diffusion-control of termination reactions.     

Effect of SnCl4 on the radical-initiated polymerization of diethyl itaconate: Kinetical and ESR studies

The effect of SnCl₄ on the polymerization of diethyl itaconate ( 1 ) with dimethyl 2,2′-azoisobutyrate ( 2 ) in benzene was investigated kinetically and ESR spectroscopically. The polymerization rate (R_p) at 50°C shows a flat maximum on varying the SnCl₄ concentration. The molecular weight of the resulting polymer decreases with increasing SnCl₄ concentration. The overall activation energy of the polymerization is lowered from 52 to 33 kJ · mol^?1 by the presence of SnCl₄, (0,342 mol · L^?1). An NMR study revealed that 1 and SnCl₄ form 1:1 and 2:1 complexes with a large stability constant in benzene. The propagating polymer radicals in the absence and presence of SnCl₄ are ESR-observable as a five-line spectrum under the actual polymerization conditions. The complexed polymer radicals show further three-line splitting due to two methylene hydrogens of the ethyl ester group. The polymer radical concentration increases with the SnCl₄ concentration. The rate constant (k_p) of propagation was determined using R_p and the polymer radical concentration. k_p (6,3–2,9 L · mol^?1 · s^?1 at 50°C) decreases with increasing SnCl₄ concentration. The presence of SnCl₄ (0,342 mol · L^?1) reduces the activation energy of propagation from 29 to 21 kJ · mol^?1. The rate constant (k_t) of termination was estimated from the decay curve of the polymer radicals, k_t (3,1–1,1 · 10⁵ L · mol^?1 s^?1) also decreases with the SnCl₄ concentration. The activation energies of termination in the absence and presence of SnCl₄ (0,342 mol · L^?1) are 30 and 24 kJ · mol^?1, respectively. Suppression of propagation and termination by SnCl₄ seems to be explicable in terms of an entropy factor.     

Kinetic and ESR studies on radical polymerization. Radical polymerization behavior of N-octadecylmaleimide in benzene

The polymerization of N-octadecylmaleimide ( 1 ) initiated with azodiisobutyronitrile ( 2 ) was investigated kinetically in benzene. The overall activation energy of the polymerization was calculated to be 94,2 kJ·mol^?1. The polymerization rate (R_p) at 50°C is expressed by the equation, R_p = k[ 2 ]^0,6[ 1 ]^1,7. The homogeneous polymerization system involves ESR-detectable propagating polymer radicals. Using R_p and the polymer radical concentration determined by ESR, the rate constants of propagation (k_p) and termination (k_t) were evaluated at 50°C. k_p (33 L · mol^?1 · s^?1 on the average) is substantially independent of the monomer concentration. On the other hand, k_t (0,3 · 10⁴ – 1,0 · 10⁴ L · mol^?1 · s^?1) is fairly dependent on the monomer concentration, which is ascribable to a high dependence of k_t on the chain length of rigid poly( 1 ). This is the predominant factor for the high order with respect to the monomer concentration in the rate equation. In the copolymerization of 1 (M₁) and St (M₂) with 2 in benzene at 50°C, the following copolymerization parameters were obtained: r₁ = 0,11, r₂ = 0,09, Q₁ = 2,1, and e₁ = +1,4.     

Synthesis of poly(2,6-dimethylphenylene sulfide) by photooxidative polymerization

Photo-oxidation of bis(3,5-dimethylphenyl) disulfide proceeds in the presence of aromatic nitriles as sensitizers. Catalytic amounts of 9,10-dicyanoanthracene act as an electron mediator of the transfer from the disulfide to oxygen in the presence of biphenyl as a co-sensitizer. The photo-redox system enabled an efficient formation of poly(thio-2,6-dimethyl-1,4-phenylene) through electrophilic reaction of the sulfonium cation produced in the photo-oxidation.     

Oxidative polymerization of 2,6-bis(3-methyl-2-butenyl)phenol

Oxidative polymerization of 2,6-bis(3-methyl-2-butenyl)phenol ( 1 ) was carried out by copperpyridine catalyst. 1 was oxidatively polymerized to yield poly[oxy-2,6-bis(3-methyl-2-butenyl)-1,4-phenylene] ( 2 ) in a similar manner as it has been observed for 2,6-dimethylphenol ( 3a ). 2 is an oily material with a degree of polymerization of 6,2. 1 and 3a copolymerized with similar reactivity to form the copolymer 4 (degree of polymerization 16 to 29). The 3-methyl-2-butenyl groups in the polymer show enough chemical reactivity for an addition of bromine or graft-polymerization.     

