مجله ایرانی پلیمر
سال:1384 | دوره: | شماره: |تعداد مقالات:9

There have been reports about the studies of simultaneous chlorination and carboxylation of polyethylene affected by gaseous chlorine and maleic anhydride (MA) in carbon tetrachloride solution within the range of 90-110°C. In this study, photchemical chlorination of polyisobutylene (PIB) in the presence of MA, and, in particular, the kinetics of this process was investigated. Photochemical chlorocarboxylation of polyisobutylene was carried out in the mixture of carbon tetrachloride and chloroform. The order of the reaction with regard to reactant concentrations and the value of the reaction rate constant were found. By the method of quantitative description of substitution sites on the polymer chain, the ratio of the rate constants of the chlorination and carboxylation reactions was calculated. The effect of the neighboring unit, i.e., a decrease in the chlorination rate under the accepting effect of maleic anhydride (scavenging effect) was observed. The time of the reaction corresponding to the maximum value of the scavenging effect was established.

Physical properties and thermal behaviours of polymers vary by molecular weight or stereoisomers. These properties also change in the presence of polymeric and nonpolymeric additives. Conductive polymers are insoluble in original organic solvents and their processibility are limited. In this research, the processible conducting polymers are synthesized and their electrical properties and thermal behaviour are studied. The blends of polyvinyl acetate (PVAc), polystyrene (PS) and polyvinyl chloride (PVC) with polypyrrole (PPy) and polyaniline (PANi) are prepared. On the other hand, the percentages of compounds of these blends for suitable electrical properties, solubility and processability are optimized. All the samples were prepared in the smooth form and thin film. A four-point probe method is adopted to examine the electrical DC conductivity. It is found that the conductivity of the blends is decreased but their processibility and solubility are increased. Thermal stability of polypyrrole and polyaniline blends were investigated by scanning thermal analysis (STA), differential scanning calorimetry (DSC) and thermal gravimetrical analysis (TGA). As it is evident from the results, the prepared blends are much more stable compared with polypyrrole, polyaniline and host polymers.

The acrylate–silicone emulsions were prepared by emulsion copolymerization of methylmethacrylate (MMA), butylacrylate (BA), methacrylic acid (MAA) with vinyltriethoxysilane (VTES), and auxiliary agents at 85°C in the presence of potassium persulphate (KPS) as initiator. Alkylphenol ethersulphate and Arkupal N-300 were used as anionic and non-ionic emulsifiers, respectively. The resulting copolymers were characterized by using Fourier transform infrared spectroscopy (FTIR). Thermal properties of the copolymers were studied by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The morphology of copolymers was also investigated by scanning electron microscopy (SEM) and then the effects of temperature, agitation speed, initiator and VTES concentrations on polymerization rate are discussed. The obtained polymers with high solid content (43%) were used in the emulsion paints as a binder. The experimental results show that these polymers supply very useful properties such as excellent storage stability, UV light, washing and abrasion resistance with good brushing in the above mentioned paints. The calculations of monomer conversion versus time and monomer conversion indicate that by increasing the VTES concentration, the polymerization rate and the number of polymer particles decrease, respectively.

The pulping of rice straw with diethylene glycol, diethylene glycol + ethylene glycol and diethylene glycol+ ethylene glycol + 2% NaOH was studied in order to investigate the effects of the cooking variables (temperature and different organic solvent mixtures) on the properties of obtained pulp (cooking yield, Kappa number, freeness (CSF)) and paper (breaking length, burst index, folding endurance, tear index). Delignification was increased by increasing the temperature and hand sheet papers with better bondability of fibres were obtained, but the strength or length of the fibres with increasing temperature were decreased. With the use of 2% sodium hydroxide in cooking solvent papers with superior mechanical properties were obtained. Properties that are sensitive to bondability of fibres, such as, breaking length, burst index, folding endurance, were increased with increasing of temperature, but another property sensitive to length or strength of fibres, that is, tear index, was decreased with increasing of temperature.

Today cords are used generally for reinforcing rubber compounds. To increase interfacial adhesion of cords to rubber, they are coated by an adhesive (usually RFL (resorcinol-formaldehyde-latex) base). These composites are used in many industries such as tyre and belt industries. Adhesion strength between the cord and rubber determines durability and performance of composites. In a recent paper, temperature which is an effective factor in cord/rubber adhesion decrease was reported to be used for determination of interfacial interactions breakage instead of traditional methods such as swelling method and load of static/ dynamic forces. For this purpose adhesion has been measured in a wide range of temperatures (25-170°C). Stable/labile interactions ratios are evaluated from adhesion-temperature curves as well. Also authors have compared the adhesion of different cords(N6, N66 and PET) to rubber and have determined the best vulcanization temperature for them.

