Iranian polymer journal
Volume:12 Issue: 6, 2003

Carboxy-terminated liquid natural rubber (CTNR) was prepared by a photochemical reaction, involving masticated natural rubber and maleic anhydride. CTNR is tried as a modifier in filled NR and NR latex vulcanizates. The ageing and oil resistance of the NR vulcanizates and the ageing resistance of the NR latex vulcanizates were studied and compared with those containing conventional plasticizer and depolymerized NR. CTNR can improve the tensile properties, ageing and oil resistance of NR vulcanizates and the tensile properties and ageing resistance of the NR latex vulcanizates. The vulcanizates containing CTNR are found to possess better rubber-filler interaction.

Due to the presence of polar monomers acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) in the conventional hydrogel contact lenses, the major protein component of the human tear, lysozyme is extensively adsorbed onto their surfaces. The adsorption of lysozyme onto the surface of contact lenses leads to limitations in their applications. The presence of electrolytes in the human tear, in particular NaCl, affects the adsorption of lysozyme. The present study measures the concentration of lysozyme adsorbed from solutions with similar concentrations of artificial tear onto the surfaces of AA and HEMA hydrogels by UV spectroscopy. The adsorption results are treated by the Langmuir adsorption isotherm and the constants of this isotherm are evaluated. The effect of various factors such as protein concentration, ionic strength, pH and temperature on the adsorption of lysozyme are examined and discussed in the light of theobtained results.

Methacrylate monomers were synthesized in four steps based on methacrylic acid and substituted phenols in the present investigation. In the first step, 4-(ω- hydroxy alkoxy) benzoic acids with ω = 2 and 6 were synthesized with the reaction of 4-hydroxy benzoic acid (PHB) and ω-chloroalkanol. The products were refluxed with methacrylic acid for 20 h to obtain the products of the type 4-(ω-methacryloyloxy alkoxy) benzoic acid. The products were chlorinated with thionyl chloride to obtain 4-(ω- methacryloyloxy alkoxy) benzoyl chloride. Finally, the chlorinated products were reacted with 4-methoxy and 4-hexyloxy phenols in dry benzene with triethylamine as catalyst at 0-5°C in nitrogen atmosphere for 3 h to obtain the methacrylate monomers. These monomers have been polymerized by free-radical polymerization technique at 50-60°C. The viscosity-average molecular weight (MV) of the synthesized polymers was calculated by Mark-Houwink''s equation with K and α values 3.87 * 10-3 dL/g and 0.42, respectively. Finally, the phase transitions and the transition enthalpies of polymers from the dynamic scans by differential scanning calorimetric analysis (DSC) gave an inference about the presence of nematic-isotropic and smectic-isotropic transitions in polymers. These liquid crystalline orders were further confirmed by X-ray diffraction analysis.

Reactive dyestuffs are used more than other suitable dyes in dyeing and printing of cotton fabrics with relatively good washing fastness. Time, temperature and alkali concentration constitute the most important parameters affecting the fixation process, in other words, the colour yield. Reactive dyes are fixed on cotton through a covalent link formed between the reactive group of the dyestuff and hydroxyl groups of cellulose. It is the aim of this research to present a model for colour yield as a function of these three parameters. For this purpose, two phase wet fixation dyeing trials were carried out for 9 reactive dyestuffs belonging to vinyl sulphone, monocholorotriazine, dichlorotriazine and trichloropyrimidine groups. The samples were padded with dyestuff solution, dried and fixed in fixation baths with conditions according to a matrix of time, temperature and alkali concentraion values. After measuring the reflectance values of these samples, their K/S and FK values were calculated. These values with their related parameters were used to obtain models through regression analysis. From the first set of obtained models for the nine dyestuffs, only one met the necessary conditions. Modification was carried out for the other eight and at the end five other models could be accepted as a representation of the colour yield of the dyes as a function of time, temperature and alkali concentration.

Electrochemical polymerization of various ratios of pyrrole and N-methylpyrrole monomers were performed in aqueous toluene-4-sulphinic acid sodium salt (T4SNa) electrolyte, using galvanostatic method. The pH of electrolyte was adjusted by p-toluene sulphonic acid (PTSA). In order to prevent corrosion of mild steel substrates during coating deposition, all samples were pretreated in 0.5 M oxalic acid solution, employing galvanostatic method. This would passivate the steel substrate and facilitate the coating process as well. Corrosion resistance of coated substrates was investigated in 1 M NaCl solution using Tafel polarization technique. In addition, by using scanning electron microscopy (SEM), morphological characterization of coatings produced, was investigated. The ratio of 1 to 1 (pyrrole/N-methylpyrrole) could play an important role on corrosion properties of the resulting coated mild steel.

