مجله ایرانی پلیمر
سال:1381 | دوره: | شماره: |تعداد مقالات:7

Polyacrylamide (PAAm) hydrogels were synthesized by partial cross-linking of PAAm using p-formaldehyde as curing agent. The cross-linking reaction was studied using differential scanning calorimeter (DSC) and cure kinetics was determined. The dynamic DSC scans of freshly mixed reaction mixture that showed an endothermic peak corresponding to cure at 75±1° C, indicate multiple reactions. The FTIR studies of curing reactions indicated that alkaline hydrolysis of PAAm was also occurring during curing as evident by generation of carboxylic group in the cured PAAror hydrogels. In the initial phase of cross-linking reaction and at lower temperature rapid hydrolysis occurred which was endothermic in nature, but at higher temperature curing reaction was favoured. Isothermal cure kinetics revealed that curing reaction was n th order type and followed third order kinetics. The study also indicates that with the degree of conversion 0 .25-0.26. both curing and hydrolysis occurs simultaneously but at higher conversions curing reaction proceedes alone. The swelling studies also indicates that the swelling index of PAAm hydrogels increases with decreasing curing agent concentration: but increases with increasing swelling duration and curing time, and molecular weight of polymer.

Phase morphology, state of compatibility and various properties of blends of polycarbonate (PC) with bottle-grade and fibre-grade polyethylene terephthalate (BPET and FPET, respectively) were investigated. It was found that these blends have two-phase separated morphology with partial miscibility. Scanning electron micrographs revealed separated domains of PC-rich and PET-rich zones. PC domains appear spherical increasing in size from 2 mum for PC20/FPET80 up to about 5 mum for PC60/FPET40 blend. Further increase in PC content up to 80% caused phase inversion in which FPET appears as finely dispersed domains in continuous PC matrix. T0 of PC-rich phase decreased from 153 °C for pure PC down to 140 °C for PC20/BPET80. Similar trend was observed in PC/FPET blends. Also, T0 of BPET-rich blend increases from 90 °C for pure BPET up to 98 °C for PC60/BPET40. Melting temperature of PET remains practically unchanged with partial compatibility of the blends. Tensile modulus, yield strength and impact resistance of the blends conform to an additive blend properties. Blends show good chemical resistance properties. Viscosity ratio of PC to PET was about 4 to 6, suggesting ease of PC/PET processing in manufacturing process.

Considerable progress has been made in characterizing and understanding the properties of polyaniline doped with some protonic acids. In this work polyaniline was synthesized by chemical method in the presence of HCI, then undoped polyaniline was obtained with NH3 solution. The undoped polyaniline was doped with the protonic acid such as sulphosalicylic; acid, salicylic acid and citric acid. The protonic acids can be used to dope poly-aniline (PANI) by mixing a protonic acid in common solvents such as N-methyl pyrrolidone and dimethylformamide. The structure and properties of protonic acid doped-PANI are investigated by UV-vis, IR and conductivity measurement. It is found that the PANI, therein, is doped by protonation of imine nitrogen. In the case of protonation-doped PANI, polarons/bipolarons are generated as reflected in the presence of UV-vis absorption peaks at 420 and 850 nm. The minimum amount of appropriate acid to obtain optimum level of doping was estimated by UV spectroscopy. Also polyaniline base Was doped with these acids by blending in the solid-state. The electrical conductivity in the solid state increased several times after heating the mixture and increasing the heating time. The dependence of the electrical conductivity on the composition of blends differs for the partly protonated polyaniline and mixtures of protonated polyaniline with an excess acid.

The influence of polyacrylic acid (PAA) and a blend of polyacrylic acid with hexafluorozirconic acid treatments on the performance of an epoxy/polyester powder coating on a 1050 Al substrate has been studied and compared to the performance of the same system using a so-called chromate/phosphate conversion coating. The chemical interactions between pretreatments and Al substrates were examined using FTIR spectroscopy and various accelerated test methods were also employed. Two mechanical adhesion measurement methods were used under wet and dry conditions, namely a vertical pull-off test in the dry state and the tape test under dry and wet conditions. The water permeation of the differently pretreated powder coated samples was studied using a capacitance measurement method. FTIR results showed two modes of interaction; namely ionic and complex formation between COO- and AL3+, Various experiments revealed that PAA improved only the dry adhesion but as a standing alone treatment it did not provide an overall improvement-in anti-corrosive performance. The water uptake measurements proved that pretreatment does not considerably affect the properties of the coatings during water permeation stage. The use of various techniques revealed that relatively good performance of the powder coating is due to a high ohmic resistance of the coating prior to and after saturation with water, reasonably low water solubility and good adhesion to the substrate.

A few new thiodiols and thiocarboxylic acids were obtained by condensation reaction of bis(4-mercaptophenyl)ether with some halogen alcohols or halogen acids, respectively, in aqueous sodium hydroxide solution. By melt polyaddition of one of these alcohols, i .e. 4,4'-bis(2-hydroxy-hexylthio)diphenyl ether with hexamethylene diisocyanate (HDI) a new linear polyurethane was obtained, and by melt polycondensation of one of these acids, i .e. diphenyl ether-4,4'-bis(thiovaleric acid) with 1,6-hexanediol, a new polyester was obtained. The structures of monomers and polymers were confirmed by elemental analysis, FTIR and 1 H NMR spectroscopies. Some physicochemical, thermal and mechanical properties of the obtained polymers were described.

Drug-loaded cylindrical polymer matrices, composed of poly (N-vinyl-2-pyrrolidone) and poly(acrylamide-co-maleic acid) have been synthesized and the release of vitamin B2 from these gels has been studied at the physiological temperature 37°C. The devices show strong pH-dependent release behavelour, thus offering a maximum release at pH 7.4. The initial amount of drug loaded into the device and the diameter of the cylindrical samples also affect the release kinetics. With the increase in the maleic acid content inside the device having maximum 43.0 mM, the release rate has been found to increase, whereas further increase in the acid content slows down the release rate. Finally, the release of riboflavin from the devices has been explained onthe basis of the swelling-dependent mechanism

Three main methods area usually used for the synthesis of star-shaped polymers, where each one has its own advantages and disadvantages. Among these techniques, "in-out" method is the best one to produce hetero-arm star polymers with narrow molecular weight distribution and long arms with active sites at the end of the second-generation arms. This method, however, has some difficulties during the synthesis of hetero-arm star polymers with styrene or dienes as the second monomers. The reason is that in the "out" step, the carbanions of the growing chains attack the existing double bonds of the other cores and produce an irreversible gel. The new "in-in" method mentioned in this paper, is used to synthesize double-star polystyrene polymers with relatively narrow molecular weight distribution and without occurrence of any gelation during the process; With the monomers, which are able to attack the existing double bonds of the cores of the star polymers, it is also possible to produce hetero-arm star polymers using this new method.