Iranian polymer journal
Volume:20 Issue: 8, 2011

Herein, we synthesized and characterized polythiophene/single-walled carbonnanotubes nanocomposite. Thiophene (Th) and 2-(2-thienyl) pyrrole (TP) wereselected as interfacial modifiers for a SWNT-poly(Th-TP) nanocomposite. Theelectrical conductivity and thermal stability can be dramatically improved by in-situpolymerization of a thin layer of self-doped conducting polymer around and along thesingle-walled carbon nanotubes (SWNTs) beside the bulk polymer. The resultingcable-like morphology of the SWNT-poly(Th-TP) composite structure was characterizedwith Fourier transform infrared (FTIR), ultraviolet-visible spectroscopy (UV-Vis),field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis(TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Ramanspectroscopy. Also, the morphology of the film was investigated using a scanningtunneling microscopy (STM). The characterization of the molecular structure hasindicated that thiophene and TP molecules are adsorbed onto the surface of SWNTs topolymerize and SWNTs have been used as the core in the formation of a hybrid SWNTpoly(Th-TP) composite. Transmission electron microscopy analysis revealed that in theSWNT-poly(Th-TP) composite, SWNT constitutes the core and poly(Th-TP) acts as theshell. TGA data confirm that the presence of SWNT in the composite is responsible forthe high thermal stability of the whole material in comparison with pure poly(Th-TP).The standard four-point-probe method was utilized to measure the conductivity of thesamples. The conductivity through SWNT-poly(Th-TP) is as high as 38 Scm-1, wellabove the normal conductivity value of bulk poly(Th-TP) films (~1.67 × 10-1 Scm-1). Inaddition numerous physical properties of the nanocomposite were measured and theobtained results are discussed.

Alternating block copolymers of poly(4,4'-dioctyloxy-3,3'-biphenylene vinylene)-alt-(1,4-naphthalene vinylene) (P1), poly(4,4'-dioctyloxy-3,3'-biphenylenevinylene)-alt-(1,5-naphthalene vinylene) (P2), poly(4,4'-dioctyloxy-3,3'-biphenylenevinylene)-alt-(2,6-naphthalene vinylene) (P3), poly(4,4'-dioctyloxy-3,3'-biphenylenevinylene)-alt-(9,9'-dioctyl-2,7-fluorenylene vinylene) (P4), and poly[(4,4'-dioctyloxy-3,3'-biphenylene vinylene)-alt-(1,2-bis(2-thienylethylene)-5,5'-vinylene)] (P5) weresynthesized through Wittig polycondensation of aryl bis(methyl triphenylphosphonium)dibromide with aryl dialdehyde. The effect of positional isomers was studied using threenaphthalene isomers, viz., 1,4, 1,5 and 2,6 linking positions, respectively. All thealternating copolymers showed good solubility in organic solvents. The synthesizedpolymers were characterized by GPC, 1H NMR, FTIR and TGA. Thermal analysis ofthe polymers showed that they have thermal stability up to 250°C and their glasstransition temperatures are around 50-70°C. The optical properties of the polymersboth in solution and films were investigated. Optical studies of the polymers revealedthat all the polymers except P5 had absorption maxima between 347 nm and 360 nmand emission maxima in the range 430-460 nm in solution whereas polymer P5 hadabsorption maxima at 452 nm and emission maxima at 515 nm. 4,4'-Dioctyloxy-3,3'-biphenylene in the polymer backbone caused blue shift in optical properties comparedwith polymers having either of phenylene or 4,4'-biphenylene backbones. Opticalproperties of the polymers showed they are promising materials for opto-electronicdevices, as well.

Afacile procedure for fabrication of a poly(urethane urea)-based porous scaffoldwith proper porosity, pore size and mechanical strength for bone tissueengineering is reported in this work. For this purpose, sodium chloride(inorganic porogen) and polyethylene glycol (polymeric porogen) in particulate formwith pre-defined mesh sizes were mixed with the polymer and subjected to compressionmoulding process under optimum condition. Leaching out the impregnatedporogen particles by soaking in water (as a safe solvent) led to the final scaffold withdesired morphology. The porogen ratios and contents were verified in relation to poremorphology and mechanical properties of the scaffolds. Porosity and pore size of thescaffolds were independently controlled by the ratio and the particle size of the addedporogen. An increase in pore interconnectivity was observed as the sodiumchloride/polyethylene glycol ratio was increased. Scaffolds with a total porogen contentof 80-85 (wt%) displayed acceptable mechanical properties for bone tissue engineeringapplications. Our results revealed that a highly porous three-dimensional scaffold(>85 (v%)) with a well interconnected porous structure could be achieved by thiscombinatory process. The scaffold with a NaCl/polyethylene glycol ratio of 60/25exhibited a suitable morphology for osteoblast cells attachment and growth.

