Effect of oxygen on the γ-radiation-induced polymerization of ethylene

The effects of oxygen on the γ-radiation-induced polymerization of ethylene were studied at a temperature of 30°C.; the pressure was 400 kg./cm.², the dose rate was 1.9 × 10⁵ rad/hr.; and oxygen content was from 1–2000 ppm. The main product was solid polymer, and no liquid product was found. The gaseous products were hydrogen, acetylene, higher hydrocarbons, carbon dioxide, aldehydes, and acids. Several kinds of carbonyls similar to those formed in γ-ray oxidized polyethylene were observed in the polymer. The polymer yield and the degree of polymerization decreased markedly with increasing oxygen content, while the amount of carbonyls in the polymer increased. The number of moles of polymer chain and the amounts of hydrogen and acetylene were found to be almost independent of the oxygen content. The polymerization of pure ethylene was not affected by carbon dioxide and formic acid. On addition of acetaldehyde, the polymer yield and the degree of polymerization decreased markedly, while the number of moles of polymer chain increased. In the polymerization of ethylene containing oxygen, both the rate of oxygen consumption and the carbonyl content of the polymer increased, while the inhibition period decreased by the addition of acetaldehyde. It was found that the degree of polymerization after the inhibition period is almost independent of the reaction time in the presence of acetaldehyde, while it increases with the time in the absence of acetaldehyde.     

Photoinitiation. V. Effect of medium polarity on the acrylonitrile polymerization photoinitiated by naphthalene

The heterogeneous polymerization of acrylonitrile photoinitiated by naphthalene is influenced by the polarity of the reaction medium. The rate of initiation increases with the increasing dielectric strength of the reaction medium. A similar trend is observable for Stern–Volmer constants of naphthalene fluorescence quenching by acrylonitrile. The ratio k_p/k_t^1/2 of the rate constant for propagation and termination reactions is not influenced by a change in the polarity of the reaction medium. The effect of viscosity on the value of k_p/k_t^1/2 known for polymerization in a homogeneous medium was not observed in the reaction systems studied.     

Polymerization of aromatic nuclei. XVI. Mechanism of chain propagation in the polymerization of benzene by aluminum chloride–cupric chloride

A study was made of the mechanism of benzene polymerization by aluminum chloride-cupric chloride. Our main effort was devoted to propagation with the aim of resolving a literature conflict as to whether a cationic or radical pathway is involved. When equimolar mixtures of benzene and haloarene are polymerized, the resulting copolymers are composed almost exclusively of benzene monomer. This approach is based on the known relative reactivities of the monomers toward electrophilic and radical species. The amount of haloaromatic present in the copolymer was determined by elemental analyses and confirmed by infrared spectroscopy. These results are strongly indicative of propagation by an electrophilic moiety. The presence of oxygen in the reaction mixture was found to have no significant effect on the rate or yield of the polymerization, in contrast to a previous published report. The progress of the reaction was followed by titration of the evolved hydrogen chloride. Phenyl radicals, obtained by the thermal decomposition of benzoyl peroxide in benzene, were found to be incapable of initiating the polymerization in the presence of cupric chloride. Increased yields of biphenyl and the presence of chlorobenzene point to oxidation of intermediate radicals by cupric chloride. None of the experimental evidence is satisfactorily interpreted by radical propagation. The data are nicely rationalized on the basis of cationic chain extension, apparently via a radical cation initiator.     

Oxygen‐mediated polymerization initiated by oltipraz‐derived thiones

A pyrrolopyrazine‐thione derived from oltipraz, a compound that has been investigated as a chemopreventive agent, affords radicals in the presence of thiols and oxygen via a redox cycle, an attribute that suggests its suitability as an initiator for oxygen‐mediated polymerization. Here, we explore the utilization of this pyrrolopyrazine‐thione, generated in situ from a precursor, as an initiator for the radical‐mediated thiol–ene polymerization. While the pyrrolopyrazine‐thione was shown to be capable of generating radicals in the presence of atmospheric oxygen and thiol groups, the reaction extents achievable were lower than desired owing to the presence of unwanted side reactions that would quench radical production and, subsequently, suppress polymerization. Moreover, we found that complex interactions between the pyrrolopyrazine‐thione, its precursor, oxygen, and thiol groups determine whether or not the quenching reaction dominates over those favorable to polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1373–1382     

