Kinetic investigations on the photopolymerization of di- and tetrafunctional methacrylic monomers in polymeric matrices. ESR and calorimetric studies. II. Postpolymerization reactions

The reaction kinetics in the dark of photopolymerized mono- and dimethacrylates in a polymeric binder has been studied. Electron spin resonance spectroscopy (ESR) provided useful information regarding the nature of the radicals involved in postpolymerization reactions. Computer simulations were performed to study the decay of the propagating radicals by considering normal bimolecular termination and transfer reactions of the radicals to the binder. Differences were found in the termination reactions for mono- and difunctional monomers when they were photopolymerized in a solid medium. Absolute kinetic constants for H-transfer reaction with the binder, relative kinetic rate constants for radical–radical coupling, and average lifetimes for the radicals have been calculated. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2785–2791, 1998     

Photopolymerization kinetics of ionic liquid monomers derived from the neutralization reaction between trialkylamines and acid‐containing (meth)acrylates

Polymerizable ionic liquids were synthesized from the neutralization reaction between trialkylamines (tributylamine, trihexylamine, trioctylamine, 2‐(dimethyl‐amino)ethyl acrylate, and 2‐(dimethylamino)ethyl methacrylate) and acid‐containing (meth)acrylates to study the kinetics of their photopolymerization. The ionic liquids formed from acrylic acid and methacrylic acid with trialkylamines showed low or moderate increases in rate compared to their monofunctional analogues. The ionic liquids formed from (meth)acrylic acid and a tertiary amine with a pendant acrylate exhibited rates typical of traditional di(meth)acrylates, although the (meth)acrylates were not covalently attached to the same molecule. All of the phosphate‐based ionic liquids exhibited very rapid polymerization rates and strong dependence on the initial viscosity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3009–3021, 2007     

Kinetic and ESR studies on radical polymerization of methyl methacrylate in the presence of fullerene

The effect of fullerene (C₆₀) on the radical polymerization of methyl methacrylate (MMA) in benzene was studied kinetically and by means of ESR, where dimethyl 2,2′-azobis(isobutyrate) (MAIB) was used as initiator. The polymerization rate (R_p) and the molecular weight of resulting poly(MMA) decreased with increasing C₆₀ concentration ((0–2.11) × 10⁻⁴ mol/L). The molecular weight of polymer tended to increase with time at higher C₆₀ concentrations. R_p at 50°C in the presence of C₆₀ (7.0 × 10⁻⁵ mol/L) was expressed by R_p = k[MAIB]^0.5[MMA]^1.25. The overall activation energy of polymerization at 7.0 × 10⁻⁵ mol/L of C₆₀ concentration was calculated to be 23.2 kcal/mol. Persistent fullerene radicals were observed by ESR in the polymerization system. The concentration of fullerene radicals was found to increase linearly with time and then be saturated. The rate of fullerene radical formation increased with MAIB concentration. Thermal polymerization of styrene (St) in the presence of resulting poly(MMA) seemed to yield a starlike copolymer carrying poly(MMA) and poly(St) arms. The results (r₁ = 0.53, r₂ = 0.56) of copolymerization of MMA and St with MAIB at 60°C in the presence of C₆₀ (7.15 × 10⁻⁵ mol/L) were similar to those (r₁ = 0.46, r₂ = 0.52) in the absence of C₆₀. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2905–2912, 1998     

Kinetic and ESR studies on radical copolymerization of p-tert-butoxystyrene and di-n-butyl maleate in benzene

The copolymerization of p-tert-butoxystyrene (TBOSt) (M₁) and di-n-butyl maleate (DBM) (M₂) with dimethyl 2,2′-azobisisobutyrate (MAIB) in benzene at 60°C was studied kinetically and by means of ESR spectroscopy. The monomer reactivity ratios were determined to be r₁ = 2.3 and r₂ = 0 by a curve-fitting method. The copolymerization system was found to involve ESR-observable propagating polymer radicals under practical copolymerization conditions. The apparent rate constants of propagation (k_p) and termination (k_t) at different feed compositions were determined by ESR. From the relationship of k_p and f₁ (f₁ = [M₁]/([M₁] + [M₂])) based on a penultimate model, the rate constants of five propagations of copolymerization were evaluated as follows; k₁₁₁ = 140 L/mol s, k₂₁₁ = 3.5 L/mol s, k₁₁₂ = 61 L/mol s, k₂₁₂ = 1.5 L/mol s, and k₁₂₁ = 69 L/mol s. Thus, a pronounced penultimate effect was predicted in the copolymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1449–1455, 1998     

