Iranian polymer journal
Volume:18 Issue: 7, 2009

The gas phase polymerization of butadiene on new heterogenized bifunctional cobalt-containing catalytic dithiosystems was studied. Earlier, some highly active and efficient homogeneous bifunctional catalyst-stabilizers were developed on the bases of Ni- and Co-dithioderivatives (such as O,O-disubstituted dithiophosphates and N,N-dithiocarbamates) in combination with aluminium organics (such as dialkylaluminiumchlorides, alkylaluminium-dichlorides, and aluminoxanes) for butadiene solution polymerization and simultaneous stabilization of end polymer. The problem of separating homogeneous catalysts from the reaction medium is still the most important obstacle in blocking its large scale applications in industry. A number of potential methods for homogeneous catalyst separation and recovery have been or are presently being developed, such as a two-phase catalysis and heterogenization on inorganic or organic supports. Cobalt-containing bifunctional catalytic dithiosystems have been heterogenized on various supports (such as silica gels, aluminium oxides, zeolites, carbon black, etc.) by direct deposition or pre-alumination methods. Theobtained data demonstrate that the pre-alumination method of immobilization of bifunctional cobalt-containing catalytic dithiosystems shows very high activity in gas phase polymerization of butadiene. These catalysts’ productivity reaches ~650.0- 2200.0 kg PBD/g Co.h, which is much higher than the output of solution process using the same homogeneous catalysts (57.0 kg PBD/g Co.h) and the known gas phase process using the heterogenized neodymium-catalysts (500.0 kg PBD/g Nd.h). High activities of heterogenized bifunctional cobalt-containing catalytic dithiosystems allow the development of principally a new ecologically favourable and economically feasible technology of butadiene gas phase polymerization process by involving them as rawmaterials not only for pure butadiene, but also butadiene as C4 fraction of pyrolysisproduct.

The PMMA electrets were prepared by thermal polarization method. UV-vis absorption and thermally stimulated discharge current (TSDC) spectra have been recorded in PMMA electrets of 10 μm thickness. The PMMA electrets are polarized at 333 K with different polarizing fields. The observed TSDC and UV-vis spectra are the function of polarizing field. It has been found that absorption decreases with increasing field. The TSDC peak (α peak obtained at high temperature) is shifted towards lower temperature region with increasing field. The observed activation energy with the low temperature peak (β peak) is found to be varied between 0.21-0.55 eV, while for α peak it varies from 0.50 to 0.91 eV. The TSDC peaks are explained on the basis of theoretical predictions; however, the decrease in band gap energy of PMMA electret could be explained on the basis of UV-vis absorption peak. The configuration of UV-vis absorption in the region 200-900 nm gives the method of characterizing band gap energy. The dipolar and space charge polarizations are possible mechanisms to explain the TSDC in PMMA electrets. The optical micrographsdistinguish the molecular structure of polarized and unpolarized (i.e., pristine) samples.

To investigate the swelling and mechanical behaviours of protective materials during sorption and desorption with various solvents would be helpful to predict the failure of these materials. However, elastomers with high chemical resistance are usually used as protective materials and in order to reuse these materials after decontamination, studies are imperative to investigate the failure prediction of protective materials. In this article, the effects of various organic solvents on the swelling and elastic properties of polychloroprene (CR) materials as protective substances were systematically studied. Different aromatic (toluene, anisole, and o-dichlorobenzene) and aliphatic (methyl ethyl ketone and ethyl acetate) solvents with various chemical structures, molar volumes and Ra values (the level of polymer-solvent interaction calculated from the Hansen solubility parameters theory) were considered. The swelling behaviour and the tensile properties of the CR immersed in each solvent for different periods are characterized. The chemical structure and the molar volume of solvents have been found to give better correlations than Ra values on the swelling rates and maximum equilibrium swelling of CR when Ra values are close together. It is also shown that the swelling of CR decreases after the leachable additives are completely removed. The elastic property changes are indication of partial degradation of CR after swelling by solvents in the following order: toluene > anisole > methyl ethyl ketone > ethyl acetate. It has also been found that tensile property changes of CR after contact with solvents at low deformation are more prominent than changes at large deformation. In addition, the presence of leachable additives in CR shows reduction in the tensile properties of CR during partial swelling with various solvents.

Poly(vinylidene fluoride) (PVDF) was filled with carbon fibres of different content. All filled and unfilled PVDF composites were tested against CGr15 ball and representative testing was performed. The effects of carbon fibre content on tribological properties of the composites were investigated. The incorporation of carbon fibre into PVDF can either increase or reduce friction coefficient and reduce volumetric wear of the materials in sliding against stainless steel under dry sliding condition. The friction and wear properties of the PVDF composites filled with carbon fibre varied with the change of carbon fibre content. Friction coefficients of all the filled PVDF composites and neat PVDF increase with the increased loading and the reciprocating sliding frequency. The volumetric wear for unfilled and all filled PVDF composites increased with increasing applied load, but they exhibited different relationships between volumetric wear and load. The optimum wear resistance property of the composite was obtained when the carbon fibre content is 20 vol%, that means the carbon fibre and PVDF matrix combine well. The adherence and plastic deformation are primary wear mechanisms for the neat PVDF under dry sliding. When incorporated with carbon fibre, the adherence and plastic deformation are greatly reduced, and so the wear resistance is improved.

