Kinetics and mechanism of the thermal decomposition of potassium persulphate ions in aqueous solutions at 50°C in the presence of nitrogen gas and methacrylonitrile monomer

The initial rate of persulphate (I) decomposition at 50°C in the presence of nitrogen and methacrylonitrile (MAN) in an unbuffered aqueous solution (pH 4–7) may be written as: in the concentration ranges of persulphate (I) (0.25–2.50) × 10^?2 (m/dm³) and of (MAN) 0.18–0.36 (m/dm³). During the reaction, a white substance (polymethacrylonitrile) separates out in the colloidal state or in the precipitate form from the medium depending on the ionic strength of the medium. The pH of the medium was found to decrease rapidly and continuously with time in the absence of methacrylonitrile, but it decreased slowly and continuously with time in the presence of the monomer, MAN. If an additional quantity of MAN is injected late in a run, the rate of persulphate decomposition is further accelerated in a given run. However, the rate of persulphate decomposition is found to decrease continuously in the presence of MAN with time, i.e., as the monomer is converted to polymer. It is suggested that MAN accelerates the decomposition of persulphate ions, due to the following reactions in the aqueous phase: and where (M_j^˙)w is a-water soluble oligomeric or polymeric (j = 1–10) free radical. The estimated values of k₅ and k₁₀ are 1.05 × 10^?5 and 1.14 × 10³ (in dm³/m/s), respectively.     

A one-point intrinsic viscosity method for polyethylene and polypropylene

A statistical analysis of dilute solution viscosity data for a wide range of polyethylene and polypropylene samples in Decalin at 135°C has shown that the Martin equation fits the experimental data better than the Huggins equation at higher values of [η]c. A grand average k of 0.139 is applicable to both polymers. Based upon this, tables have been calculated permitting the ready determination of [η] from a single relative viscosity measurement at a known concentration. The Martin equation has been put into a universal form, permitting [η] to be calculated from a measured η_sp if k and c are known. Graphs relating η_sp to [η] are included for use of the Martin equation over wide ranges of both k and c. It was found that the Solomon and Ciuta equation fits the experimental polyethylene and polypropylene data, and the reasons for this are discussed.     

Evaluation of the termination mode in the radical polymerization of 2,2,2‐trifluoroethyl α‐fluoroacrylate

The mode of termination of 2,2,2‐trifluoroethyl α‐fluoroacrylate (FATRIFE) in radical polymerization was studied, and only termination by recombination occurred, which led to telechelic macromolecular structures. The radical polymerization in acetonitrile was carried out to synthesize oligomers with a low number average degree of polymerization ( )_cum (about 20), using tert‐butylcyclohexyl peroxydicarbonate (TBCPC) as initiator at 75 °C. The initial [TBCPC]₀/[FATRIFE]₀ molar ratio was monitored to evaluate its influence on the ( )_cum of α‐fluoroacrylic oligomers. The ¹H NMR analysis of the polymers showed that the ( )_cum values obtained were higher than 40, in spite of a high C₀ value. To explain these results, the mode of termination was evaluated using the following kinetic law: . The development of kinetic relationships allowed us to calculate the ratio k_prt/k_i·k_p as about 17–30 mol s l^?1, and to confirm that primary radical termination (PRT) was in competition with bimolecular macromolecular termination (BMT). © 2002 Society of Chemical Industry     

Catalytic oxidation of benzene to maleic anhydride in a continuous stirred tank reactor

The kinetics of the vapor phase oxidation of benzene has been studied over an industrial catalyst in a continuous stirred tank reactor in the temperature range from 280 to 430°C and at atmospheric pressure. The products obtained are maleic anhydride, carbon oxides and water. The rate of the overall reaction (disappearance of benzene) is represented by the following expression based upon a steady state adsorption model The rate of formation of maleic anhydride is correlated by the equation which allows for a homogeneous depletion of maleic anhydride. The rate constants k_B, k_O, k_2(g) were found to follow Arrhenius behavior.      