Amacroporous resin microbeads of methyl methacrylate-divinylbenzene copolymer was synthesized by radical suspension polymerization with divinylbenzene in the presence of a pore-creating agent, petroleum ether. They have big specific surface area and a large degree of porosity was covered on all surface of the resin. This macroporous polymer carrier was aminated by hydrazine hydrate, to produce a large number of amino groups onto the carrier. Papain was immobilized on the porous polymer carrier by a glutaraldehyde cross-linking method or a diazo-coupling method. The determining factors involved with the activity recovery of the immobilized papain and the enzymic properties of the resulting immobilized papain were studied in comparison with free papain, for which casein was chosen as a substrate. The results show that the activity recovery of immobilized papain can reach 60.1%. At the same time, the stability, resistance against inhibition, the Michaelis constant Km, and reusability of the immobilized enzyme were also investigated. The results indicated that the immobilized papain by this percentage reached had not only higher activity recovery, but also is had remarkable stability, better reusability and environmental adaptability than free papain.

Graft copolymerization of vinyl monomers including acrylamide (AAm), acrylic acid (AAc) and methyl methacrylate (MMA) onto starch (St) has been carried out under nitrogen atmosphere in aqueous solution using potassium dichromate, Cr(VI), as redox initiator, individually. Dependence of graft yield upon monomer, starch and initiator concentration is investigated as well as reaction temperature by using gravimetry method. Rate equations obtained are: Rg = [AAm]0.93[I]0.49[St]0.52, Rg=k[AAc]0.95[I]0.44 [St]0.46 and Rg = k[MMA]0.95[I]0.44[St]0.46 for St-g-PAm, St-g-PAAc and St-g-PMMA graft polymers, respectively. The kinetics of grafting process has been evaluated by bromometry titration. Finally, activation energies within temperature 50-55°C for St-g-PAAm, St-g- PAAc and St-g-PMMA syntheses are found to be 48.16, 46.13 and 49.06 kJ/mol.k, respectively. Based on results observed, a suitable mechanism is proposed to justify the results.

Cross-linked polystyrene supported AlCl3 and FeCl3 and silica gel supported AlCl3 have shown to be mild and chemoselective heterogeneous catalysts for dithioacetalization of carbonyl compounds. 1,3-Dithiolanes are obtained in excellent yields in the presence of Ps-AlCl3, Ps-FeCl3 and SiO2-AlCl3 from various aldehydes and ketones containing electron donating and withdrawing groups. The chemoselectivity of these catalysts toward aldehydes and ketones is successfully employed in the chemoselective dithioacetalization. The results show that these catalysts are able to discriminate between aldehydes and ketones, and aliphatic and aromatic ketones. The order of catalytic activities of these catalysts was SiO2- AlCl3> Ps- FeCl3> Ps-Fecl3 These polymeric catalysts are stable (as a bench top catalyst) and can be easily regenerated and used.

The properties of polyurethanes strongly depend on the microstructure, functionality, and molecular weight of their initial polyol used. Therefore, in this work, microstructure of polybutadiene-ol, a pre-polymer used for producing special purpose polyurethanes was determined by two analytical methods, namely, FTIR and 1H NMR spectroscopy. In the FTIR method, after obtaining εi (molar absorption in each wavelength) of a specified polyol, the microstructure (trans, vinyl and cis content) of prepolymer was measured by analyzing IR absorption bands in 966 cm-1, 912 cm-1, and 725 cm-1 due to trans,1,2-vinyl and cis configurations, respectively. In the 1H NMR spectra of polyols, microstructure was determined using the ratio of peak areas of various protons (alkylic, olefinic and methylenic) as well as signals at 2.5-4.5 ppm which indicate the position of hydroxyl groups in the back-bone of the polyol. Determination by NMR spectroscopy is an easier method and the information obtained on microstructure of the polyol is more precise than the FTIR method. Finally we established an equation to convert values obtained by FTIR to NMR.