IR study of chlorination of alumina employing mixtures of gaseous chlorine and carbon monoxide

The chlorination of an alumina with BET surface area of 100 m²/g has been studied in situ by transmission IR measurements at about 670 K. The chlorinating gases consisting of Cl₂ and CO were employed individually and in equimolar proportion. The IR results do not reveal the presence of a phosgene surface species which could support the only mechanism proposed so far to explain the chlorination. A detailed alternative reaction mechanism is suggested for the high temperature chlorination reaction, taking into account the IR results, together with the known electron donor-acceptor properties of the activated alumina and the reaction gases: Cl₂ molecules accept electrons from oxide ions with a lower coordination number on the alumina surface, leading to the formation of Cl^?and O_ad. While Cl^? yields AlCl₃, O_ad reacts further with CO producing CO₂.     

Some aspects of the chlorination of bauxite

Removal of iron and titanium impurities in bauxite by selective chlorination has been obtained by controlling the addition doses of coke and restricting the temperatures to below 323 K. The chlorination of iron and titanium free bauxite has been studied as regards the effect of coke addition, Cl₂ flow rates and partial pressures and temperatures. The rate equation 1-(1 - R)^1/3 = kt has been shown to fit the experimental data. It is concluded that the diatomic Cl₂ molecule does not dissociate to atomic Cl during chlorination.     

Synthesis of pentavalent imidovanadium complexes and their catalyses for the polymerization of ethylene and propylene

Imidovanadium complexes with cyclopentadienyl (Cp) ligands—(Cp)V(?NC₆H₄Me‐4)Cl₂ (1), (Cp)V(?N^tBu)Cl₂ (2), and (^tBuCp)V(?N^tBu)Cl₂ (3; ^tBuCp = tert‐butylcyclopentadienyl)—were synthesized through the reaction of imidovanadium trichloride with (trimethylsilyl)cyclopentadiene derivatives. The molecular structure of 3 was determined by X‐ray crystallography. The monocyclopentadienyl complex 1 exhibited moderate activity in combination with methylaluminoxane [MAO; 10.3 kg of polyethylene (mol of V)^?1 h^?1 atm^?1], whereas similar complexes with bulky ^tBu groups, 2 and 3, were less active. (2‐Methyl‐8‐quinolinolato)imidovanadium complexes, V(?NR)(O ?N)Cl₂ (R = C₆H₃ⁱPr₂‐2,6 (4) or n‐hexyl (5), O ?N = 2‐methyl‐8‐quinolinolato), were obtained from the reaction of imidovanadium trichloride with 2‐methyl‐8‐quinolinol. Upon activation with modified MAO, complex 4 showed moderate activities for the polymerization of ethylene at room temperature. The complex 5/MAO system also exhibited moderate activity at 0°C. The polyethylenes obtained by these complexes had considerably high melting points, which indicated the formation of linear polyethylene. Moreover, the 5/dried MAO system showed propylene polymerization activities and produced polymers with considerably high molecular weights and narrow molecular weight distributions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1008–1015, 2005     

Kinetics and parameters affecting degradation of purified natural rubber

Purified natural rubber (PNR) was obtained by treatment of high ammonia NR latex with proteinase enzyme for 24 h, followed by double centrifugation. The PNR was later redispersed into latex form with 0.5% (w/v) sodium dodecyl sulfate. The degradation of PNR was performed in latex form by using a combination of the radical initiator potassium persulfate (K₂S₂O₈) and propanal. The intrinsic viscosity [η] of the degraded rubber or liquid rubber that was obtained depended on various parameters such as the initiator concentration, amount of propanal, dry rubber content, reaction time, and temperature. It was found that the [η] of the rubber can be reduced from 4.31 to 0.19 for the PNR after a 25‐h reaction time using 5% dry rubber content PNR latex, 1 part per hundred rubber (phr) of K₂S₂O₈, and 32 phr of propanal at 80°C. The kinetics of the degradation reaction were investigated. The highest rate constant found was 11.33 × 10^?2 s^?1. The activation energy of the degradation reaction was 76.56 kJ mol^?1. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3546–3555, 2003     

Evidence of ionic components in vulcanization mixtures by means of electric current measurements: Investigations with natural rubber/sulfur/zinc bis(dimethyldithiocarbamate) and comparison mixtures

