Cationic polymerization of formaldehyde in liquid carbon dioxide. Part II: A kinetic study of the polymerization

The kinetic behavior on the polymerization of formaldehyde with and without acidic catalyst, in liquid carbon dioxide, in the temperature range of 30 to 50°C. was investigated. In the polymerization without catalyst both the polymer yield and the degree of polymerization increased with reaction time and also with rising temperature. With acidic catalyst, such as acetic acid and dichloroacetic acid, both the polymer yield and the degree of polymerization increased more than that in the polymerization without catalyst. The overall rate of polymerization with and without acidic catalyst was expressed by the first-order rate equation with respect to monomer concentration. From the results it was concluded that the polymerizations belonged to a type of successive polymerization with rapid initiation and no termination. The rate constant and the activation energy of each elementary process of polymerization were estimated on the basis of the results.     

Cationic polymerization of formaldehyde in liquid carbon dioxide. Part I

A cationic polymerization of formaldehyde which gave a high molecular weight polymer was studied in liquid carbon dioxide at 20–50°C. In the polymerization without any catalyst both the rate of polymerization and the molecular weight of the resulting polymer increased rapidly with a decrease in the loading density of the monomer solution to the reaction vessel, and also increased with an increase in the initial monomer concentration. From these results it was concluded that the initiating species could be ascribed to an impurity contained in the monomer solution. Both the rate of polymerization and the degree of polymerization of the polymer also increased with rising temperature. The carboxylic acid added acted as a catalyst in the polymerization because of increase in the polymer yield, the molecular weight of polymer formed, and the number of moles of polymer chain with increasing dissociation constant of acid used. It was concluded that the polymerization in liquid carbon dioxide proceeded by a cationic mechanism. Methyl formate had no influence on the polymerization, but methanol and water acted as a chain-transfer agent.     

Two-stage irradiation study on propagation and termination in the γ-radiation-induced polymerization of ethylene in liquid carbon dioxide

The propagation and termination reaction in the γ-radiation-induced ethylene polymerization in liquid carbon dioxide were investigated by a two-stage irradiation. After irradiation at high dose rate, the polymerization occured at a considerable rate under the extremely low dose rate without initiation. The absolute propagation rate was determined in the second stage to be proportional to the square of ethylene fugacity and depended slightly on dose rate. The apparent activation energy for the propagation reaction is ?9 kcal./mole. From these observations which are the same as those in bulk polymerization, it is concluded that carbon dioxide acts as a diluent of ethylene monomer in the propagation reaction. Also, carbon dioxide was shown to be inactive to the growing radicals without irradiation, but oxygen which is produced by the radiolysis of carbon dioxide at high dose terminates the growing radicals with formation of carbonyl in the polymer.     

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.     

Effect of active acidic compounds on storage stability of coker naphtha

Coker naphtha was separated into ten distillation fractions equal in volume via Engler distillation. It was found that the mercaptan sulphur compounds were mainly concentrated in the lighter fractions, whereas the basic nitrogen compounds were concentrated in the heavier fractions. The gum content increased gradually with increasing the boiling point of each fraction after storage for 21 days under ambient conditions (25°C, 101 kPa). The active organic acidic compounds in coker naphtha extracted with aqueous solution of 20 mass % NaOH represented 0.26 mass %. The GC-MS analysis of the active organic acidic compounds showed the amounts of small molecule thiols, thiophenols (including benzyl mercaptan) and phenolic compounds to be 2.6%, 4.4% and 90.0%, respectively. After removal of the active acidic compounds by caustic scrubbing, the increase in the rate of gum formation was much slower than that of the blank coker naphtha after 27 days of storage under ambient conditions, indicating that the effect of these acidic compounds on the gum formation is more significant than with basic nitrogen compounds. It is demonstrated that the storage stability of coker naphtha was decreased in the presence of large amounts of phenolic compounds, which may accelerate the acid-catalysed polymerisation of olefins.     

