Iranian polymer journal
Volume:20 Issue: 9, 2011

Anovel and environmentally friendly catalytic system based on palladium nanoparticlessupported on poly (N-vinylimidazole) (PVI) grafted silica was prepared.The advantages of this system lie not only in its easy separation from the products,recycling and preventing the loss of metal, it has also excellent chemical andthermal stability, good accessibility and the dispersion of catalytic sites. The complexationof (PVI)-grafted silica with PdCl2 was carried out to obtain the heterogeneouscatalytic system. X-ray diffraction (XRD) technique and transmission electronmicroscopy (TEM) image showed that palladium dispersed through the support innanometer size and there was no change in the size and morphology of the palladiumnanoparticles after coupling reactions. This catalytic system exhibited excellent activity incross-coupling reactions of aryl iodides, bromides and also chlorides in Heck,Sonogashira and Suzuki reactions in short reaction times and high yields. The use ofaryl chlorides in cross-coupling reactions is usually hardly successful, but excellent resultswere gained in the presence of tertabutylammonium bromide (TBAB) as an additive.Elemental analysis of Pd by inductively coupled plasma (ICP) technique and hotfiltration test showed low leaching of the metal into solution from the supported catalystand that the catalyst behaves as a heterogeneous system. The catalyst can be reusedseveral times in repeating coupling reactions cycles without considerable loss in itsactivity

Tussah silk fibroin (TSF), a fibrous biopolymer from wild silkworm of the speciesAntheraea pernyi, was first electrospun using 1,1,1,3,3,3-hexafluoro-2-propanol(HFIP) as solvent at a concentration of 8% (by weight). The effect of processingparameters on the morphology, structure and mechanical properties of electrospunTSF nanofibres was investigated. The electrospun TSF nanofibres presented theband-like morphology using a rectangular aluminium foil as collecting plate and theaverage diameters ranged from 245 nm to 439 nm according to different spinningparameters. At a spinning distance of 10 cm, the increase of spinning voltage inducedthe conformation transition of TSF nanofibres from α-helix to β-sheet and random coil;however, at a spinning voltage of 15 kV, the increase of spinning distance induced theconformation transition of TSF nanofibres from random coil to α-helix. Nevertheless,the variation of processing parameters could not change the fact that α-helix andβ-sheet conformations co-existed in the fibres and α-helix was the main structure. Themechanical properties of non-woven TSF nanofibrous mats depended more on theassembly of the fibres than on the fibre structure, and the nanofibrous mats with smalldiameters showed higher mechanical properties. The study showed that the thin andrelative uniform rod-like nanofibres with an average diameter of 245 nm could beobtained through a rotary roller as a collecting device. The nanofibrous scaffoldprepared in this paper makes a promising candidate scaffold for tissue engineeringbecause of the especial tripeptide sequence of Arg-Gly-Asp (RGD) in TSF.

In this work the coexistence effect of Cloisite 30B and multi-walled carbon nanotubes(MWCNT) on the crystal transformation of the polyvinylidene fluoride (PVDF) matrixis reported. It was found that at a constant rate of 3% (by weight) total modification,a higher percentage of beta crystal was evolved in PVDF matrix as compared with thatof 3% (by weight) of each nanomaterial in the whole nanocomposite system. Thesechanges in the crystalline structure were quantitatively and qualitatively studied usingFTIR and WXRD techniques, respectively. The FTIR technique confirmed the formationof 80%, 71% and 84% of beta crystal for the three prepared composites. Thesmall-angle X-ray scattering (SAXS) technique revealed a 10-time increase in thed-spacing of the nanoclay in nanocomposites as compared with that in raw nanocaly.The morphology of the nanomaterials and the state of dispersion were investigatedusing SEM and TEM techniques. The synergism observed was assigned to differencesin surface conformations and aspect ratio of the nanomaterials. These nanocompositesensured formation of beta crystals without any need to apply strain. Meanwhile, thepiezoelectric constant (d33) of the hot-pressed samples was found to be zero. To attainpiezopyroelectric characteristics, there was a need to cold-drawing, probably by smallerstrain which resulted in better mechanical properties and anisotropy of the resultinghybrid nanocomposite

