Iranian Polymer Journal
Year:2005 | Volume:14 | Issue:2 (56)|Papers Count:10

In view of their sensitivity to oxidation and to doping gases, it would seem natural to use conducting polymers as chemical sensors. The first graft copolymer of polypyrrole films has been synthesized by chemical and electrochemical polymerization of pyrrole in the presence of poly(para-chloromethylstyrene-co-styrene-co-pyrrolemethylstyrene), PCMS-co-S-co-PMS. Electrochemical synthesis of PCMS-co-S-g-PPy was carried out using a conventional three electrodes system with a SCE reference, platinum wire counter electrode, GC disk working electrode and tetrabutylammonium hexafluorophosphate in acetonitrile. The copolymer produced exhibits an electrical conductivity comparable to that of polypyrrole. Then prepared films were exposed to hydrogen halides, hydrogen cyanide, halogens, 1-3-5 trichloromethyl benzene (TCMB), methylbenzyl bromide (MBB), bromoacetone (BA) and cyanogen bromide (CB). Thermal stability of PCMS-co-S-g-PPy was investigated by scanning thermal analysis (STA), differential scanning calorimetry (DSC) and thermal gravimetry analysis (TGA). TGA thermogramme of copolymer showed a multi-step thermal degradation behaviour. This measurement showed that copolymer has excellent thermal stability. The response mechanism of this compound to a selection of gases and vapours was investigated, by measuring its electrical conductivity by a four-point probe method. This gas sensor may have advantages compared to other sensors in its ability to operate at room temperature, low gas and vapour concentration and solubility, stability in air, sufficient diffusion, and its selectivity.

Bis(cyclopentadienyl) zirconium dichloride (Cp2ZrCl2) as a homogeneous metallocene catalyst was manufactured in laboratory scale under highly controlled conditions. Ethylene polymerization was carried out using this catalyst while, methylaluminoxane (MAO) was used as a cocatalyst. Activity of 5759 gPE/mmol Zr.h at [Al]/[Zr] molar ratio of 770/1 was obtained. Polymer yield was increased with increasing in [Al]/[Zr] ratio to a limiting value. Addition of hydrogen as a chain transfer agent up to 120 cm3/L solvent, increased the activity of the catalyst. Polymerization was carried out at monomer pressure of 1 to 5 atm, and temperature of 40oC to 80oC. Polymerization activity was increased with increasing temperature to 60oC and slightly decreased with more increase in temperature. Upon the addition of catalyst a sudden increase of 10oC in temperature was observed, particularly when polymerization temperature was higher than 50oC. This increase could be due to high rate of polymerization which at high temperature could affect catalyst activity. Monomer pressure up to 2 atm increased productivity of catalyst. Increase in [Al]/[Zr] ratio, polymerization temperature and H2 concentration decreased Mv of polymer obtained. Melting point of polymer also decreased with increasing [Al]/[Zr] ratio. Density of obtained polyethylene was 0.940-0.950 g/cm3. Tg of one of the polymer samples was determined which was 99.9oC.

A number of composite membranes have been investigated for the separation of water from miscible organic-water mixtures. Organic solvents under study were ethanol, propanol-2 and acetone. Each composite membrane consisted at least of two fused layers. One layer was prepared from a mixture of natural rubber latex solution and the other layer from a solution of hydrophilic colloid between 1.25 to 20 percent by weight on a dry rubber basis. Four hydrophilic colloids, each of different molecular mass, were used in the preparation of each type of membrane. Each composite membrane was vulcanized before use in an all stainless steel membrane cell. These perm-selectivities have been compared with only those obtained from the use of vulcanized natural rubber latex membranes. A special novel design of this cell along with the entire equipment used have been described and discussed. The method of forming a thin film as well as the techniques for checking its soundness have also been presented and discussed. Finally, the proposed mechanism and a model that may be responsible for enhancing the permeation of water through the composite membranes have been discussed. The incorporation of a layer of alginic acid hydrocolloid in the composite membrane did increase the separation factor for water from ethanol-water mixtures by a factor of 24 in comparison to that for a natural rubber membrane alone. Similarly, the separation factors for water with hydrocolloids hydroxypropyl methyl cellulose and methyl cellulose from the solutions containing propanol-2 and acetone were 13.50 and 11, respectively.

As the first part of a continued research on conversion of carboxymethyl cellulosesodium salt (CMC) to useful  biopolymer-based materials, large numbers of cyanide functional groups were introduced onto CMC by grafting with polyacrylonitrile (PAN). The graft copolymerization reactions were carried out under nitrogen atmosphere using ceric ammonium nitrate (CAN) as an initiator. Evidence of grafting was obtained by comparing FTIR spectra of CMC and the graft copolymer as well as solubility characteristics of the products. The synthetic conditions were systematically optimized through studying the effective factors including temperature and concentrations of initiator, acrylonitrile monomer, and CMC. The overall activation energy for the grafting was estimated to be 39.7 kJ/mole. Finally, the CMC-g-PAN copolymer was characterized thermally by using differential scanning calorimetry and thermogravimetric analysis methods.

