Selectivity of the OsHCl(CO)(O2)(PCy3)2 catalyzed hydrogenation of nitrile–butadiene rubber

A new homogeneous catalyst precursor has been discovered for the hydrogenation of carbon–carbon unsaturation resident within acrylonitrile–butadiene copolymers. The hydrido‐phosphine complex OsHCl(CO)(O₂)(PCy₃)₂ (1) selectively and quantitatively saturates olefin, leaving the copolymer's nitrile functionality intact. However, the process suffers from an undesirable crosslinking reaction that is not demonstrated by the established rhodium technology. The extent of this crosslinking is dependent on the process conditions and can be minimized by operating with a low catalyst concentration and high H₂ pressure. Kinetic studies have identified a previously unknown unexpected influence of olefin on the polymer crosslinking process. In light of this new information, the prevailing mechanism for this class of reactions has been reconsidered. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1618–1626, 2001     

Hydrogenation of natural rubber in the presence of OsHCL(CO)(O2)(PCY3)2: Kinetics and mechanism

The homogeneous catalyst precursor, OsHCl(CO)(O₂)(PCy₃)₂, was utilized for the hydrogenation of natural rubber to convert the unsaturated structure to a saturated form, providing an alternating ethylene‐propylene copolymer. A detailed kinetic investigation was carried out by monitoring the amount of hydrogen consumption during the reaction using a gas‐uptake apparatus. ¹H NMR spectroscopy was used to determine the final olefin conversion to the hydrogenated product. Kinetic data, collected according to a statistical design framework, defined the influence of catalyst and polymer concentration, hydrogen pressure, and reaction temperature on the catalytic activity. The kinetic results indicated that the hydrogenation rate exhibited a first‐ shifted to zero‐order dependence on hydrogen at lower hydrogen pressure, which then decreased toward an inverse behavior at pressures higher than 41.4 bar. The hydrogenation was also observed to be first‐order with respect to catalyst concentration, and an apparent inverse dependence on rubber concentration was observed due to the impurities in the rubber. The hydrogenation rate was dependent on reaction temperature, and the apparent activation energy over the temperature range of 125–145°C was found to be 122.76 kJ/mol. Mechanistic aspects of the hydrogenation of natural rubber in the presence of OsHCl(CO)(O₂)(PCy₃)₂ were proposed on the basis of the observed kinetic results. The addition of some acids and certain nitrogen containing materials showed an effect on the hydrogenation rate. The thermal properties of hydrogenated natural rubber indicated that the thermal stability increased with increasing % hydrogenation of the rubber. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4499–4514, 2006     

Hydrogenation of cis‐1,4‐poly(isoprene) catalyzed by OsHCl(CO)(O2)(PCy3)2

The quantitative hydrogenation of cis‐1,4‐poly(isoprene) (CPIP) provides an easy entry to the alternating copolymer of ethylene–propylene, which is difficult to prepare by conventional polymerization. The homogeneous hydrogenation of CPIP, in the presence of OsHCl(CO)(O₂)(PCy₃)₂ as catalyst, has been studied by monitoring the amount of hydrogen consumed during the reaction. The final degree of olefin conversion measured by computer‐controlled gas uptake apparatus was confirmed by infrared spectroscopy and ¹H nuclear magnetic resonance analysis. Kinetic experiments for CPIP hydrogenation in toluene solvent indicate that the hydrogenation rate is first order with respect to catalyst and carbon–carbon double bond concentration. A second‐order dependence on hydrogen concentration for low values and a zero‐order dependence for higher values of the hydrogen concentration was observed. The apparent activation energy for the hydrogenation of CPIP over the temperature range of 115–140°C was 109.3 kJ/mole. Mechanistic aspects of this catalytic process are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 142–152, 2003     

Hydrogenation of cis‐1,4‐polyisoprene catalyzed by Ru(CHCH(Ph))Cl(CO)(PCy3)2

Hydrogenation is a useful method which has been used to improve oxidative and thermal degradation resistance of diene‐based polymers. The quantitative hydrogenation of cis‐1,4‐polyisoprene which leads to an alternating ethylene–propylene copolymer was studied in the present investigation. To examine the influence of key factors on the reaction, such as catalyst concentration, polymer concentration, hydrogen pressure, and temperature, a detailed study of the hydrogenation of cis‐1,4‐polyisoprene catalyzed by the Ru complex, Ru(CH?CH(Ph))Cl(CO)(PCy₃)₂ was carried out by monitoring the amount of hydrogen consumed. Infrared and ¹H‐NMR spectroscopic measurements confirmed the final degree of hydrogenation. The hydrogenation of cis‐1,4‐polyisoprene followed pseudo‐first‐order kinetics in double‐bond concentration up to high conversions of double bond, under all sets of conditions studied. The kinetic results suggested a first‐order behavior with respect to total catalyst concentration as well as with respect to hydrogen pressure. The apparent activation energy for the hydrogenation process, obtained from an Arrhenius plot, was 51.1 kJ mol^?1 over the temperature range of 130 to 180°C. Mechanistic aspects of the catalytic process are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3259–3273, 2004     