Biopolymer chitin, the most abundant natural amino polysaccharide, and its most important derivative, chitosan, are recently considered as the subjects for extensive worldwide academic and industrial research. In spite of potential applications of chitin and chitosan, it is necessary to establish efficient appropriate modifications to explore fully their high potential. A variety of chemical modifications are employed to modify these carbohydrate polymers. The present article provides a comprehensive review on one of the most promising approaches to modify chitin and chitosan, i.e., graft copolymerization, with an emphasis on the synthetic aspects. Both chemically- and radiation-initiated graft copolymerization of various vinyl monomers onto the trunk polymers are investigated. Meanwhile, the limited cases of polycondensation and oxidative coupling are presented as the non-vinyl graft copolymerization methods. Then, the ring-opening graft copolymerization is described and the cases of the cyclic monomers a-aminoacid N-carboxy anhydrides and e-caprolactone are investigated. An extensive description of the “grafting onto” approach is provided. The preformed polymers discussed here for grafting onto chitin/chitosan include living poly(2-alkyl oxazolines), poly(ethylene glycol)s, block polyethers, poly(ethylene imine)s, poly(2-hydroxyalkanoate)s, polyurethanes, poly (dimethylsiloxane)s, and dendrimer-like hyperbranched polymers. Chitin/chitosan multiple modification including graft copolymerization is also investigated. Regioselective grafting using derivatives such as 6-iodo-, mercapto-, deoxy(thiosulphato)-chitins, and Ntrichloroacetyl chitosan are described as suitable approaches to achieve chitin/chitosan graft copolymers with well-known structures.

The nucleation effect of 6 pigment dyes, namely: C.I Pigment Yellow 83, Red 48, Blue 15, Violet19, Black 7 and White 6 on the microstructure of mass dyed BCF polypropylene, i.e. crystallization temperature, melting point, percentage crystallinity, and birefringence has been studied by means of polarizing light microscope, DSC and FTIR. Tenacity and thermal shrinkage have also been studied. The results indicated that Yellow 83, Blue 15 and Black 7 act as monoclinic nucleating agents, whereas Violet 19 and White 6 act as hexagonal nucleating agents. The nucleation effect of Red 48 seems to be negligible. Depending on the type of nucleation, the above mentioned parameters characterizing the microstructure of the fibres are affected. The birefringence of all coloured polypropylene fibres decreased as a result of pigment dyes added to the fibres. This leads to a reduction of the tenacity and thermal shrinkage of mass dyed BCF yarns.

Two optically active dianhydrides were prepared from the reaction of L-aspartic acid with either pyromellitic dianhydride (PMDA) or benzophenone tetracarboxylic dianhydride (BTDA) and subsequent transformation of tetraacids to dianhydrides using thionyl chloride. Solution polycondensation reaction of the prepared dianhydrides with different aliphatic and aromatic diisocyanates (MDI, PPDI, NDI, HMDI, H12MDI and IPDI) resulted in the preparation of twelve novel optically active polyimides. The optimal conditions for polyimidations (reaction time and temperature programming) were obtained via study of the model compounds. The resulting polyimides showed inherent viscosities in the range of 0.18-0.55 dL/g and showed good solubility in polar aprotic solvents. The monomers, model compounds and polymers were characterized by FTIR, 1HNMR spectroscopies and elemental analysis, and their physical and optical properties were studied as well.

The compatibilizing effect of hyperbranched poly(amide-ester) grafted polypropylene (PP-HBP) had been investigated in polypropylene (PP)/poly(vinyl chloride) (PVC) blends. In this work, PP/PVC/PP-HBP blends were prepared by melt mixing. Mechanical and rheological properties and phase morphologies of the blends were studied as a function of PP-HBP. The results showed that the tensile strength of the blends reached the maximum value when the content of PP-HBP was 5 phr and then dropped on the increase of PP-HBP. The impact strength of the blends showed a small change as that of pure PP/PVC blend, and the viscosity of the PP/PVC/PP-HBP blends was higher than that of pure PP/PVC when the amount of PP-HBP added was£ 5 phr. The viscosity of the PP/PVC/PP-HBP blends was lower than that of pure PP/PVC blend when PP/PVC blend contained PP-HBP > 5 phr. The scanning electron microscopy (SEM) showed that a two-phase morphology was characteristic of all blends. In presence of PP-HBP, the PVC spherical droplets of the minor phase dispersed in a PP continuous matrix phase, whereas there was a large difference among the minor-phase particle sizes. The SEM photos also confirmed that PP-HBP could enhance the adhesion at the interface and reduce the phase separation of PP/PVC blend. The tensile strength of the blends was in accordance with their morphology.