The fracture toughness was determined for cellular polymers by micromechanicalmodelling using finite element analysis. In this study, mode I and mode II offracture toughness were evaluated with a 2D-solid model using fracture analysiscode FRANC2D/L. Simulation was performed for open cell polyurethane foams ofdifferent densities. Two cases were considered: constant cell length, l, and variable cellwall thickness; the former for constant cell wall thickness, t, and the latter for variablecell length. For estimation of fracture toughness the applied loads were progressivelyincreased to the point reaching the fracture strength of the solid material (130 MPa) inan un-cracked strut in front of the crack. The estimated fracture toughness wasindependent on crack length, indicating that the obtained values could be consideredas material property. The values of the fracture toughness of polyurethane foams arein the range of 10-3-10-1 MPa.m0.5. Lower values were obtained for mode II fracturetoughness. A strong dependency of the fracture toughness on the density of thecellular material was featured by present study. The obtained results for mode Ifracture toughness were compared with Gibson-Ashby micromechanical model, bywhich a good agreement was obtained. While, mode II fracture toughness wascompared with Choi and Sankar micromechanical models. The predicted fracturetoughness was finally validated with some experimental data. Another advantage of thismodel was to obtain a fully described the stress field in the solid struts. The stressdistribution in the first un-cracked strut showed a combined stress (bending andtension) for mode I loading, while for mode II loading a pure bending appeared

Copolymerizations of pyrrole (Py) with N-pentylpyrrole (NPPy) and N-dodecylpyrrole(NDPy) were carried out by chemical and electrochemical oxidationmethods. Nanoparticles made of conjugate copolymers with different feed ratiosof monomers were prepared by chemical polymerization (conventional and interfacialmethods) in presence of iron (III) chloride hexahydrate (FeCl3.6H2O) as the oxidant.Nanostructure copolymers with higher conductivity were synthesized by simply tuningthe preparation conditions in a two-phase medium (toluene-water as solvents). The Npentylpyrroleand N-dodecylpyrrole monomers were synthesized with higher purityfrom pyrrole. Fourier transform infrared spectroscopy, scanning electron microscopyand four probe conductivity measurement techniques were applied for the characterizationof the copolymers. The conductivity of the copolymers obtained by interfacialmethod using toluene as an organic phase was 5-6 times higher than the copolymerobtained by a conventional method (for molar ratio of Py:NPPy, 30:70). In electrochemicalmethod, copolymer thin films were synthesized with different feed ratios ofmonomers by cyclic voltammetry in lithium perchlorate-acetonitrile (LiClO4/CH3CN)electrolyte on the surface of the glassy carbon (GC) as the working electrode.Deposition conditions on the GC, influence of the molar ratio of monomers on theelectroactivity and formation of copolymers were studied using cyclic voltammetry

Radical grafting of acrylic acid (AA) monomer onto the aromatic polyamidereverse osmosis (APRO) membrane was performed. The physical adsorption byfree radical initiator technique was applied to modify the surface of theasymmetric membrane. The hydrophobic initiator adsorbed on the APRO membranewas used to initiate the water-soluble monomer in aqueous phase. The APROmembrane was immerged into ether solution of benzoyl peroxide (BPO). The BPO wasphysically adsorbed onto the membrane surface. The hydrophobic initiator wasinhibited to diffuse through membrane surface into the aqueous solution of the acrylicacid monomer because of a hydrophilic/hydrophobic barrier. The grafting process wastriggered by the residing BPO on the membrane surface in an aqueous medium at70°C for a certain time interval. The surface changes of grafted membrane werecharacterized with ATR-FTIR, SEM, AFM and contact angle measurements. The resultsshowed the PAA is successfully grafted on the APRO membrane surface. When thegrafting rate of PAA was increased from 0% to 8.02%, the edge of leaf-like surface ofAPRO membrane was gradually curled and the roughness of APRO membrane wasdecreased about 36% (Ra). These changes of membrane surface increased thehydrophilicity of the APRO membrane surface and the contact angle decreased byabout 50%.

Poly(vinylidene dichloride)-diethylene triamine supported palladium complex(PVDC-DTA-Pd) was prepared from poly(vinylidene dichloride) by a simplemethod. In contrast with other polymer-supported catalysts, the greatestadvantage of the catalyst system was that the cost of the catalyst was remarkably lowdue to the easily obtained materials and the simple synthetic route. Heck reactions ofaryl iodides with acrylic acid catalyzed by PVDC-DTA-Pd could be performedefficiently in water. Yield of cinnamic acid was 99.6% as the coupling of iodobenzenewith acrylic acid was carried out in water at 90°C for 3 h in the air. Both electron-richand electron-deficient aryl iodides reacted with the alkenes to give the correspondingtrans-products. When styrene was adopted as alkene, high yields were obtained inDMF rather than in water because the hydrophilicity of styrene was poor. Highactivities for aryl bromides and activated aryl chlorides were also found when thereactions were carried out in tetrabutylammonium bromide to afford the coupledproducts in moderate to good yields. However, high temperature (120°C) and inertatmosphere were required. The catalyst can be recovered easily by filtration andre-used for Heck reaction. Yield of the cinnamic acid was up to 78.5% at the cycle offive, which indicated the high stability and good re-usability of PVDC-DTA-Pd.