Effect of oxygen on the polymerization of vinyl chloride. I. Kinetic features

The effect of oxygen on the liquid-phase polymerization of vinyl chloride at 55°C in the presence of an added initiator, bis(4-tert-butylcyclohexyl) peroxydicarbonate (Perkadox 16), has been studied by the technique of tumbled dilatometry. With this method, at constant initiator concentration, the induction period showed a half-order dependence on the initial oxygen concentration. At a constant initial oxygen concentration, the induction period varied inversely as the square root of the initiator concentration. Under the experimental conditions empolyed, the polyperoxy radicals with chloroalkyl (～CH₂?HCl) endgroups were not wholly scavenged by molecular oxygen but could undergo various decomposition reactions. The degree of conversion of the initial oxygen to peroxidic compounds did not exceed 30% by weight and was dependent on the shape of the reaction vessel empolyed. The existence of other oxidation products has been demonstrated. At 55°C, the average velocity constant for decomposition of the peroxide products from vinyl chloride, measured in dichloromethane solution, was found to be 8 × 10^?5 sec^?1. A kinetic scheme involving a predominant cross-termination reaction is proposed to explain the experimental results.     

1H NMR study of the kinetics of substituted aniline polymerization. I. Homopolymerization of 2‐methoxyaniline

We studied the kinetics of the oxidative chemical homopolymerization of 2‐methoxyaniline (OMA) in aqueous acid solutions by monitoring OMA depletion with ¹H NMR spectroscopy. We used the same semiempirical kinetic model used for aniline (ANI) homopolymerization to evaluate the experimental data. The reaction kinetics of OMA homopolymerization was similar to that of ANI, although we obtained longer induction and propagation times for OMA. This was attributed to steric hindrance of the bulky methoxy substituent during the coupling reaction. Furthermore, it was suggested that a lower OMA polymerization rate could also be related to a lower concentration of nonprotonated OMA molecules in the reaction solution due to a higher pK_a value for OMA than for ANI. This may also explain the lower OMA end conversion (90%) compared with that of ANI (96%). The OMA end conversion was not influenced substantially by reaction conditions; it was lower than 90% only when high acid or low oxidant (oxidant‐deficient oxidant/OMA ratio) concentrations were applied. Because the oxidant took an active part in polymerization, it markedly influenced the polymerization rate, especially the initiation rate. The OMA initiation and propagation rates increased with increasing oxidant and initial monomer concentrations and with the reaction temperature, but there was no uniform trend in the correlation between the homopolymerization rate and acid concentration. The activation energies of the OMA initiation and propagation were 57 and 10 kJ/mol, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2471–2481, 2001     

以壳聚糖为模板的对苯二酚氧化聚合反应表观动力学研究

以壳聚糖为模板在酸性溶液中实现了对苯二酚的氧化聚合.该反应必须在氧气存在的条件下才能进行.动力学研究表明该氧化聚合反应是以选取机理进行的模板聚合反应.当壳聚糖残基与对苯二酚的摩尔比小于0.8时,反应速度与壳聚糖浓度成正比.当壳聚糖残基与对苯二酚的摩尔比大于0.8时,反应速度不再随壳聚糖浓度提高而提高.反应对对苯二酚而言是一个一级反应.反应的活化能为71.6kJ/mol.     

Radiation-induced,solid-state polymerization of derivatives of methacrylic acid. I. Postirradiation polymerization of zinc methacrylate

The postirradiation polymerization of the crystalline, anhydrous, monohydrate, and dihydrate forms of zinc methacrylate was studied. The anhydrous salt polymerized readily in the temperature range 50–150°C., the monohydrate did not polymerize at all, and the dihydrate polymerized at about 100°C. Aging of the anhydrous salts greatly affected the rate of polymerization; this was shown to be due mainly to the formation of peroxides by reaction with air. Polymerization could be initiated thermally, without irradiation, in monomer which had been aged in contact with air, apparently by decomposition of the peroxides. The rate of the postirradiation polymerization was increased when air was present during irradiation and decreased when air was present during polymerization. The rate of polymerization increased with temperature, corresponding to an apparent activation energy of 10 kcal./mole. The dihydrate lost one molecule of water rapidly under vacuum at 20°C. and slowly on heating at 50°C. in a sealed vessel, forming a crystalline monohydrate. Slow thermal polymerization and rapid postirradiation polymerization occurred at 100°C. without the formation of any monohydrate, indicating that the polymerization was concurrent with the phase change.     

