Photopolymerization initiated by charge-transfer complex. VI. Photopolymerization of methyl methacrylate with the use of isoquinoline–chlorine charge-transfer complex

Polymerization of methyl methacrylate in visible light was studied at 30°C using the isoquino-line–chlorine charge-transfer complex as the photoinitiator. Analyses of kinetic and other data indicate that the polymerization proceeds via a radical mechanism and the termination is initiator dependent. Chain termination via degradative chain (initiator) transfer appears to be significant.     

Photopolymerization initiated by charge-transfer complex. I. Photopolymerization of methylmethacrylate with the use of quinaldine-bromine and lutidine–bromine charge-transfer complexes as photoinitiator

Photopolymerization of MMA was carried out with quinaldine–bromine (QN–Br₂) and lutidine–bromine (LU–Br₂) charge-transfer complexes as initiators. The rate of polymerization R_p increased with rising monomer concentration and the monomer exponent was computed as unity. At first the rate of polymerization accelerated and then reduced as the initiator concentration was increased. The initiator exponent was 0.5. The reaction was carried out at three different temperatures and overall activation energy was calculated at 4.0 kcal/mol. The kinetic data and other evidence indicate that the overall polymerization takes place in a radical mechanism. A suitable mechanism is suggested.     

Mechanism of charge–transfer polymerization. II. Propagation mechanism of the polymerization of N-vinylcarbazole with organic electron acceptors

Copolymerizations of N-vinylcarbazole with both isobutyl vinyl ether and N-vinyl-pyrrolidone initiated by some organic electron acceptors have been investigated for the purpose of elucidating the propagation mechanism in the charge-transfer polymerization. Copolymerizations of the same system catalyzed by authentic cationic catalysts have also been made for comparison. The results indicate that the propagation mechanism of the charge-transfer polymerization studied is catio ie.     

Mechanism of N-vinylcarbazole polymerization on Co(II)–13X molecular sieve

Kinetics of polymerization of N-vinylcarbazole over Co(II)-13X molecular sieves in toluene have been studied. The rate of polymerization (R_p) has been found to be second order with respect to percent exchange level of Co(II) and also to the NVC concentration at all the reaction temperatures of 40, 50 and 60°C. The rate increases with decreasing pH of the original exchanging salt solution up to a pH of about 3.5, beyond which it falls. The overall activation energy of polymerization has been found to decrease with increase in monomer concentration, exchange level of Co(II), and the hydrogen ion concentration of the original exchange solution. Average degree of polymerization also follows a similar trend. A mechanism of polymerization involving simultaneous propagation on both metal ion Co(II) and proton on a zeolite surface has been suggested. The two propagation routes are characterized by an average activation energy of 10.36 kcal/mol and 5.40 kcal/mol on the metal ion and proton centers, respectively.     

Vinyl polymerization by carbon black V. Solvent effect and the kinetics of the polymerization of N-vinylcarbazole

The polymerization of N-vinylcarbazole has been carried out at 60°C under nitrogen with different grades of carbon black, N220, N110, N330, and N660 as heterogeneous catalysts. The order of efficiency of the catalysts in regard to the polymerization is: N220 > N110 > N660 > N330. Effect of solvent polarity on the polymerization has been studied with acetonitrile, 1,2-dichloroethane, and toluene-nitrobenzene mixtures. Nitrobenzene, with highest polarity, affords the highest rate, which decreases with decreasing nitrobenzene percentage in the solvent mixture. These features suggest the polymerization to be cationic in nature. The relative viscosities of the polymers are low, but tend to increase only slightly with increasing nitrobenzene content. The rate of polymerization can be expressed by the relation A suitable kinetic model has been presented in conformity with the experimental findings.     

