Determination of kinetic rate constants in electrochemically initiated anionic polymerization of 1,3-butadiene

The rate constants for electrochemically initiated polymerization were determined by employing a pulsing technique. An electrochemical titration was conducted in which polymer chains were initiated electrochemically, propagated in the absence of current, and terminated electrochemically. The concentrations of supporting electrolyte and monomer were chosen to correspond to those employed in electropolymerization syntheses. The temperature range ?10°C to ?72°C gave k_p = 1.45 × 10² exp {2600/RT}. The Arrhenius parameters are compared to those from previous studies and are interpreted in terms of ion-pair propagation. Precise control of molecular weight distributions is implicit from an accurate knowledge of the kinetic parameters and is reported separately.     

The flash photolysis—shock tube technique using atomic resonance absorption for kinetic studies at high temperatures

A flash photolysis-shock tube technique is described for making kinetic measurements at high temperature. Coupled with sensitive atomic resonance absorption detection, this method allows bimolecular rate constants for atom-molecule reactions to be measured directly under conditions free from kinetic complications. Experiments were performed in the reflected shock regime, and the temperature and density were calculated using ideal shock wave theory in this initial work. Results for the reaction of atomic hydrogen with ammonia are presented to illustrate the potential of the technique. The values of the Arrhenius rate parameters found in these experiments, 900 K ≤ T ≤ 1850 K, were A = (1.14 ± 0.12) × 10^?10 cm³ molecule^?1 s^?1 and E_a = 13,216 ± 242 cal mol^?1. This result gives rate constants that are about five times larger than those from previous studies. Although corrections for nonidealities in the reflected shock region are anticipated and under investigation, the expected changes will be relatively small and thus the large discrepancy noted here will remain.     

Retardation of discoloration of poly(vinyl chloride) and decolorization of discolored poly(vinyl chloride) with diimide

Retardation of discoloration of poly(vinyl chloride) with diimide was studied in dimethylformamide at 130°C. with the use of p-toluenesulfonylhydrazide (PSH) as a source of diimide. A process was proposed that involved prolonging the induction periods of discoloration by inhibiting the development of conjugated polyene structure. The optimum proportion of PSH was one fourth of the poly(vinyl chloride), the best results. Furthermore, poly(vinyl chloride) discolored by thermal degradation in o-dichlorobenzene or gamma-ray irradiation under vacuum was decolorized in solution at 130°C. by addition of PSH. The decolorized poly(vinyl chloride) thus obtained was thermally stable compared with that obtained by oxidative methods.     

Suspension polymerization of vinyl chloride initiated by in situ generated diisobutyryl peroxide

It was found that diacyl peroxides can be formed in situ in a polymerization medium by the reaction of an acid anhydride with hydrogen peroxide. For the specific application to aqueous vinyl chloride polymerization, an initiator system based on the base-catalyzed reaction of isobutyric anhydride with hydrogen peroxide to produce diisobutyryl peroxide gave very good results. In contrast, the acid chloride was completely ineffective as a peroxide precursor in this reaction. Studies pointing to diisobutyryl peroxide as the initiating species; investigations of reactant stoichiometry; and comparison of the in situ system with preformed diisobutyryl peroxide were conducted. It was shown that this system makes possible the polymerization of vinyl chloride at 30°C at rates comparable to those obtained with dialkyl peroxydicarbonates at 50°C, thus demonstrating the ability of this system to initiate vinyl chloride polymerization at low temperature. The rates of vinyl chloride polymerization with the use of different concentrations of in situ diisobutyryl peroxide at 30, 40, and 50°C were determined. Similarly, polymerization rates with the use of combinations of in situ diisobutyryl peroxide and n-propyl peroxydicarbonate were determined. The data obtained demonstrate rapid initiation of the polymerization reaction and a reduction in polymerization time made possible by this dual initiator system. These results were verified in pilot-plant and commercial-scale PVC polymerizations.     

Competitive unimolecular reactions at low pressures. The pyrolysis of cyclobutyl chloride

The thermal decomposition of cyclobutyl chloride has been investigated over the temperature range of 892–1150 K using the technique of very low-pressure pyrolysis (VLPP). The reaction proceeds via two competitive unimolecular channels, one to yield ethylene and vinyl chloride and the other to yield 1,3-butadiene and hydrogen chloride, with the latter being the major reaction under the experimental conditions. With the usual assumption that gas-wall collisions are «strong,» RRKM calculations, generalized to take into account two competing pathways, show that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by log k₁(sec^?1) = (14.8 ± 0.3) ? (61.1 ± 1.0)/Θ for vinyl chloride formation and log k₂(sec^?1) = (13.6 ± 0.3) ? (55.7 ± 1.0)/Θ for 1,3-butadiene formation, where Θ = 2.303 RT kcal/mol. The A factors were assigned from previous high-pressure low-temperature data of other workers assuming a four-center transition state for 1,2-HCl elimination and a chlorine-bridged biradical transition state for vinyl chloride formation. The activation energies are in good agreement with the high-pressure results which were obtained with a conventional static system. The difference in critical energies is 4.6 kcal/mol.     