Hydrogenation of epoxidized natural rubber in the presence of palladium acetate catalyst

Expoxidized natural rubber has been selectively hydrogenated in the presence of a homogeneous palladium acetate catalyst. The hydrogenated product has been characterized by infra-red and nuclear magnetic resonance spectroscopies. No change is noted in the epoxy content of the polymer after the reaction. The catalyst is highly selective in reducing carbon-carbon double bonds in the presence of epoxy groups. Natural rubber has also been hydrogenated for a comparative study. The rate constant of hydrogenation is decreased with increase in epoxy content of the polymer.     

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     

Degradation and life prediction of a natural rubber engine mount compound

To assess and predict the functional life of a natural rubber engine mount compound, the mechanical property changes were determined under accelerated aging conditions. The rubber was aged at temperatures ranging from 70 to 110°C for times ranging from 1 h to 5 weeks. Tensile and fatigue measurements were used to characterize the aging trends and mechanisms of the engine mount compound. With the time–temperature superposition approach, the activation energy was found to be about 98 kJ/mol for the elongation at break, 93 kJ/mol for the tensile strength, and 60 kJ/mol for the fatigue life. The tensile strength after aging for 13 weeks at 50°C was predicted to be 18.73 MPa, which was very close to the experimental value of 19.04 ± 2.25 MPa. With a 50% reduction in the tensile strength used as the failure criterion, it was predicted that the tensile strength of the engine mount compound would take 80 days to decrease by 50% at 70°C. At 23°C, it would last approximately 140 times (31 years) its lifetime at 70°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Semi-rigid foams of calcium silicate (CaSiO3) embedded in natural rubber latex

Semi-rigid foams were prepared by NR latex with 0, 2, 5, 10, 20 and 30?phr CaSiO₃ added in a sulphur-curing system. The main composition of eggshell is made of 96.23%wt of CaCO₃ and 3.77%wt of other oxide compounds. The CaSiO₃ induced a spontaneous polarisation and reinforced the NR matrix due to ionic charge contents of Ca²⁺, Si⁴⁺ and O^2? in its structure. Furthermore, the CaSiO₃ was found to enhance the mechanical, thermal and physical properties of the composite foams. The suitable condition to prepare the semi-rigid composite foams was by adding 30?phr CaSiO₃ in the NR latex with the sulphur-curing system. The obtained bulk density, the relative composite foam density, the compressive strength, the contact angle with water, and acetone at the water to acetone ratio of 1:1 were found to be 1.2230?g?cm^?3, 0.3611, 588.10?kPa, 103.3°, 26.5° and 85.3°, respectively.     

Grafting of poly(vinyl alcohol) on natural rubber latex particles

Poly(vinyl alcohol) (PVA) was grafted on natural rubber (NR) latex particles (NR‐g‐PVA) using potassium persulfate to generate active radicals on both NR particle surface as well as PVA molecules. ¹H‐ and ¹³C‐nuclear magnetic resonance spectroscopy suggested a possibly chemical attachment of PVA on the NR. The amount of graft‐PVA expressed in term of grafting percentage (%G) increased almost linearly with the amount of PVA adding to the NR latex. Measuring by dynamic light scattering, the particle size of NR‐g‐PVA particles was larger than the size of unmodified NR, also it increased with the molecular weight and %G of PVA. Transmission electron microscopy images of the NR‐g‐PVA latex particles revealed that the size of PVA‐grafted NR particle was enlarged by a layer of graft‐PVA surrounding the NR particle. Given by the graft‐PVA layer surrounding NR particles, the NR‐g‐PVA latex particles possessed better colloidal stability as lowering pH compared with the unmodified NR latex. Comparing with unmodified NR particles, the electrophoretic mobility of NR‐g‐PVA particles was lower due to the presence of graft‐PVA that shifted the shear plane further away from the surface of the particles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of Fe-Mn/K/Al2O3 Fischer-Tropsch Catalyst and Its Catalytic Kinetics for the Hydrogenation of Carbon Monoxide