Photopolymerization of methyl methacrylate using a morpholine–sulfur dioxide charge-transfer complex as the photoinitiator

Photopolymerization of the vinyl monomer (M) of methyl methacrylate (MMA) was kinetically studied by using near-UV/visible light at 40°C and employing a morpholine (MOR)–sulfur dioxide (SO₂) charge-transfer (C-T) complex as the photoinitiator. The rate of polymerization (R_P) was found to be dependent on the morpholine: sulfur dioxide mole ratio; the 1 : 2 (MOR–SO₂) complex acted as the latent initiator complex C which underwent further complexation with the monomer molecules to give the actual initiating complex I. Using the 1 : 2 (MOR–SO₂) C-T complex as the latent initiator, the observed kinetics may be expressed as R_P [MOR–SO₂]^0.27[M]^1.10. Benzoquinone behaved as a strong inhibitor. Polymers obtained tested positive for the incorporation of a sulphonate-type end group. Polymerization followed a radical mechanism. Kinetic nonideality as revealed by a low initiator exponent and monomer exponent of greater than unity was explained on the basis of a prominent primary radical termination effect. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1973–1979, 1998     

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).     

Studies on the charge-transfer complex and polymerization. Part XIII. Dilution and solvent effects in radical terpolymerization

In the terpolymerization of 2-chloroethyl vinyl ether—maleic anhydride—acrylonitrile and p-dioxene—maleic anhydride—acrylonitrile systems the compositions of the terpolymers obtained from feed of the same mole fraction were found to be changed beyond the limit of error for the given amounts and kinds of solvent. This change was considered to be divided into two parts. The first part, discussed quantitatively, was due to a dilution effect on the equilibrium complex formation between donor and acceptor monomer, and the second, as tentatively proposed, was due to a solvent effect on the reactivity of the complex.     

Photopolymerization of methyl methacrylate by use of a quinoline–bromine charge-transfer complex as the photoinitiator

Polymerization of MMA was carried out in presence of visible light (440 nm), quinoline-bromine charge-transfer complex being used as the photoinitiator. The initiator exponent was observed to be 0.5 up to 0.014 M initiator concentration; when chloroform was used as the solvent, the monomer exponent was found to be unity. The polymerization was inhibited in presence of hydroquinone but little inhibitory effect was observed in the presence of air. An average value of k²_p/k_t for this photopolymerization system was found to be (1.08 ± 0.22) × 10^-2. Kinetic and other evidence indicates that the overall polymerization takes place by a radical mechanism.     

Mechanism of the three-dimensional polymerization of glycol methacrylates. II. The system glycol monomethacrylate–glycol dimethacrylates–solvents

The three-dimensional polymerization of the system glycol monomethacrylate–glycol dimethacrylates–solvents has been studied. The kinetic dependences thus obtained were interpreted in terms of the dependence of rate constants of the individual reactions on the properties of the medium used. The three-dimensional polymer formed was characterized in the range from medium to the highest conversions.     

Stereocontrol in the cationic polymerization of N-vinylcarbazole

The dependence of the steric microstructure of cationically polymerized poly(N-vinylcarbazole) (PVK) upon catalyst, polymerization temperature, and polymerization solvent has been investigated. The effect of polymerization temperature variation was found to be small, whereas the choice of catalyst and polymerization solvent was found to have a strong influence upon the PVK steric microstructure. A correlation was found between the syndiotacticities X_s and the π^* solvent polarities of the polymerization solvents for a given catalyst. A decrease in X_s with increasing π^* solvent polarity was observed using BF₃OEt₂ and AlEt₂Cl catalysts and has been interpreted in terms of propagation via contact ion-pair ring structures reversibly formed between the active end group and a preceding repeating unit. The increase in X_s with increasing π^* solvent polarity observed with several of the catalysts investigated has been interpreted in terms of chain ion pairs whose separation increases with increasing π^* solvent polarity. The influence of the various Lewis acid catalysts upon the steric microstructures of cationically polymerized PVK allowed the following order of nucleophilicity to be established:      

Mechanism of charge-transfer polymerization. XI. Radical copolymerization of N-vinylindole with electron-accepting monomers

N-Vinylindole (NVI) was copolymerized with such electron-accepting monomers as fumaronitrile (FN) or diethyl fumarate (DEF) under initiation with a radical catalyst. The compositions of the copolymers varied from 1:1.1 to 1:1.85 (NVI:FN or DEF). The FN or DEF content in the copolymer increased with increase in the molar fraction of the FN or DEF monomer in the monomer feed. It was suggested that both copolymers have a 1:1 recurring unit of NVI and the electron-accepting monomer, thus being alternating copolymers, and that further addition of the electron-accepting monomer to the indole ring occurred at its electron-rich β-carbon atom.     

