Photopolymerization of methyl methacrylate using hydrogen peroxide as the photoinitiator

Photopolymerization of MMA with the use of H₂O₂ as the photoinitiator under visible light at 30°C was studied. Kinetic features in bulk monomer and in the presence of different diluents differ significantly. Usual free radical kinetics with square-root dependence of rate on initiator, indicating bimolecular termination of chain radicals, were observed for bulk polymerization. On dilution with various solvents polymerization was found to be retarded to different (usual and more than usual) extents, the observed monomer exponent value being much higher than unity in many cases. This deviation from normal kinetics has been interpreted in terms of the predominance of degradative initiator transfer in the diluted systems.     

Novel solvent effects in the photopolymerization of methyl methacrylate by use of quinoline–bromine charge-transfer complex as photoinitiator

Photopolymerization of MMA was carried out at 40°C in diluted systems by use of quinolinebromine (Q–Br₂) charge-transfer complex as the initiator and chloroform, carbon tetrachloride, chlorobenzene, dioxane, THF, acetone, benzene, toluene, quinoline, and pyridine as solvents. The results showed variable monomer exponents ranging from 1 to 3. For chloroform, carbon tetrachloride, and chlorobenzene, the monomer exponent observed was unity; for other solvents used, the value of the same exponent was much higher (between 2 and 3). Initiation of polymerization is considered to take place through radicals generated in the polymerization systems by the photodecomposition of (Q–Br₂)–monomer complex (C) formed instantaneously in situ on addition of the Q–Br₂ complex in monomer. The kinetic feature of high monomer exponent is considered to be due to higher order of stabilization of the initiating complex (C) in presence of the respective solvents. In the presence of the retarding solvents, very low or zero initiator exponents were also observed, depending on the nature and concentration of the solvents used. The deviation from the square-root dependence of rate on initiator concentration becomes higher at high solvent and initiator concentrations in general. This novel deviation is explained on the basis of initiator termination, probably via degradative chain transfer involving the solvent-modified initiating complexes and the propagating radicals.     

Photopolymerization of methyl methacrylate with the use of bromine as photoinitiator

Low concentrations of bromine (0.008–0.06M) were used to initiate photopolymerization of MMA in bulk and in diluted (near bulk) systems, the diluents or solvents used being benzene, toluene, dioxane, tetrahydrofuran, carbon tetrachloride, chloroform, methylene chloride, and methanol. Polymerization in bulk follows usual free-radical kinetics. Inert solvents (benzene, toluene) as well as the other solvents used enhance the rate of polymerization MMA even when used in the range of catalytic concentrations (0.04–0.4M). An initiation mechanism involving solvent molecules appears to be predominant in diluted systems.     

Photopolymerization of methyl methacrylate with the use of iodine monobromide as photoinitiator

Iodine monobromide easily induces photopolymerization of methyl methacrylate (MMA) at 40°C under visible light. Initiator exponent and monomer exponent values were found to be 0.5 and 2, respectively, at low initiator concentrations, while the corresponding values at high initiator concentration conditions were zero and 3. The chain transfer constant of IBr at 40°C was found to be 13.0. Kinetic and other data indicate a radical polymerization mechanism involving complexation of monomer molecules with iodine monobromide prior to radical generation, and termination is believed to take place biomolecularly at low IBr concentrations and unimolecularly, involving reaction with the initiator, at high IBr concentrations (initiator termination).     

Photopolymerization of methyl methacrylate with the use of iodine as the photoinitiator

Kinetics of photopolymerization of MMA at 40°C with the use of iodine as the photoinitiator was studied. At low range of iodine concentration (< 0.0004M), the rate of polymerization was proportional to square root of iodine concentration and the monomer exponent was 2.5, while at a higher range of iodine concentration, (0.0005–0.002M) the initiator exponent and monomer exponent were zero and 3.6–3.8 (i.e., close to 4), respectively. The chain-transfer constant of iodine at 40°C was found to be 6.0. Polymerization was found to be largely inhibited in the presence of relatively high concentrations of iodine (> 0.005M) and also in presence of hydroquinone. Kinetic and other data indicate a radical mechanism of polymerization involving complexation of monomer molecules with iodine prior to radical generation, and termination is believed to take place bimolecularly at low iodine concentrations and unimolecularly, involving reaction with iodine, at high iodine concentrations (initiator termination).     

