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Hydroformylation of nitrile rubber and its characterization
Abstract
Selective homogeneous catalytic hydroformylation of nitrile rubber (NBR) has been carried out in presence of trans-chlorocarbonylbis(triphenylphosphine)rhodium(I) [trans-RhCl(CO)(PPh3)2] and hydridocarbonyltris(triphenylphosphine)rhodium(I) [RhH (CO)(PPh3)3] as catalysts. At 363 K, under 5.6 MPa pressure (CO: H2 = 1 : 1) in presence of 0.43 mmol/l catalyst, the amount of hydroformylation is 25% in the case of trans-RhCl (CO)(PPh3)2 and 30% in the case of RhH (CO)(PPh3)3 for NBR with 40 mol-% acrylonitrile. Reaction kinetics suggest that both the reactions are pseudo-first order with respect to olefinic substrate and catalyst concentration. The rate of the reaction is higher in the case of RhH(CO)(PPh3)3. The characterization of the products by IR and NMR spectroscopy shows the formation of internal aldehyde groups from 1,4-units and terminal branched aldehyde groups from 1,2-units of the copolymer. Measurements on intrinsic viscosity [eta] and glass transition temperature (T(g)) suggest a decrease in [eta] and an increase in T(g) with the degree of formyl functionalization. Gel formation has been observed at higher degree of hydroformylation.
Ionic polychloroprene rubber was prepared by reaction of poly-chloroprene rubber with acetyl sulfate at different times (2, 4, 6, 8, 12 and 15 h) and temperatures (25, 35 and 45°C). The product was characterized by IR and NMR spectroscopic methods. The modification increased with increasing reaction time and temperature. The modified rubber had lower intrinsic viscosity in chloroform and higher values of tensile strength, modulus and energy to break.
Some of the most important commercial polymers are diene polymers, e.g., natural rubber (polyisoprene, PI) and styrene butadiene rubber SBR). Their usefulness to scientists and engineers comes not only from their desirable physical properties, but also because they may be used as a base for a variety of chemical modification reactions that are made possible because of the presence of olefinic groups within the polymers.
In the present work, the metallocene-based polyethylene–octene elastomer (POE) was chemically modified by solution grafting of acrylic acid in presence of benzoyl peroxide. The relative proportions of graft and gel formation were optimized through %weight gain, Fourier Transform infrared spectroscopy, elemental analysis and proton nuclear magnetic resonance spectroscopy. The gel formation in the POE matrix was found to be the prime competitor. The effect of grafting at its maximum level on various physicomechanical properties was thoroughly investigated, using X-ray diffraction analysis, differential scanning calorimetry, mechanical, dynamic mechanical, and thermogravimetric analysis. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
In this investigation, solution grafting of acrylic acid (AA) in presence of benzoyl peroxide (BPO) was carried out onto metallocene-based “poly(ethylene-octene) elastomers” (POE) as well as “poly(ethylene-butene) elastomers” (PBE), to impart polarity on the non-polar rubbery matrix and also to study the effects of crystallinity and pendant chain length on the “grafting percentage” and “percent gel yield” at optimized conditions for all the POE and PBE systems. Reaction parameters were optimized on the basis of the relative proportions of graft and gel formations obtained through %weight gain, Fourier Transform infrared spectroscopy and elemental analysis. The effect of grafting at its maximum level on various physico-mechanical properties was also thoroughly investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC), mechanical, dynamic mechanical (DMTA), and thermogravimetric analysis (TGA) and the properties were correlated with the structure of the modified polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5529–5540, 2007
A number of analytical techniques are available for the measurement of the residual unsaturation in HNBR polymers. However, to insure that high-quality HNBR products are produced, it is necessary to use a standard procedure throughout the industry which is quick, accurate, and precise. The two infrared methods discussed in this paper show good agreement with one another, as shown by the respective mean values in Table V. Thus, in the absence of a totally independent and universally accepted standard procedure, this crosscheck between two separate and absolute measurements for the degree of hydrogenation is the best possible support for their precision (1H-NMR spectroscopy for IR method #1 and IR spectroscopy for IR method #2). The two iodometric methods each exhibit significantly poorer precision ( 10 to 100 times) than either of the infrared methods. This is not surprising, since these wet chemical techniques are not discriminatory to any type of unsaturation present in the HNBR nor are they inh...
A detailed study has been made, using infrared and nuclear magnetic resonance techniques, of the interaction of carbon monoxide and hydridocarbonyltris(triphenylphosphine)rhodium(I), RhH(CO)(PPh3)3. The latter, which dissociates in solution to the square complex trans-RhH(CO)PPh3)2, initially forms the dicarbonyl complex RhH(CO)2(PPh3)2; in the presence of CO, this species loses hydrogen to give a yellow dimeric complex (Ph3P)2(CO)Rh(CO)2Rh(CO)(PPh3)2. These reactions are reversed by hydrogen to re-form RhH(CO)(PPh3)2. By sweeping with an inert gas, the yellow dimer loses carbon monoxide to form a red, solvated dimer, (Ph3P)2(S)Rh(CO)2Rh(S)(PPh3)2, which reacts with carbon monoxide to re-form the yellow dimer.
The use of complexes of rhodium of the type trans-RhX(CO)(PR3)2, (X = halogen, R = aryl) as hydroformylation catalysts for alkenes is studied. It is shown that an inhibition period is removed by addition of hydrogen halide acceptors and that the halide complex undergoes hydrogenolysis to form a hydrido-species. The hydrido-species is only one of several complexes in equilibrium but it appears that the principal active catalytic species is RhH(CO)2(PPh3)2. This species is formed by addition of carbon monoxide to the monocarbonyl complex RhH(CO)(PPh3)2. The latter is also formed by dissociation when the stable crystalline complex RhH(CO)(PPh3)3 is dissolved in benzene or other solvents. With RhH(CO)(PPh3)3 as catalyst, alkenes undergo rapid hydroformylation even at 25°/1 atm.; with alk-1-enes the ratio of straight- to branched-chain aldehyde formed is considerably higher than the ratios normally found in hydroformylation reactions, being ca. 20 at 25°. Hydrogen atom exchange and isomerisation reactions of alkenes with RhH(CO)(PPh3)3 are described.
