Ali Güner

Hacettepe University, Engüri, Ankara, Turkey

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Publications (65)106.62 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To enhance the solubility and ocular permeability of immunosuppressive agent, cyclosporine A (CsA), three types of delivery systems were prepared using (2-hydroxypropyl)-β-cyclodextrin (HPβCD), and 2-hydroxyethyl methacrylate (HEMA). Those systems are (i) hydrogels of HPβCD with crosslinking agent ethylene glycol diglycidylether, (ii) poly(HEMA) hydrogels, and (iii) different amounts of HPβCD-containing poly(HEMA) hydrogels indicated as poly(HEMA-co-HPβCD). In the presence of HEMA, hydrogels have desired mechanical integrity with lower equilibrium content than that of hydrogels without HEMA. CsA was loaded into the HPβCD-based hydrogels by embedding from its aqueous suspensions in higher amounts than that of the poly(HEMA) hydrogels that were loaded by CsA–HPβCD complex solution. Although the poly(HEMA) hydrogels are releasing total CsA in 3 days, long-term release was realized from HPβCD-based hydrogels. For subconjunctival administration, regarding to the amounts of loaded CsA, release profiles, and mechanical integrity, the most suitable system is poly(HEMA-co-HPβCD) hydrogels in high HPβCD content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40397.
    Journal of Applied Polymer Science 01/2014; · 1.40 Impact Factor
  • Hatice Kaplan Can, Ali Güner
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    ABSTRACT: Crosslinked N,N′-Diethylaminoethyl (DEAE) groups containing dextran microbeads have been used in human serum albumin (HSA) adsorption-desorption studies. For the HSA adsorption onto positively charged hydrophilic DEAE dextran microbeads, the adsorption kinetic was slightly decreased by the changing concentration of the protein solution. Adsorption kinetics and equilibrium isotherms for the adsorption of HSA on crosslinked DEAE dextran have been determined experimentally. Modeling of the adsorption processes on DEAE dextran microbeads were realized by applying different adsorption isotherms. Among the several isotherm equations, Langmuir and Freundlich adsorption isotherms were investigated depending on the two temperatures. These were only slightly dependent on the initial concentration of HSA but were considerably affected by the pH of the medium. The HSA adsorption capacity factor and the adsorption equilibrium constant were obtained and mathematical modeling of adsorption, adsorption rate constants and maximum adsorption were determined. Besides the adsorption mechanism, optimum ionic strength and optimum pH also were investigated. Desorption studies and desorption ratio of the system were determined for optimum medium conditions. It was been proved both experimentally and theoretically that human HSA is adsorbed by electrostatic attraction, ion-exchange, hydrophobic interaction and/or hydrogen bonding.
    Journal of Macromolecular Science Part A 11/2012; 49(11). · 0.81 Impact Factor
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    ABSTRACT: Novel functional temperature‐sensitive amphiphilic P‐containing polymers were synthesized by complex‐radical ternary polymerization of vinylphosphonic acid (VPA), styrene (S), and maleic anhydride (MA). Charge transfer complexes (CTCs), complex‐formation constants (K c ) between acceptor and donor monomer systems and the complexed monomer reactivity ratios were investigated by 1H‐NMR analysis. Contrary to theoretical predictions, the VPA…S complex is more active as compared to MA…S complex in the ternary system since VPA monomer can form the CTC both with S monomer and strong H‐bonded complex with MA monomer. The terpolymer compositions, characterizations, and structure–property relationships of a series of poly(VPA‐co‐S‐co‐MA)s were investigated by GPC, FTIR, Raman, 1H‐NMR, 13C‐NMR, DEPT‐135, 31P‐NMR, TGA‐DSC, DMA, XRD, viscometry, and titration. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
    Journal of Applied Polymer Science 01/2012; 125(5). · 1.40 Impact Factor
  • Dilek Mete, Cemile Göksel, Ali Güner
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    ABSTRACT: The miscibility behavior and intermolecular interactions among Dextran (Dx) with different molecular weight and Polyvinylpyrrolidone (PVP) blends were studied as dilute aqueous solutions at 25 °C by viscosity method. The intrinsic viscosity and the interaction coefficient were experimentally measured for each polymer-water as well as for Dx-PVP-water systems. These results served for the prediction of miscibility of the Dx/PVP blends with various blend compositions by using,,,, and parameters. Except Dx4/PVP with its all compositions (Dx4 with nominal molecular weight of 110 000), other blend systems are found to be almost miscible. The density measurements of these polymer solutions and their blends were conducted in order to compare with the viscosity findings. Lastly, all Dx with different molecular weight, PVP and their blends were characterized by infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC).
