Iranian Polymer Journal
Year:2007 | Volume:16 | Issue:1 (79)|Papers Count:7

Oxidative and non-oxidative dopings of polyaniline in various acidic media with different concentrations have been studied by electrochemical quartz crystal nanobalance technique. Polyaniline was synthesized electrochemically on the gold electrode of quartz crystal using a galvanostatic electropolymerization method (1 mA/cm2). Electrochemically synthesized polyaniline film was exposed to different concentrations of various acidic solutions and the changes in the mass (frequency) of the polymer were recorded. Results showed that the extent and the rate of non-oxidative doping depend on the concentration and nature of dopant acid. The rate of doping in the case of a number of tested inorganic acids was as the order of: H3PO4<HCl<HClO4<H2SO4. Exposure of doped polyaniline to ammonia solution (0.5 M) resulted a mass reduction in the polymer film due to the non-oxidative undoping process. Further experiments showed that this doping/undoping behaviour is a completely reversible process. Mass changes of the polymer in oxidative doping/undoping process were also recorded. It was also found that at pH values lower than 1, the total mass change during oxidation of the polymer was dependent on acid (or proton) concentration. However, at pH values over 1, the mass change during oxidation was independent of acid (or proton) concentration. These two observations support two different mechanisms of doping suggested by other workers.  

Hydrogels produced by in situ polymerization have been extensively studied as iomaterials in applications such as scaffolds for tissue engineering and drug delivery systems. In situ polymerization process allows the hydrogel to be generated in vitro or in vivo from a low viscosity solution of monomer or low molecular weight polymer by free radical pathway. In this study, polyethylene glycol-diacrylate (PEG-DA) macromer has been synthesized by esterification of PEG with acryloyl chloride and characterized by NMR and FTIR spectroscopies and swelling study. Crosslinking was initiated by a pair of redox initiator, i.e. ammonium persulphate and N,N,N',N'-tetramethylethylenediamine. The conversion rate of the macromers to a cross-linked network was determined using 1H NMR and dynamic oscillatory test at 370C and continuous disappearance of vinyl group upon addition of redox agent to a macromer solution was evaluated.  

For the first time, we report the optimization of reaction conditions for the synthesis of novel thermally modified optically active poly(amide-imide-ether-urethane) s (PAIEU)s prepared by diisocyanate route. The effects and importance of different reaction parameters such as reaction temperature, reaction time, and soft segment length on the controlling of chain growth of the resulting copolymers were investigated. Thus, four different series of PAIEUs based on different molecular weight of polyethylene glycol (PEG)s were synthesized through the reaction of a new imide containing diacid, with 4,4'-methylene-bis-(4-phenylisocyanate) (MDI). A linear correlation was constructed using experimental values of viscosities of the resulting copolymers based different molecular weights of PEGs at different reaction temperatures, and reaction time. The influence of each parameter was studied by factorial design analysis. Analysis of variance (ANOVA) was also used to evaluate the significance of the linear regression model (correlation). The statistical parameters reveal strong evidence that the constructed correlation is reliable.

Highly active supported catalyst of Ziegler-Natta type was prepared by reaction of a Grignard reagent. The starting chemicals for preparing MgCl2, the support, were butyl magnesium chloride which mixed with AlCl3 and CH3Si(OC2H5)3, following to two steps treatment of the chemicals with TiCl4 in toluene. Ti  oncentration in the solid catalyst was 3.19%. Slurry polymerization of ethylene was carried out using the catalyst in dry heptane, while, triethylaluminium was used as cocatalyst. The cocatalyst effects, such as cocatalyst/catalyst molar ratio, polymerization time, temperature, H2 concentration and the monomer pressure on activity of the catalyst were studied. There was an optimum [Al]/[Ti] molar ratio and temperature to obtain the highest activity of the catalyst. The maximum activity was obtained at 60ºC, and [Al]/[Ti]=714:1. Productivity of 14700 g PE/mmol Ti.h was obtained at monomer pressure of 8 bar. Addition of hydrogen decreased the activity of catalyst and the viscosity average molecular weight (Mv) of the polymer obtained, while, increasing monomer pressure increased its activity. Density of the polymer obtained was 0.93- 0.95 g/cm3 which is in the range of high density polyethylene. Melting point of the polymer was in the range of 140-1440C.

The TiO2/poly (St-co-MAA) core/shell composite particles were prepared via emulsion polymerization. The cetyltrimethyl ammonium bromide (CTMAB) was used as surfactant of emulsion polymerization. The effect of the styrene/MAA weight ratio on the morphology of the composite particles was investigated. The inorganic/organic core/shell composite particles were characterized by Fourier transform infrared spectra (FTIR), translation electron microscope (TEM), thermogravimetric analysis (TGA) and particle size analyzer. The results of FTIR and TGA measurements showed that TiO2 was successfully coated by poly (St-co-MAA). The particle size analysis and TEM result of the resulting composite particles indicated that these particles had a narrower size distribution and regularly spherical core/shell morphology. At the same time, there was one TiO2 particle within each TiO2/poly (St-co-MAA) composite particle and the average particle diameter of composite particles was 191 nm. In addition, the results showed that the conversion of monomers was 78.0% in this emulsion polymerization and copolymer of poly (St-co-MAA) constituted of 62.6% composite particles. The encapsulation was best when the styrene/MAA weight ratio was 3/2, and the encapsulation efficiency reached 85.8%.

Atom transfer radical copolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) with PVAc-CCl3 telomer as macroinitiator and CuCl/N,N,N',N',N''-pentamethyldiethylenetriamine (PMDETA) catalyst system in bulk at 80ºC was investigated. The molecular structure of the poly(vinyl acetate-b-MAco- MMA) block terpolymers were characterized by 1H NMR and FTIR spectroscopies and gel permeation chromatography (GPC). The composition and end chain functionality of MA units in terpolymer increased with mole fraction of MA in the feed. The chain configuration of terpolymer indicated that the syndiotacticity of MMA repeating unit in terpolymer increased from 31.9 to 52.5 with MMA mole fraction in the feed. The experimental and theoretical number average molecular weights of terpolymer were studied. The molecular weight distributions of the synthesized block terpolymers were narrowed from 1.77 in macroinitiator to about 1.27-1.44. The theoretical number average molecular weight of terpolymer increased with overall molar conversion and composition of MMA unit in terpolymer. The overall propagation rate constants in ATRP of MA and MMA were calculated and increased with mole fraction of MA in the feed.

The concept of combining synthetic polymers with naturally derived biopolymers and resorbable bioceramics has been recently considered as an effective solution for orthopedic tissue engineering. In the present study, based on a biomimetic approach, a novel 3D biodegradable porous hybrid biomaterial consisting of poly(L-lactic acid) (PLLA), chitosan, gelatin, and b-tricalcium phosphate (b-TCP) was developed. Macroporous LLA/b-TCP scaffolds were prepared by freezeextraction/ particulate leaching method and embedded with porous chitosan/gelatin/b - TCP sponges. The influences of chemical, physical, and structural properties of the scaffolds prepared on the attachment and differentiation of mesenchymal stem cells into osteoblasts and the proliferation of the differentiated cells were investigated. Osteogenically induced cultures revealed that cells were well-attached, penetrated into the scaffold and uniformly distributed. The expression of early and late phenotypic markers of osteoblastic differentiation was upregulated in the scaffolds cultured in osteogenic medium.