Kinetic and ESR studies on radical polymerization behavior of N‐(2‐phenylethoxycarbonyl)methacrylamide

Polymerization of N‐(2‐phenylethoxycarbonyl)methacrylamide (PECMA) with dimethyl 2,2′‐azobisisobutyrate (MAIB) was investigated in tetrahydrofuran (THF) kinetically and by means of electron spin resonance (ESR). The overall activation energy of the polymerization was calculated to be 58 kJ/mol. The initial polymerization rate (R_p) is expressed by R_p = k[MAIB]^0.3[PECMA]^2.3 at 60 °C. Such unusual kinetics may be ascribable to primary radical termination and to acceleration of propagation due to monomer association. Propagating poly(PECMA) radical was observed as a 13‐line spectrum by ESR under practical polymerization conditions. ESR‐determined rate constants of propagation (k_p, 4.7–10.5 L/mol s) and termination (k_t, 4.6 × 10⁴ L/ml s) at 60 °C are much lower than those of methacrylamide and methacrylate esters. The Arrhenius plots of k_p and k_t gave activation energies of propagation (24 kJ/mol) and termination (25 kJ/mol). The copolymerizations of PECMA with styrene (St) and acrylonitrile were examined at 60 °C in THF. Copolymerization parameters obtained for the PECMA (M₁) − St(M₂) system are as follows: r₁ = 0.58, r₂ = 0.60, Q₁ = 0.73, and e₁ = +0.22. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4264–4271, 2000     

ESR and quantum chemical studies of the structures and thermal transformations of the radical cations of vinylcyclopropane in irradiated frozen Freon matrices. Simulation of radical processes in solids

Thermal transformations of vinylcyclopropane radical cations (VCP^.+) in X-ray-irradiated frozen Freon matrices (CFCl₂CF₂Cl and CFCl₃) were studied by ESR; radical processes involving VCP^.+ in solid VCP were simulated.Gauche- andanti-VCP ^.+ were found to be the primary radical cations, however, the former, unlike the latter, is stable only under gas-phase conditions. The thermodynamic equilibrium betweenanti-VCP^.+ and its less stable distonic form,dist(90,0)-C ₅H₈ ^.+, is established in frozen Freon matrices and the VCP host matrix; the structure of dist(90,0)****-C ₅H₈ ^.+ is stabilized by a molecule ofanti-VCP. In CFC₃, along with dist(90,0)-C₅H₈ ^.+,-dimeric resonance [anti-VCP]₂ ^.+ complex was detected. A general scheme of the transformations of VCP^.+ in the solid phase has been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 11–21, January, 1994.     

Photoinitiated polymerization of methacrylic monomers in a poly(methyl methacrylate) matrix: A comparative study with other matrices (styrene–butadiene–styrene,polystyrene, and polybutadiene)

The kinetics and mechanism of the photoinitiated polymerization of 1,6‐hexanediol dimethacrylate (HDDMA) in a poly(methyl methacrylate) (PMMA) matrix were studied. The maximum double‐bond conversion, the maximum polymerization rate, the intrinsic reactivity, and the kinetic constants for propagation and termination were calculated. For this system, a reaction‐diffusion termination mechanism occurred from the start of the polymerization, and it was predominantly maintained until high monomer concentrations, probably because of the relatively high intermolecular attraction force between the PMMA matrix and HDDMA monomer. In addition, a comparative study of the photoinitiated polymerization of methacrylic monomers in four different polymeric matrices [styrene–butadiene–styrene (SBS), polystyrene (PS), polybutadiene (PB), and PMMA] was carried out. The aggregation state, vitreous or rubbery, of the monomer–matrix system and the intermolecular strength of attraction in the monomer–matrix system and growing macroradical and matrix systems were the principal factors influencing the kinetic and mechanistic behavior of these systems. When PB and SBS were used as matrices, crosslinked polymerized products were obtained as a result of the participation of double bonds of the matrix in the polymerization process (copolymerization). PS sequences in the SBS and PS matrices also took part in the polymerization process through the coupling of the benzylic radical to the growing macroradical. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 120–127, 2002     

ESR and quantum-chemical studies of the structure and thermal transformations of vinylcyclopropane radical cations in irradiated frozen Freon matrices. Simulation of radical processes in the gas phase