Polymerization of vinyl chloride in the presence of precipitants. I

The kinetics of bulk and precipitation polymerization of vinyl chloride has been studied over wide range of reaction temperature by using γ-ray induced initiation. The autoacceleration effect, which has been observed by many investigators in the case of chemically initiated bulk polymerization of vinyl chloride above 40°C and has been the most controversial aspect of the bulk polymerization of vinyl chloride, was found to disappear in the bulk polymerization below 0°C. In the bulk polymerization at 40°C, the autoacceleration effect was observed up to 20%, in agreement with the results of previous investigators, and a pronounced effect of the size of polymer particles on the time–conversion curve was observed. The kinetics of precipitation polymerization of vinyl chloride in the presence of some nonsolvents was successfully described by a oneparameter equation. A kinetic scheme, which clearly explains the zero-order reaction behavior of bulk polymerization at low temperature and the kinetic behavior of precipitation polymerization described by the empirical equation, is proposed. The autoacceleration effect in the bulk polymerization at 40°C was considered to be essentially the same phenomenon as the small retardation period observed in the bulk polymerization at low temperature.     

Radical block polymerization of vinyl chloride. II. Synthesis and characterization of vinyl chloride block copolymers

Peroxidized polypropylene has been used as a heterofunctional initiator for a two-step emulsion polymerization of a vinyl monomer (M₁) and vinyl chloride with the production of vinyl chloride block copolymers. Styrene, methyl-, and n-butyl methacrylate and methyl-, ethyl-, n-butyl-, and 2-ethyl-hexyl acrylate have been used as M₁ and polymerized at 30–40°C. In the second step vinyl chloride was polymerized at 50°C. The range of chemical composition of the block copolymers depends on the rate of the first-step polymerization of M₁ and the duration of the second step; e.g., with 2-ethyl-hexyl acrylate block copolymers could be obtained with a vinyl chloride content of 25–90%. The block copolymers have been submitted to precipitation fractionation and GPC analysis. Noteworthy is the absence of any significant amount of homopolymers, as well as poly(M₁)n as PVC. The absence of homo-PVC was interpreted by an intra- and intermolecular tertiary hydrogen atom transfer from polypropylene residue to growing PVC sequences. The presence of saturated end groups on the PVC chains is responsible for the improved thermal stability of these block polymers, as well as their low rate of dehydrochlorination (180°C). Molecular aggregation in solution has been shown by molecular weight determination in benzene and tetrahydrofuran.     

Non-isothermal kinetic study on the decomposition of Zn acetate-based sol-gel precursor

The paper presents a non-isothermal kinetic study of the decomposition of Zn acetate-based gel precursors for ZnO thin films, based on the thermogravimetric (TG) data. The evaluation of the dependence of the activation energy (E) on the mass loss (Δm) using the isoconversional methods (Friedman (FR), Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) has been presented in a previous paper. It was obtained that the sample dried at 125°C for 8 h exhibits the activation energy independent on the heating rate for the second decomposition step. In this paper the invariant kinetic parameter (IKP) method is used for evaluating the invariant activation parameters, which were used for numerically evaluation of the function of conversion. The value of the invariant activation energy is in a good agreement with those determined by isoconversional methods. In order to determine the kinetic model, IKP method was associated with the criterion of coincidence of the kinetic parameters for all heating rates. Finally, the following kinetic triplet was obtained: E=91.7 (±0.1) kJ mol⁻¹, lnA(s⁻¹)=16.174 (±0.020) and F1 kinetic model.     

Polyene sequence distribution in thermally degraded poly(vinyl chloride)

A kinetic model for the formation of polyene sequences during the thermal degradation of poly(vinyl chloride) in nitrogen is proposed. The model includes a propagation step of the “zipper” type and termination by crosslinking. The initiation can occur randomly or at weak links in the polymer chain. The rate of polyene growth increased with increasing polyene sequence length and passed through a flat maximum at n = 7. The average polyene sequence length was almost constant up to about 0.5% conversion, but then slowly decreased with increasing conversion. This was the result of a larger extent of termination reactions (crosslinking) at higher conversions. At 0.2–0.5% conversion an average polyene sequence length of about 6 was observed. The degradation was carried out in nitrogen at 190°C. The experimental results were obtained from ultraviolet-visible spectrophotometric measurements.     

