Polyurethane-POSS hybrids: Molecular dynamics studies |
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Authors: | KN Raftopoulos L Apekis B Janowski J Jaczewska |
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Affiliation: | a Department of Physics, National Technical University of Athens, Iroon Polytechneiou 9, Zografou, Campus, 157 80, Athens, Greece b Department of Chemistry and Technology of Polymers, Krakow University of Technology, ul. Warszawska 24, 31-155 Krakow, Poland c M. Smoluchowski Institute of Physics, Jagiellonian University, ul. Reymonta 4, 30-059 Krakow, Poland d The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, ul.Radzikowskiego 152, 31-342 Krakow, Poland |
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Abstract: | A series of hybrid polyurethane-POSS materials have been synthesized on the basis of poly(tetramethylene glycol) (Terathane 1400®) as soft component, 4,4′-methylenebis(phenylisocyanate) (MDI) as hard component, and 1,4-butanediol as chain extender. POSS particles properly modified have been tethered on the main chain by substitution of the chain extender to weight fractions up to 10%. AFM measurements indicate the formation of POSS crystallites in the PU matrix, extended structures at low POSS content and more regular, smaller structures at higher POSS content. A detailed investigation of molecular mobility by means of Differential Scanning Calorimetry (DSC), Thermally Stimulated Depolarization Currents (TSDC) and, mainly, Broadband Dielectric Relaxation Spectroscopy (DRS) has been conducted in all samples of the series and in addition in neat Terathane, as reference. Four relaxations have been studied in detail: two secondary relaxations γ and β, the segmental α relaxation (dynamic glass transition) and an α′ relaxation slower than α associated with crystallinity in neat Terathane and with the presence of hard microdomains in the polyurethane and the hybrids. Secondary relaxations remain unaffected by POSS. The glass transition temperature rises by a few degrees and, in consistency with that, segmental dynamics slightly slows down with increasing POSS content. In addition, the dielectric strength of the segmental relaxation decreases with increasing POSS content, suggesting that a fraction of polymer is immobilized, making no contribution to the relaxation. These results are discussed in relation to morphology. |
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Keywords: | Dielectric spectroscopy Polyurethane-POSS nanocomposites Polymer dynamics |
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