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Structuration et renforcement du polystyrene par des copolymeres styrene/butadiene a gradient de composition

Abstract : Polystyrene is a brittle material at room temperature. Blending with a styrene/butadiene tapered block copolymer produces a nanostructured material which is tough and transparent. These copolymers are formed by a two step anionic polymerization to give the following sequence, polystyrene-b-(polybutadiene-tap-polystyrene)-b-polystyrene, S1-(B/S)tap-S2. Structuration and properties of pure copolymers and blends with polystyrene strongly depend on the asymmetry between S1 and S2 styrene blocks and the presence of the tapered block. The asymmetry and shape of the tapered profile have been determined by following the monomer conversion during model syntheses. The asymmetry is found to be responsible for a shift of the phase diagram towards higher styrene composition. Modelling the dynamic mechanical analysis of extruded copolymers has allowed us to validate the effect of the tapered block. It enlarges the interphase and increases the volume of soft phase. Blending with different high molecular weight polystyrenes under shear produces a transparent nanostructured material. The high viscosity of the matrix leads to a fine dispersion of the copolymer even if the components are immiscible. Upon cooling, the system is trapped in a non equilibrium state. In traction at room temperature, the strain at break of the blends increases abruptly at a critical volume fraction of copolymer, which varies with the molecular architecture of the latter. A universal curve is obtained when mechanical properties are presented as a function of the fraction of amount of soft phase.
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https://tel.archives-ouvertes.fr/tel-00012106
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Submitted on : Monday, April 10, 2006 - 5:08:11 PM
Last modification on : Wednesday, December 9, 2020 - 3:12:46 PM
Long-term archiving on: : Saturday, April 3, 2010 - 11:09:45 PM

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  • HAL Id : tel-00012106, version 1

Citation

Stephane Jouenne. Structuration et renforcement du polystyrene par des copolymeres styrene/butadiene a gradient de composition. Physique [physics]. Université Pierre et Marie Curie - Paris VI, 2005. Français. ⟨tel-00012106⟩

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