Liquid carbon dioxide as a solvent for the radiation polymerization of ethylene

The usefulness of liquid carbon dioxide as a solvent for polymerization of ethylene was studied. The effect of liquid carbon dioxide on the polymerization was investigated under conditions of the pressure of 400 kg./cm.² over the temperature range 20–45°C. by using γ-radiation and AIBN as initiators. The infrared spectrum of the polymers showed that carbon dioxide had little effect on the polymer structure. The polymers contained no combined carbon dioxide and only small amounts of vinylidene unsaturation. The methyl content of the polymers was 0.5–4.0 CH₃/1000C. The polymer yield and molecular weight were found to be decreased by the addition of carbon dioxide in both polymerization by γ-radiation and AIBN. The number of polymer molecules formed per unit time increased with the content of carbon dioxide in the γ-ray polymerization, and was constant in the case of AIBN. The advantages of the use of liquid carbon dioxide as a solvent in this polymerization were also considered from the viewpoints of the continuous process, the separation of polymer, the stability of carbon dioxide to radiation, and commercial applications.     

Polymerization initiated by an electron donor–acceptor complex. Part IV. Kinetic study of polymerization of methyl methacrylate initiated by the charge-transfer complex consisting of poly-2-vinylpyridine and liquid sulfur dioxide

A kinetic study has been made of the polymerization of methyl methacrylate (MMA) initiated by a charge-transfer complex of poly-2-vinylpyridine (electron donor) and liquid sulfur dioxide (acceptor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free-radical intermediates, as with the pyridine-liquid sulfur dioxide complex system. The association constants K of acceptor and polymer electron donors which range widely in their molecular weight were determined spectrophotometrically, and it has been found that both K and overall rate of polymerization R_p of MMA decrease with increasing molecular weight of polymer donor; contrary to this, molecular weight of PMMA formed increases with increasing molecular weight of the polymer donor. Other kinetic behaviors was essentially the same as in the pyridine–liquid sulfur dioxide system, i.e., R_p is proportional to the square root of the concentration of the complex and to the 3/2-order of the monomer concentration; R_p is clearly sensitive to the carbon tetrachloride concentration at low concentration of carbon tetrachloride, but for a higher concentration it is practically independent of the carbon tetrachloride concentration. It has been deduced from a kinetic mechanism for the initiation that a primary radical may be produced from the reduction of carbon tetrachloride by an associated complex consisting of liquid sulfur dioxide–polymer donor and the monomer.     

Chemical recycling of poly(methyl methacrylate) by pyrolysis. Potential use of the liquid fraction as a raw material for the reproduction of the polymer

Pyrolysis of poly(methyl methacrylate) (PMMA) was studied as an effective way to recycle this polymer and recover its monomer methyl methacrylate (MMA). Experiments were carried out in a laboratory fixed bed reactor using either a model polymer or a commercial product based on PMMA as feedstock. Gaseous and liquid products obtained from polymer degradation were analysed and it was found that the oil fraction constituted mainly of the MMA monomer. Thus, the possibility of directly using the liquid product for the reproduction of the polymer was further investigated. Polymerizations accomplished in a differential scanning calorimeter using azo-bis-isobutyronitrile as initiator and different reaction temperatures. Results obtained were compared to corresponding data from polymerization of neat monomer. It was found that the pyrolysis liquid fraction can be polymerized and produce a polymer similar to the original PMMA. However, even small amounts of other organic compounds (mainly methyl esters) included in this fraction act as non-ideal reaction retarders, altering the reaction rate curve and lowering the glass transition temperature and the average molecular weight of the polymer produced.     

The Effect of Carbon Dioxide on the Alkali-Metal Initiation of Polyisoprene

The structures of polymers formed when alkali metals are placed in the vapor phase above isoprene monomer, both in the presence and absence of carbon dioxide, were investigated. In the absence of carbon dioxide, the polymers were all gel-like and soluble. In the presence of carbon dioxide, however, insoluble popcorn polymers were formed. The structures of the soluble polymers varied from primarily cis in the case of lithium to trans for sodium and potassium initiation. In the presence of carbon dioxide the three alkali metals produced polymers having similar structures, predominantly trans. In the absence of carbon dioxide most of the polymerization proceeds anionically with the majority of the free radical sites of the initially formed radical anion being removed by a transfer reaction or by dianion formation. The presence of carbon dioxide, however, leads to the formation of car boxy late ions that prevent anionic polymerization. Then, due to the structural orientation of the radical anion on the surface, free-radical polymerization occurs, leading to microgelation and popcorn polymerization. This results from cross-linking caused by mechanical rupture of the growing chains.     

