Iranian polymer journal
Volume:11 Issue: 4, 2002

Polyimides are a sophisticated family of materials, which have applications in highly technical end uses from aerospace to microelectronics. Their diversity is such that it leads them into applications as fibres, films, moulding powders, coatings and composite prepregs where their major advantage, a high resistance to heat, places them in a niche other polymers cannot enter. The objective of this review is to tie together some of the early with the more recent literature data concerning the synthetic aspects of diisocyanate derived polyimides, their solution behaviour, and imidization characteristics.Its aim is to provide an up-to-date picture of the important factors involved in polyimide preparation and leave more detailed information to be gathered by the readers from the many key references cited if they desire. This will hopefully provide the readers with a more complete as well as correct picture of the rudiments of diisocyanate derived polyimides in addition to hopefully simulating research interests in those areas which are less completely understood. This large and complex family Of polymers will continue to bedeveloped, even though certain products have been sold for more than 35 years. Future developments will include blends and alloys to optimize processing, physical, thermal or other attributes. This `high tech" family will need many of the high and low temperature requirements of the automotive, aerospace, electrical/electronics and medical industries as they develop further in the 21 st century.

Chitosan has the ability to adsorb substantial quantities of dyestuff from aqueous solution. Currently, it may be a useful adsorbent for the effluent of textile mills. The design procedure for batch study has been investigated for dyestuffs. The effect of several factors governing the dye adsorption such as dosage, temperature, pH and particle size have been investigated. The batch adsorption kinetic study satisfied the model proposed by increasing dosages at generalized rate constant (6. 26 to 5. 64 k /min), intra-particle diffusion (kr = 3. 13 to 4. 63 mglg, 0. 5 min) and Langergrens rate constant (kp = 0. 1952 to 0. 1663 per min). Adsorption was found to increase on increasing temperature (30°C, 45°C and 60°C), increasing pH (6. 7, 8. 5 and 9.5) and on decreasing particle size (1. 651 mm, 0. 384 mm and 0. 177 mm). Maximum amount of dye adsorption occurred at temperature level 60°C (29. 9 mg/g); at pH level 9. 5(29. 8 mglg) and particle size 0. 177 mm (30. 0 mglg). Also, desorption studies are evaluated at different temperatures and pH.

The aim of this study was to clarify the performance of a membrane controlled reservoir system (MCRS) for scopolamine hydrobromide (SH) under in vitro condition by determination of the role of membrane on SH rate control. In this method SH was incorporated into two polymers (polyisobutylene and polybutyl acrylate) and SH rate across ethylene-vinyl acetate copolymer (EVA) and ethyl cellulose (EC) membranes were measured. The results obtained showed that in the EVA membrane, the permeability of SH across membrane increased with the increase of vinyl acetate percentage incopolymer. Microscopic studies of EVA membrane surface showed that the size of surface porosity increases with the increase of vinyl acetate percentage in the copolymer and according to the results obtained, it showed an increase in drug''s release rate. In the case of EC membrane, the results showed that the rate of release increases with the increase of porosity size of EC surface despite of having high molecular weight.

Nucleophilic aromatic substitution reaction of 5-amino-t-naphthol and also 4- aminophenol with bis(4-chlorophenyl)sulphone in N-methyl-2-pyrrolidone as solvent in the presence of K2CO3 resulted in prepara-tion of two aromatic sulphone ether diamines. Polycondensation reaction of the prepared diamines with 4-chloroformylphthalic anhydride yielded thermally stable poly(sulphone ether amide-imide)s. The prepared polymers were characterized by conventional methods. Physical and mechanical properties of polymer including thermal behaviour, thermal stability, solution behaviour, solution viscosity, andmodulus were studied. According to the obtained results, the prepared poly- (sulphone ether amide-imide)s showed physical and thermal properties that lied between corresponding poly(sulphone ether amide)s and poly(sulphone imides. This was an important aspect of structure-property relationships.

Aromatic-aliphatic polyamides containing azo groups were synthesized by both low-temperature solution and phosphorylation polycondensation methods from 2,2''-dimethyl-4,4''-azodianiline (2,2''-dimethyl-4,4''-diamino azo benzene) and 2,3-dimethylpentanedioic acid, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, chlorosuccinic acid and a-chloro-a''- methyl adipic acids. In addition to this, based on 2,2''-dimethoxy-4,4''-azodianiline and succinicladipic acid, polyamides have been synthesized followingthe above polymerization procedures. The polymers were characterized by viscosity, solubility, IR, UV-visible, TGA and DTA studies. Activation energy has been calculated for the thermal degradation of the polyamides.

Polyacrylamide is prepared by free radical polymerization mechanism in aqueous solution, using ammonium persulphate as initiator. Poly(acrylamide- co-sodium acrylate) or partially hydrolyzed polyacrylamide (PI-IPA) with different degrees of hydrolysis was obtained by alkaline hydrolysis of polyacrylamide using sodium hydroxide as hydrolyzing agent. The intrinsic viscosity of copolymers with different degrees of hydrolysis was measuredwith Ubbelohde capillary viscometer in 0. 2 M sodium sulphate solution and related molecular weights {law) were estimated using Mark-Houwink equation. The results show that the intrinsic viscosity of copolymers increases with increasing the hydrolysis degree. We also found that sodium hydroxide as a hydrolyzing agent influences the M u of parent polymer and causes significant reduction in product My, while slight reduction has been reported. The degrees of hydrolysis of copolymers were determined based on a standard back titration method. In addition to titration method, IR spectra bands identified the carboxyl groups.