Release of cationic drugs from loaded clay minerals

The adsorption of promethazine chloride [10-(2-dimethylammonium propyl) fenothiazine chloride] and buformin hydrochloride (1-butylbiguanidine chloride) on montmorillonite was studied in previous work. The present article focuses on the desorption of these molecules from their organocomplexes in a medium of artificial intestinal juice (pH 7.0 ± 0.1) at the temperature of the human body (37 ± 0.5 °C). The desorption was investigated by kinetic studies, basal spacing measurements and Fourier transform IR studies. Important quantitative differences were observed: buformin, which adsorbed in a monolayer coverage, exhibited a very high desorption rate, whereas promethazine formed a pseudotrilayer arrangement and showed a lower dissolution rate. Received: 20 January 2001 Accepted: 8 March 2001     

Polymerization of aromatic nuclei. XIV. Polymerization of toluene with aluminum chloride–cupric chloride

The polymerization of toluene with aluminum chloride and cupric chloride was performed in carbon disulfide and in a neat system. The solvent reaction produced an insoluble, light-brown product which did not melt below 350°C. In the neat system, polymerization was much more vigorous, yielding a dark, purple-brown solid with mp ～250°C and molecular weight of 634. Infrared, NMR, and ultraviolet spectroscopy, along with elemental analysis and oxidative degradation, indicated that the backbone chain contains o-polyphenylene units with the methyl group situated in the 4-position. Some p-polyphenylene structures may also be present. Evidence for small amounts of benzyl and polynuclear moieties was obtained. The mechanistic aspects are discussed. Our principal conclusions concerning oligomer structure are in disagreement with those of Kuwata.     

γ-Ray-induced copolymerization of ethylene and vinyl chloride in liquid carbon dioxide

The γ-ray-induced copolymerization of ethylene and vinyl chloride with the use of liquid carbon dioxide as a solvent was studied under a total pressure of 400 kg/cm², with a dose rate of 2.5 × 10⁴ rad/hr at 30°C. A rubberlike, sticky polymer is obtained when the molar concentration of vinyl chloride is less than 30% in the monomer mixture, and the polymer is a white powder at higher concentrations of vinyl chloride. Infrared, x-ray, and differential thermal analyses confirm that the polymerization products are noncrystalline, true random copolymers. The rate of copolymerization decreases markedly when a small amount of vinyl chloride is added to ethylene monomer. In the range of vinyl chloride concentration higher than 5%, however, the rate and the molecular weight of copolymer increase with increasing concentration of vinyl chloride. It has been concluded from kinetic considerations based on these results that the rate of initiation increases proportionally with the concentration of vinyl chloride. Further, the growing chain radicals are shown to be deactivated by the cross-termination reaction between the radicals with terminal unit of ethylene and vinyl chloride, and no transfer reaction occurs.     

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.     

2-Hydroxy-3-ionene chloride

The condensation of dimethylamine with epichlorohydrin gave an almost quantitative yield of 2-hydroxy-3-dimethylaminopropyl chloride which was polymerized via the Menschutkin reaction to give 2-hydroxy-3-ionene chloride. This cationically charged polymer was obtained in greater than 90% yields as a white to tan solid when precipitated into acetone. Number-average molecular weights of up to 10,000 and intrinsic viscosities of up to 0.11 dl/g in 0.4M potassium bromide were found. These low molecular weights were attributed to several impurities that were identified as being produced by side reactions. Thermal analysis of the polymers showed an endothermic transition at 32–39°C with the onset of decomposition occuring at about 200°C.     