A K promoted iron-manganese catalyst was prepared by sol-gel method, and subsequently was tested for hydrogenation of carbon monoxide to light olefins. The kinetic experiments on a well-characterized Fe-Mn/K/Al₂O₃ catalyst were performed in a fixed-bed micro-reactor in a temperature range of 280-380 ℃, pressure range of 0.1-1.2 MPa, H₂/CO feed molar ratio range of 1-2.1 and a space velocity range of 2000-7200 h^-1. Considering the mechanism of the process and Langmuir-Hinshelwood-Hogan-Watson (LHHW) approach, unassisted CO dissociation and H-assisted CO dissociation mechanisms were defined. The best models were obtained using non-linear regression analysis and Levenberg-Marquardt algorithm. Consequently, 4 models were considered as the preferred models based on the carbide mechanism. Finally, a model was proposed as a best model that assumed the following kinetically relevant steps in the iron-Fischer-Tropsch (FT) synthesis: (1) CO dissociation occurred without hydrogen interaction and was not a rate-limiting step; (2) the first hydrogen addition to surface carbon was the rate-determining steps. The activation energy and adsorption enthalpy were calculated 40.0 and -30.2 kJ·mol^-1, respectively.     

热裂解气相色谱法测定天然胶乳中的干胶含量

研究热裂解气相色谱法测定天然胶乳中的干胶含量。试验结果表明,干胶含量与裂解主要产物峰面积呈现良好的线性关系,采用标准曲线法测定天然胶乳中的干胶含量,重复测定的相对标准偏差为0.14%,与国标法的平均相对误差为1.51%,定量分析结果准确,操作简便。     

胶乳法氯化天然橡胶干燥历程中脱氯化氢反应动力学

新型工艺胶乳法氯化天然橡胶(CNR)产品在干燥过程中会有HCl脱出,其脱出量对CNR的制备、性能等有一定的影响。采用电导法可连续测定CNR在干燥历程中脱HCl量及速率,这是研究CNR在低温下热降解行为的有效方法。用改进工艺的"胶乳法"制备出湿的CNR,并在一定温度下通入氮气进行干燥,在此历程中会发生脱氯化氢反应,其反应过程可分为诱导期、恒速期和低速期。文中使用Friedman法分析该过程在恒速期、低速期的反应动力学参数,其脱氯化氢反应分别为0级反应、1级反应,活化能分别为26.65,36.79 kJ/mol。在80℃以下对产品进行加热(或干燥),虽有少量HCl脱出,但并不会对产品质量造成影响。所以干燥温度应以低于80℃为宜。     

Physicochemical and antimicrobial properties of natural rubber latex films in the presence of vegetable oil microemulsions

A series of vegetable oil microemulsions are formulated and incorporated into NR latex to study the potent antimicrobial activity of vegetable oil‐plasticized NR latex film against the adherent bacteria on the treated film. The particle size of latex incorporated with 2.50 phr of oil has attained up to 424 nm after incubated at 35 ± 2 °C for 24 h. The tensile stress of all NR latex films are relatively low, ranged 0.289 to 0.511 MPa. All emulsions are found compatible with NR and the low contact angles (<90°) corresponded to no oil blooming onto the surfaces of NR latex films. The crosslink densities are in good correlation with tensile strengths. The potent antimicrobial properties of the NR latex films are investigated from the viability assessment of the adherent tested Escherichia coli ATCC 25922 (E. coli ATCC 25922) and Staphylococcus aureus ATCC 25923 (S. aureus ATCC 25923). Results shows that NR latex film incorporated with palm kernel oil/soybean oil blend, NR‐E(P/S = 7/3), has significantly killed the adherent S. aureus with 92.5% reduction but showed no significant log reduction in E. coli. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44788.     

Physical properties of natural rubber/organoclay nanocomposites compatibilized with epoxidized natural rubber

Onium ion‐modified montmorillonite (organoclay) was melt compounded with natural rubber (NR) in an internal mixer and cured by using a conventional sulfuric system. Epoxidized natural rubber with 50 mol % epoxidation (ENR 50) was used in 10 parts per hundred rubber (phr) as a compatibilizer. The effect of organoclay with different filler loading up to 10 phr was studied. Cure characteristics were determined by a Monsanto MDR2000 rheometer, whereas the tensile, compression, and tear properties of the nanocomposites were measured according to the related ASTM standards. While the torque maximum and torque minimum increased slightly, both scorch time and cure time reduced with the incorporation of organoclay. The tensile strength, elongation at break, and tear properties went through a maximum (at about 2 phr) as a function of the organoclay content. As expected, the hardness, moduli at 100% (M100) and 300% elongations (M300) increased continuously with increasing organoclay loading. The compression set decreased with incorporation of organoclay. The dispersion of the organoclay in the NR stocks was investigated by X‐ray diffraction and transmission electron microscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1083–1092, 2006     

Polymerization of acrylonitrile using potassium peroxydisulfate as an initiator in the presence of a multisite phase‐transfer catalyst: A kinetic study