    Macromolecular Symposia 03/2011; 302(1):257 - 265.
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    ABSTRACT: Functional copolymer/organo-silicate [N,N′-dimethyldodecyl ammonium cation surface modified montmorillonite (MMT)] layered nanocomposites have been synthesized by interlamellar complex-radical copolymerization of preintercalated maleic anhydride (MA)/ organo-MMT complex as a ‘nano-reactor’ with n-butyl methacrylate (BMA) as an internal plasticization comonomer in the presence of radical initiator. Synthesized copolymers and their nanocomposites were investigated by dynamic mechanic analysis, X-ray diffraction, SEM, and TEM methods. It was found that nanocomposite dynamic mechanical properties strongly depend on the force of interfacial MA…organo-MMT complex formation and the amount of flexible n-butyl ester linkages. An increase in both of these parameters leads to enhanced intercalation and exfoliation in situ processes of copolymer chains and the formation of hybrid nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
    Journal of Applied Polymer Science 06/2010; 118(5):2904 - 2913. · 1.40 Impact Factor
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    ABSTRACT: Solution thermodynamics of PEG samples in aqueous and nonaqueous (methanol, chloroform, tetrahydrofuran, and dimethylsulfoxide) solutions have been investigated by viscometric studies at 25, 30, 35, and 40°C. The hydrodynamic expansion factor, ah, and the unperturbed root mean square end-to-end distance, , found for the system indicated that the polymer coils contract as the temperature is raised. The long-range interaction parameter, B, was also evaluated and a significant decrease with increasing temperature was observed. The theta temperatures, θ, obtained from the temperature dependence of (1/2 − χ) and the second virial coefficient, A2, are quite good in agreement with the calculated values evaluated via extrapolation and interpolation methods. The thermodynamic interaction parameter, χ, was evaluated through the sum of the individual values of enthalpy and entropy dilution parameters for PEG samples. The restrictions applying to the establishment of concentration regimes, short-range, and long-range interactions are discussed. A parallelism is found between solubility profiles obtained by solution viscometry and solubility parameter approaches for PEG/solvent systems. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
    Journal of Applied Polymer Science 03/2010; 117(2):1100 - 1119. · 1.40 Impact Factor
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    ABSTRACT: New functional terpolymers of citraconic anhydride (CA), styrene (S) and vinylphosphonic acid (VPA) were synthesized at different compositions by complex-radical ternary polymerization. Studied ternary acceptor-donor-acceptor system was described as a binary copolymerization of two monomer complexes of CA…S (1) and VPA…S (2). The monomer reactivity ratios of these complexes were determined by 1H NMR analysis for monomer mixtures before and after reactions by modified Jaacks equations: rI = r1(Kc1/Kc2) = 1.99, rII = r2(Kc2/Kc1) = 0.16; r1 = 18.59, r2 = 0.018 (taking into account Kc for the corresponding monomer complexes). Copolymerization constants verify the fact that complexed monomer pairs have a tendency towards random copolymerization. Monomer unit compositions and characterizations of a series of poly(CA-co-S-co-VPA)s were investigated by FTIR, Raman, 1H NMR, 13C NMR, DEPT-135, 31P NMR, GPC and thermal properties were investigated by TGA and DSC methods. Molecular weight and thermal stability increased with increasing VPA content in terpolymer. Dynamic mechanical properties were investigated by DMA and all terpolymers show typical viscoelastic behavior of an amorphous polymer. Solution properties were also studied by viscometry and titration.Graphical abstract
    Polymer. 01/2010; 51(10):2125-2132.