Chemical kinetic simulations behind reflected shock waves

Chemical kinetic simulations that more accurately consider reaction conditions behind reflected shock waves in a high pressure shock tube have been conducted by accounting for (1) time‐dependent temperature and pressure variations in contrast to assuming constant temperature and pressure, (2) the inclusion of reactions during quenching by cooling in contrast to the assumption of zero kinetic contributions, and (3) real gas behaviors in contrast to assuming ideal gas conditions. The primary objective of the current work is to assess the degree of uncertainty associated with assuming constant temperature and pressure and that no reactions occur during the finite time of quenching and prefect gas behavior. The assessment of the subsequent effect of the uncertainty on chemical kinetic modeling is evaluated by conducting extensive comparative studies. In order to achieve this purpose, available CHEMKIN II and CHEMKIN Real Gas codes were utilized and modified to adopt the proposed approaches. From our computational experiments, it is found: (1) For shock tube experiment with less than a 15% endwall pressure increase, the conventional assumptions lead to reasonable accuracy in predicting stable species; (2) during reaction quenching, the consumption of radical species occurs efficiently and is nearly complete once the pressure drops to 50% of its highest value, but concentrations of stable species are insignificantly perturbed by reactions occurring during quenching; and (3) at elevated pressures, the real gas effects, which are a combination of nonideal P–V–T (state variables), thermodynamic, and kinetic behaviors, affect kinetics by speeding the reaction progress up slightly and do not significantly influence the development or validation of a detailed kinetic model from shock tube data that are obtained in a wide temperature range. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 75–97, 2006     

Thermal stability of ketoprofen

The purpose of this investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the ketoprofen—involving active substance’s thermal decomposition—was performed under isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 260; 265; 270; 275; and 280 °C. The thermogravimetry/derivative thermogravimetry data were processed by three differential methods: isothermal–isoconversional, Friedman’s isothermal–isoconversional, and isothermal model-fittings. The obtained results are in good accordance with those obtained under non-isothermal conditions of a previous study, and confirm the necessity for the kinetic parameters to be determined, under different thermal conditions, by the adequate calculation methods.     

Electrophilic aromatic substitution. 14. [1] A kinetic,NMR, and Raman study of the aluminum chloride-catalyzed reaction of p-toluene-sulfonyl chloride with benzene and toluene in dichloromethane

Vacuum line kinetic studies of the reaction of p-toluenesulfonyl chloride and benzene or toluene, using aluminum chloride as the catalyst and dichloromethane as the solvent were determined at 25°C by means of gas chromatography. The reaction is first-order in arene, tosyl chloride, and in AlCl₃ as catalyst. Noncompetitive results are k_T/k_B=22±7 with a product sulfone isomer distribution: ortho, 14±1%; meta, 4.3±0.2%; and para 82±1%. With hexadeuteriobenzene k_H/k_D was determined to be 1.8±0.1. Rate constant ratios and product isomer distributions were also determined competitively: with AlCl₃, k_T/k_B=30±2; % ortho, 13±1; % meta, 4.0±0.5; % para, 84±3; with SbCl₅, k_T/k_B=40±4; % ortho 10.3±0.4; % meta, 4.7±0.2; and % para, 85.0±0.5. The k_T/k_B ratio for AlCl₃ and the meta sulfone product percentages for both AlCl₃ and SbCl₅ are considerably higher than those reported in the literature. NMR and Raman studies suggest a molecular complex between p-tosyl chloride and AlCl₃, with coordination through oxygen as the dominant species and the probable electrophile in CH₂Cl₂. A reaction mechanism consistent with the kinetic and spectroscopic results is proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 367–372,1998     

Preparation and properties of polyarylates from 5-t-butylisophthaloyl chloride and various bisphenols

Polyarylates containing a t-butyl pendant group were prepared from 5-t-butylisophthaloyl chloride and various bisphenols through the phase-transfer catalyzed two-phase polycondensation. The polyarylates having inherent viscosities up to 3.1 dL/g were obtained quantitatively. They were readily soluble in various solvents such as chloroform, m-cresol, and pyridine. Coloreless, transparent, and flexible films could be cast from the chloroform solutions of the polymers. The polyarylates had glass transition temperatures between 210 and 320°C, and did not lose weight below 350°C, with 10% weight loss being recorded at 395–450°C in air.     

Metal-containing initiator systems. VI. Polymerization of butadiene with metal–organic halide systems

The polymerization of butadiene with binary initiator systems consisting of some activated metals and organic halides was investigated at 60°C. From the results obtained, it was found that systems of reduced nickel and methyltrichlorosilane or dimethyldichlorosilane were most effective for the polymerization, and those of reduced nickel and carbon tetrachloride, benzyl chloride, benzyl bromide and benzoyl chloride, showed moderate activity. The polybutadienes obtained with these systems were observed to contain product of more than 80% cis-1,4 microstructure. From detailed studies on the reduced nickel–methyltrichlorosilane system, these polymerization mechanisms were explained by the hypothesis that the initiation occurred through the reaction of the dissociated transition state complex with the monomer or with a trace amount of water, and then the propagation proceeded via a coordinated cationic mechanism. These systems did not show a good activity for the cis-1,4 polymerization of isoprene.