Continuous low‐level current (CLLC) measurements for detecting ionic species in the course of vulcanization reactions were applied to investigate the vulcanization of a mixture of natural rubber (NR), sulfur (S), and zinc bis(dimethyldithiocarbamate) (ZnDMTC). A dc voltage was applied to the reaction mixture in a special vulcanization mold and the current (e.g., in the range of 10⁻⁹ A) was measured. Temperature‐dependent current maxima were found after reaction times t_max. The simplest explanation is that transitory ionic species occur during vulcanization. An activation energy (E_a ) = 116.4 kJ/mol, similar to that obtained in previous chemical investigations, was determined from the decrease of t_max with increasing temperature. The maxima corresponded to reaction times where a strong increase of polymer crosslinking was observed, as measured using vulcametry. For comparison, dc measurements were carried out with the corresponding mixture without elemental sulfur (NR/ZnDMTC) and mixtures containing zinc stearate (ZnST) instead of zinc bis(dimethyldithiocarbamate) (NR/S/ZnST and NR/ZnST). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2206–2212, 2000     

Compatibility of liquid deproteinized natural rubber having epoxy group (LEDPNR)/poly (L‐lactide) blend

Reaction after mixing of liquid epoxidized natural rubber/poly(L ‐lactide) blend was performed to enhance the compatibility of the blend. The liquid epoxidized natural rubber was prepared by epoxidation of deproteinized natural rubber with peracetic acid in latex stage followed by depolymerization with peroxide and propanal. The resulting liquid deproteinized natural rubber having epoxy group (LEDPNR) was mixed with poly(L ‐lactide) (PLLA) to investigate the compatibility of the blend through differential scanning calorimetry, optical light microscopy, and NMR spectroscopy. After heating the blend at 473 K for 20 min, glass transition temperature (T_g) of LEDPNR in LEDPNR/PLLA blend increased from 251 to 259 K, while T_g and melting temperature (T_m) of PLLA decreased from 337 to 332 K and 450 to 445 K, respectively, suggesting that the compatibility of LEDPNR/ PLLA blend was enhanced by a reaction between the epoxy group of LEDPNR and the ester group of PLLA. The reaction was proved by high‐resolution solid‐state ¹³C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermoplastic elastomeric hydrogenated styrene-butadiene elastomer: Optimization of reaction conditions,thermodynamics, and kinetics

Thermoplastic elastomeric hydrogenated styrene—butadiene (HSBR) elastomer was prepared by diimide reduction of styrene-butadiene rubber in the latex stage. The products were characterized by infrared, ¹H-NMR, ¹³C-NMR spectroscopy, and differential scanning calorimetry (DSC). The standard free energy change, ΔG⁰ at 298°K is −44.7 × 10⁴ kJ/mol, indicating that the formation of HSBR is thermodynamically feasible. The value of heat change of the reaction at constant volume, ΔU_T is −41.6 × 10⁴ kJ/mol. The effect of different reaction parameters on the level of hydrogenation, calculated from nuclear magnetic resonance spectroscopy, was also investigated. The degree of hydrogenation increases with the increase in reaction time, temperature, the concentration of reactants and catalyst. A maximum of 94% hydrogenation was obtained under the following conditions: time, 4 h; temperature, 45 ± 2°C; pH, 9.36; cupric sulphate (CuSO₄ · 5H₂O) catalyst concentration, 0.0064 mmol; hydrazine concentration, 0.20 mol; and hydrogen peroxide concentration, 0.26 mol. The diimide reduction of SBR is first-order with respect to olefinic substrate, and the apparent activation energy is 9.5 kJ/mol. The glass transition temperature increases with the increase in saturation level due to development of crystalline segments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1151–1162, 1997     

Hydrogenation of synthetic cis‐1,4‐polyisoprene and natural rubber catalyzed by [Ir(COD)py(PCy3)]PF6

In the presence of chlorinated solvents, the catalytic complex [Ir(COD)py(PCy₃)]PF₆ (where COD is 1,5‐cyclooctadiene and py is pyridine) was an active catalyst for the hydrogenation of synthetic cis‐1,4‐polyisoprene and natural rubber. Detailed kinetic and mechanistic studies for homogeneous hydrogenation were carried out through the monitoring of the amount of hydrogen consumed during the reaction. The final degree of olefin conversion, measured with a computer‐controlled gas‐uptake apparatus, was confirmed by Fourier transform infrared spectroscopy and ¹H‐NMR spectroscopy. Synthetic cis‐1,4‐polyisoprene was used as a model polymer for natural rubber without impurities to study the influence of the catalyst loading, polymer concentration, hydrogen pressure, and reaction temperature with a statistical design framework. The kinetic results for the hydrogenation of both synthetic cis‐1,4‐polyisoprene and natural rubber indicated that the hydrogenation rate exhibited a first‐order dependence on the catalyst concentration and hydrogen pressure. Because of impurities inside the natural rubber, the hydrogenation of natural rubber showed an inverse behavior dependence on the rubber concentration, whereas the hydrogenation rate of synthetic rubber, that is, cis‐1,4‐polyisoprene, remained constant when the rubber concentration increased. The hydrogenation rate was also dependent on the reaction temperature. The apparent activation energies for the hydrogenation of synthetic cis‐1,4‐polyisoprene and natural rubber were evaluated to be 79.8 and 75.6 kJ/mol, respectively. The mechanistic aspects of these catalytic processes were discussed on the basis of observed kinetic results. The addition of some acids showed an effect on the hydrogenation rate of both rubbers. The thermal properties of hydrogenated rubber samples were determined and indicated that hydrogenation increased the thermal stability of the hydrogenated rubber but did not affect the inherent glass‐transition temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4219–4233, 2006     