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    ABSTRACT: Functional copolymer/organo-silicate [N,N′-dimethyldodecyl ammonium cation surface modified montmorillonite (MMT)] layered nanocomposites have been synthesized by interlamellar complex-radical copolymerization of pre-intercalated itaconic acid (IA)/organo-MMT complex as a “nanoreactor” with n-butyl methacrylate (BMA) as an internal plasticization comonomer in the presence of radical initiator. Comparative analysis of physical structure, dynamic mechanical analysis parameters, and surface morphology of the obtained copolymers and their nanocomposites indicated that the interlayer H-bonding and flexible n-butyl ester linkages take place an important role in interlamellar copolymerization and intercalation/exfoliation of copolymer chains. It was found that nanocomposites' dynamic mechanical properties strongly depended on the force of interfacial H-bonding and amount of BMA units. An increase in both of these parameters leads to enhanced intercalation and exfoliation insitu processes of copolymer chains and the formation of hybrid nanocomposites. Copyright © 2009 John Wiley & Sons, Ltd.
    Polymers for Advanced Technologies 11/2009; 22(9):1349 - 1358. · 1.64 Impact Factor
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    ABSTRACT: The purpose of this study was to investigate the cytotoxic effects of poly(MA-alt-AA) and poly [MA-co-AA-co-(VA)] in cell culture model. Complex-radical copolymerization (CTC) of maleic anhydride (MA), and acrylic acid (AA) and ternary polymerization of (MA), vinyl acetate (VA) and AA, considered as acceptor−donor−acceptor systems, were carried out. For the cytotoxicity study, cells were incubated at initial density of 50,000 cells/mL in 24-well plates. After 24-h incubation, the culture medium was removed and fresh medium containing five different dilutions of polymers were added separately. Cell viability and proliferation were assessed on 1st and 5th days. Apoptosis was assessed using propidium iodide/acridine orange (PI/AO) staining at the 1st and 5th days of incubation. Kruskal-Wallis test was applied to compare the effects of different dilutions on cell viability at each evaluation period. The results showed that there were differences between co- and terpolymer in view of cell proliferation and apoptotic response. The results suggest that functional groups in co- and terpolymer group may cause apoptotic cell death without effecting cell proliferation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
    Journal of Applied Polymer Science 10/2009; 115(3):1366 - 1370. · 1.40 Impact Factor
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    ABSTRACT: Hydrogels synthesized from a polysaccharide-based polymer, dextran, in the presence of two crosslinking agents, N,N′-methylenebisacrylamide and epichlorohydrin, were evaluated for the oral colon-specific delivery of polypeptide drugs. These novel dextran hydrogels had significantly greater swelling ratios than recently developed dextran hydrogels. A model protein, bovine serum albumin, was loaded into 50% (by weight) crosslinker-containing dextran hydrogels in two ways: during the crosslinking reaction and by a soaking method. The loading capacity was varied between 22 and 25 mg/g of dry gel, depending on the loading procedure. In vitro release experiments were performed with a simulated gastrointestinal system in the presence and absence of dextranase. The diffusion exponents were calculated by means of a semiempirical power-law equation for the release of protein from swellable hydrogel discs. Bovine serum albumin was mainly released by Fickian diffusion, and this indicated that its hydrodynamic diameter (7.7 nm) was smaller than the hydrogel mesh size (∼19 nm). The release of bovine serum albumin from both hydrogel types was substantially higher than expected, especially in the presence of dextranase, and this was attributed to the high swellability of the hydrogels. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