Thermal trasfomations of vinylcyclopropane (VCP) radical cations (RC) in X-ray irradiated frozen Freon matrices, CFCl₂CF₂Cl and CFCl₃, were studed by ESR. Radical processes involving VCP^.+ in very rarefied and moderately thickened gaseous VCP were simulated. Monomolecular cleavage of the cyclopropane ring ofgauche-VCP^.+ (1) occurs to give the more thermally stable distonic radical cationdist(0.90)-C₅H₈ ^.+ (3). As the density of VCP increases RC3 adds at the double bond ofanti-VCP to give the distonic RC,^.CH₂CH₂CHCH(CH₂)₃CHCHCH₂ ⁺ (5). Under the same conditions, the less thermally stableanti-VCP^.+(2) undergoes monomolecular isomerization into RC1 or reacts withanti-VCP with the rearrangement (as in the condensed phase) to give its distonic form,dist(90.0)-C₅H₈ ^.+ (4). The MNDO-UHF method was adapted for quantum-chemical analysis of the constants of isotropic hyperfine coupling with¹H and¹³C nuclei in neutral and charged hydrocabon radicals, since the standard version of this method inadequately reproduces the structural parameters of low-symmetry (C ₁,C _s) paramagnetic species. A quantum-chemical analysis of the radiospectroscopic information and of the stereoelectronic control of thermal transformations of conformers of RC1 and2 into their structurally nonequivalent distonic forms3 and4, respectively, was carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 212–235, February, 1995.This work was carried out with the financial support of the Russian Foundation for Basic Research (Project No. 93-03-04075).     

Kinetic and EPR studies on radical polymerization. Radical polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate

The polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (1) with dimethyl 2,2-azobisisobutyrate (2) was studied, in benzene, kinetically and spectroscopically with the electron paramagnetic resonance (EPR) method. The polymerization rate (R _p) at 50°C is given by the equation:R _p=k[2]^0.48 [1]^2.4. The overall activation energy of polymerization was calculated to be 34 kJ·mol^–1. From an EPR study, the polymerization system was found to involve EPR-observable propagating polymer radicals of 1 under the actual polymerization conditions. Using the polymer radical concentration, the rate constants of propagation (k _p) and termination (k _t) were determined. With increasing monomer concentration,k _p(1.54.3 L·mol^–1·s^–1 at 50°C) increases andk _t (1.0·10⁴4.2·10⁴ L·mol^–1·s^–1 at 50°C) decreases, which seems responsible for the high dependence ofR _p on the monomer concentration. The activation energies of propagation and termination were calculated to be 11 kJ·mol^–1 and 84 kJ·mol^–1, respectively. For the copolymerization of 1(M ₁) and styrene (M ₂) at 50°C in benzene the following copolymerization parameters were found:r ₁=0.2,r ₂=0.53, Q₁=0.57, ande ₁=+0.7.     

Reaction kinetics and gel effect on the polymerization of 2‐ethoxyethyl methacrylate and 2(2‐ethoxyethoxy) ethyl methacrylate

Polymerization kinetics at several temperatures of 2‐ethoxyethyl methacrylate (EEMA) and 2(2‐ethoxyethoxy) ethyl methacrylate (DEMA) in bulk and in dioxane solutions are described. The gel effect was never detected at monomer concentrations equal to or lower than 1 mol L^?1, although in the bulk polymerization both monomers display the gel effect at very low conversions. Because of the influence of the efficiency factor f on the polymerization rate, a theoretical kinetic interpretation of the changes in f with monomer and initiator concentrations and kinetic parameters was performed to achieve a better understanding of the mechanisms involved in radical polymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3987–4001, 2002     

Kinetic and ESR studies on the radical polymerization of α‐n‐(α′‐methylbenzyl) β‐ethyl itaconamates derived from racemic and (s)‐α‐methylbenzylamines

The polymerization of α‐N‐(α′‐methylbenzyl) β‐ethyl itaconamate derived from racemic α‐methylbenzylamine (RS‐MBEI) by initiation with dimethyl 2,2′‐azobisisobutyrate (MAIB) was studied in methanol kinetically and with ESR spectroscopy. The overall activation energy of polymerization was calculated to be 47 kJ/mol, a very low value. The polymerization rate (R_p ) at 60 °C was expressed by R_p = k[MAIB]^0.5±0.05[RS‐MBEI]^2.9±0.1. The rate constants of propagation (k_p ) and termination (k_t ) were determined by ESR. k_p was very low, ranging from 0.3 to 0.8 L/mol s, and increased with the monomer concentration, whereas k_t (4–17 × l0⁴ L/mol s) decreased with the monomer concentration. Such behaviors of k_p and k_t were responsible for the high dependence of R_p on the monomer concentration. R_p depended considerably on the solvent used. S‐MBEI, derived from (S)‐α‐methylbenzylamine, showed somewhat lower homopolymerizability than RS‐MBEI. The k_p value of RS‐MBEI at 60 °C in benzene was 1.5 times that of S‐MBEI. This was explicable in terms of the different molecular associations of RS‐MBEI and S‐MBEI, as analyzed by ¹H NMR. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4137–4146, 2000     