Kinetics of the γ-radiation-induced polymerization of ethylene in liquid carbon dioxide

The γ-radiation-induced polymerization of ethylene with the use of liquid carbon dioxide as a solvent, was studied from the viewpoint of kinetics. The polymerization was carried out at conversions less than 10% under the pressure ranging from 100 to 400 kg./cm.², dose rates 1.3 × 10⁴?1.6 × 10⁵ rad/hr., and temperatures of 20–90°C. The concentration of carbon dioxide varied up to 84.1 mole-%. The polymerization rate and the polymer molecular weight were observed to increase with reaction time. This observation, however, becomes less pronounced with increasing concentration of carbon dioxide and with rising temperature. The exponents of the pressure and the dose rate were determined to be 2.3 and 0.85 for the rate, and 2.0 and ?0.20 for the molecular weight, respectively. From the kinetic considerations for these results, the effect of carbon dioxide on the initiation and termination reaction in the polymerization was evaluated.     

Size control of phase‐separated liquid crystal droplets in a polymer matrix based on the phase diagram

When a mixture of liquid crystal (LC) and photo reactive monomer is irradiated by UV light, polymerization occurs and LC droplets form through phase separation, producing polymer dispersed LCs (PDLCs). Although size control of LC droplets and reduced amounts of LC in PDLC films are important in applications, precise size control of LC droplets at a low LC fraction has not yet been accomplished. In this study, the phase diagrams of the LC/initial monomer and the LC/polymer during polymerization were used to control LC droplet size at various LC fractions. Both the relative position of the sample in the initial phase diagram and the shift of the phase separation line during polymerization were shown to be important in determining the size of LC droplets. Our results are expected to provide a new strategy for precise size control of LC droplets especially at a low LC fraction range, which would be a great help for PDLC applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Polymerization initiated by an electron donor–acceptor complex. Part I. Polymerization of methyl methacrylate initiated by liquid sulfur dioxide–pyridine complex in the presence of carbon tetrachloride

The polymerization of methyl methacrylate can be initiated by a charge-transfer complex of liquid sulfur dioxide and pyridine in the presence of carbon tetrachloride. The molar ratio of sulfur dioxide and pyridine which participated in the complex was found from a spectrophotometric study to be 2:1. The polymerization proceeds through free-radical intermediates. The overall rate of polymerization is proportional to the square root of the concentration of the complex, and the values of k_p/k_t^1/2 under the various polymerization conditions were satisfactorily consistent with the literature value. For the activation energy of the overall reaction, 8.2 kcal./mole was obtained, and for initiation, 9.7 kcal./mole was evaluated from the values of k_p/k_t^1/2. It was deduced from a kinetic mechanism for the initiation that a primary radical may be produced from the reduction of carbon tetrachloride by an associated complex consisting of liquid sulfur dioxide–pyridine complex and the monomer.     

Thermal degradation of phenyl methacrylate-methyl methacrylate copolymers

The degradation behaviours of poly(phenyl methacrylate), four phenyl methacrylate-methyl methacrylate copolymers which span the composition range, and poly(methyl methacrylate) have been compared by using thermogravimetry in dynamic nitrogen and thermal volatilisation analysis (TVA) under vacuum, with programmed heating at 10°C/min. Volatile products have been separated by subambient TVA and identified and the cold ring fraction and partially degraded polymer have been examined by ir spectroscopy. Poly(phenyl methacrylate) resembles poly(methyl methacrylate) in degrading completely to monomer. Copolymers of phenyl methacrylate and methyl methacrylate are more stable than the homopolymers. On degradation, the major products are the two monomers. Minor products from all the copolymers include carbon dioxide, dimethylketene, isobutene and formaldehyde. Copolymers with low and moderate phenyl methacrylate contents show the formation of anhydride ring structures in the cold ring fraction and partially degraded copolymer, together with small amounts of methanol in the volatile products. Carbon dioxide is a more significant product at lower phenyl methacrylate contents.The mechanism of degradation is discussed.     

Preparation and degradation of salts of poly(methacrylic acid). I. Lithium,sodium, potassium,and caesium salts

The polymers of lithium, sodium, potassium, and caesium salts of methacrylic acid have been prepared by free radical polymerization of the respective monomers in methanol solution. The degradation behavior of the polymers has been investigated by thermal volatilization analysis, thermogravimetry, and product analysis. These materials are stable to about 350°C under programmed heating at 10°C/min in vacuo. The principal degradation products are monomer, the corresponding isobutyrate, carbonate, oxide, carbon dioxide, and a fraction of liquid volatiles that is complex and contains a variety of aldehydes and ketones. The mechanism of degradation is discussed in detail.     