    Journal of Applied Polymer Science 09/2009; 115(2):740 - 747. · 1.40 Impact Factor
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    ABSTRACT: Cibacron Blue F3GA-attached magnetic poly(2-hydroxyethyl methacrylate) [mPHEMA] beads were prepared by suspension polymerization of HEMA in the presence of magnetite (Fe3O4) nanopowder. Average diameter size of the mPHEMA beads was 150–200 μm. The characteristic functional groups of Cibacron Blue F3GA-attached mPHEMA beads were analyzed by Fourier transform infrared spectrometer (FTIR) and Raman scattering spectrometer. The lysozyme adsorption and desorption characteristics of Cibacron Blue F3GA-attached mPHEMA beads were also investigated using FTIR and Raman spectroscopic techniques. When the Raman spectrum of lysozyme adsorbed mPHEMA is evaluated characteristic Amide-I band appears at 1657 cm−1. The intensity of this band decreases in the spectrum of lysozyme desorbed mPHEMA sample. When the characteristic bands of lysozyme adsorbed and desorbed mPHEMA samples are compared, the band intensities of desorbed sample are lower than those of lysozyme adsorbed sample except for the band appearing at 656 cm−1 (Tyr vCS). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
    Journal of Applied Polymer Science 06/2008; 108(6):3454 - 3461. · 1.40 Impact Factor
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    ABSTRACT: Alternating copolymer of maleic anhydride (MA) with N-isopropylacrylamide (NIPA) has been synthesized. Spectral characterization of this copolymer has been achieved by FTIR, Raman, 1H, 13C NMR spectroscopic methods. Besides hydrodynamic behavior of the copolymer has been also investigated by viscometric method for comparison with that obtained from the solubility profile through algorithmic calculations. As a consequence of the algorithmic calculations DMSO has been determined as the best solvent for the copolymer, poly(MA-alt-NIPA), which is also supported by the viscometric results.
    Carbohydrate Polymers 01/2008; 72(4):682-694. · 3.92 Impact Factor
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    ABSTRACT: Magnetic poly(2-hydroxyethyl methacrylate) mPHEMA beads carrying Cibacron Blue F3GA were prepared by suspension polymerization of HEMA in the presence of Fe3O4 nano-powder. Average size of spherical beads was 80-120 microm. The beads had a specific surface area of 56.0m(2)/g. The characteristic functional groups of dye-attached mPHEMA beads were analyzed by Fourier transform infrared spectrometer (FTIR) and Raman spectrometer. mPHEMA with a swelling ratio of 68% and carrying 28.5 micromol CibacronBlueF3GA/g were used for the purification of lysozyme. Adsorption studies were performed under different conditions in a magnetically stabilized fluidized bed (i.e., pH, protein concentration, flow-rate, temperature, and ionic strength). Lysozyme adsorption capacity of mPHEMA and mPHEMA/Cibacron Blue F3GA beads were 0.8 mg/g and 342 mg/g, respectively. It was observed that after 20 adsorption-desorption cycle, mPHEMA beads can be used without significant loss in lysozyme adsorption capacity. Purification of lysozyme from egg white was also investigated. Purification of lysozyme was monitored by determining the lysozyme activity using Micrococcus lysodeikticus as substrate. The purity of the desorbed lysozyme was about 87.4% with recovery about 79.6%. The specific activity of the desorbed lysozyme was high as 41.586 U/mg.