Benzophenone-sensitized photopolymerization of methyl methacrylate using dimethyl aniline–maleic acid combination as photoinitiator

Benzophenone (BP)-sensitized photopolymerization of methyl methacrylate (MMA) in near UV/visible light was studied at 40°C using dimethylaniline maleic acid (DMA—MA) combination as the photoinitiator. An instantaneous 1:1 complexation between DMA and MA takes place when they are mixed together in acetonitrile. Also, instantaneous complex formation occurs between DMA and MMA and between MA and MMA when they are dissolved in MMA in low concentrations, separately. Interestingly, when equimolar proportions of DMA and MA are mixed together in MMA, there is indication for further instantaneous complexation between (DMA—MMA) complex and (MA—MMA) complex forming the actual initiating species in the photopolymerization system. Initiator exponent was 0.28 and monomer exponent varied between 0.0 to 1.8 depending on the nature of the solvent and range of dilution used. Analysis of kinetic data indicates a free radical mechanism for the polymerization with initiator-dependent termination. Chain termination via degradative initiator transfer is quite significant; but the degradative effect becomes much less prominent in the higher range of initiator concentration indicating that the reinitiation reaction following the initiator transfer process assumes more proportionate significance as the initiator concentration is increased, probably as a result of higher reinitiation efficiency. Polymers obtained gave evidence for the incorporation of aromatic (amine) end groups in them.     

Photochemistry and photopolymerization activity of p-nitroaniline in the presence of N,N-dimethylaniline as a bimolecular photoinitiator system

The photoreduction behavior of p-nitroaniline (pNA) in the presence of N,N-dimethylaniline (DMA) induced by both steady-state (365 nm) and laser (337 nm) irradiation has been analyzed. The stoichiometry of the photoreduction reaction revealed that several amino radicals derived from DMA were generated by each photoreduced pNA molecule. The polymerization kinetics of the lauryl acrylate monomer (LA) photoinitiated by the pNA/DMA system has been studied by differential scanning photocalorimetry (Photo-DSC). The rate of polymerization was found to be proportional to the square root of both the incident light and the coinitiator DMA concentration. The order of the polymerization reaction with respect to monomer and initiator concentration was determined, as well as the polymerization behavior under aerobic conditions. The polymerization efficiency of this photoinitiated system was much higher than that obtained with conventional aromatic ketone photoinitiators. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3801–3812, 1997     

Photopolymerization of methyl methacrylate with the use of morpholine-chlorine charge transfer complex as the photoinitiator

Polymerization of methyl methacrylate (MMA) was kinetically studied under photo condition using near UV visible light at 40°C and employing morpholine (MOR)–chlorine (Cl₂) charge transfer (C-T) complex as the photoinitiator. The rate of polymerization (R_p) was dependent on morpholine/chlorine mole ratio; the 1 : 2 (MOR–Cl₂) C-T complex acted as the latent initiator complex, C, which underwent further complexation with the monomer molecules to give the actual initiator complex, I. Using 1 : 2 (MOR-Cl₂) C-T complex as the latent initiator, the initiator exponent evaluated for bulk photopolymerization of MMA was 0.071 and monomer exponent determined from studies of photopolymerization in benzene diluted system was 1.10. Benzoquinone behaved as a strong inhibitor and the polymers tested positive for the incorporation of chlorine atom end groups. Polymerization followed a radical mechanism. Kinetic nonideality as revealed by low (≪0.5) initiator exponent and a monomer exponent of greater than unity were explained in terms of primary radical termination effect. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1681–1687, 1997     