Epoxidation of low-molecular-weight Euphorbia lactiflua natural rubber with “in situ” formed performic acid

Summary The epoxidation of low-molecular-weight natural rubber isolated from Euphorbia lactiflua latex was accomplished. The reaction was performed using formic peracid formed in situ from hydrogen peroxide and formic acid. Different temperatures, ratio of H₂O₂ to isoprene units and H₂O₂ to HCOOH were used. The products were characterized by infrared spectroscopy (IR), ¹H and ¹³C nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and elementary analysis. ¹H-NMR was used quantitatively to calculate epoxidation levels. Maximum epoxidation reached was 89.4%. DSC results record a linear relationship between percent epoxidation and Tg.     

Conductive polyaniline/poly(vinylphosphonic acid) blends

In-situ polymerization of aniline in poly(vinylphosphonic acid) (PVPA) resulted in conductive polyaniline/PVPA blends with conductivities in the order of 10⁻² S/cm. The blends were characterized by FTIR and UV-vis spectroscopy. Thermogravimetric analysis showed that the blends have good thermal stability. Received: 17 July 1997/Revised: 16 September 1997/Accepted: 22 September 1997     

Copolymerization of 1-butene and 1-hexene with supported titanium catalyst

With TiCl₄/MgCl₂ (Ti) and Al(i-Bu)₃ (Al) as catalysts, the thermoplastic copolymer of 1-butene(Bt) and 1-hexene(He) was synthesized successfully. The effects of Bt/He, Ti/(He+Bt), Al/Ti, temperature and reaction time on conversion, catalyst efficiency(CE), intrinsic viscosity([η]) and insoluble content were studied. The copolymer was analyzed with Fourier transform-infrared (FTIR) and nuclear magnetic resonance (¹H-NMR). Results showed that the optimal polymerization conditions were: He/Bt = 0.25, temperature 40°C−50°C, Al/Ti = 400−500, Ti/(Bt+He) = 3 × 10⁻⁵ − 4 × 10⁻⁵, time 4 h. Intrinsic viscosity was found to increase with increasing Ti/(Bt+He) and decreasing Al/Ti and polymerization temperature. When the molar content of He, Al/Ti and polymerization temperature increased, the insoluble content in CH₂Cl₂ of copolymers decreased. When Ti/(Bt+He) and reaction time increased, the insoluble content in CH₂Cl₂ of copolymers also increased. The crystallization and stereoregularity of poly(1-butene) decreased with the addition of He. Translated from China Synthetic Rubber Industry, 2006, 29(6): 429–434 [译自: 合成橡胶工业]     

Effects of redox initiator on graft copolymerization of methyl methacrylate onto natural rubber

Effects of cumene hydroperoxide (CHPO)/tetraethylene pentamine (TEPA), tert‐butyl hydroperoxide (TBHPO)/TEPA, and potassium persulfate (K₂S₂O₈)/sodium thiosulfate (Na₂S₂O₃) redox initiator on methyl methacrylate (MMA) grafted natural rubber by emulsion polymerization were investigated. The optimum reaction condition for each redox initiator on the grafting of natural rubber was studied. The grafted poly(methyl methacrylate) (PMMA) stays on the surface of rubber particles. CHPO dissolves very well in the oil phase and TBHPO dissolves moderately in the oil phase, and K₂S₂O₈ /Na₂S₂O₃ initiation is water‐soluble. Each can interact with TEPA in the aqueous phase. CHPO was found to give a higher grafting efficiency. To promote a greater grafting efficiency and yield a lower homopolymer content of PMMA, vinyl neo‐decanoate (VneoD) was added. Percentages of grafting of MMA on natural rubber latex initiated by CHPO/TEPA, TBHPO/TEPA, and K₂S₂O₈/K₂S₂O₃ of 84.4, 74.5, and 61.1, respectively, were in good agreement with percentages of PMMA in the aqueous phase as 7.2, 12.0, and 17.9 by CHPO, TBHPO, and K₂S₂O₈. VneoD produces allylic radicals on polyisoprene chains, favoring the grafting reaction with other vinyl monomers. CHPO/TEPA is thus a better redox system for grafting of MMA monomer on natural rubber latex. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2587–2601, 2006     

