Iranian Polymer Journal
Year:2008 | Volume:17 | Issue:2|Papers Count:6

The highly oriented light-emitting films of polyfluorene-based conjugated polymers blended with ultrahigh molecular weight polyethylene (U-PE) are prepared by using a tensile deformation technique. The high dichroic ratios of blue light (58 in photoluminescence (PL)) from the poly (9,9-dioctylfluorene) (PFO)/U-PE blending film and of green light (36 in PL) from the poly(9,9-dioctylfluorene) containing one fluorenone unit (PFF)/PFO/U-PE blending film are obtained. In the PFO/U-PE blending film, the variation of the photophysical properties of the blending films with the drawing ratio is discussed in detail which suggests that the conjugated polymer chains are forced to a highly dispersed and oriented condition in the oriented PE matrix. The green band (g-band) of the blending film containing PFF is also studied and found in such a highly oriented condition, and a set of new evidence was obtained demonstrating the keto-defect origin of g-band.

Agreat number of studies of new polymer syntheses has been focused on the preparation of high-performance polymers. Imide polymers and their copolymers are a well-established class of high-performance polymers that show good combination of mechanical, electrical, and thermal properties. This paper reviews the synthesis and properties of polyimides and copolyimides with different structures specially those containing pyridine ring in their structure. Advantages of using a pyridine nucleus are relayed on two factors. First, high thermal stability derived from its molecular symmetry and aromaticity, and second, improved solubility of the pyridine (in respect to phenyl group) containing polymers because of increased dipoledipole interactions of polymer-solvent system. This discussion covers different structures of pyridine-based polyimides and their physical and thermal properties. The subtle variations in the structure of the monomers have a great effect on the properties of the final polyimides. Various structural features that are important for understanding the structure/property relationships have been discussed.

Currently, in situ forming polymeric gels and networks have attracted much attention due to their potential applications as injectable devices in drug delivery and tissue engineering. To this end, biodegradable hydrogels were developed based on poly (ethylene glycol)-co-fumaric acid macromers. These macromers were synthesized through direct polycondensation of poly (ethylene glycol) of different molecular weights and fumaric acid using dicyclohexylcarbodiimide (DCC) as an esterification promoting agent. They were fully characterized by spectroscopic methods (i.e., Fourier transform infrared and proton nuclear magnetic resonance spectroscopies) and gel permeation chromatography and thermal analysis (i.e., differential scanning calorimetry) techniques. Thermal characterization showed that the produced macromers have lower crystallinity than the original precursors. The molecular weight and the degree of oligomerization of the macromers were also substantially affected by the molecular weights of the initial PEGs. The macromers were cross-linked by redox mechanism in the presence of water soluble initiation system consisting of ammonium persulphate and N,N,N¢,N¢-tetramethylethylenediamine. The swelling properties of the cross-linked gels were also examined which showed a significant dependency to the initial molecular weight of PEGs. Our results have suggested that these biodegradable hydrogels are potentially applicable in drug delivery and tissue engineering applications.

The preparation and characterization of polyaniline/polystyrene (PANI-PS) composite are described. The polyaniline composite was synthesized by chemical polymerization of aniline in polystyrene emulsion matrix. The effects of dioctyl phthalate (DOP), N-methyl-pyrrolidone (NMP) and mineral oil as plasticizer on improving the processability of PANI-PS composite are investigated by melt flow index (MFI) determination. It has been found that, among three tested plasticizers, DOP is more compatible with the composite. Using 35% (w/w) DOP, the MFI value of 0.093 g/10 min was recorded at 170°C. The DSC measurements of PANI-PS composite show a softening point at 106°C indicating that the obtained composite is melt processable above this temperature. Based on solubility studies, the composite is soluble in conventional organic solvents. The conductivity of about 0.013 S/cm is obtained for a free standing film of composite. Also the composite has shown excellent adhesion properties onto the steel plate. Cyclic voltammetric studies have revealed that the synthesized composite is electroactive, too.

Kinetics of radical telomerization of vinyl acetate (VAc) with CDCl3 as a telogen in the presence of AIBN initiator was studied by 1H NMR. Structure of the chains was analyzed in detail by 1H NMR spectroscopy technique. It was observed that two telomers with different α-ends including trichloromethyl- and dichloromethyl-terminated VAc telomers were formed during the telomerization reaction. Therefore, two different mechanisms of the transfer reaction to CDCl3 telogen have been proposed which were supported in details by the abstraction of either deuterium or chlorine radicals from CDCl3 molecules. 1H NMR analysis also allowed us to calculate the conversion of VAc (XVAc), number-average degree of polymerization (DPn), telomer percentage (%), and the ratio of the abstractions of deuterium radicals to chlorine radicals (RD/Cl) from CDCl3 molecules. These results showed that at the same conversion, at first, DPn decreases with increase of the initial concentration of AIBN but then increases.Also, DPn at the same conversion decreases by increasing of the R0 and decreasing of the reaction temperature. Moreover, at the same conversion, telomer percentage increased by decreasing [AIBN]0 and reaction temperature while decreased by decreasing of the R0 (or equivalently [CDCl3]). The highest yield of telomer was about 60%. There was not any significant difference between the RD/Cl at various conditions used in VAc telomerization by CDCl3. 1H NMR analysis showed that the rate of the abstraction of deuterium radical from CDCl3 molecule is favoured relative to its rate of chlorine radical abstraction.

In this article, pH and temperature double responsive poly (N-isopropylacrylamideco- IA) hydrogels were prepared by copolymerization in mixed solvents of water and dimethylsulphoxide (DMSO) above zero. The freshly fabricated P(NIPAAm-co-IA) hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) techniques to investigate their chemical compositions, structures, and morphologies. The results showed that all of these gels have similar chemical compositions and structures but differ in surface morphologies. The hydrogels prepared with highest DMSO/water ratios have porous surfaces, while the other gels exhibit smooth and dense surfaces.Temperature and pH sensitivities of the resultant hydrogels were examined through swelling ratios and deswelling/reswelling kinetics experiments, as well. The results indicated that only hydrogels prepared in the highest DMSO/water ratio media exhibited improved properties such as higher swelling ratios, faster deswelling and reswelling kinetics compared with traditional P(NIPAAm-co-IA) hydrogels, as the other hydrogels possessed lower swelling ratios and slower deswelling and reswelling dynamics. We have proposed that there maybe an energy barrier existed for conformation transitions in the process of removal of DMSO by water. Only the gels which could overcome the energy barrier exhibited expanded network structures and improved properties while, the other gels maintained their contracted network structures and poor properties.