Photopolymerization of methyl methacrylate and other vinyl monomers with the use of N-bromosuccinimide as photoinitiator

Polymerization of MMA was done in the presence of visible light (440 nm) with the use of N-bromosuccinimide (NBS) as the photoinitiator. The initiator exponent and intensity exponent were 0.5, and the monomer exponent was found to be unity. The polymerization was inhibited in the presence of hydroquinone. The average k_p²/k_t for this photopolymerization system was found to be 0.296 × 10^?2 and the activation energy of photopolymerization was 4.67 kcal/mole. Kinetic and other evidence indicate that the overall polymerization takes place by a radical mechanism. With NBS as the photoinitiator, the order of polymerizability at 40°C was MMA, EMA ? MA ? VA, and styrene could not be polymerized under similar conditions.     

Preparation of Pt/polypyrrole-ferrocene hydrogen peroxide sensitive electrode for the use as a biosensor

A polypyrrole electrode with ferrocene mediator is prepared and its sensitivity to hydrogen peroxide is investigated. The polypyrrole is deposited upon a 0.5 cm² Pt plate by the polymerization of pyrrole by scanning the electrode potential between 0.0 and 0.9 V at a scan rate of 50 mV/s. The platinum/polypyrrole-ferrocene (Pt/PPy-Fc) electrode is prepared by adding ferrocene to the coverage medium. The electrode’s sensitivity to hydrogen peroxide is investigated at room temperature using 0.025 M phosphate buffer at pH 7. The working potential is 0.7 V, the concentrations of pyrrole and ferrocene are 0.2 M and 10 mM. Polypyrrole was coated on the electrode surface within 26 cycles. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 2, pp. 160–164. The text was submitted by the authors in English.     

Reactions of hydrogen atom with hydrogen peroxide

Rate coefficients are calculated using canonical variational transition state theory with multidimensional tunneling (CVT/SCT) for the reactions H + H2O2 --> H2O + OH (1a) and H + H2O2 --> HO2 + H2 (1b). Reaction barrier heights are determined using two theoretical approaches: (i) comparison of parametrized rate coefficient calculations employing CVT/SCT to experiment and (ii) high-level ab initio methods. The evaluated experimental data reveal considerable variations of the barrier height for the first reaction: although the zero-point-exclusive barrier for (1a) derived from the data by Klemm et al. (First Int. Chem. Kinet. Symposium 1975, 61) is 4.6 kcal/mol, other available measurements result in a higher barrier of 6.2 kcal/mol. The empirically derived zero-point-exclusive barrier for (1b) is 10.4 kcal/mol. The electronic structure of the system at transition state geometries in both reactions was found to have "multireference" character; therefore special care was taken when analyzing electronic structure calculations. Transition state geometries are optimized by multireference perturbation theory (MRMP2) with a variety of one-electron basis sets, and by a multireference coupled cluster (MR-AQCCSD) method. A variety of single-reference benchmark-level calculations have also been carried out; included among them are BMC-CCSD, G3SX(MP3), G3SX, G3, G2, MCG3, CBS-APNO, CBS-Q, CBS-QB3, and CCSD(T). Our data obtained at the MRMP2 level are the most complete; the barrier height for (1a) using MRMP2 at the infinite basis set limit is 4.8 kcal/mol. Results are also obtained with midlevel single-reference multicoefficient correlation methods, such as MC3BB, MC3MPW, MC-QCISD/3, and MC-QCISD-MPWB, and with a variety of hybrid density functional methods, which are compared with high-level theory. On the basis of the evaluated experimental values and the benchmark calculations, two possible recommended values are given for the rate coefficients.     