The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

The fracture behavior of a piperidine/bisphenol A diglycidyl ether (A) resin has been determined in bulk and as an adhesive using the linear elastic fracture methods developed by Mostovoy¹. The effect of adding carboxy-terminated butadiene–acrylonitrile (CTBN) elastomer to resin A was investigated. The opening-mode fracture energy () of resin A was 120 to 150 J/m², and largely attributable to plastic deformation. Fractographic evidence was obtained for plastic flow at the crack tip during crack initiation. Propagation was unstable due to the rate dependence of the plasticity. There were no significant differences in the bulk and adhesive fracture behavior. Addition of 5–15% CTBN to resin A produced minute elastomer particles which increased to ～4000J/m² (at 15%). Further CTBN addition resulted in an elastomer–epoxy blend and a decrease in fracture energy. Fractography again indicated that crack initiation involved plastic deformation but that the elastomer had greatly increased the volume in which the deformation occurred. The adhesive fracture of the elastomer–epoxy was found to be strongly dependent on the crack-tip deformation zone size (r_yc) in that was a maximum when bond thickness was equal to 2 r_yc. At bond thicknesses less than 2 r_yc, there was a restraint on the development of the plastic zone resulting in lower values.     

Specific hydroxide ion catalysis of the endwise depolymerization of cellulose

The endwise depolymerization (unzipping reaction) of hydrolyzed cotton cellulose (x = 200) in water under a nitrogen atmosphere was followed at 98°C at several alkalinities in the pH range of 8.0–10.5. The observed apparent first-order rate constant k₁ was invariable at low alkalinity (k₁ = k₀), while above pH 8.5, k₁ increased with pH. The data conform with the expression where [SH] denotes substrate concentration. The specific hydroxide ion catalysis is considered to involve ionization of the anomeric hydroxyl group at the reducing chain end that leads to elimination of the glucosidic oxygen atom bearing the polymer chain from C4 of the terminal D-glucose residue. In this initiation process, the glucosidic oxygen is eliminated as an anion so that rapid propagation of the unzipping along the polymer chain may occur. Thus, entire chains will depolymerize. The kinetic chain length v is defined as the ratio k₁:k_t, where k_t is the pseudofirst-order rate constant for chain terminations, and a value of v ～ 100 D-glucose residues was found at all the alkalinities investigated.     

Kinetics of o-Xylene oxidation over sintered vanadium pentoxide in a spinning catalyst basket reactor

Kinetics of vapor phase oxidation of o-xylene has been studied over sintered and compacted vanadium pentoxide in a continuous stirred tank catalytic reactor in the temperature range of 450–517°C at atmospheric pressure. The major product obtained is phthalic anhydride. The other products are maleic anhydride and carbon dioxide. The reaction rate data are well represented (with average absolute deviation less than 6%) by the following expression derived by applying the steady-state oxidation-reduction model of Mars and van Krevelen to a parallel reaction scheme and assuming first order with respect to both o-xylene and oxygen: Significantly, the activation energies for all three postulated reactions with rate constants k₁, k₂, and k₃ turn out to be identical having a value of 14.8 kcal/mole, which may be taken to imply that there is only one rate-influencing reaction step for all the products and not three as assumed in deriving this equation.     

Bestimmung der Temperaturabhängigkeit der Inhibierungsperiode und der Radikalbildungskonstante von AIBN bei der Polymerisation von Methylmethacrylat

The dependence on temperature of the specific reaction rate quotient of the inhibition period has been determined as by dilatometric measurement of the inhibition period caused by dissolved oxygen, and by the initial rate of the methyl methacrylata polymerisation, using azoisobutyronitrile (AIBN) aa initiator. In the examined concentration range the initial polymerisation rate and the reciprocal of the inhibition period are strictly proportional to the root of the initiator concentration, the yield of free initiator radicals is thus independent of the initiator concentration. It is, therefore, possible to determine the radical forming constant k_R of AIBN represented by the equation The fraction of the radicals recombining in the cage can be determined from k_R and the decomposition constant k_z; at 60°C for example it amounts to 24%. This value corresponds very well to the value obtained by the gas-chromatographic investigation of the recombination products by VOGT and DULOG.     