The smart polymers are of particular interest due to their quick response to externalenvironmental chemical and/or physical stimuli, such as temperature, pH,ionic strength, electric field, and photo-irradiation. These polymers may be usedin many fields, such as protein adsorption, immobilization and separation, stimuliresponsivecontrolled releases and biotechnology. In the present work, a graft copolymerof poly(vinylidene fluoride) with poly(N-isopropylacrylamide) (PVDF-g-P(NIPAAm))was synthesized by atom transfer radical polymerization (ATRP) directly using poly(vinylidene fluoride) (PVDF) as a macroinitiator. The copolymer can be readily castinto temperature-sensitive microfiltration membranes by the phase inversion technique.The effect of molar feed ratio of NIPAAm/PVDF on the properties of the copolymerswas studied. The bulk and surface compositions of the membranes were obtained byelemental analysis and X-ray photoelectron spectroscopy (XPS), respectively. XPSresults of the copolymer membranes obtained by phase inversion technique revealeda substantial surface enrichment of the grafted P(NIPAAm). The thermal stability of thecopolymers was investigated by thermogravimetric analysis (TGA). The permeability ofwater through the pristine PVDF membrane exhibited the almost temperatureindependent flux behaviour. However, the rate of water flux through the PVDF -g-P(NIPAAm) membrane increased with the increase in permeate temperature from20ºC (below the LCST) to 50ºC (above the LCST), with the most drastic increase beingobserved at the permeate temperature of about 32ºC. The temperature-dependent permeation rate may result from the change in conformation of the P(NIPAAm) chains inthe PVDF-g-P(NIPAAm) membrane. The thermoresponsive membranes obtained viathe present approach may be applied to the biomedical and biotechnology fields.

The influence of alternative blowing agents on the mechanical properties and microstructure of rigid polyurethane (RPU) foam and their relationship were examined. The compression, creep and stress relaxation tests were conducted on RPU foams. For compression test, loading was applied at a rate of 5 mm/min; and for creep tests, a constant stress (0.12 MPa) was applied for 15 min and the strain was recovered for the next 15 min. In stress relaxation experiments the constant strain (3%) was applied for 15 min in the rise and transverse directions. The results of mechanical properties showed that the stiffness of the samples in the rise direction was higher than the transverse direction. Furthermore, the yield strain for all the samples in the transverse direction was higher than the rise direction. Creep and stress relaxation results, showed that the RPU foam in the rise direction exhibited higher creep recovery and lower stress decay than the transverse direction. RPU foam which was blown with n-pentane showed the highest creep recovery and the lowest stress decay, and the foams blown with cyclopentane showed the lowest creep recovery and the highest stress decay at both directions. The microstructures of the foams were studied with an optical microscope. The results of microstructural studies indicated that the RPU foam with the smallest cell size and the narrowest cell size distribution exhibited the highest compressive strength and modulus. RPU foam blown with n-pentane produced the smallest average cell size and narrowest cell size distribution which led to the highest compressive strength and modulus, and the foams blown with cyclopentane produced the largest average cell size and the broadest cell size distribution leading to the lowest compressive strength and modulus.

Asuspension solid-state grafting approach was employed to prepare a functional PP (FPP)-methacryloxyethyltrimethyl ammonium chloride grafted PP (PP-g-(Stco- DMC)). The non-isothermal crystallization kinetics of pure PP and FPP/PP(10/90) blends have been investigated under non-isothermal conditions by differential scanning calorimetry (DSC). The Avrami analysis modified by Mandelkern and a method combined with Avrami and Ozawa equations were employed to describe the non-isothermal crystallization kinetics of samples. Ultimately it was shown that the nucleation in FPP/PP blends facilitated by the electrostatic interactions between the quaternary ammonium cations resulted in high crystallization rates during the crystallization process. However, electrostatic interaction became stronger as the amounts of DMC increased, chain diffusion and mobility of the crystallizable segments diminished, and thus the crystallization process was slowed down when FPP (DGFPP = 13.23%) was added. In addition, the activation energy for the transport of the polymeric segment to the growing crystal surface was also obtained according to the Kissinger method.

Polyethylene with a viscosity average molecular weight (Mv) as high as 3.42×106 was synthesized. The Mv increased with monomer pressure, while higher polymerization temperature decreased the molecular weight of the resulting polymer. The method of polymerization involved slurry using morphologically improved bisupported catalyst of spherical SiO2/MgCl2/TiCl4. Triethylaluminium (TEA) was used as a cocatalyst, and hydrogen served as the chain transfer agent. The crystallinity of the obtained polymer was between 50% and 60%, indicating semicrystalline polyethylene. Morphological study reveals that the main damage suffered by the catalyst particles was due to chemical interactions with the cocatalyst at the early stages of the polymerization. The rate/time profile of the polymerization decayed with the highest activity at the beginning of the polymerization. The behaviour also affected the morphology of the polymer particles which could be due to the sudden fragmentation that resulted from fast-growing polymer particles. The optimal activity was obtained at [Al]:[Ti] = 770:1 molar ratio at 60ºC. The polymerization was first order with respect to the monomer concentration. Polymerization activity was stable between 55ºC and 70ºC.