Mehmet S. Eroglu

Levan Nanostructured Thin Films by MAPLE Assembling

Synthesis of nanostructured thin films of pure and oxidized levan exopolysaccharide by matrix-assisted pulsed laser evaporation is reported. Solutions of pure exopolysaccharides in dimethyl sulfoxide were frozen in liquid nitrogen to obtain solid cryogenic pellets that have been used as targets in pulsed laser evaporation experiments with a KrF* excimer source. The expulsed material was collected and assembled onto glass slides and Si wafers. The contact angle studies evidenced a higher hydrophilic behavior in the case of oxidized levan structures because of the presence of acidic aldehyde-hydrogen bonds of the coating formed after oxidation. The obtained films preserved the base material composition as confirmed by Fourier transform infrared spectroscopy. They were compact with high specific surface areas, as demonstrated by scanning electron and atomic force microscopy investigations. In vitro colorimetric assays revealed a high potential for cell proliferation for all coatings with certain predominance for oxidized levan.

Preparation and thermal characterization of block copolymers by macroazonitriles having glycidyl azide and epichlorohydrin moieties

Poly(glycidyl azide) (PGA) an energetic polymer and polyepichlorohydrin (PECH) were condensed with 4,4′ azobis(4-cyanopentanoyl chloride) (ACPC) to prepare macro-azo-initiators. Block copolymers containing each of these polyethers as a block segment combined with polystyrene (PS) or poly(vinyl acetate) (PVAc) have been drived by the polymerization of monomers initiated with this macro-azo-initiators. Thermal properties of block copolymers were investigated with differential scanning calorimetry (DSC) and thermogravimetry. DSC traces showed single glass transition temperatures in between the related segments of copolymers. Dynamic thermogravimetric analysis revealed the individual degradation behaviors of block segments

Thermal decomposition of poly(glycidyl azide) as studied by high-temperature FTIR and thermogravimetry

Thermal decomposition of poly(glycidyl azide) (PGA) has been studied by using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and high-temperature FTIR spectrometry. By using DSC and TGA techniques, the first stage weight loss of PGA due to exothermic decomposition of pendant azide (N3) groups was explained in terms of the energy released at every stage of decomposition. From the glass transition temperature (Tg) measurements, it was observed that Tg values of PGA increased with increasing quantity of decomposed N3 groups. The course of the decomposition reaction was also studied by taking successive FTIR spectra. It was observed that during the first stage weight loss process of PGA, the main chain was not decomposed thermally; inter- and intramolecular linking reactions accompanied the side chain decompositions.

Dielectric Properties of Polymer Composites Filled with Different Metals

Electrically conductive composite systems based on polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) filled with metal powders of Al and Cu have been studied. The composite preparation conditions allow the formation of a random distribution of metallic particles in the polymer matrix. Dependence of the dielectric and conductivity properties of the PVC and PMMA/fillers was studied over a broad range of frequency and volume fraction of metal fillers. The experimental results could be explained by means of the conductivity of fillers and the interface polarization between polymers and fillers. Percolation was also seen in this study when the volume fraction of conducting fillers was close to critical value, in which the composites undergo an insulator‐conductor transition. The relation among the dielectric property and the fillers with different conductivity was proposed.

Comprehensive characterization of chitosan/PEO/levan ternary blend films

Ternary blend films of chitosan, PEO (300,000) and levan were prepared by solution casting method and their phase behavior, miscibility, thermal and mechanical properties as well as their surface energy and morphology were characterized by different techniques. FT-IR analyses of blend films indicated intermolecular hydrogen bonding between blend components. Thermal and XRD analysis showed that chitosan and levan suppressed the crystallinity of PEO up to nearly 25% of PEO content in the blend, which resulted in more amorphous film structures at higher PEO/(chitosan+levan) ratios. At more than 30% of PEO concentration, contact angle (CA) measurements showed a surface enrichment of PEO whereas at lower PEO concentrations, chitosan and levan were enriched on the surfaces leading to more amorphous and homogenous surfaces. This result was further confirmed by atomic force microscopy (AFM) images. Cell proliferation and viability assay established the high biocompatibility of the blend films.