Through of 13 C and 1 H NMR spectroscopy, it is shown that hydroformylation of the 1,4-cis-PB using a PPh 3 /Rh molar ratio of ca. 165 at 353 K and 2066 kPa of 1:1 CO/H 2 results in the exclusive formation of the internally branched aldehyde product. Hydroformylation of the 1,2-syndiotactic PB under similar reaction conditions yield the terminal-branched aldehyde as the majour product, with a trace amount of the iso-branched product. The initial reaction rate for hydroformylation of 1,2-syndiotactic-PB is about six times greater than that obtained for of 1,4-cis-PB
The microstructures of hydrogenated acrylonitrile-butadiene rubbers (NBRs) with various degrees of hydrogenation were investigated by pyrolysis gas chromatography (PyGC) and infrared and nuclear magnetic resonance spectroscopy. Characteristic peaks on the pyrograms by PyGC, specific absorption bands in the IR spectra, and resonance peaks in the 1H NMR spectra were interpreted in terms of the microstructures of the hydrogenated NBRs. Characteristic peaks in 13C NMR spectra were interpreted in terms of the sequence distribution and hydrogenation mechanisms. PyGC and 13C NMR also supplied good complementary information about longer sequence along the chains and the mechanisms of the hydrogenation reaction.
The chemical modification of unsaturated polymers via catalytic hydrogenation offers a potentially useful method for altering and optimizing the physical and mechanical properties of macromolecules. A study involving the hydrogenation of an acrylonitrile-butadiene copolymer has been carried out in the presence of RhCl(P(C6H5)3)3 which under mild reaction conditions provides quantitative hydrogenation of carbon-carbon unsaturation without any hydrogenation of the nitrile functionality. The selectivity of the catalyst for terminal versus internal double bonds present in the polymer is markedly influenced by the nature of the solvent media. In order to appreciate the important factors which influence the nature and extent of this reaction, a detailed kinetic study has been carried out under experimental conditions where the reaction is chemically controlled. The reaction kinetics exhibit unusual effects on substrate dependence and hydrogen dependence as well as solvent media. The kinetic results and spectral observations are consistent with a mechanism in which the active catalyst RhClH2(P(C6H5)3)2 interacts with the carbon-carbon unsaturation within the copolymer in a rate-determining step. The nitrile functionality present in the copolymer also interacts with the active catalyst and inhibits the rate of hydrogenation.
Homogeneous catalytic hydrogenation of nitrile rubber (NBR) having various acrylonitrile contents was carried out with tris(triphenylphosphine)chlororhodium(I) under high pressure. Thermodynamic parameters of hydrogenation reaction show that the reaction is thermodynamically feasible. Optimum reaction conditions were developed by varying the reaction parameters-temperature, time, pressure, catalyst concentration, and solvent. Reaction of NBR at a catalyst concentration of 0.02 mmol, under 5.6-MPa hydrogen pressure at 373 K in chlorobenzene for 11 h, was found to be optimum for complete hydrogenation. The activation energy of the reaction was 22 kJ/mol. Carboxylated nitrile rubber and polybutadiene rubber were also used. The hydrogenated product was characterized by IR and NMR spectroscopies, iodine value, molecular weight, glass transition temperature (T(g)), and stress-strain behavior.
A new class of polymeric materials has been prepared and subjected to preliminary evaluation. These materials were obtained by hydroformylation of diene-based polymers. The olefinic bonds were saturated and aldehyde groups attached.
The extent of reaction may be varied at will up to 100% double bond conversion. The properties of these polymers are dominated by the active aldehyde groups. One of the chief characteristics of simple aldehydes is their ability to polymerize forming mainly aldehyde trimers and tetramers. This same phenomenon has been shown to occur with polymeric aldehydes with consequent gel formation. The gelling tendency has been closely related to the aldehyde content per unit volume which may be conveniently varied by (1) the concentration of the initial polymer, (2) the degree of unsaturation in the polymer, and (3) the extent of double bond conversion. Any combination which gives a free aldehyde concentration in excess of 1 × 10−4 mole/ml. is very prone to gel. The loose gels can be readily reversed by conditions which depolymerize aldehydes. The propensity of the aldehyde polymers to crosslink upon evaporation of the solvent was used to form films. These films were not discolored by ultraviolet light but under such treatment became quite brittle. The products may be stabilized by conversion of the aldehyde groups to more stable derivative, in particular the acetal. The extent of acetal formation has been shown to be controlled by steric factors. Complete polyacetal formation was possible only when the aldehyde groups were well dispersed along the polymer chain. Certain aldehyde derivatives (acetals, oximes) are thermoplastic. They soften at lower temperature than commercial plastics.
In the present work, a noble synthetic method was adopted for the hydrogenation reaction of nitrile elastomers using homogeneous catalyst system. Six-membered cyclopalladate complex of 2-Benzoyl pyridine was used as catalyst. The acrylonitrile content (ACN) of the NBRs was varied from 33% to 51%. The hydrogenation reaction was also carried out for carboxylated nitrile rubber (XNBR) and Polybutadiene rubber (BR) under identical condition for comparison. The advantage of this kind of reaction is that it can be stopped at any stage to get the desired degree of hydrogenation. The reaction was carried out at two different pressures, times and temperatures by keeping the same catalyst concentration. The reaction products were characterized.