The novel "core - shell" polyacrylate composite hydrosols based on interpenetratingpolymer networks (IPN) were synthesized through a new two-step andsoap-free emulsion polymerization with seed hydrosol particles with noadditional emulsifier. The diameter of the hydrosol particles is much smaller than thatof the conventional emulsion, so it makes hydrosol particles show much betterstability and coating film properties. The obtained "core-shell" composite hydrosolparticles formed by the soft core of BA copolymer and the hard shell of MMA copolymerwere characterized by infrared analysis and transmission electron microscope(TEM). The damping properties of polyacrylate IPN, linear IPN, copolymer and blendcomposed of the same recipe were investigated by dynamic mechanical analysis(DMA) and scanning calorimetry (DSC). The results indicated that the polyacrylate IPNhydrosol exhibited the best damping properties because of its microheterogeneousstructure and the synergy effect between both BA and MMA components. While, thepolyacrylate copolymer demonstrates only a narrow glass transition range and thepolyacrylate blend demonstrates only two independent narrow glass transition ranges.The damping properties of the PBA/PMMA IPN hydrosol were investigated in detailsthrough different series of experiments. The results demonstrated that the IPNachieved better damping properties and processing performance under the conditionsof 100% neutralization of AA with DEAE, DVB cross-linking agent content of 0.1% andMMA/BA as main monomers with a ratio of 6/4. As far as the novel soft core and hardshell P(BA-co-HEMA)/P(MMA-co-AA-co-HEMA) composite hydrosol is concerned, itsdamping properties are mainly due to the ratio of main monomers MMA/BA presentedin this work.

Anovel tissue adhesive composed of urethane pre-polymer and chitosan gel wassynthesized in a two-step procedure. The first step of the procedure was carriedout under nitrogen atmosphere at 60°C and 24 h and the final formulation wasprepared using a urethane pre-polymer and 2% chitosan gel. The presence andquantity of NCO groups in the adhesive were determined using FTIR spectroscopy andtitration methods. The presence of the urethane band and NCO free groups in theadhesive were confirmed at 1514 cm-1 and 2261 cm-1, respectively and the quantity ofNCO free groups was calculated as 21%. The molecular weight of urethane prepolymerin the adhesive was measured 2444.7 g/mol using GPC. The relative peelresistance of the adhesive bonds between flexible adherents was 15.1 N for urethanepre-polymer and 14.6 N for the final formulation of tissue adhesive. Chitosan gel wasused in this tissue adhesive to increase its biocompatibility. The structure of thesynthesized adhesive which exhibited a porous structure due to the presence ofchitosan gel was illustrated using SEM technique. The surface energy of the adhesivewhich was lower than its values for gelatin, skin and blood was determined by contractangle measurment as 33.65 mN/m. Cytotoxicity of the tissue adhesive was determinedon growth and viability of various cells, using CaCO2, T47D, HT29 and NIH3T3 celllines which showed adhesive's non-cytotoxic nature. The skin irritation test, carried outaccording to ISO 10993-10, suggested that the compound is non-irritant.

Aseries of PE/SiO2 nanocomposites, namely PE2D, PE5D, PE7D and PE10D,were prepared via reactive extrusion from the mixtures of vinyl functionalizednano-SiO2 (v-SiO2), Dicumyl peroxide and PE. For comparison, PE/SiO2nanocomposite (PE7) was also prepared by the same method from a mixture of v-SiO2and PE. SEM and TEM micrographs showed that the above products were composedof nanocomposite. Xylene extraction results showed that, except PE7, nanocompositescontained gel. FTIR Spectra showed the existence of SiO2 in the gels, meaning thatSiO2 nanoparticles were covalently bonded to PE chains, i.e., PE2D, PE5D, PE7D andPE10D were nanocomposites formed by covalent bonds between SiO2 and PE.Studies based on DSC show that all the nanocomposites have Tm of close values andPE7 has higher crystallinity than other nanocomposites. Mechanical properties wereinvestigated through tensile tests and the results show that covalently bonded PE/SiO2nanocomposites have better performance compared to PE7. In this respect, the tensilestrength, modulus, and elongation-at-break of PE7D are given as 41.5 MPa, 349 MPaand 1060% which are as high as 170%, 126% and 125% of the values for pure PE.While the tensile strength, modulus, and elongation-at-break of PE7 are only 109%,108% and 109% of the values for pure PE, indicating the significant effect of covalentbond between polymer matrix and nanoparticles.

Amathematical model based on the Cahn-Hilliard non-linear theory of phaseseparation has been developed. The model equation has been solved using adiscrete cosine transform spectrum method to provide dynamic spatial concentrationfield of a polymer blend and predicting the morphology evolution during thecourse of a temperature-induced phase separation process. The model shows anaccurate qualitative agreement with experimental observation using parameters of thepolystyrene/polyvinylmethylether blend and different initial concentrations of the blendhave been tested in relation to the microstructure, transient and later stages of blendmorphologies. It has been observed that kinetics and morphology of the phaseseparated blend are affected by the initial concentration of the blend. In this study,different types of microstructures, e.g., droplet-like and rod-like morphologies havebeen identified. It is concluded that the initial concentration of each component of theblend and temperature are the most important variables which control the kinetics ofphase separation and blend morphology. The mathematical model provides a suitabletool for better understanding of the kinetics and phase separation process as well asthe microstructure of the polymer blends. The discrete cosine transform methodfor solving a high non-linear partial differential equation is considered as a suitablenumerical approach where the other conventional mathematical numerical methodssuch as finite element and finite volume methods require many computational facilities.The model is very useful for studies of the early and later stages of phase separationprocess and provides information on concentration profile of the separated phaseswhich would be useful in the determination of the interfacial properties.