The influence of some synthesis parameters on Ziegler-Natta catalyst performance

The role of di-n-butyl ether (DBE) in the synthesis of highly active and stereospecific catalyst for propylene polymerization has been investigated. The ether was used as internal base (IB) or complexed with TiCl₄ and diethylaluminium chloride (DEAC) in iso-octane solution (System A) or complexed with triethylaluminium (TEA) in toluene solution (System B). Many differences were observed in the catalyst performance. The activity, the catalyst stereospecificity and the polymer bulk density were evaluated.     

Photosynthetic membranes, 21. Immobilization of catalase by photochemically grafted ultrafiltration membranes

Catalase has been immobilized in membranes prepared by photoinduced grafting onto microporous polymeric supports and its catalytic activity on hydrogen peroxide decomposition has been studied under ultrafiltration conditions by means of a recirculation apparatus. The membranes showed a very good catalytic performance and the enzyme reaction took place exclusively within the membrane structure. Initial reaction rates measured in the temperature range 5 – 35°C as a function of both substrate concentration and enzyme amount immobilized per unit membrane surface indicate that the mechanism of action of catalase is not altered after immobilization.     

Mechanical stability of trimethylolpropane trimethacrylate-based polymers

Trimethylolpropane trimethacrylate (TRIM) was homopolymerized and copolymerized with methyl methacrylate (MMA), glycidyl methacrylate (GMA), and acrylamide (AA), respectively, in various solvents and at various temperatures. For comparison, poly(styrene-co-divinyl benzene) [poly(S-co-DVB)] gels were selected. The mechanical stability was measured by compression of the swollen gels. The porogen served as swelling agent. The compression moduli increased with increasing TRIM concentration in the polymerization. The compression moduli of poly(TRIM) could be increased by copolymerization with low concentrations of comonomer. Low polymerization temperature decreased the mechanical strength of poly(TRIM). A good solvent increased the compression modulus. TRIM-based gels were at least as mechanically stable as were poly(S-co-DVB) gels.     

Thermo-oxidative degradation of some polymer couples containing HNBR

Summary In this paper thermal behavior of some HNBR blends with CPE, PVC, CR and NBR at three temperatures, 150, 170 and 190°C is presented. Changes in characteristic IR bands, gel fraction, and chlorine content were assessed. Some mechanistic differences between the studied systems, regarding the involvement the depletion of chlorine and modification in gel content, were pointed out. Cyclization of nitrile structure was also observed by means of 2240 cm⁻¹ band ascribed to >C=NH. Kinetic considerations are presented. Received: 3 June 2002/Revised version: 14 November 2002/ Accepted 20 November 2002 Correspondence to Traian Zaharescu     

Niobium-containing catalysts—the state of the art

This review article is devoted to the materials containing niobium, which have been discovered or developed in the past few years and exhibit the potential application in heterogeneous catalysis. Niobium oxides and mixed oxides as well as sulfides, nitrides (oxynitrides), carbides (oxycarbides), and phosphates are considered. Among the catalytic processes in which Nb-containing materials were tested, liquid and gas phase oxidation is described in details, and the role of niobium in the prevention of the catalyst from SO₂ poisoning is mentioned.     

Heavy Metals Bioremediation from Polluted Water by Glass-Ceramic Materials

The objective of this research was to study the removal of cadmium and lead from an aqueous solution through a biological treatment. For this purpose a glass-ceramic material was manufactured from industrial and urban wastes. Biofilms of microorganisms found in wastewater were developed on its surface, and continuous tests were conducted in the presence and absence of the biofilm to analyze the glass-ceramic's ability to remove the heavy metals from an aqueous environment. The results suggest that this bioremediation process, developed on an industrial scale, could represent an alternative to the chemical processes currently used.     

High‐resolution 13C–nuclear magnetic resonance study of heterogeneous amorphous polymers

The combination of solid‐state nuclear magnetic resonance (NMR) techniques is very helpful for examining the behavior of heterogeneous amorphous polymers. With the magic‐angle spinning (MAS) technique, employing special conditions, only the mobile fraction of the molecule can be assigned. Cross‐polarization magic‐angle spinning (CPMAS) permits the evaluation of changes in the NMR line shapes and chemical shifts. The employment of proton spin‐lattice relaxation times (T₁ and T₁ρ) gives useful information on the molecular dynamic in heterogeneous polymers. From these parameters the response of the molecular mobility behavior of the polymer chains can be obtained. The results of the present work are discussed in this article in terms of molecular mobility and domain formations of heterogeneous amorphous polymers in order to understand the relations in the structure–mobility property. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 473–476, 2003     

Controlling the phase stability of polymer blends through the introduction of impenetrable interfaces

In this work, the effect of the introduction of modified solid surfaces into polymer blends on the phase‐separation process was investigated. Glass fibers with surfaces having different chemistries were introduced into polystyrene–poly(methyl methacrylate) blends. The glass fibers used either had fully hydrated surfaces or had surfaces covered with a random copolymer, poly(styrene‐co‐methyl methacrylate). The copolymer was synthesized by free‐radical polymerization of styrene and methyl methacrylate in the presence of previously vinyl silane‐treated glass fibers. The copolymerization and grafting procedures were investigated by FTIR and thermal analysis. Blends containing the fibers were studied using FTIR microscopy and optical microscopy. FTIR microscopy results showed that the composition of the phases in the blends was shifted by using fibers with different surface chemistries. Fibers with grafted copolymers were capable of narrowing the immiscibility region in the phase diagram, while fully hydrated fibers were able to expand the gap. It was proposed that interfacial interactions regulated by a hydrophilic–hydrophobic type of forces were responsible for guiding the described phase‐separation process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1619–1627, 2003     

Compatibility of polysaccharide/maleic copolymer blends. IV. Thermal behavior of hydroxypropyl cellulose‐containing blends

The compatibility of the hydroxypropyl cellulose (HPC) with maleic acid–vinyl acetate copolymer in the solid state was studied by thermogravimetry, thermo‐optical analysis, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and optical microscopy. It was established that physical interactions are prevalent in blends with a high content of HPC, whereas chemical interactions predominate in blends with a medium and low content of HPC. By increasing the temperature, the thermochemical reactions are favored. Thermal properties are dependent on the mixing ratio of the components. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2585–2597, 2003