Iranian polymer journal
Volume:12 Issue: 2, 2003

Asimple and convenient method, which proceeds through pyrylium salts, was applied for the synthesis of four new aromatic diamines based on 2,9-dimethyl [5a,10b] dihydrobenzofuro [2,3-b] benzofuran. Their preparation was based on the one-pot reaction of aldehydes with methyl ketones in the presence of boron trifluoride. Specially, because of aromatic structure, these diamines may be used in the synthesis of several types of heat stable polymers, such as polyamides and polyimides. 1H NMR and IR spectroscopy, as well as elemental analysis accomplished characterization of diamines. All diamines were obtained in good to excellent yields.

Some random three-component copolymers have been prepared by condensing of formaldehyde with various aromatic amines. The compositions of the copolymers have been determined by known methods. Selective complexation of copolymers have been carried out with PAA, PEI, PVP and some transition metal ions (e.g., Cu2+) by adding the components in various sequences. The relative complexation ability of different -NH2 groups, associated with the various comonomer units, has been interpreted in terms of the nature of substituents present at the para position of the comonomer units. The formation of these complexes has been studied by conductometry, potentiometry and viscometry techniques. A scheme has been presented to explain the mode of interaction of the various components.

The acrylamide based curing agents (ACAs) were prepared from methyl methacrylate- acrylamide copolymers by further methylolation and subsequent etherification with butanol. These were characterized for their various physico-chemical characteristics. Various sets of these ACAs were blended with hydroxyl functional acrylic resin to prepare the stoving compositions. After stoving the films were studied for their various properties and compared with the conventional melamine-formaldehyde based curing agent (CMFCA) containing compositions. The films were also characterized by thermogravimetric analysis (TGA) and IR-spectra. The result reveals that the properties of certain compositions based on ACAs were remarkably better than those of CMFCA based coatings.

In this paper, large size polyethylene (PE) pipes (1000 mm in diameter), buried underground, are analyzed to determine the effect of both internal and external pressure on their mechanical behaviour. The effect of surrounding soil and temperature change caused during pipe installation and operation is also included. To determine the real cause of failure (which occurs during operation), two types of reinforcement have been considered. The first model deals with a pipe reinforced by external PE rings (core tube) and in the second, a corrugated layer is used as a reinforcement. The failure cause in each case has been analyzed and the relationship between pipe thickness, maximum pipe stress, temperature drop, internal pressure, pipe depth, and elasticity of foundation has been investigated to set a design basis for any further applications.

The main objective of this research was preparation of polymeric compound that to be able to deoximate the ketone and aldehyde oximes to their corresponding carbonyl compounds. In this work poly[4-vinyl-N,N’-dichlorobenzenesulphonamide] (I) was prepared and used as reagent for deoximation of keto and aldoximes. The first step of this work involved the preparation of polymeric reagent. Poly[4-vinyl-N,N’ dichlorobenzenesulphonamide] was prepared by the reaction of sodium p-styrenesulphonate with PCl5 and ammonia, polymerization with AIBN, and then chlorination with Cl2(g) to yield the corresponding chlorinating polymer in excellent yield as a semi-solid, which was identified by 1H NMR and IR spectroscopy. This material proved to be a very powerful chlorinating agent and was found to be easily recovered, regenerated and reused. This polymeric reagent was used for oxidation of aldehyde and ketone oximes to their corresponding carbonyl compounds under microwave irradiation. For this purpose a mixture of oximes, CCl4 and poly[4-vinyl-N,N’ dichlorobenzenesulphonamide] were used and then irradiated in a domestic microwave oven at a power output of 700 W for the appropriate time. Since this polymer reagent (I) contains two chlorine atoms which are attached to nitrogen atom it is very possible that this reagent upon heating or under microwave irradiation releases in situ Cl+ which could act as an electrophilic species.