Characteristic analysis of cavitation bubbles in carbon dioxide fluid

After analysing the characteristics of bubble cavitation in high-pressure carbon dioxide (CO₂) fluid, cavitation conditions and some correlative physical characteristics are investigated. The results show that the ultrasonic intensity of liquid carbon dioxide to make cavitation occur is affected by the initial radius of the bubbles, hydrostatic pressure, temperature and vapour pressure within the bubbles in liquid CO₂. At the low frequency of ultrasound, the phase-speed of the liquid CO₂ gradually approaches the sound speed of the pure liquid when void fraction increases. At high frequency, the phase-speed is nearly equal to the sound speed in the liquid under different void fractions. The attenuation of ultrasound in liquid carbon dioxide reaches a maximum near the resonance frequency and then decreases when frequency either increases or decreases. At the resonance frequency, the phase-speed and the attenuation increase when the void fraction increases.     

Mass spectrometric analysis of high-purity carbon dioxide

A high-vacuum, low-temperature, continuous separation technique has been used in conjunction with a mass spectrometer for the analysis of carbon dioxide containing vpm amounts of H(2), He, CH(4), Ne, N(2), CO, O(2) and Ar. The method relies on the condensation of carbon dioxide on the walls of a glass U-tube, cooled in liquid nitrogen, connected between an inlet and the ion source. A high-pressure carbon dioxide sample thus enters the inlet leak but only the impurities pass through the U-tube and reach the ion source, resulting in considerable gain in sensitivity and elimination of interference from carbon dioxide. The sensitivity of the method is several orders of magnitude better than the normal mass spectrometric method.     

New polymers and copolymers based on 1-trifluoromethyl-1-ferrocenyl-2,2,2-trifluoroethyl methacrylate

Carbon-chain ferrocene-fluoro-containing (co)polymers are synthesized by the free-radical polymerization of 1-trifluoromethyl-1-ferrocenyl-2,2,2-trifluoroethyl methacrylate and its copolymerization with methyl methacrylate in organic solvents and supercritical carbon dioxide. The structures, solubilities, molecular masses, and thermal characteristics of these (co)polymers are studied. It is found that the introduction of 1–5 mol % of the ferrocene-fluoro-containing monomer in the chain of poly(methyl methacrylate) improves its thermal resistance and thermo-oxidative stability.     

GC—MS方法测定等离子体引发丙烯酸酯聚合引发活性种

在等离子体引发的液态丙烯酸酯类单体聚合体系中加入大量链转移剂乙硫醇,得到了端基带有引发活性种的低聚物,利用气相色谱-质谱的多离子检测手段,测定了活性种的结构,结果表明:引发活性种是单体在等离子体区裂解生成的酯基碎片[-C—O—R].进而解释了丙烯酸酯类单体可以由等离子体引发聚合,而苯乙烯不能引发聚合的问题.     

Characterization of liquid products of automobile tire pyrolysis

The liquid product of automobile tire pyrolysis and its fractions were studied. The amount of the liquid hydrocarbon fraction is 40–45% of the total weight of pyrolysis products. The hydrocarbon fraction is similar in its characteristics to low-sulfur heavy crude oil. Fractionation of the hydrocarbon fuel was performed. The maximal yield of the light distillation fraction is 39% (temperature interval 180–340°C). The extent to which the characteristics of the light fraction obtained meet the regulations was evaluated. The light fraction of hydrocarbon fuel produced by pyrolysis is recommended for use as a component of diesel motor fuel after additional purification.     

超临界二氧化碳流体环境中导电聚吡咯复合材料的制备

以聚苯乙烯(PS)和锌盐中和的磺化聚苯乙烯(Zn-SPS)膜为基体, 在超临界二氧化碳(SC-CO₂)环境中用化学氧化法原位制备了聚吡咯(PPy)导电复合材料. 由于SC-CO₂对聚合物基体的强溶胀作用, 吡咯分子高效地扩散到基体内部进行聚合而形成导电通路, 得到比传统的水溶液法更高的电导率. 聚合物基体的性质对复合材料的导电性和形貌产生重要影响. 在相同条件下, Zn-SPS/PPy的电导率比PS/PPy高3~4个数量级, 而它们的体积逾渗阈值分别为2.7%和6.2%, 远远低于理论预测值(16%).