    International Journal of Biological Macromolecules 09/2007; 41(3):234-42. · 2.60 Impact Factor
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    ABSTRACT: The interaction of some selective Cl- and N-containing functional crosslinking agents such as epichlorohydrin (ECH), N,N′-methylenebisacrylamide (MBAM), and bifunctional agents such as glutaraldehyde (GA) and glycidylmethacrylate (GM) with dextran (Dx) in aqueous solutions were studied by viscometric and spectroscopic methods. The dynamic viscosities of Dx-crosslinker aqueous solutions have been measured at physiological temperature, 37°C and in the concentration range of 0.22–0.4 g/dL. Concentration of crosslinkers were kept constant at 0.001–0.35 mol/L. Viscosity behavior of the solutions was interpreted using the Huggins and Kraemer equations. Moreover, the interaction between hydroxyl groups of the Dx with crosslinkers in aqueous solutions, structure properties was also confirmed thereby use of Raman and FTIR spectroscopy. For the Dx/crosslinker systems, the decreasing order of interaction was determined as ECH > GA > MBAM > GM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007
    Journal of Applied Polymer Science 04/2007; 105(3):1177 - 1187. · 1.40 Impact Factor
  • Murat Barsbay, Ali Güner
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    ABSTRACT: The miscibility of dextran, Dx, and poly(ethylene glycol), PEG, have been studied in solid state by FTIR, Raman, DSC and XRD methods. In order to investigate the effect of solvent on the miscibility of Dx and PEG, their homopolymers and blends having different compositions were cast from aqueous and DMSO solutions. Following the above mentioned experimental methods, it has been seen that specific interactions causing partial miscibility exist between Dx and PEG and these interactions occur to a higher extent by choosing DMSO as the solvent, that is, the choice of solvent has a great influence on the miscibility behavior of the polymer blends.
    Carbohydrate Polymers - CARBOHYD POLYM. 01/2007; 69(2):214-223.
  • C. Özdemir, A. Güner
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    ABSTRACT: Solubility of systems involving four different molecular weights of poly(ethylene glycol) (PEG) in tetrahydrofuran (THF), chloroform, dimethylsulfoxide (DMSO), methanol and water have been investigated by different algorithmic approaches as the mathematical application of the “like dissolves like” principle. In this study, the solubility parameters and their components for PEG and solvents have been evaluated by using of atomic group contribution methods; Small, van Krevelen–Hoftyzer (VKH), Hoy and Breitkreutz methods, respectively. Then their 2-dimensional graphs (Bagley, Henry and Hoernschemeyer diagrams) and 3-dimensional graph (Hansen diagram) have been drawn by creating the solubility profiles of the polymer in selected solvents. The dissolving capability of these solvents has been discussed. In addition the solubility parameters have been calculated by use of the van der Waals volume in the selected molecule or repeating unit of the polymer instead of the molar volume which is used in atomic group contribution methods (Askadskii approach). Surface tensions of the polymer and solvent systems have been calculated with this method and solubility criteria of PEG have been explained after a serial calculation steps. In addition, influence of molecular weight of PEG on solubility has been also analyzed. As a consequence of algorithmic calculations, THF has been determined as the best solvent whereas water is found to be the weakest solvent for polymer/solvent systems.
    European Polymer Journal 01/2007; 43(7):3068-3093. · 3.24 Impact Factor
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    ABSTRACT: In this study, we have synthesized dextran hydrogels by the crosslinking reactions of dextran with some selective Cl-, and N-containing functional monomers, such as epichlorohydrin (ECH), N,N′-methylenebisacrylamide (MBAm), and glutaraldehyde (GA). Crosslinking reactions were carried out in the basic aqueous solutions (2.8NNaOH) at 25–50°C. The optimum conditions for effective crosslinking, i.e., temperature, crosslinking time, and amount of crosslinker, were determined for each system. The hydrogel discs of 3 mm diameter and 1.5 mm thickness were subjected to a number of Tris-buffer solutions of desired pH (2.0–9.0) at 37°C. Swelling kinetics of the hydrogels were evaluated with second–order swelling model. The pH-dependent swelling of hydrogels was strongly influenced by the functional group of crosslinker and crosslinker content. While the hydrogels prepared with ECH and MBAm shows higher swelling ability at basic medium than that of acidic medium, GA-containing hydrogels exhibited just the opposite behavior. Mesh sizes (ξ) and average molecular weights between crosslinks (Mc) were estimated from swelling data using the Flory-Rehner theory. Characterization studies were completed by Fourier transform infrared spectroscopy and thermal gravimetric analysis. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4213–4221, 2006