Peroxide cross-linking of polyethylene is one of the most important methods for the production of cross-linked polyethylene (PEX). The kinetic study of the crosslinking reaction of low density polyethylene (LDPE) in the presence of 2,4- diphenyl-4-methyl-1-pentene (MSD), pentaerythritol triacrylate (PETA) and divinylbenzene (DVB) as the co-agent and dicumyl peroxide(DCP) as the cross-linking agent was carried out by differential scanning calorimeter (DSC, non-isothermal condition), rheometer and internal mixer (isothermal condition). The reaction was first order and independent of DCP and the co-agent concentration. The activation energy and ln ko (ln ko defined as the intercept of ΔH vs.1/T) did not change with DCP concentration but energy of activation decreased with co-agent and the highest decrement was observed with respect to MSD. The overall reaction rate constant (with constant value of DCP) increased with temperature due to the faster decomposition rate of peroxide at higher temperatures. By comparison of the three methods used, it was found that the different results obtained were in good agreement with each other. However, because of the higher shear rate and mechanical stress experienced in the internal mixer, the measured overall reaction rate constants were of higher values with respect to those obtained from other methods.

Today, the fabrication of complex-shaped ceramic parts in large quantities has been limited to the processes required extensive and expensive machining (i.e., injection moulding or pressure slip-casting). These technologies for shaping ceramics, however, possess several shortcomings that limit their use as a complex-shape forming method. Because of these limitations, “gel-casting” which was lacking in above deficiencies, has been proposed as a general and desired method for shaping any ceramic powder. In this work, gel-casting of α-alumina is investigated based on in situ polymerization and gelation of acrylamide monomers as the setting mechanism for forming the greenpart. Special attention was paid to the preparation of fluid, castable slurries with a highloading level of α-Al2O4 (>80 wt.%) and low viscosity (0.65 Pa.s) by using polyelectrolyte dispersants (i.e., poly(methacrylic acid) salts), also gelation of acrylamide (effect of gelation factors on idle time), mould materials, drying of parts through the liquid desiccant drying method and its comparison with conventional drying technique, green machining, debinding and sintering.

Poly (vinyl alcohol)-chitosan blend films were prepared by casting the respective polymer solutions. The glutaraldehyde was used as a cross-linking agent. A series of PVA-chitosan blends were prepared by varying the ratio of the constituents. Mechanical and physical properties of blended films such as tensile properties in the dry and wet states, water uptake, surface tension and contact angle were characterized. Blending PVA and chitosan improved strength and flexibility of the films in the dry and wet states. Cross-linking with glutaraldehyde improves tensile strength and decreases elongation of the films. PVA Content in the blends increases water uptake while cross-linking the films with glutaraldehyde causes less hydrophilicity. Water uptake in PVA-chitosan blends can be controlled by variation of their contents, cross-linking agent and the pH of solution. Blending of PVA and chitosan improves bulk and surface hydrophilicity of blended films.

The purpose of this study was to develop a homogeneous and stable graphite sealant that seals polyester vascular grafts to improve the thromboresistant of grafts. Water colloid dispersion of graphites were prepared using graphite (1-3), sugar, gelatin and double distillated water. The knitted crimped polyester fabric vascular grafts with 10 and 12 mm inside diameter were coated via electrophoresis method using water colloid dispersion of graphite. Several mechanical cleaning were carried out on grafts and then the grafts were heated for 2 h at 150°C. The number of adhered platelets was determined by lactate dehydrogenase (LDH) activity measurement. Scanning electron microscopy (SEM) was performed on the graphite coated for evaluating the morphology of vascular grafts surface and also studying the morphology of adhered platelet to polyester fabric grafts. The results showed homogeneous coating of graphite on polyester vascular grafts. SEM observations showed that the platelet adhesion on non-coated vascular grafts surface were relatively high in comparison with the graphite coated fabrics. It was also observed that the graphite coating on polyester vascular grafts reduced the number of adherent platelets and prevents platelet activation and spreading on the surface. Reduction of platelet adhesion was attributed to the coated surfaces.