In this article, the kinetics and mechanism of the free‐radical polymerization of acrylonitrile (AN) using potassium peroxydisulfate (PDS) as a water‐soluble initiator in the presence of synthesized 1,4‐bis(triethyl methyl ammonium) benzene dichloride (DC‐X) as a phase‐transfer catalyst (PTC) were studied. The polymerization reactions were carried out under inert and unstirred conditions at a constant temperature of 60 ± 1°C in cyclohexane/water biphasic media. The rate of polymerization (R_p) increased with an increase in the concentrations of AN, PTC, and PDS. The order with respect to the monomer, initiator, and PTC was found to be 1.0, 0.5, and 0.5, respectively. R_p was independent of the ionic strength and pH of the medium. However, an increase in the polarity of the solvent slightly increased the R_p value. On the basis of the obtained results, a mechanism is proposed for the polymerization reaction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Compounding of poly(dimethyl siloxane) to reduce tack in natural rubber

Tack in natural rubber latex was reduced by compounding poly(dimethyl siloxane) (PDMS) emulsion in concentrated latex. Sheet and dipped film surfaces were examined with Fourier transform infrared spectroscopy using attenuated total reflection (FTIR–ATR) and by contact angle measurements. Autohesive tack and tensile properties were also determined. For both sheet and dipped film, FTIR–ATR showed that the PDMS concentration was higher at the glass surface than at the air surface. The contact angle of ethylene glycol on the rubber decreased with increasing PDMS content. Autohesive tack for sheet and dipped film also decreased with increasing PDMS amount; however, annealing for 1 week at 70°C in air did cause tack to rise in the sheets. The rubber surface could be made nonadhesive by addition of sufficient PDMS. PDMS caused a decrease in tensile strength for the sheet, especially after annealing; however, PDMS did not cause a substantial decrease in percentage elongation for the sheets, except at relatively high PDMS contents. The tensile strength and percentage elongation for dipped film was not affected by PDMS over the much more limited PDMS concentration range studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 519–526, 2001     

Cyclization reaction in poly(acrylonitrile/itaconic acid) copolymer: An isothermal differential scanning calorimetry kinetic study

The kinetics of the cyclization reaction in the poly(acrylonitrile/itaconic acid) (PAN) copolymer in the temperature range 175–200°C was studied by isothermal differential scanning calorimetry (DSC). The reaction conforms to an n^th‐order autocatalytic model, with an overall order of 2. The kinetic parameters were derived by multiple regression analysis. The activation energy is 110.3 kJ/mol for the acid‐catalyzed reaction and 153.2 kJ/mol for the autocatalytic part. The autocatalysis indicates the catalysis of the nitrile group cyclization by the initially formed pyrimidine groups. The kinetic parameters were used to predict the reaction profile at a given temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 915–920, 2003     

P(MMA-co-AM)两亲性共聚物改性天然乳胶的研究

以甲基丙烯酸甲酯(MMA)和丙烯酰胺(AM)为共聚单体,合成了不同配比的两亲性共聚物P(MMA-co-AM) 乳液,并将制得的P(MMA-co-AM) 共聚物乳液按设定比例与天然乳胶(NRL)共混。通过红外光谱、透射电镜、扫描电镜、力学及耐溶剂性测试,研究了不同共聚单体配比的P(MMA-co-AM)及其添加量对NRL性能的影响。结果表明,两亲性的P(MMA-co-AM)共聚物乳液可有效填补乳胶薄膜表面的孔洞,增强其拉伸强度。利用单体质量比为90:10的P(MMA-co-AM)共聚物乳液,当NRL与共聚物乳液质量比为8:2时,形成的乳胶膜拉伸强度提高了54.19%,而断裂伸长率无显著降低,力学性能最优。同时乳胶膜的耐溶剂性也得到了较大提高。     

Acrylonitrile polymerization initiated by Ce(IV)–cyclohexanone redox system in presence of surfactant

The rate of polymerization of acrylonitrile, using the Ce(IV)–cyclohexanone redox system as an initiator, was studied kinetically, in the presence of 0.015M sodium dodecyl sulfate (SDS), over a temperature range of 25–45°C. The rate of polymerization (R_P), percentage of monomer conversion, and rate of Ce(IV) consumption (?R_Ce) were found to increase with the concentration of SDS, above its CMC. The effect of [AN], [Ce(IV)], [H⁺], and the ionic strength were also studied. The overall activation energies for the polymerization processes were computed to be 23.14 and 17.64 kcal/mol in the absence and presence of 0.015M SDS. A suitable kinetic mechanistic scheme for the free‐radical mechanism was proposed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2066–2072, 2003     

天然胶乳改性研究进展

介绍了天然胶乳的特点,综述了天然胶乳填料改性（纳米粒子改性和非纳米粒子改性）及化学改性（氯化、环化、环氧化、接枝聚合）的研究进展,分析了目前天然胶乳改性存在的问题,并展望了未来的发展趋势。