Chlorination of irradiated polyethylene single crystals: 2: XES and e.s.c.a. analysis of irradiated-chlorinated PE

Chlorination of irradiated polyethylene single crystals was characterized in this study by the X-ray energy spectroscopy and electron spectroscopy for chemical analysis techniques. Results presented show that PE chlorination was extensive, even in unirradiated PE single crystals at 298 K in the dark. The data obtained indicates that PE chlorination consists of a two-step mechanism: (1) a fast uptake with occurs in the first few minutes of chlorine exposure, constituting approximately 50% of total uptake, followed by (2) a slower, approximately first-order rate of uptake. A first-order rate constant of 5 × 10^?4s^?1 was estimated for all of the irradiation doses and temperatures studied. The similarity in chlorine uptake trends for both unirradiated and irradiated samples at various temperatures suggests that the rate of Cl₂ diffusion is the rate determining step. Although the magnitude of chlorine uptake increased with increasing irradiation dose, the rate of uptake remained constant. Rapid uptake probably occured in the amorphous surface zones, followed by a slower step attributable to Cl₂ diffusion into the crystalline regions and subsequent chlorination there.     

Study of Thermal Degradation Kinetics of Elastomeric Powder (Ground Tire Rubber)

This paper investigates the use of thermogravimetric analysis to study the kinetics of thermal degradation of ground tire rubber (GTR) obtained from reclaimed tires. We analyzed the composition of GTR and determined the content percentage of its components (volatile compounds, rubber, and ash) using thermogravimetric analysis (TGA). T ₁ and T ₂ temperature peaks corresponding to the maximum normalized weight loss rate (NWLR) of the two main rubber components of tires NR (natural rubber) and a BR/SBR (butadiene/styrene-butadiene rubber blend) using the Gaussian deconvolution method has been determined. The influence of GTR particle size and heating rate on reaction rates (dx/dt) and on degradation time during the degradation process has been analyzed.     

Study on hot air aging and thermooxidative degradation of peroxide prevulcanized natural rubber latex film

The air‐aging process at 120°C and the thermooxidative degradation of peroxide prevulcanized natural rubber latex (PPVL) film were studied with FTIR and thermal gravity (TG) and differential thermal gravity (DTG) analysis, respectively. The result of FTIR shows that the ? OH and ? COOH absorption of the rubber molecules at IR spectrum 3600–3200 cm^?1, the ? C?O absorption at 1708 cm^?1, and the ? C? OH absorption of alcohol at 1105 and 1060 cm^?1 increased continuously with extension of the aging time, but the ? CH₃ absorption of saturated hydrocarbon at 2966 and 2868 cm^?1, the ? CH₃ absorption at 1447 and 1378 cm^?1, and the C?C absorption at 835 cm^?1 decreased gradually. The result of TG‐DTG shows that the thermal degradation reaction of PPVL film in air atmosphere is a two‐stage reaction. The reaction order (n) of the first stage of thermooxidation reaction is 1.5; the activation energy of reaction (E) increases linearly with the increment of the heating rate, and the apparent activation energy (E₀) is 191.6 kJ mol^?1. The temperature at 5% weight loss (T_0.05), the temperature at maximum rate of weight loss (T_p), and the temperature at final weight loss (T_f) in the first stage of degradation reaction move toward the high temperature side as the heating rate quickened. The weight loss rate increases significantly with increment of heating rate; the correlation between the weight loss rate (α_p) of DTG peak and the heating rate is not obvious. The weight loss rate in the first stage (α_f1) rises as the heating rate increases. The final weight loss rate in second stage (α_f2) has no reference to heating rate; the weight loss rate of the rubber film is 99.9% at that time. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3196–3200, 2004     

On the stability and in situ epoxidation of natural rubber in latex by performic acid