The electron beam radiation technique has been explored as the latest and most effective means of forming chemically active sites on LDPE surface. In this novel work a solventless grafting of 2-hydroxyethyl methacrylate (HEMA) on to LDPE surface was conducted. Thus prepared active sites were exploited to subsequently solventless graft copolymerization of HEMA onto LDPE by high energy electron beam radiation (10 MeV) at dose range of 10 up to 200 kGy at atmospheric pressure in air. As HEMA could not wet LDPE surface, its synthesized tacky polymer was used for coating and then grafting purposes. LDPE film and sheet surfaces were impregnated with the prepared adhesive and were irradiated. FTIR Spectra showed that the concentration of characteristic bonds of poly(HEMA-g-LDPE) (C=O in ester groups, in hydroxyl groups as C-OH, and ether carbon bonds as C-O) increased with increasing irradiation dose, also, the percentage of grafting significantly increased up to 60%. The hydrophilicity of the grafted surface considerably increased compared to that of the ungrafted ones as contact angle measurements showed a 72% decrease. Furthermore, the yields of gel content measurement were investigated and the topology of the surface and cross-section of poly(HEMAg- LDPE) films and sheets was studied by means of SEM. Moreover, the mechanism of achieving up to 70% cross-linked network in solid semi-crystalline LDPE is discussed.

Selectivity in interpolymer complex formation involving a typical four-component phenolic copolymer (p-chlorophenol-p-aminophenol-p-toluidine-p-cresol- HCHO copolymer), polyelectrolytes such as polyethylene imine (PEI) and Polyacrylic acid (PAA), a non-ionic homopolymer polyvinyl pyrrolidone (PVP), and some transition metal ions (e.g., Cu (II), Ni (II)) have been studied in dimethylformamide (DMF)-methanol solvents mixture. The coordinating groups of phenolic copolymer form complexes through hydrogen bonding and ion-dipole interactions. The different stages of interactions have been studied by several experimental techniques, e.g., viscometry, potentiometry and conductometry. Some schemes have been suggested to explain the mode of interaction between these components.

The Organic/Inorganic hybrid coating based on epoxy resin and sol-gel materials (tetraethoxysilane) have been prepared and studied. These hybrid networks possess excellent optical transparency and nano-scale microphase separation. These hybrid materials can be used for coating aluminium alloy (AA) substrates. Formation of the inorganic phase, from tetraethoxysilane (TEOS) by sol/gel process, organic phase and hybrid network were characterized by Fourier transform infrared (FTIR), attenuated total reflection (ATR), 29Si NMR Spectroscopy, and thermal gravimetry analysis (TGA). Chemical structure of the obtained network affected the morphology of the coating, and the morphology of the fractured surface was observed by scanning electron microscopy (SEM). It was found that the average diameter of the particle size is 167 nm, which indicated the transparency of the hybrid system. TGA Results showed that the cross-linking between the epoxy resin and silica increases the thermal stability of the system.

Waterborne polyurethane as a new polymer dispersion was synthesized by using relatively hydrophilic polyols. The polymer was prepared from polycaprolactone (Capa 225), toluene diisocyanate (TDI), 1,4-butane diol (BDO) as a chain extender, and dibutyltin dilaurate catalyst. Grafted polyurethane was prepared with chlorinated poly(ethylene glycol monomethylether) (PEGMME) in the presence of NaH catalyst. Chlorinated PEGMME was also prepared by reaction of PEGMME with thionyl chloride in dried toluene. FTIR and 1H NMR of the waterborne polyurethanes were studied. The effects of various molecular weights of poly(ethylene glycol monomethylether) (PEGMME) as non-ionic hydrophilic segments were studied. The particle size and viscosity of dispersion were systematically analyzed. It is found that by increasing the molecular weight of the grafted PEGMME, the particle size of the dispersed polyurethane is decreased, and viscosity is increased.

A new class of optically active poly(amide imide urethane) (PAIU) thermoplastic elastomers were synthesized via the reaction of NCO terminated polyether polyols with an imide containing optically active amino acid-based dicarboxylic acid chain extender according to a two-step diisocyanate route. In the first step, 4,4'-methylene-bis-(4-phenylisocyanate) (MDI) (6) was reacted with polyethyleneglycol-diols (PEG)s such as PEG-400, PEG-600, PEG-1000 and PEG-2000 to produce the diisocyanate-terminated polyether polyol (soft segment). The chain extension of the above soft segment with bis(p-amido benzoic acid)-N-trimellitylimido-L-leucine (BPABTL) (5) was the second step to furnish a series of new optically active PAIUs. The prepared PAIUs were characterized by conventional methods, and their physical properties such as solution viscosity, solubility, thermal stability and thermal behaviour were studied. The copolymerization reactions were performed in the presence of triethylamine (TEA), pyridine (Py), dibutyltin dilurate (DBTDL) and no catalyst, respectively. The resulting multiblock copolymers had inherent viscosities in the range of 0.12-0.55 dL/g. These copolymers are optically active, thermally stable and soluble in amide-type solvents. Some structural characterizations and physical properties of these new optically active PAIU thermoplastic elastomers are reported.

AHaake viscometer was used for viscosity measurements of aqueous polyvinyl alcohol mixtures at temperatures of 288, 298, and 308 K. It was observed that at low concentration of polyvinyl alcohol, variations of the measured shear stress (τ) versus shear rate (γ) were linear and therefore, the Newtonian behaviour of the studied mixtures is considered. The modified Eyring viscosity model previously proposed by the authors was used to test the measured data for aqueous polyvinyl alcohol mixtures. It was shown that the model is well capable to fit the data and the parameters, of the modle are evaluated.