Photoinduced ionic polymerization. VII. Cationic polymerization of cyclohexene oxide in solid state

Photopolymerization of cyclohexene oxide in the presence of electron acceptors was studied in a bulk system (in liquid as well as in solid states). The polymerization was proved to proceed by a cationic mechanism in both states by the effect of inhibitors. In a liquid phase the light intensity dependence of the rate of polymerization and the molecular weight distribution showed a contribution of a free ionic polymerization. Any discontinuous phenomenon in the rate as well as in the molecular weight was not discerned between liquid(above ?36°C) and plastic crystal (between ?36 and ?81°C) phases. A quantum yield of monomer consumption as high as 8 × 10³ was observed in the plastic crystal phase. Below ?81°C in the normal crystal phase the rate as well as the molecular weight was remarkably suppressed.     

Effect of thiourea on the radical polymerization of vinyl monomers. Part II. Effect of diphenyl thiourea on the polymerization of methyl methacrylate with benzoyl peroxide as initiator

The polymerization of methyl methacrylate (MMA) initiated by benzoyl peroxide (BPO) in the presence of diphenyl thiourea (DPTU) has been studied. It was found that the BPO–DPTU catalyst system was not an effective accelerating system but showed a relatively strong retarding effect. With DPTU derivatives, the polymerization rate was found to decrease with the increase in the electron-attracting forces of substituents attached to the phenyl groups of DPTU. In the polymerization of MMA initiated by AIBN, the addition of DPTU to the reaction systems affected neither the polymerization rate nor the degree of polymerization. From this fact, it might be concluded that DPTU itself serves as a radical scavenger. It seems most probable from the results of kinetic studies, iodometric titration, and from the effect of an oxidation product of DPTU (diphenyl formamidine disulfide) that the retardation effect observed is attributable to the action of the disulfide (DPFDS). By extending the Alfrey-Price scheme for the copolymerization reactions to the chain-transfer reactions, the Q and e values of DPFDS were determined. The apparent chain-transfer constants for DPTU and its derivatives were calculated by means of rate measurements and were correlated with substituent constants. The mechanism of the polymerization is discussed on the basis of these results.     

Redox polymerization of 2-hydroxyethyl methacrylate (HEMA). I. Influence of surfactants on polymerization kinetics

Oxidation of ferrous orthophenanthroline (FeP) by peroxydiphosphate (PP) in aqueous medium at pH 1 was followed spectrophotometrically. Kinetic analysis has shown that oxidation occurs via the formation of an intermediate complex between FeP and PP. Equi-librium and rate constants were calculated. Influence of surfactants on the oxidation of FeP by PP was also Investigated. The equilibrium constant for complex formation was found to be higher in the presence of surfactants. The enhanced complex formation has been attributed to the ionic interactions between the charged surfactant and the ionic species in the reaction medium. Polymerization of HEMA initiated by the redox system,FeP/PP, was carried out in aqueous medium, under the conditions of excess reductant over oxidant and excess oxidant over reductant. The polymerization followed different mech-anisms under these conditions; with excess oxidant, the growing polymer radicals underwent oxidative termination, while with excess reductant, primary radical termination was pre-ferred. The effect of surfactants on the aqueous polymerization of HEMA using the redox system FeP/PP was also investigated. In addition to the decrease in rate, the polymerization followed a different mechanism in the presence of surfactants, the growing radicals ter-minated by mutual interaction. © 1995 John Wiley & Sons, Inc.     

Radiation-induced solid-state polymerization of methacrylic acid. II. In-source polymerization

The in-source polymerization of methacrylic acid in the solid state with γ-rays was studied. The conversion rates at various temperatures were obtained as well as the radical concentrations by the measurements of ESR spectrum. The rate of polymerization was found to be proportional to I^0.65 at 0°C. The results could be interpreted on the basis of the assumption that the rate of propagation is proportional to the concentration of the propagating radical, of the monomer, and of the polymer. The addition of water to the monomer seems to accelerate the polymerization reaction. The change of the line shape of the propagating radical during polymerization was interpreted in terms of the change of the matrix which surrounds the propagating radical.     