Stopped-flow spectrophotometric determination of hydrogen peroxide with hemoglobin as catalyst

A rapid and sensitive method was proposed for the determination of hydrogen peroxide based on the catalytic effect of hemoglobin using o-phenylenediamine as the substrate. Stopped-flow spectrophotometric method was used to study the kinetic behavior of the oxidation reaction. The catalytic effectiveness of hemoglobin was compared with other four kinds of catalysts. The initial rate of the formation of the reaction product 2,3-diaminophenazine at the wavelength of 425 nm was monitored, permitting a detection limit of 9.2x10(-9) mol/l H(2)O(2). A linear calibration graph was obtained over the H(2)O(2) concentration range 5.0x10(-8)-3.5x10(-6) mol/l, and the relative standard deviation at a H(2)O(2) concentration of 5.0x10(-7) mol/l was 2.08%. Satisfied results were obtained in the determination of H(2)O(2) in real samples by this method.     

The oxidation of cinnamaldehyde with alkaline hydrogen peroxide

The oxidation of cinnamaldehyde (3-phenyl-2-propenal) by alkaline peroxide results in epoxidation of the double bond to form cinnamaldehyde epoxide (3-phenyl-2,3-epoxy-propanal) which undergoes further reaction by ring opening and side chain cleavage to yield benzaldehyde and acidic fragments. The reactions are first-order in the organic substrates and perhydroxyl anion and second-order overall. In the presence of alkali alone, two further reactions take place in which cinnamaldehyde and cinnamaldehyde epoxide side chains are cleaved by reaction with hydroxide ion to form benzaldehyde and side chain fragments. These reactions are first-order in the organic substrates and hydroxide ion and second-order overall. Increasing solvent polarity accelerates the rates of reaction and reaction mechanisms have been proposed to describe the observed kinetic behavior. The stereoselectivity of the epoxidation reaction has been examined in terms of an existing model for epoxidation of α, β-unsaturated ketones by alkaline peroxide. © 1993 John Wiley & Sons, Inc.     

Photopolymerization of methyl methacrylate and some other vinyl monomers with the use of chlorine as photoinitiator

Low concentrations (0.001–0.03M) of chlorine easily induce photopolymerization of MMA at 40°C. Kinetic data indicate that polymerization follows a radical mechanism involving complexation of monomer by the initiator and initiation takes place through radical generation during photodecomposition of the initiator-monomer complex. Termination appears to take place bimolecularly. The k_p²/k_t value for MMA polymerization at 40°C was found to be 0.83 × 10^?2. Rates of chlorine-initiated photopolymerization were found to decrease in the order MMA, EMA ? VA, Sty > MA.     

Photopolymerization of methyl methacrylate with the use of tetrahydrofuran–bromine charge-transfer complex as the photoinitiator

The polymerization of MMA was kinetically studied in the presence of visible light (using a 125-W high-pressure mercury vapor lamp with fluorescent coating, without a filter), a THF—bromine charge-transfer complex being used as the photoinitiator. The initiator exponent was 0.5 in bulk polymerization. The monomer exponent varied from about 1.2 to about 2.5, depending on the nature of the solvent used; the initiator exponent also varied in diluted systems, depending on the nature and proportion of the solvent, the variation being from a value of 0.5 in bulk system to zero or almost zero at about 25% (v/v) solvent concentration. Other kinetic parameters, viz., k_p²/k_t and the activation energy for polymerization, were determined and are reported. Kinetic and other evidence indicates that the photopolymerization takes place by a radical mechanism and termination is bimolecular in nature in bulk systems; in dilute systems, termination by initiator complex assumes predominance, particularly at high solvent concentrations (≥25% v/v).     

The effects of aromatic solvents on the photopolymerization rates of isoprene,ethyl methacrylate,and styrene

The photochemical polymerization rates of isoprene, ethyl methacrylate, and of styrene in various aromatic solvents were measured. The average lifetimes of propagating radicals were measured by the rotating sector method. The polymerization rate constants, K_p, were determined and compared with dipole moments (μ) and Hammett σ constants for the aromatic solvents. Linear correlations of log(k_p/k_{p, benzene}) vs. μ and σ were obtained.