Iranian polymer journal
Volume:17 Issue: 5, 2008

Some of physical and structural characteristic features of exopolysaccharide (EPS) produced by indigenous soil bacterium Bacillus strain CMG1403 were studied by general analytical methods. EPS was isolated as high molecular weight, homogeneously white polymer containing 85.85% organic and 12.78% moisture content. In organic solvents such as methanol, ethanol, isopropanol and acetone, it exhibited flocculant properties whereas in distilled water and alkaline solution (0.1-1% NaOH) showed suspension gelling properties on stirring. Quantitatively, 92.13% hexoses as neutral sugars and 7.86% uronic acids were detected in purified EPS. This was confirmed by paper chromatographic separation of acid hydrolysate, that EPS produced by CMG1403 was an acidic heteropolysaccharide containing glucuronic acid, galactose and mannose. Degree of polymerization of these sugar units in EPS was estimated in terms of relative molecular weight, dispersed from >2×104 - <25×104 Da. This high molecular weight EPS was found to absorb 435 times more water than its own dry weight and also had the capacity to retain more than 40% of supplied water even at 60ºC for 20 days. Further, bacterial and fungal strains test could use the purified EPS as sole carbon source and their growth could not be inhibited. So it may be deduced that it is biodegradable and does not display in vitro antimicrobial activity. Therefore, based on these results, acidic heteropolysaccharide produced by Bacillus strain CMG1403 could be suggested to serve as non-toxic, biodegradable and environmental friendly water absorbent and thickening agent.

Acopolymer hydrogel of polyacrylic acid poly(ethylene glycol) was prepared by potassium diperiodatocuprate (III). In this work we considered many reaction conditions which can affect the conversion and hydrogel efficiency, such as reaction time, concentration of initiator, reactants and cross-linking agent. In the optimal conditions, temperature was 35ºC, concentration of potassium diperiodatocuprate (III) was 1.76 ×10-3 mol/L, the weight ratio of polyacrylic acid-poly(ethylene glycol) was 5:1 with reaction time of 80 min, cross-linker was 0.1 mg/mL, hydrogel efficiency (HE) could reach 0.90 and total conversion was 0.98. At the same time the effects of pH, poreforming agent of the hydrogel and cross-linker on swelling ratio were also investigated. The maximum swelling ratio of the hydrogel was obtained at pH 7 while the pore-forming agent was 0.08 mg/mL, the weight ratio of polyacrylic acid-poly(ethylene glycol) was 25:1, and the cross-linker was 0.05 mg/mL. The hydrogel was synthesized successfully as confirmed by infrared spectroscopy, and the experimental result indicated that potassium diperiodatocuprate (III)/poly(ethylene glycol) redox system was an efficient initiator for this reaction. Meanwhile, we also used scanning electron microscope (SEM) to study the structure of the hydrogel. SEM showed that there are many microporesformed in the microporous hydrogel compared to the traditional hydrogel, whichobviously improved the swelling capacity.

Polymeric nanofibres that mimic the structure and function of the natural extracellular matrix (ECM) are produced by electrospinning and have attracted great interests in biomedical applications in the last several years. Electrospinning is an efficient process whereby polymeric nanofibres are formed in a high-voltage electrostatic field. Compared to the conventional electrospinning, the gas-jet/electrospinning method can generate thinner and more uniform nanofibres with higher efficiency. Recently, polyethersulphone (PES) has drawn significant attention as a commercially available material with unique properties, which make it extremely suitable for fabrication of some biomedical materials. In this paper, the cyto-compatibility of a novel nanofibrous scaffold made of PES was examined by culturing human umbilical vein endothelial cells and rat osteoblasts. This scaffold was prepared by gas-jet/electrospinning and was made up of ultrafine fibres with the average diameter 126 nm and wellinterconnected pores. Cell attachment and proliferation and cell-matrix interaction were assayed by 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyl tetrazolium bromide (MTT) analysis, Vi CELL automated cell counter and scanning electron microscopy (SEM) imaging. The results of cell behaviour on the nanofibrous structure showed that both ECV-304 endothelial cells and osteoblasts adhered and proliferated well on the PES nanofibrous matrix. In addition, the cells maintained a normal phenotypic shape on the nanofibres. This may result from the cyto-compatibility of PES and the three-dimensional structureof electrospun nanofibres. Overall, these results strongly support the cyto-compatibilityof the gas-jet/electrospun PES nanofibrous structure and suggest potential uses ofthis biomaterial matrix as scaffolds for biomedical applications.