Radical polymerization of methyl methacrylate initiated by an enolizable ketone–carbon black system

The polymerization of methyl methacrylate (MMA) initiated by an enolizable ketone (R₁? CO? CH₂? CO? R₂)-carbon black system was investigated. Although enolizable ketone itself could not do so, the polymerization of MMA was initiated by enolizable ketone in the presence of carbon black. In addition, a chloranil-enolizable ketone system was able to initiate the polymerization of MMA. It was found that the enol form of the ketone and quinonic oxygen groups on the carbon black surface played an important role in the initiation system; namely, it was considered that the polymerization was begun by the ketone radical (R₁? CO? CH? CO? R₂) formed by a one-electron transfer reaction from enolate ion to quinonic oxygen groups. The effect of solvent on the process was also studied. The rate of the polymerization increased, depending on the solvent used, in the following order: benzene < 1,4-dioxane < dimethyl sulfoxide < N,N-dimethylformamide < N-methyl-2-pyrrolidone. Furthermore, it became apparent that during the polymerization poly(methyl methacrylate) was grafted onto the carbon black surface (grafting ratio was ca. 40% when benzene was used as solvent) and the carbon black obtained gave a stable colloidal dispersion in organic solvent.     

An oxygen-tolerant photo-induced metal-free reversible addition-fragmentation chain transfer polymerization

We report herein a visible light-induced metal-free living polymerization with high oxygen tolerance that can be performed in aqueous media. In contrast with ordinary living/controlled radical polymerizations, oxygen can be present throughout the entire reaction process. This reaction can be photo-induced and proceeds at room temperature. First, we have successfully synthesized a well-defined polymer in an ambient atmosphere by the photo-induced radical polymerization method, using acrylic acid as a monomer and fluorescein as a photocatalyst. However, the subsequent chain extension reaction did not occur, possibly due to oxidation of the chain transfer agent (CTA). Despite this, we found that the addition of vitamin C (ascorbic acid) imparted the process with oxygen tolerance. We conducted a systematic study to optimize the best concentrations of the key reagents including the monomer, CTA, fluorescein, and vitamin C. Through these optimizations we were able to synthesize in the presence of oxygen a series of well-defined poly(acrylic acid)s (PAAs) with dispersities (Ð) below 1.3 and molecular weights that closely matched the theoretical values. The kinetic study showed that the molecular weight of the produced PAA increased linearly with the conversion of the monomer, and chain extension reaction also yielded a block polymer with a higher molecular weight than that of the previous polymer. Therefore, we developed a novel photo-induced living polymerization method that can be conducted both in the absence of oxygen and in the presence of air. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2437–2444     

Ionic complex of Vanadyl(IV) in the polymerization of 2-hydroxyethyl methacrylate as probed by EPR

The vanadyl ionic complex VO(DMSO)₅(ClO₄)₂ (I) exhibits high catalytic activity in the polymerization of 2-hydroxyethyl methacrylate (HEMA). The changes in the vanadium oxidation state during polymerization under argon and in the presence of oxygen were studied by EPR. Under aerobic conditions, the HEMA chain propagation radical was detected; this indicates the presence of a radical chain polymerization pathway caused by the ability of I to perform one-electron reduction of molecular O₂. The radical generation rate is controlled by the initial concentration of I: its increase results in the formation of inactive species, presumably, μ-peroxo complexes V^v-O-O-V^v. It was shown by kinetic methods that the radical-chain pathway initiated by the reaction of I with O₂ is not crucial in the HEMA polymerization.     

Radiation-induced polymerization of glass-forming systems. IV. Effect of the homogeneity of polymerization phase and polymer concentration on temperature dependence of initial polymerization rate