Postirradiation polymerization and ESR studies of γ-irradiated N-tert-butylacrylamide

Postirradiation polymerization of γ-irradiated N-tert-butylacrylamide was studied at 80, 85, 90, and 100°C, and the activation energy was found to be 183 kJ · mol^?1. By ESR spectroscopy, the half-life for the second order decay of the irradiated monomer was found to be 13,8 h at 25°C with a decay rate constant of 4,5 · 10⁶ g · mol^?1 · h^?1. The effect of oxygen and sulfur dioxide on γ-irradiated N-tert-butylacrylamide was also studied. It was observed that oxygen reacts with N-tert-butylacrylamide free radicals resulting in a characteristic peroxyl radical spectrum. The signal decays rapidly and disappears in about 100 h. The decay was found to be of second order with a rate constant of 1,3 · 10⁷ g · mol^?1 · h^?1 and a half-life of 3,8 h at 25°C. In contrast to the situation with atmospheric oxygen, an appreciable fraction of the free radicals does not react rapidly with sulfur dioxide. The changes in the ESR spectra indicate that at least a large fraction of the original N-tert-butylacrylamide radicals, generated in the irradiated sample, react with sulfur dioxide rapidly to give sulfonyl radicals. Their decay is second order with a rate constant of 4,5 · 10⁶ g · mol^?1 · h^?1 and a half-life of 8,3 h.     

Synthesis and condensation polymerization of N-(3-carboxy-2-hydroxypropyl) derivatives of purine bases

4-(1,3-Dimethyl-2,6-dioxo-2,6-dihydropurin-7-yl)-3-hydroxybutyric acid ( 4a ) and 4-(6-amino-9-purinyl)-3-hydroxybutyric acid ( 4b ) were synthesized through the addition reaction of theophylline or adenine, respectively, to 1-chloro-2,3-epoxypropane followed by cyanization and acidic hydrolysis. Condensation polymerization of 4a was carried out using dicyclohexylcarbodiimide, 2,4,6-triisopropylbenzenesulfonyl chloride or p-toluenesulfonyl chloride as dehydrating agents in dimethylformamide or pyridine. The oligoester of 4a was obtained as a white powder with a molecular weight > 700, according to gel filtration measurement.     

Kinetic and electron paramagnetic resonance studies on radical polymerization. Radical-initiated polymerization of methyl N-phenylitaconamate in N,N-dimethylformamide

The polymerization of methyl N-phenylitaconamate(methyl 2-methylenesuccinanilate ( 1 )) with dimethyl 2,2′-azodiisobutyrate ( 2 ) was studied in N,N-dimethylformamide (DMF) kinetically and by means of electron paramagnetic resonance (EPR) spectroscopy. The polymerization rate (R_p) at 55°C is given by the equation: R_p = k[ 2 ]^0,58 · [ 1 ]^1,6. The overall activation energy of the polymerization was calculated to be 54,2 kJ/mol. The number-average molecular weight of poly( 1 ) was in the range between 5000 and 17000. From an EPR study, the polymerization system was found to involve the EPR-detectable propagating polymer radical of 1 at practical polymerization conditions. Using the concentration of polymer radicals, the rate constants of propagation (k_p) and termination (k_t) were determined for 55°C. The rate constant of propagation k_p (between 8,4 and 12 L · mol^?1 · s^?1) tends to somehow increase with increasing monomer concentration. On the other hand, k_t (between 1,9. 10^?5 L · mol^?1 · s^?1) increases with decreasing monomer concentration, which results from a considerable dependence of k_t on the polymer-chain length. Such monomer-concentration-dependent k_p and k_t values are responsible for the high dependence of R_p on the monomer concentration. Thermogravimetric results showed that thermal degradation of poly( 1 ) occurs rapidly at temperatures higher than 200°C and the residue at 500°C amounts to 26% of the initial polymer. For the copolymerization of 1 (M₁) with styrene (M₂) at 55°C in DMF the following copolymerization parameters were found: r₁ = 0,52, r₂ = 0,31, and Q, e values Q₁ = 1,09 and e₁ = +0,55.     

Electron spin resonance (ESR) estimation of propagation rate constants of radical polymerization of butyl methacrylate

Propagation rate constants (k_p) for the free radical polymerization of butyl methacrylate (BMA) in toluene solution were measured by ESR spectroscopy in the temperature range from –30 to 90°C. The polymerization was photochemically induced at a constant initiator concentration of di‐tert‐butyl peroxide (tBPO). The Arrhenius parameters A and E_a were estimated to be (3.40 ± 0.4)>×10⁶ M^–1·s^–1 and (22.0 ± 1.0) kJ/mol, respectively. The k_p values estimated from ESR analysis were compared with the corresponding data obtained from the pulsed laser polymerization (PLP).     