Anovel core/shell latex particle was successfully prepared by seeded emulsion polymerization. The rubbery core was made of poly (butyl acrylate) (PBA) with a slight cross-linked structure, while the glassy shell was poly (methyl methacrylate) (PMMA) containing a small amount of itaconic acid (ITA). The resulting core/shell latex particle PBA/P(MMA-ITA) should possess the function both of toughening the PBA core and the compatibilization of P(MMA-ITA) shell as well. The latex particles were characterized by transition electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and non-aqueous acidbase titration. The results showed well-defined core/shell morphology with the diameter of 50~65 nm and the cross-linkers diethylene glycol diacrylate (DEGDA), diallyl phthalate (DAP), and trihydroxymethylpropyl triacrylate (TMPTA) appeared the highest cross-linking efficiency. The monomer ITA has copolymerized with MMA successfully, and P(MMA-ITA) copolymer has been linked onto the surface of PBA core both by chemical bond and physical adsorption. The PBA/P(MMA-ITA) latex particles were core/shell structure indeed, and varying the ITA dosage and core/shell proportion, its size, Tg, and ITA content in shell layer would change relatively.

Many attempts have been made in the last decade to improve the solubility and processability of polyaniline (PANI) and various procedures have been devised in this direction, such as copolymerization, "precursor", "composite" and emulsion methods. It seems that the presence of an electron withdrawing group or an electron donating group decreases orbital overlap of the π-electrons and the nitrogen lone pair and leads to enhancement of solubility and processability of PANI. NPhenylglycine (PG) has a similar structure to aniline, but it has a carboxyl group at the site of nitrogen. Polymerization of PG in presence of template results in a water-soluble, conducting polymer. A strong polyelectrolyte acid such as sulphonated polystyrene (SPS) is the most favourable template. Poly (N-phenylglycine) (PPG) was prepared by the chemical method using ammonium persulphate (APS) as an oxidant in the presence of SPS as a template. The product was characterized by Fourier transform infrared (FTIR) and the ultraviolet-visible (UV-vis) spectroscopy. Cyclic voltammetry studies showed only one set of redox peaks and redox reversibility demonstrated the electroactivity of PPG as well. The electrical conductivity of polymer was measured by four-point probe method. The results showed that polymer yield and conductivity decrease as the ratio of template to monomer increases.

Poly(ethylene terephthalate) (PET) nanofibres were prepared by gas-jet/electrospinning of its solution of 15 wt% concentration in the mixture of phenol and 1,1,2,2-tetrachloroethane (50/50, w/w). The morphologies of gas-jet/electrospun fibres collected on a clean stainless steel plate and three different coagulation baths were observed under a scanning electron microscope. These coagulants were water, ethanol and the mixture of water and ethanol: 50/50 (v/v). Preliminary study on the effect of different coagulation baths as collector on the morphology of gas-jet/electrospun PET nanofibres was carried out. In particular, on the surface of the fibres obtained from the water coagulation bath, many short branches appeared. The beaded fibres were evident in the SEM image of the PET nanofibres collected in an ethanol bath. Smooth fibres without bead can be obtained using mixture of water and ethanol: 50/50 (v/v) as the coagulation bath. The average diameters of fibres collected in water, ethanol and water/ethanol bath, were 87, 105 and 84 nm, respectively. Compared with the average diameter (90 nm) of fibres collected on a metal plate, the diameter of fibres collected in water and water/ethanol coagulation baths decreased, while the diameter of fibres collected in ethanol bath increased. Among three coagulants, the morphology and the average diameter of PET nanofibres collected in the mixture of water and ethanol was best and thinnest, respectively.

In this study styrene was thermally polymerized by solution method in the presence of low molecular weight polybutadienes (PBDs) at 100, 175, 250ºC. Two types of PBD with various contents of 1, 2-vinyl and cis/trans isomers were employed. Using PBDs of low molecular weight allowed the study of grafting mechanisms by solubleژ grafted products obtained for liquid nuclear magnetic resonance (NMR) characterization. The effect of polymerization temperature and the type of polybutadiene on grafting degree were investigated. It is shown that grafting of polystyrene (PS) on PBD increases with increasing 1, 2-vinyl content and temperature of polymerization. Accordingly, PBD with high 1, 2-vinyl content and polymerization at 250ºC gave the highest grafting efficiency. However, grafting was identical for cis and trans isomers in 1, 4-PBD. Liquid 13C {1H} NMR spectroscopy using distortion enhancement by polarization transfer (DEPT) techniques were performed and a mechanism of grafting was proposed based on addition reaction with reducing the unsaturated olefinic double bonds without formation of any quaternary olefinic or aliphatic carbons. With quantitative analysis of triad sequences of 1, 2-PBD methylene carbon before and after grafting, it was shown that polystyrene chains mainly graft on syndiotactic sequences of 1, 2 PBD.