Radiation-induced graft polymerization of acrylic acid onto fluorinated polymers. I. Kinetic study on the grafting onto poly(tetrafluoroethylene-ethylene) copolymer

Direct radiation-induced grafting of aqueous acrylic acid (AAc) onto poly(tetrafluoroethylene-ethylene) (ET) film has been studied. The effect of grafting conditions such as monomer concentration, exposure dose, dose rate, and film thickness on the grafting yield was investigated. The dependence of the grafting rate on monomer concentration was found to be 1.2 order. The dependence of the grafting rate on dose rate was found to be 0.6 order regardless of the film thickness. The relationship between the grafting rate and film thickness gave a negative first-order dependence. The results suggest that the grafting process is mainly controlled by monomer diffusion, and it was concluded that this grafting system proceeded by the front mechanism. The swelling behavior increases linearly with degree of grafting. The electrical conductivity and mechanical properties for the trunk and grafted polymer were investigated at different irradiation doses in air and under vacuum irradiations. © 1992 John Wiley & Sons, Inc.     

Functional monomers and polymers. LIII. Kinetic study on the oxidation of Cu(I)·polyvinylimidazole complexes by molecular oxygen

The autoxidation of Cu(I) complexes with imidazole and polyvinylimidazole derivatives was studied by observing the formation of the corresponding Cu(II) complexes with a stopped-flow technique. The reaction was second order and proportional to the concentrations of Cu(I) and oxygen. In the Cu(I)-imidazole complex pH variation was without effect in the range of 7.5-8.6. The oxidation rate of Cu(I).polyvinylimidazole complexes, on the other hand, decreased with a rise in pH. The activation parameters of the Cu(I)·polyvinylimidazole complexes, compared with those of the Cu(I).imidazole complex, were characterized by large enthalpic requirements coupled with favorable entropies of activation. This was explained by the fact that a conformational change in the polymeric ligands took place during oxidation.     

Kinetic and thermodynamic studies of the nonisothermal decomposition of anhydrous copper(II) formate in different gas atmospheres

The thermal decomposition of anhydrous (orthorhombic) copper(II) formate was studied by programmed rising-temperature methods (TG, DTG, DTA and DSC) to about 250 °C in flowing gas atmospheres of nitrogen (inert), hydrogen (reducing) and air (oxidizing). The degradation reaction, anion breakdown, proceeded to completion in two distinct, but partially overlapping, rate processes and apparent Arrhenius parameters, calculated by the Ozawa nonisothermal kinetic method, agreed satisfactorily with the literature results. It was concluded that the two consecutive processes, contributing to the overall reaction, involved stepwise cation reduction: Cu²⁺→Cu⁺→Cu⁰, with copper(I) formate as intermediate. This mechanism is similar to that proposed in previous studies of the decompositions of copper(II) oxalate, malonate, maleate, fumarate, mellitate and squarate. For all of these reactants, the Cu⁺ salt has been identified as an intermediate, exhibiting a (slightly) lower relative reactivity than the corresponding Cu²⁺ salt. For copper(II) formate the response curves in the three different gaseous atmospheres were generally similar, showing that neither oxidizing nor reducing conditions caused a marked change in reactivity. The temperature of reaction initiation in H₂ was slightly diminished and the temperature of the second stage of reaction in O₂ was raised appreciably. It is believed that electron transfer contributed to the control of reactivity and that the gases present appreciably influence the rates of the contributory reactions occurring.     

Electron Spin Resonance(ESR)Spectroscopy of the Transition-metal Complexes and Clusters I.Systematic Investigations of Real-and Complex-Orbital Methods for Calculating the d-Orbital Energies of a Low-spin(S=1/2)nd~5(t_2~5,~2T_2)(n=3

１ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｃａｌｃｕｌａｔｉｏｎｓｉｎｔｈｅｆｉｒｓｔｐａｐｅｒｓｈｏｗｅｄｔｈａｔｒｅａｌ ａｎｄｃｏｍｐｌｅｘ ｏｒｂｉｔａｌｍｅｔｈｏｄｓｄｅｒｉｖｅｄｆｒｏｍａｍｏｄｅｌｏｆｅｌｅｃｔｒｏｎｉｃ ｉｎｔｅｒｓｕｐｐｌｅｍ...     