    Journal of Applied Polymer Science 12/2006; 102(5):4213-4221. · 1.40 Impact Factor
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    ABSTRACT: The miscibility behavior of dextran (Dx) with synthesized functional binary poly(citraconic anhydride-acrylamide) (poly(CA-alt-AAm) and ternary poly(citraconic anhydride-acrylamide-vinyl acetate) (poly(CA-co-AAm-co-VA) copolymers was investigated in dilute aqueous solutions by viscometry and in a solid state by Fourier transform infrared (FTIR) spectroscopy. The relative viscosities of each polymer and their blends with Dx/related copolymer ratios of 20 : 80, 50 : 50, and 80 : 20 were measured at body temperature, 37°C, in bidistilled and deionized water. Starting with the classical Huggins equation, results of the viscosity measurements of each parent polymer and their blends were interpreted in terms of miscibility parameters: Δk, Δb, α, β, ΔB, and μ. Based on the sign convention used with these criteria, the miscibility between Dx and related copolymers was found to increase with the weight fraction of Dx in the blends and with the number of AAm units in the copolymer composition. From FTIR spectral analysis, supporting results were achieved that explained the interactions between Dx and the copolymers. Miscibility behavior was also investigated theoretically with Askadskii's miscibility criterion, and the theoretical calculations provided strong evidence supporting the experimental results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2132–2141, 2006
    Journal of Applied Polymer Science 08/2006; 102(3):2132 - 2141. · 1.40 Impact Factor
  • Hatice Kaplan Can, Ali Güner
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    ABSTRACT: Adsorption of proteins on solid surfaces is widely studied because of its importance in various biotechnological, medical, and technical applications, e.g., biosensors, cardiovascular implants, and chromatography. Adsorption thermodynamics has been studied on the microbeads of N,N′-diethylaminoethyl (DEAE) Dextran anion exchanger for the human serum albumin (HSA) at 25, 30, 35, 40, and 45°C. As a result, some thermodynamic parameters like Freundlich constants, thermodynamic equilibrium constant (KD), standard free energy changes (ΔGassoc), standard entropy changes (ΔSassoc), and standard enthalpy change (ΔHassoc) have been evaluated. Using the linear Van't Hoff plot, ΔHassoc value of the system for the interaction of bovine serum albumin (BSA)-adsorbed crosslinked DEAE dextran microbeads was determined as 20.650 kJ/mol. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3942–3947, 2006
    Journal of Applied Polymer Science 06/2006; 101(6):3942 - 3947. · 1.40 Impact Factor
  • Cemile Özdemir, Ali Güner
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    ABSTRACT: The unperturbed molecular dimensions of poly(ethylene glycol) (PEG) samples (of different molecular weights) have been evaluated in aqueous solutions from viscosity measurements at 25, 30, 35, and 40°C. The unperturbed dimension, Kθ, has been determined from extrapolation methods, i.e., Kurata–Stockmayer–Fixman (KSF), Inagaki–Suzuki–Kurata (ISK), and Berry equations. The hydrodynamic expansion factor, αη, as well as the unperturbed root-mean-square end-to-end distance, 〈r2〉, found for the system indicated that the polymer coils contract as the temperature is raised from 25 to 40°C. The long-range interaction (excluded volume) parameter, B, was also evaluated and a significant decrease was found for the PEG/water system between 25 and 40°C. The theta temperatures, θ, were obtained from the temperature dependence of (1/2 − χ) and the second virial coefficient was detected in the temperature interval of 25–40°C for the system and quite a good agreement with the calculated values evaluated via extrapolation and interpolation methods was observed. The thermodynamic interaction parameter χ was evaluated through the sum of the individual values of enthalpy and entropy dilution parameters, χH and χS, for PEG samples. All the unperturbed molecular dimensions of PEG/water system were calculated and compared according to Mw and Mn values of PEG samples. Calculated values were interpreted mainly on the basis of hydrogen-bond formation between polymer segments and PEG-water molecules in solution. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 203–216, 2006
    Journal of Applied Polymer Science 04/2006; 101(1):203 - 216. · 1.40 Impact Factor