New catalysts for the oxidative polymerization of 2,6-dimethylphenol, 3. Copper(I) cluster complexes

The catalytic activities of various copper(I) clusters in the oxidation of 2,6-dimethylphenol (XOH) in pyridine and the preparative oxidative polymerization of XOH with these complexes were investigated. It was found that the copper(I) cluster containing 1,2-dicyano-1,2-ethenedithiolate ligands is more effective in the oxidative polymerization of XOH than the complex containing isomeric ligands. The electric conductivities of these Cu(I) complexes are small.     

Thermal polymerization of bis(4-fluoro-2,6-dibromophenolato)bis(pyridine)copper(II) complex in solution and in solid state

The synthesis of the bis(4-fluoro-2,6-dibromophenolato)bis(pyridine)copper(II) complex was achieved from aqueous solution, and its characterization was performed by means-of IR and CHN elemental analysis. Thermal polymerization of this complex was carried out in toluene and in solid state. The structural analysis of the polymers was performed with ¹H NMR, ¹³C NMR and FTIR analysis; the glass transition temperature was found to be at 160°C. 4-Fluoro-2,6-dibromophenolate, with the non-chelating ligand pyridine, displays selectivity in favor of 1,2-catenation.     

Asymmetric radical-initiated copolymerization of (−)-menthyl sorbate with styrene

The radical-initiated copolymerization of (?)-menthyl sorbate ((?)-3-p-menthyl 2,4-hexadienoate) with styrene was carried out in benzene with 2,2′-azoisobutyronitrile as an initiator at 50°C to give an optically active copolymer 1 . While the chiral menthyl group of the copolymer was removed by hydrolysis with aqueous alkali, the hydrolyed copolymer was still optically active. Therefore, asymmetric induction must have occurred during copolymerization.     

Kinetic studies of ethylene polymerization in ethyl chloride. Molecular weight distribution of polyethylene

Polymerization kinetics of ethylene in ethyl chloride in the presence of two soluble catalytic systems has been studied. In ethyl chloride polymerization rate remains constant over a long period of time. Polymerization rate is of the first order in ethylene and varied antibatically with concentration of Al(C₂H₅)₂Cl. Molecular weight of polyethylene increases directly with ethylene concentration. At high concentration of Al-alkyl its participation in the termination of polymer chains is appreciable. Growth (K_p) and termination (K_t) constants are determined when polymerizing ethylene in ethyl chloride and benzene in the presence of system A: in ethyl chloride K_p = 68.1/mole·sec, K_t = 7.5 1./mole·sec, in benzene K_p = 8.3 1./mole·sec, K_t = 0.6 1./mole·sec. For System B in ethyl chloride K_p = 110 1./mole·sec. The molecular weight distribution of polyethylene synthesized with the system A is bimodal, and that with system B is unimodal. Experimental data are discussed from the view point of existence of two types of active centers.     

New catalysts for the oxidative polymerization of 2,6-dimethylphenol. Bis(1,2-dicyanoethylene-1,2-dithiolato)cuprate(2-) complexes

The catalytic activities of various bis(1,2-dicyanoethylene-1,2-dithiolato)metal ( 1a–f ) complexes were investigated. It was found that copper bis(1,2-dicyanoethylene-1,2-dithiolato)cuprate(2-) ( 1a ) catalyzes the oxidative polymerization of 2,6-dimethylphenol in the presence of molecular oxygen. At some polymerization conditions this catalyst is much more active than the well-known copper(II)-pyridine complex.     

Kinetic studies of the injection of comonomers during polymerization of ethene and propene with MgCl2-supported Ziegler-Natta catalysts

The effects of injecting ethene, propene, 1-hexene, 2-methylpropene, 3,3-dimethyl-1-butene, cis-2-butene, trans-2-butene, 2,3-dimethyl-2-butene, cyclopentene, styrene, 1,3-butadiene and 1,4-pentadiene during polymerizations of ethene and propene have been investigated. Catalysts used were a supported MgCl₂/EB/TiCl₄ ballmilled catalyst and precipitated MgCl₂/2-EH/TiCl₄/DIBP catalysts activated with triethylaluminium in presence of EB. (EB = ethyl benzoate, 2-EH = 2-ethylhexanol, DIBP = diisobutyl phthalate). The polymerizations were performed at 50°C, in a heptane slurry at 1 atm (1.00 · 10⁵ Pa) total pressure. The instantaneous polymerization rate was observed by continuous monitoring of the monomer consumption, the time resolution of the measurements being less than one second. Two different kinetic effects can be observed after injection of the comonomer. First there is an immediate rate change, usually a rate reduction. Then a secondary effect may follow, which is a slow, and sometimes significant and persistent, activation. The two effects obviously have different causes, and for none of these we found single causes that can explain all the observations. The strongest immediate effect was observed after addition of dienes and indicates a direct association of the comonomer to the active center. A marked nonlinearity in the response may hint to inhomogeneity in the structural environment of the active centers. Addition of α-olefins during ethene polymerization gave the strongest secondary effect. In general the immediate effects were stronger during propene polymerization than during the polymerization of ethene. A significant difference in the effects of cis-2-butene and trans-2-butene in the polymerization of propene indicates that steric effects may be important.     

