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Characterisation of Poly(ethylene oxide)s of Different Molecular Weights

Poly(ethylene oxide) (PEO) is the simplest structure of water-soluble polymers and among polyethers it is the only one readily soluble in water. PEO is miscible with water in all ratios due to hydratation of the ether oxygen.1 It is commercially available in wide range of molecular weights (100 000 - 8 000 000). PEO can be used as a long fibre dispersing agents in the manufacturing of paper and adhesives, as a friction reduction, flocculating or thickening agent, as lubricants and has a variety of further application.2 High-molecular-weight (HMW) PEO can be used in packaging, particularly one-use packaging and agricultural films. It has been also widely used to prepare sustained release dosage forms. Upon mixing with an appropriate electrolyte salts PEO possesses solid polymer-electrolyte properties. Low-molecular-weight (LMW) PEO was investigated as processing aid for the model formulations containing HMW PEO. After use, depending on their characteristics and particular applications, water-soluble polymers are discarded as dilute aqueous solutions or into solid waste disposal systems.3 The aim of this work was to compare the characteristics of PEO in the wide range of molecular weights. The investigated polymer powders (supplied by Aldrich) were PEO 3 (Mv= 300 000), PEO 10 (Mv=1 000 000) and PEO 50 (Mv=5 000 000). The thermal characteristics were determined by differential scanning calorimetry (Perkin Elmer DSC-4) in temperature range 30 - 150 oC. All DSC heating curves have one endotherm which represents the melting of the crystalline phase while one exotherme on cooling curves represents the pre-crystallisation process. The melting and crystallisation temperatures, Tm and Tc, are relatively low, about 62oC and 44oC, respectively, and they increase by increasing molecular weight of the polymer. Viscosity measurements of PEO-water solutions were made at 25, 30, 40 and 45oC by using Ostwald viscometer. Efflux times of each polymer were measured by the serial dilution technique. From the efflux measurement, the specific viscosity,  sp, was calculated at different concentrations. The intrinsic viscosity, [ ], was determined by plotting reduced viscosity,  sp/c, against the solution concentrations, c, according to the Huggins and Kreamer extrapolation equations. From the slopes of these extrapolated straight lines constants kH and k' were calculated and the interactions of solvent on polymer chain segments were evaluated. It was found, at all investigated temperatures, that intrinsic viscosity is higher for higher molecular weight of polymers. By increasing temperature intrinsic viscosity of all the investigated PEOs lowers . IR spectroscopic measurements were performed on Perkin Elmer Spectrum One FT-IR spectrophotometer. FT-IR spectra of PEOs of different molecular weights were showed absorption bands characteristic for semi-crystalline PEO. Three sharp bands at 1150, 1097 and 1057 cm-1, which correspond to the vibrations of the ether groups, are the evidence that investigated polymers have crystalline regions. IR spectra do not show any differences which can be prescribed to the different molecular weight of PEOs. REFERENCES 1. M.M. Crowley et al., Biomaterials 23 (2002) 4241-4248 2. A. Sionkowska, J.Photochem. 177 (2006) 61-67 3. S. Morlat and J.L. Gardette, Polymer, 42 (2001) 6071-6079

DSC; PEO; FT-IR spectroscopy

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