Thermodynamics of semi-interpenetrating polymeric networks based on crosslinked poly(cyanurate) and linear poly(urethane) in the temperature region from T → 0 to 350 K

The temperature dependences of the heat capacity of linear poly(urethane) (PU) (M _n = 4·10⁴), which was synthesized from 4,4′-diphenylmethane diisocyanate, oligo(butylene glycol adipinate) (M _n = 1000), and chain-elongating agent butane-1,4-diol, and three samples of related semi-interpenetrating polymeric networks containing 25, 50, and 75 wt.% of crosslinked poly(bisphenol A) cyanurate were studied in a region of 6–350 K by adiabatic vacuum calorimetry. Their combustion energies were determined in a calorimeter with a static bomb and an isothermic shell. The thermodynamic functions of the compounds under study for the temperature region from T → 0 to 350 K, enthalpies of combustion, and thermodynamic characteristics of formation from simple substances at T = 298.15 K and p = 0.1 mPa were calculated. The thermodynamic parameters of formation of the semi-interpenetrating networks were calculated. The dependences of the isotherms of the thermodynamic properties and thermodynamic compatibility of the semi-interpenetrating networks on their composition were determined. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 648–654, April, 2006.     

Chain transfer by addition-fragmentation mechanism. VII. Radical polymerization of vinyl monomers in the presence of ethyl 2-[1-(trimethylsilylperoxy)ethyl]propenoate and related compounds

Ethyl 2-[1-(trimethylsilylperoxy)ethyl]propenoate 1 , ethyl 2-[1-(dimethylvinylsilylperoxy)-ethyl]propenoate 2 , ethyl 2-[1-(1-(2-ethoxycarbonyl-1-methyl-2-propenylperoxysilyl)-1-methylethylperoxy)ethyl]propenoate 3 , and 2-phenyl-2-trimethylsilylperoxypropane 4 were synthesized and added to the free radical polymerization of vinylic monomers. 1 and 2 were found to show no homopolymerizability but act as effective chain transfer reagents in radical polymerizations of methyl methacrylate (MMA), styrene (St), and n-butyl acrylate (BA). The estimated chain transfer constants (C_tr) are as follows: C_tr ( 1 ) = 0.15 for MMA, 0.90 for St, and 2.03 for BA at 60°C; C_tr ( 2 ) = 0.12 for MMA, 1.16 for St, and 1.9 for BA at 60°C. ¹H–NMR spectra of poly(St) formed in the presence of 1 is consistent with the view that the polymers bear an oxirane at one terminal and an trimethylsilyloxy fragment at the other end. Moreover, peroxysilane 4 showed very low transfer properties by direct homolytic substitution (SH₂). These findings indicate that the ethyl 2-[1-(substituted dimethylsilylperoxy)ethyl]-propenoates 1–3 undergo chain transfer reaction via a intramolecular homolytic substitution (SHi) following an addition process. Preparation of poly(styrene) up to high conversion in the presence of 3 yielded to the formation of the corresponding polymeric structures bearing hydrolysable C(SINGLE BOND)O(SINGLE BOND)Si(SINGLE BOND)O(SINGLE BOND)C bonds. © 1996 John Wiley & Sons, Inc.     

Effect of ascorbic acid (vitamin C) on the ESR spectra of the red and black hair: pheomelanin free radicals are not always present in red hair

Increased incidence of melanoma in the population with red hair is conditioned by synthesis of pheomelanin pigments in the skin and their phototoxic properties. The recent research has shown that free radicals of pheomelanin are produced not only by the influence of UV irradiation, but also in UV‐independent pathways of oxidative stress. It has been ascertained, that the color of the hair is not always determinant of the amount of pheolemanin radicals in red hair. Therefore, in order to evaluate the risk of melanoma in different individuals, it is necessary to define the amount of free radicals of pheomelanin in red hair using ESR spectroscopy method. Besides, it is very important to find effective antioxidant, capable of neutralizing free radicals of pheomelanin. It was proved that ascorbic acid neutralizes free radicals of pheomelanin very effectively. The main goal of our research was to define the presumably optimal concentration of ascorbic acid as an antioxidant and study the kinetics of the influence of this concentration on red and black hair. It has been found out, that ascorbic acid influences the free radicals of red and black hair, and its appropriate optimal concentration is 10 mM. The obtained results can be considered in dermatology and cosmetology. Copyright © 2015 John Wiley & Sons, Ltd.