Photoconductive polymers and copolymers of N-(2-propynyl) carbazole and N-(2-propynyl)phenothiazine

Homopolymers of N-(2-propynyl)carbazole, its copolymers with acetylene, and the homopolymer of N-(2-propynyl)phenothiazine were prepared using Ti(OBu)₄/AIEt₃ as the catalyst. The homopolymer of the carbazole derivative was also prepared by its metathetic polymerization catalyzed with the system WOCl₄/Ph₄Sn. Homopolymers of both monomers and the copolymer of N-(2-propynyl)carbazole with a small quantity of acetylene are photoconductive.     

Kinetic aspect of the emulsion polymerization of cyclothexyl methacrylate

The emulsion polymerization kinetics of cyclohexyl methacrylate (CHMA) at 50°C using a mixture of anionic and nonionic surfactants was investigated. The product of the propagation rate constant (K_p) and the number of radicals per particle (n?) increased monotonously with the volume-average particle diameter (D_v). The value of K_p was estimated to be 260 L/(mol · s). Changing the monomer mass fraction in the recipe (from 0,14 to 0,40), the value of n? remained constant and close to 0,5. On the other hand, increasing the initiator concentration ([I]), the value of n? increased rapidly and then leveled off.     

Kinetic study of the polymerization of N,N′-methylenebis(acrylamide) in aqueous dispersion systems

The aqueous-phase polymerization of N,N′-methylenebis(acrylamide) initiated by potassium peroxodisulfate in the absence and in the presence of the anionic emulsifier sodium dodecylsulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization is found to be proportional to the 0,75 and 0,24 oder with respect to potassium peroxodisulfate and N,N′-methylenebis(acrylamide) concentrations, respectively. On the other hand, it is independent of the concentration of sodium dodecylsulfate. This agrees with the polymerization of a monomer soluble in water. Therefore, the equations for a homogeneous polymerization were applied to evaluate the experimental results. The calculated ratio k_p/k_t^0,5 of the rate constants of propagation k_p and termination k_t for the N,N′-methylenebis(acrylamide) polymerization at zero conversion in the absence of emulsifier are scattered in the interval between 3,1 and 3,4 dm^1,5 · mol^?0,5 · s^?0,5 and in the presence of emulsifier in the interval between 2,4 and 3,5 dm^1,5 · mol^?0,5 · s^?0,5. They are close to those obtained for the homogeneous polymerization of acrylamide in the aqueous phase. The lower values of k_p/k_t^0,5 ≈ 0,3–0,6 dm^1,5 · mol^?0,5 · s^?0,5 determined for the polymerization of N,N′-methylenebis(acrylamide) for conversions between 30 and 60% follow from the hindered termination reaction within the polymer particles. The polymer dispersions formed are unstable. The growth of the polymer particles proceeds predominantly by coalescence. This suggests a kinetics which does not follow the Smith-Ewart theory but is characterized by a continuous particle nucleation and agglomeration. The interval 1 occurs at the beginning of the dispersion polymerization when polymer particles are being formed. Interval 2 follows, once the number of polymer particles has been fixed.     

Oxidative polymerization of 2,6-dimethylphenol with semiconducting organic polymeric metal complexes containing the bis(ethylene-1,2-dithiolato)-copper(II) structure, 2

If an insoluble polymeric complex 1 which possesses both the bis(ethylene-1,2-dithiolato)Cu(II) a Cu(II)phthalocyanine type structure is treated with a pyridine solution of the Cu(II)-pyridine complex in a low concentration, the filtrate obtains a high activity for the oxidative polymerization of 2,6-dimethylphenol. This might be due to a partial decomposition followed by a partial dissolution of the polymer complex. The catalytic behaviour of the soluble part of the polymeric complex 1 was studied. The activity of this mixed catalyst system consisting of Cu(II)Py and the soluble part of 1 was found to be 6–50times higher than that of Cu(II)Py alone under the applied conditions.