The aggregative stability of natural rubber (NR) latex stabilized by nonionic, fatty alcohol ethylene oxide condensate surfactant (Verol S-15) was studied in the presence of formic acid. Natural rubber latex having an additional 3–5 phr surfactant is stable at pH 2 when acidified by formic acid and can be successfully subjected to the subsequent in situ epoxidation. Using a large ratio of H₂O₂ to isoprene unit (0.4–4.0 M/M) and large excess of H₂O₂ to HCOOH (3–13 M/M) in reaction, the in situ epoxidation can be performed with reaction mixture having dry rubber content up to 35–37% at room temperature or up to 28% at 50°C. This reaction leads to products of large range of epoxide contents and characterized by absence of side-ring opening groups, proved by IR and ¹H-NMR analysis. By infrared spectroscopy it was demonstrated a good correlation between the absorbances of the residual double bonds and of the epoxide groups versus the epoxide content in the range from 0 to approx. 60 mol % level. The solubility and gel content were studied in various solvents, demonstrating that epoxidation leads to increasing gel content at high epoxide levels and to enhancing sensitivity of the product toward polar solvents. By GPC, it was shown for the soluble fraction that epoxidation was accompanied by reducing the molecular weight and by change of the MWD compared with the original NR.     

Living tandem free radical polymerization of a liquid crystalline monomer

Treatment of 1-β-(4′-acetylphenyl)vinyl-3-vinyl-1,1,3,3-tetramethyldisiloxane (I) (an AB₂ monomer) with dihydridocarbonyltris(triphenylphosphine)ruthenium (Ru) leads to a hyperbranched material, poly[1-β-(4′-acetylphenyl)vinyl-3-vinyl-1,1,3,3-tetramethyldisiloxane] (II). I has been prepared by a Pd catalyzed Heck reaction between 4-bromo-acetophenone and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane. The structure of the soluble hyperbranched material (II) has been determined by ¹H, ¹³C and ²⁹Si NMR, as well as by IR and UV spectroscopy. It has also been characterized by GPC, TGA, DSC and elemental analysis. Polymerization occurs by Ru catalyzed addition of the aromatic C−H bonds which are ortho to the activating acetyl group of I across the C−C double bond of the terminal Si-vinyl group in an anti-Markovnikov manner. Received: 8 September 1997/Revised version: 19 October 1997/Accepted: 20 November 1997     

Chlorine reactivity and transformation of effluent dissolved organic fractions during chlorination

The trihalomethane formation potential (THMFP) and structural characteristics of dissolved organic matter (DOM) in the secondary effluent from the Wenchang Wastewater Treatment Plant (Harbin, China) were studied and the alterations in structural and chemical compositions of the DOM during chlorination were evaluated. Using XAD-8 and XAD-4 resins, DOM was fractionated into 5 fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). Results showed that HPO-A and HPI dominated in the secondary effluent, collectively accounting for more than 66% of the DOM as dissolved organic carbon, and 70-84% of the THMFP of DOM was converted from the reaction of chlorine with HPO-A and HPI. Fourier-transform infrared (FT-IR) analysis illustrated that the functional groups involved in the chlorination reaction were aromatic C=C, C-O, C=O, C-Cl and amide functional groups. Proton nuclear magnetic resonance (¹H NMR) analysis indicated that HPO-A, HPO-N, TPI-A and TPI-N had significantly decreased aromatic protons (H_Ar) after chlorination. Although HPO-A, HPO-N, TPI-A and TPI-N exhibited different fluorescence changes during chlorination, the wavelength that corresponded to the position of the normalized emission band at its half-intensity (λ_0.5) for the four fractions decreased as a result of chlorination.     

Gas-phase chlorination of aromatics over FAU- and EMT-type zeolites

Three FAU-structure type zeolites (EMC-1, USY and USY without EFAl) with different Si/Al molar ratio and their pure hexagonal analogue, the EMC-2 zeolite (EMT-structure type) were prepared and thoroughly characterized. Their catalytic properties were examined in the non-conventional gas–solid reaction requiring a strong acidity. A deeper focus was paid to the difference in activity/selectivity of these zeolites toward the continuous chlorination of aromatics (nitrobenzene and toluene) using trichloroisocyanuric acid (TCCA, C₃N₃O₃Cl₃) as chlorination agent.     

Thermal behavior of natural rubber and chlorinated rubber blends

A solid-state chemical reaction occurs when a solvent cast film of a blend of masticated natural rubber and chlorinated natural rubber is heated in the presence of air at 150°C. The thermal behavior of solvent cast films of chlorinated natural rubber, masticated natural rubber, and a 1 : 1 w/w blend (2% w/v in xylene) of these two polymers has been studied using differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, and nuclear magnetic spectroscopy. The results suggest that carbonyl groups are incorporated into the blend on heating and that the vinyl functionality of the isoprene units is modified during this apparent oxidation. Heating for 2 h at 150°C results in a material that no longer contains the rubber-like cis-1,4-polyisoprene units. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1379–1384, 1997