Nurseli Uyanık

Development and In Vitro Evaluation of a Buccoadhesive Pindolol Tablet Formulation

Controlled-release buccoadhesive tablets containing pindolol were prepared and evaluated in order to achieve constant plasma concentrations during the treatment of chronic hypertension and to improve the bioavailability of pindolol by the avoidance of hepatic first-pass metabolism. The formulations were tested for weight, hardness, friability, content uniformity, swelling rate, bioadhesive force, and drug release rate values. Carbopol 934 and NaCMC were used as bioadhesive polymers and Methocel K4M, Methocel K15M, and HPC were added as matrix-forming polymers.

Effects of synthesis‐solvent composition and initiator concentration on the swelling behaviour of poly(N‐isopropylacrylamide) P(NIPAAM), poly(NIPAAM‐co‐dimethyl itaconate), and poly(NIPAAM‐co itaconic acid) gels

The effects of synthesis-solvent composition, initiator concentration, comonomer type and monomer purity on the volume swelling ratios, and polymer-solvent interaction parameter χ have been investigated as a function of temperature. Non-ionic N-isopropylacrylamide (NIPAAM) homopolymer gels, poly[NIPAAM-co-(dimethyl itaconate)] (P(NIPAAM-co-DMI)) and poly[NIPAAM-co-(itaconic acid)] (P(NIPAAM-co-IA)) gels containing hydrophobic (DMI) and hydrophilic (IA) comonomers were prepared by free radical polymerization using potassium persulfate (KPS) –N, N, N′, N′-tetramethyl ethylene diamine (TEMED) (redox initiator) in the presence of an N, N′-methylene bis(acrylamide) (MBAAM) cross-linking agent. The synthesis-solvent composition (40/60 mixture of water/methanol and water) and initiator concentration employed significantly affected the properties of the NIPAAM gels. The transition temperatures of P(NIPAAM-co-IA) gels synthesized in water/methanol mixture were higher than that of the gel obtained in water. Furthermore, χ values of the NIPAAM homopolymer gel prepared with higher KPS content was an increasing function of temperature, while χ values of the sample obtained with lower initiator concentration changed around a critical solubility value 0.50. The results obtained also show that the interactions between monomer and solvent molecules in the reaction media (ie composition of the pregel solution) have an important effect on the formation and properties of the network structure (ie pore sizes of the gels). © 2000 Society of Chemical Industry

Determination of the monomer reactivity ratios for copolymerization of itaconic acid and acrylamide by conductometric titration method

Abstract Compositions of low conversion itaconic acid-acrylamide (IA-AAm) copolymers synthesized with solution polymerization in aqueous medium by using potassium persulfate under nitrogen atmosphere were determined by conductometric titration method. The results were evaluated by various linear and nonlinear methods. The monomer reactivity ratios were found to be r IA =1.47±0.03, r AAm =0.76±0.02 with Fineman–Ross, r IA =1.25±0.10, r AAm =0.67±0.05 with Kelen–Tudos, r IA =1.65±0.21, r AAm =0.88±0.08 with Tidwell–Mortimer methods. For this system, the analysis of results show that IA is a more reactive monomer in IA-AAm copolymerization.

Block copolymers of styrene containing oligomeric esters of terephthalic acids

A new generation of block copolymers were synthesized starting with depolymerized PET by glycolysis with some oligomeric diols. α,ω-Dihydroxy poly(dimethyl siloxane)s, hexylene glycol, poly(ethylene oxide)glycols, and ethylene glycol were used as diols. The dihydroxy-terminated depolymerization products containing a terephthalyl group and oligomeric diols were used to prepare a diradicalic macroinitiator (MI). These MIs were used to polymerize the styrene monomer. The new block copolymers obtained were characterized by physical and chemical methods and mechanical and thermal analyses.

Monomer reactivity ratios of itaconic acid and acrylamide copolymers determined by using potentiometric titration method

Abstract Itaconic acid (methylene succinic acid)–acrylamide (IA–AAm) copolymers were synthesised with solution polymerisation by using potassium persulphate. The potentiometric titration method was used to determine the copolymer compositions. The results were evaluated by various methods. The monomer reactivity ratios were found to be r IA =0.99±0.04, r AAm =0.58±0.02 with the Fineman–Ross, r IA =1.05±0.10, r AAm =0.62±0.06 with the Kelen–Tudos, and r IA =1.36±0.11, r AAm =0.77±0.06 with the Tidwell–Mortimer methods. As expected, IA is found to be the more reactive monomer in IA–AAm copolymers.