The effect of homogeneity of polymerization phase and monomer concentration on the temperature dependence of initial polymerization rate was studied in the radiation-induced radical polymerization of binary systems consisting of glass-forming monomer and solvent. In the polymerization of a completely homogeneous system such as HEMA–propylene glycol, a maximum and a minimum in polymerization rates as a function of temperature, characteristic of the polymerization in glass-forming systems, were observed for all monomer concentrations. However, in the heterogeneous polymerization systems such as HEMA–triacetin and HEMA–isoamyl acetate, maximum and minimum rates were observed in monomer-rich compositions but not at low monomer concentrations. Furthermore, in the HEMA–dioctyl phthalate polymerization system, which is extremely heterogeneous, no maximum and minimum rates were observed at any monomer concentration. The effect of conversion on the temperature dependence of polymerization rate in homogeneous bulk polymerization of HEMA and GMA was investigated. Maximum and minimum rates were observed clearly in conversions less than 10% in the case of HEMA and less than 50% in the case of GMA, but the maximum and minimum changed to a mere inflection in the curve at higher conversions. A similar effect of polymer concentration on the temperature dependence of polymerization rate in the GMA–poly(methyl methacrylate) system were also observed. It is deduced that the change in temperature dependence of polymerization rate is attributed to the decrease in contribution of mutual termination reaction of growing chain radicals to the polymerization rate.     

Emulsion polymerization of acrylonitrile. Part II. Mechanism of emulsion polymerization of acrylonitrile

The mechanism of emulsion polymerization of acrylonitrile has been studied by measuring by dilatometry and electron microscopy the adsorption of monomer into polymer particles and polymerization characteristics such as rate, degree of polymerization, the growth of the particle during polymerization, and the degree of dispersion. In the emulsion polymerization of acrylonitrile, new particles are formed during polymerization at a rate which is proportional to the rate of polymerization and the ratio of unreacted monomer. The total amount of monomer adsorbed on or in the polymer particles is rather small, but the concentration on or in the polymer particles is sufficiently high and proportional to the monomer concentration in aqueous phase. The polymerization proceeds concurrently on or in the polymer particles and in aqueous phase, but the three loci may be continuous rather than discrete. A reaction scheme is introduced here which shows the coexistence of polymerizations on or in the polymer particles and in the aqueous phase.     

Kinetics of γ-ray polymerization of formaldehyde in the presence of carbon dioxide

A kinetic study of the γ-ray polymerization of formaldehyde in toluene solution in the presence of carbon dioxide was carried out at temperatures of + 13 to ?17°C. Two modes of the polymerization, spontaneous and γ-ray polymerization, occur in this system. The γ-ray polymerization, experimentally separated from the spontaneous polymerization, was investigated. The rate of γ-ray polymerization increased slightly with the square root of carbon dioxide concentration. The rate of polymerization was also found to be proportional to the dose rate and the square of monomer concentration. The molecular weight of polymer formed was independent of the reaction condition. The apparent activation energy was estimated to be 10.3 kcal./mole. The kinetics of the γ-ray polymerization in the presence of carbon dioxide are explained quantitatively by a cationic mechanism, and the role of carbon dioxide is as an action of retardation for neutralization of the cationic initiating species, which was produced by γ-radiation, by means of a reverse reaction with an electron. Physical and mechanical properties of the polymer obtained by γ-ray polymerization were also investigated.     

Emulsion polymerization of styrene. III. Effect of Ti(III) and Cl(1) on the polymerization of styrene initiated by potassium persulfate

The emulsion polymerization of styrene initiated by potassium persulfate catalyzed by Ti⁺³ ions was studied. Two sources of Ti⁺³ ions were used: the titanium trichloride and titanium sulfate. It was found that the titanium ions used in conjunction with potassium persulfate decrease both the reaction rate and the average molecular weight. An even greater drop of reaction rate was noted when chlorine anions (TiCl₃) were present. The presence of these ions had a stabilizing effect on the polydispersity.     

The cupric sulfate–hydrazine system as an initiator of vinyl polymerization. I. The polymerization of methyl methacrylate in aqueous solution in the presence of oxygen

The cupric sulfate–hydrazine system has been used to initiate the aqueous solution polymerization of methyl methacrylate at pH 9.25 in the presence of oxygen. At cupric sulfate concentrations greater than the saturation solubility of cupric hydroxide, hydrazine is adsorbed on, and decomposes on, the surface of the hydroxide. The kinetics of the decomposition are zero-order both in the absence and the presence of monomer. The initiation of the polymerization occurs both at the surface of the cupric hydroxide on to which some monomer is adsorbed and also in solution. Below the saturation solubility of cupric hydroxide, the initiation reaction between cupric ions and hydrazine occurs in solution.