Photopolymerization initiated by charge–transfer complex. X. Photopolymerization of methyl methacrylate with the use of isoquinoline–sulphur dioxide charge–transfer complex

Aqueous polymerization of methyl methacrylate in visible light was studied using isoquinoline–sulphur dioxide (IQ–SO₂) charge–transfer complex as the photoinitiator. Analysis of kinetic and other data indicate that the polymerization proceed via a radical mechanism and the termination is dependent on the initiator concentration. Chain–termination via degradative chain (initiator) transfer appears to be predominant here.     

Free energy of an inhomogeneous polymer–polymer–solvent system. II

A complete expression for the enthalpy of mixing of inhomogeneous polymer–polymer–solvent systems applicable for small as well as large concentration fluctuations has been developed. This is used to express the free energy of inhomogeneous polymer–polymer–solvent systems in an extended form of the Landau-Ginzburg functional. The gradient energy parameters obtained here are consistent with the published results. The free energy functional has been applied to develop a generalized continuity equation for spinodal decomposition in polymer–polymer systems. A linearized version of this continuity equation has been used to study the effect of the gradient terms on the dominant wavelength during spinodal decomposition.     

Effects of metal salts on polymerization. Part V: Polymerization of N-vinylcarbazole initiated by sodium chloroaurate

The polymerization of N-vinylcarbazole (VCZ) initiated by sodium chloroaurate (NaAuCl₄·2H₂O) in nitrobenzene was studied at 30°C. The rate of polymerization (R_p) is proportional to [Au^III] [VCZ] after a short induction period. When reducing agents (ascorbic acid, ferrocene, or mercury metal) are added to the system, the rate of polymerization in the dark increases. The R_p is relatively unaffected by addition of water and N-ethylcarbazole, but the polymerization is completely inhibited in the presence of ammonia. Oxygen and DPPH act as neither inhibitors nor retarders. Kinetic treatments based on the assumption that the active initiating species is Au^II produced by reduction of Au^III by VCZ and other reducing agents explain the experimental results very well.     

Photopolymerization of methyl methacrylate and some other vinyl monomers with the use of a pyridine–bromine charge-transfer complex as photoinitiator

Polymerization of MMA was carried out under visible light (440 nm) with the use of pyridine–bromine (Py–Br₂) charge-transfer (CT) complex as the photoinitiator. Initiator exponent and intensity exponent were 0.5 and 0.43, respectively, and the monomer exponent was found to be dependent on the nature of the solvent or diluent used. The Polymerization was inhibited in the presence of hydroquinone, but oxygen had very little inhibitory effect. An average value of k_p²/k_t for this polymerization system was 1.19 × 10^?2, and the activation energy of photopolymerization was 4.95 kcal/mole. Kinetic data and other evidence indicate that the overall polymerization takes place by a radical mechanism. With Py–Br₂ complex as the photoinitiator, the order of polymerizability at 40°C was found to be MMA, EMA ? Sty, MA.     

Mathematical simulation of the oxygen–ethane reaction

Previous experimentation on the initial stages of the oxygen-ethane reaction at temperatures near 600°C demonstrated the existence of a significant induction period under homogeneous conditions. Below 0.13% conversion, the rate with oxygen is less than the rate of ethane pyrolysis in the absence of oxygen. Experiments were conducted with mixtures of ～1% ethane and ～0.4% oxygen in nitrogen using the “wall-less” technique. Mathematical simulations of the oxidative and simple pyrolyses of ethane were established by a numerical analysis. The experimentally observed induction period and the mechanisms previously proposed are supported by these computations. Steady-state conditions are much more slowly attained in the presence of oxygen than in its absence.     

Redox polymerization of acrylonitrile. Kinetics of the reaction initiated by the redox system tartaric acid–V5+

Kinetics of vinyl polymerization of acrylonitrile initiated by the redox system tartaric acid–V⁵⁺ have been investigated in aqueous sulfuric acid in the temperature range 30–40°C. The rates of polymerization and V⁵⁺ disappearance and the chain lengths of polyacrylonitrile were measured. From the results it is concluded that the polymerization reaction is initiated by an organic free radical arising from the V⁵⁺–tartaric acid reaction with termination by V⁵⁺ ions. A suitable kinetic scheme has been proposed, and the various rate and energy parameters were evaluated.