Compressive Elastic Moduli of Poly(N‐Isopropylacrylamide) Hydrogels Crosslinked with Poly(Dimethyl Siloxane)

Hydrophobically modified and thermally reversible neutral and ionic copolymer hydrogels were prepared from N‐isopropylacrylamide (NIPAAm), vinyl terminated poly (dimethylsiloxane) (VTPDMS) and itaconic acid (IA) by free radical solution polymerization, and their properties such as swelling ratio and compression modulus were studied at the 25°C. The incorporation of VTPDMS as a hydrophobic macrocrosslinker into the structures of neutral NIPAAm hydrogels increased their mechanical strength around 10 times than those of the ones crosslinked with conventional tetra functional monomer, i.e., N,N′‐methylene bisacrylamide (BIS). Compression modulus decreased with an increase in IA content for ionic samples and increased with increasing molecular weight and content of VTPDMS for neutral samples. It was assumed that in the first case, electrostatic repulsive forces resulting from the ionized carboxyl groups of IA were responsible for decreasing mechanical strength, while in the second case, hydrophobic interactions between dimethylsiloxane units of VTPDMS chains enhanced the compression moduli. According to the results presented in this work, it can be said that the right balance of hydrophobic and hydrophilic constituents and adjustment of the number of ionized groups, as well as crosslinking degree, change the structure and physical properties of NIPPAAm hydrogels.

Preparation of urea formaldehyde resin/layered silicate nanocomposites

Purpose – The purpose of the research was as follows. In situ modified urea formaldehyde resins were prepared from clay (montmorillonite) and organoclay in the presence of base catalyst. Different clay contents (1 wt%, 3 wt%, 6 wt%) were used to produce clay modified nanocomposite resins. These nanocomposites were characterized with FT‐IR, XRD as structural analysis and DSC as thermal analysis and their hardness was evaluated as mechanical analysis. The thermal results was compatible with hardness measurements and showed that using clay/organoclay added resin as a surface coating material provides significant improvement.Design/methodology/approach – During synthesis of the resin, modification was carried out using urea/formaldehyde with molar ratio of 1/1.6, under basic medium with pH=10 and with temperature of 70°C by loading pristine and organomodified layered silicates.Findings – X‐ray diffraction (XRD) results indicate that the interlayer space of pristine clay was increased significantly by one step...

Macro‐azo‐initiators having poly(ethylene glycol) units: Synthesis, characterization, and application to AB block copolymerization

Macro-azo-initiators (MAIs) having poly(ethylene glycol) (PEG) units were obtained by various multistep synthetic approaches. In the first stage, macro-azo-initiators of PEG type with azo groups inserted in the main chain were prepared. MAIs were then characterized by chemical analyses, spectral methods, 1H-NMR, GPC, and DSC techniques. They were used in the free-radical bulk polymerization of dicyclohexylitaconate to synthesize AB block copolymers of poly(ethylene glycol-b-dicyclohexylitaconate) (PEG-b-PDCHI).

Polystyrene-Organoclay Nanocomposites Prepared via In-Situ Emulsion Polymerization

In this study, polystyrene-clay nanocomposites (PSNCs) were prepared via in-situ bulk and in-situ emulsion polymerization. The effect of organoclay and the architecture of surfactant were investigated. For the investigation of the effect of surfactant, organoclays were synthesized containing clay modifiers having different structures. Trimethylhexadecyl ammonium chloride, dimethylbenzylhexadecyl ammonium chloride and dimethylbenzyl(4-vinyl) hexadecyl ammonium chloride, which is synthesized in laboratory, modified clays were synthesized. Pristine polystyrene (PS) was synthesized by bulk and emulsion polymerization for comparison, and PSNCs containing 3 wt.% organoclays were prepared by both these polymerization methods. Structural analysis of synthesized surfactant was identified by Nuclear Magnetic Resonance (NMR) Spectrometer. The interlayer spacing of silicate layers and the morphology of samples were examined by using the X-ray Diffraction (XRD) Spectrometer and Scanning Electron Microscopy (SEM) images, respectively. Thermal properties of nanocomposites were determined by Thermogravimetric analyzer (TGA) and Differential Scanning Calorimeter (DSC). It is observed that organoclays and PS were compatible to each other and each organoclay could form a nanocomposite structure with PS. PSNCs exhibited better properties than pristine PS. Nanocomposites prepared by in-situ emulsion polymerization resulted with better thermal properties and higher interlayer distances than that prepared by in-situ bulk polymerization. In order to improve some properties of PS such as thermal stability, preparation of PSNCs by in-situ emulsion polymerization has been suggested.

Effects of acetophenone‐formaldehyde resin on the degradation of high‐density polyethylene by UV‐irradiation

Purpose – Proposes to examine acceleration of photo‐oxidative degradation of high‐density polyethylene (HDPE) by using photosensitive acetophenone‐formaldehyde resin (AFR).Design/methodology/approach – Degradation of HDPE by UV light was investigated in the presence of photosensitive AFR on natural weathering. The experiments were done at constant temperatures (40, 65 and 90°C). The results were determined by FT‐IR spectrophotometric and viscometric methods. Measurement of the rate of formation of carbonyl groups on the FT‐IR showed the evidence of degradation. The carbonyl indices of photo‐oxidation of HDPE with/without AFR were determined by FT‐IR spectroscopy. The molecular weights of the samples (Mη values) were measured by viscometry.Findings – The amount of carbonyl present in the AFR containing HDPE samples and the changes in their molecular weights were found to depend on the irradiation period, temperature and amount of AFR in the mixture. The improvements in UV performance have been observed by ...