Die Wahl des optimalen Verfahrens für die Bestimmung des Primärradikalabbruchs aus Geschwindigkeitsdaten

The various plots for estimating the ratio of rate constants characteristic for primary radical termination, k₅/k₁k₂, have been examined systematically. Apart from the special case d ≡ k₃k₆/k₅² = 1 there is no exact linear relationship between the general quantity \documentclass{article}\pagestyle{empty}\begin{document}${\rm Y \equiv (\sqrt {c_S} c_{M}/v_{Br})^{n}}$\end{document} and the general variable \documentclass{article}\pagestyle{empty}\begin{document}${\rm X \equiv (\sqrt {c_S} /c_M)^{s} (v_{Br}/c_M^{2} )^{1 - s}}$\end{document}. In any case, however, Y can he expressed as a power series of X. Therefore the best way to obtain the most favourable linear representation of Y as a function of X is to choose s and n according to the condition that the coefficient of the term quadratic in X has to disappear (n ? 2 s + d = 0) and the coefficient of the X³-term also equals 0 or is at least close to 0. Under these conditions even those data can be represented in an almost perfect linear form which show variations of the quantity \documentclass{article}\pagestyle{empty}\begin{document}$({\rm \sqrt{c_{s}}c_{M}/v_{Br})}$\end{document} by a factor of \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt{2}$\end{document} or more for different initiator concentrations c_s. If additionally allowance is made for the consumption of monomer by the initiation process the desired ratio of rate constants, k_s/k₁k₂, is obtained from the plot of Y vs. X according to the equation The application of this method is illustrated using an example from literature.     

Thermal conductivity of simple gases at normal pressures

Thermal conductivity measurements available in the literature for simple gases at normal pressures (approximately 1 atmosphere) were used to obtain the product k^*λ, where the parameter, λ =M^1/2T_c^1/6/P_c^2/3. Separate relationships between k^*λ and T_R resulted for monatomic, diatomic and triatomic gases. The relationships for monatomic gases can be expressed as follows For the diatomic and triatomic gases, linear relationships resulted, when at the same reduced temperatures, their k^*λ values were plotted against (k^*λ)_m on log-log coordinates. These relationships can be expressed in equation form as follows and Thermal conductivities calculated with these relationships have been compared with experimental values and produce an average deviation of 2.8% for the monatomic gases (219 points), 4.3% for the diatomic gases (282 points) and 4.6% for the triatomic gases (242 points). In this treatment, helium and hydrogen do not follow the general pattern and consequently these substances have been treated separately.     

Densities of hydrocarbons in their saturated vapor and liquid states

The Sum and differences of the saturated vapor and liquid densities of 23 hydrocarbons were used to develop the following reduced density relationships for these saturated states The hydrocarbons considered included n-parafins, olefins, diolefins, naphthenes, and aromatics. Constants β, γ, and δ, and exponent n were found to be dependent on,. Equation (a) can reproduce liquid densities with an overall average deviation of 1.1 % over the entire temperature range, while Equation (b) was found to apply only in the interval 0.900 ≤ T_R ≤ 1.00 with an average deviation of 2.2%. For temperatures of T_k < 0.90, the saturated vapor density was found to depend on temperature as follows where k and m were also found to be Z_c dependent. Values calculated using Equation (c), when compared with 81 available experimental densities for 12 hydrocarbons, produced an average deviation of 3.0%.     

Fine structures and fracture processes in plastic-rubber two-phase polymer systems IV. Temperature and strain rate dependences of tensile properties

Yield stress (σ_Y) and elongation to break (ε_b) were measured over a wide range of temperature under three different strain rates (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}) for a series of polyvinylchloride-rubber blends, ABS polymer and high-impact polystyrene. It was found that a temperature-strain rate reduction was possible for σ_Y and the composite curve obtained by the superposition was expressed by the following relation: where K₁ and K₂ are the material constants, and A_T is the shift factor. As for ε_b, a new maximum was found at around room temperature in addition to the known maximum at around the glass transition temperature of the matrix phase. The results are discussed in terms of the craze theory for rubber toughening of plastics.     