Characterization of network structure of poly(glycidyl azide) elastomers by swelling, solubility and mechanical measurements

Poly(glycidyl azide) (PGA) networks were prepared by using Desmodur N-100 pluriisocyanate, isophorone diisocyanate (IPDI)/trimethylol propane (TMP), and hexamethylene diisocyanate (HMDI)/(TMP) reactive systems with various NCO/OH reactive group ratios. Swelling tests of these networks were carried out in tetrahydrofuran (THF) at room temperature. The number average molecular weight (Mn) and polymer solvent interaction parameter (χ1) of PGA in THF was determined by vapour pressure osmometry (VPO) to be 0.25 for the PGA-THF system at 45°C. The average molecular weights between junction points (Mc) were calculated by using the Flory-Rehner equation. For the networks prepared by three different reaction systems, a linear change of Mc with sol content was observed.

Ceric ion initiation of methyl methacrylate from poly(glycidyl azide)-diol

Abstract Polymerization of methyl methacrylate initiated by ceric ammonium nitrate in combination with poly(glycidyl azide)-diol was investigated in aqueous nitric acid. Poly(methyl methacrylate)-b-poly(glycidyl azide) copolymer was obtained. Block copolymer yield was increased using tetrabutyl ammonium hydrogen sulphate as a surfactant. The effect of nitric acid, ceric ions and diol concentration on the block copolymer yield was investigated. Block copolymers were characterized using GPC, 1H-NMR, FTIR, DSC, TGA and fractional precipitation methods.

Spectroscopic and thermal characterization of poly(glycidyl azide) converted from polyepichlorohydrin

Poly(glycidyl azide) (PGA) was synthesized by reaction of polyepichlorohydrin (PECH) with sodium azide (NaN 3 ) by using phase-transfer catalysis. A detailed analysis was performed to follow the polymer-polymer conversion reaction. Conversion of - CH 2 - Cl to - CH 2 - N 3 was achieved completely in 6 h, as determined from FTIR assignment, UV-VIS spectroscopy, and thermal analysis. In FTIR and UV-VIS spectroscopy studies, the reaction was followed from the change in characteristic peak intensities. Thermal analysis also showed that the first thermal decomposition process of PGA, which is due to the exothermic cleavage of pendant - N 3 groups, was shifted to higher temperatures, and the exothermicity was increased as the conversion proceeded. It was also found that the extent and completion of -Cl to -N 3 conversion could be easily followed by measuring the glass transition temperature and exothermic decomposition of the polymers. The quantitative analysis of the data collected from FTIR and DSC measurements showed that PECH → PGA conversion is a first-order reaction with a rate constant of k = 0.74 h -1 .

Combinatorial matrix-assisted pulsed laser evaporation: Single-step synthesis of biopolymer compositional gradient thin film assemblies

We introduce a combinatorial approach for the fabrication of organic biopolymer thin films. Structures with compositional gradient are obtained by simultaneous laser vaporization of two distinct targets. Matrix-assisted pulsed laser evaporation deposition method was applied to obtain a compositional library of levan and oxidized levan in form of thin film. The gradient of film composition and structure was demonstrated by infrared spectroscopy while in vitro cell culture assays illustrated characteristic responses of cells to specific surface regions. The method can rapidly generate discrete areas of organic film compositions with improved properties than starting materials.

Synthesis and characterization of hydroxyl terminated poly(butadiene)-g-poly(glycidyl azide) copolymer as a new energetic propellant binder

SummaryPoly(glycidyl azide), PGA, was grafted onto Hydroxyl Terminated Poly(butadiene), HTPB, via free radical mechanism. PGA-macro azoinitator and HTPB polymer mixture was casted from solution and the polymer film was kept at 90°C for 4 hours. The grafted polymer was isolated from the product by fractional precipitation and characterized by NMR and FT-IR spectroscopy. Graft copolymer structure was also confirmed that volume ratio of nonsolvent to the solution of the graft copolymer was between those of corresponding homopolymers. TGA traces of the block polymers were containing two different maxima at 253°C (for PGA units) and 469°C (for HTPB units). Because of the incompatibility of the blocks, DSC curve showed two Tgs which belong to the related segments.