Sodium metabisulphite initiated aqueous polymerisation of methyl methacrylate

Sodium metabisulphite (Na₂S₂O₅) has been found to initiate the aqueous polymerisation of methyl methacrylate (MMA) at 35°C in phosphate buffer solutions of pH 6.85 and a constant ionic strength (μ) of the media in an inert atmosphere of pure nitrogen. The reaction has a well defined induction period which is a function of the concentrations of the initiator, of the monomer and also of temperature. The polymerisation is signalled by the sudden appearance of a haze at the end of the induction period in a given run, and the polymer separates out as a coarse precipitate during the progress of the polymerisation reactions. When the conversion is over 50 per cent complete, the polymerisation media looks like a thick curd if the monomer concentration is relatively high. The rate of polymerisation is found to decrease with conversion or time in a given run, and the initial rate (v_p), obtained by extrapolating the linear yield/time versus time curves to zero time, keeping the conversion below 10 percent, is found as where (I) = initiator concentration in the range, (0.26 to 3.94) × 10^?3 (mol dm^?3), and (M) = monomer concentration in the range 0.019 to 0.141 (mol dm^?3). At high initiator concentrations, the rate of polymerisation is found to decrease. In a given run, the viscosity average molecular weights (M _v) of the polymers is found to increase quickly with a conversion of up to 25 to 30 percent, and then slowly with the further increase in conversion. (M_v) however is found to decrease with the increase of the initiator concentrations at a given conversion but increases with the increase of the monomer concentrations. Hydroquinone inhibits the polymerisation reactions, whereas air is found to increase the induction period, but later enhances the polymerisation rate in the same run. It has been shown that the bisulphite addition reaction of MMA is not important under the experimental conditions, and the polymerisation occurs by the free radical mechanism. The rate constant (k₂) of the reaction, has been estimated from the analytical data as, k₂ = 14.62 × 10^?2 (dm³ mol^?1 s^?1) at 35°C.     

The kinetics of reduction of selenious(IV) ions in hydrochloric acid with sulphur dioxide

The reduction of selenious ions to its elemental state has been found to be a function of selenious ion concentration, solution acidity, gas flow rate and temperature. The rate equation can be written as: where α = ?1/2, β = 1, γ = 0.9, E = ?53 411 kJ kg^?1mol^?1, R = 8314 kJ kg^?1 mol^?1 K^?1 and k₀ = 194. The reaction temperature starts to decrease when the conversion rate reaches a maximum. This observation can be used to determine the end of the reaction.     

Organocatalytic Regioselective Chlorosilylation of Oxirane Derivatives: Mild and Effective Insertion of Bulky Silyl Chloride by Using 4‐Methoxypyridine N‐Oxide

The highly regioselective organocatalytic chlorosilylation of oxirane derivatives using bulky silyl reagents such as (tert‐butyl)diphenylsilyl chloride (TBDPSCl) or triphenylsilyl chloride (Ph₃SiCl) was developed. The reaction was effectively catalyzed with 4‐methoxypyridine N‐oxide in the presence of sodium sulfate (Na₂SO₄). Several silylated halohydrins were obtained with complete regioselectivity and the reaction was applied to the synthesis of carvedilol.

     

A one-point intrinsic viscosity method for hydroxyethylcellulose,hydroxypropylcellulose, and sodium carboxymethylcellulose

Statistical analysis of viscosity measurements on dilute solutions of hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), and sodium carboxymethylcellulose (CMC) in the solvents water, 50/50 (v/v) water/ethanol, and 0.1M NaCl, respectively, demonstrated that the Martin equation, fits experimental data better than the Huggins equation, An average Martin k of 0.191 is applicable to a variety of HEC and HPC samples, including fractionated and unfractionated experimental and commercial preparations covering a wide range of substitution. In the case of a similar variety of CMC samples, an average k of 0.161 is characteristic. Based on these k values and using the Martin equation in the form tables were developed which permit direct reading of [η] values corresponding to single η_rel measurements at concentrations of 0.05, 0.10, 0.20, or 0.50 g/dl. Intrinsic viscosities obtained in this fashion differ from those determined by the usual dilution multipoint technique on the same samples by an average of but 2%, at an estimated time saving of 50% or more. This degree of variation is no greater than that expected in routine measurements on duplicate solutions.     

Synthesis,characterization and kinetics of terpolymerization of acrylonitrile,N-vinyl pyrrolidone and styrene

Synthesis of a series of novel terpolymers, consisting of two electron-donating monomers, viz. N-vinyl pyrrolidone (N-VP) (heterocyclic polar monomer) and styrene (Sty) (non-polar monomer), with one electron-accepting polar monomer, i.e. acrylonitrile (AN), using α,α'-azobisisobutyronitrile as radical initiator and benzene as diluent at 60°C, has been extensively surveyed. Besides the synthesis, an attempt has been made to study the kinetics and various properties of the terpolymers, such as softening temperature and chemical resistance. The system follows non-ideal kinetics and the kinetic equation for the present system can be written as This non-ideality can be explained on the basis of significant initiator-dependent termination through primary radicals and degradative chain transfer to acrylonitrile monomer. The overall energy of activation is 72.4 kJ mol^?1 and k_p²/k_t is 0.26 × 10^?3 litre mol^?1 s^?1. The effects of various additives such as imidazolium-p-chlorophenacylide (ICPY) and ZnCl₂ were also studied. ICPY functions as a chain transfer agent (C^tr = 0.43 × 10^?4), whereas ZnCl₂ accelerates the rate of reaction. IR spectroscopy was used to confirm the structure of the terpolymers.     

A kinetic model of persulfate–bisulfite-initiated acrylonitrile polymerization

The molecular weight distribution has been derived for a homopolymer polymerized in a continuous-feed reactor under homogeneous conditions. The derived equations are then compared with data obtained on polymers of acrylonitrile–co(vinyl acetate) prepared under heterogeneous conditions with the potassium peroxydisulfate–sodium bisulfite–iron redox system. The termination reaction is assumed to be effected completely by recombination of active radicals with no disproportionation. The only transfer reaction considered is the transfer-to-activator reaction The transfer and termination reactions produce polymers with different acid groups as endgroups. Each molecule, on the average, contains one sulfonate group, whereas the concentration of sulfate groups depends upon the extent of the transfer-to-activator reaction. The basic dye acceptance of the polymer depends on the number of acid groups in the polymer and hence on the activator and catalyst concentrations. Analysis of the basic dye acceptance and conversion data at a variety of catalyst and activator concentrations yields the following parameters at 50°C: k_p/k = 1.01 (1./mole sec)^1/2, k_tr/k_p = 0.2063, and k₁ [see eq. (1)] = 50.7 l./mole sec. Owing to the heterogeneous nature of the polymerization, the weight-average molecular weight of the polymer depends only on the activator concentration and the conversion and not directly on the catalyst concentration as predicted.     

Stress-strain behavior of polychloroprene vulcanizates containing polymer-gel particles

The equations of stress-strain of gel-filled polymer under large deformation were derived by using a simple model i.e. a sphere in a cubic matrix. The author finds for no adhesion between the phases: In case of perfect adhesion between the phases: where σ(α) is the stress of a blend at an elongation ratio of α, σ_R(α) the stress of a rubber matrix at α, σ_G(α_G) the stress of a gel component at α_G, σ_R (α_R) the stress of a rubber matrix at α_R, ? the volume fraction of gel. The validity of Eq 1 was shown for the polychloroprene vulcanizates containing polystyrene-gel which exhibits no adhesion with the polychloroprene matrix. This result shows the value of the model proposed here. The tensile strength of polychloroprene vulcanizates filled with polychloroprene-gel at break is discussed by the use of Eqs 2–4.     

Kinetische Untersuchungen der Reaktionen von Methylradikalen mit Allen

Kinetic Studies of the Reactions of Methyl Radicals with Allene The addition of methyl radicals to allene has been studied in the temperature range 573…595 K. The methyl radicals were produced by thermal decomposition of azomethane. It has been shown that the additions take place with a very high selectivity at the terminal carbon atoms in allene. The rate constant k₂ of the addition can be expressed by the following Arrhenius equation: