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Authors
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Kilburn, D. ; Dlubek, G. ; Pionteck, J. ; Bamford, D. ; Alam, M. A.
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Title
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Microstructure of free volume in SMA copolymers I. Free volume from Simha-Somcynsky analysis of PVT experiments
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Date
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12.01.2005
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Number
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12104
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Abstract
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The structure of the free volume and its temperature dependence between 25 and 200 °C of copolymers of styrene with maleic anhydride, SMA (0–35 mol% MA), is studied by pressure–volume–temperature (PVT) experiments and positron annihilation lifetime spectroscopy (PALS). In this first part of the work, PVT data are reported which were analysed with the Simha–Somcynsky equation of state to estimate the volume fraction of holes, <i>h</i>, which constitute the excess free volume. The temperature and pressure dependence of the specific volume <i>V</i>, the specific occupied and free volume, <i>V</i><sub>occ</sub>=(1−<i>h</i>)<i>V</i> and <i>V</i><sub>f</sub>=<i>hV</i>, and the corresponding isobaric expansivities and isothermal compressibilities for both the rubbery and glassy state are esti<br />mated. We obtained the unexpected results that (i) the occupied volume changes its coefficient of thermal expansion at <i>T</i><sub>g</sub> from <i>α</i><sub>occ,g</sub>≈0.5<i>α</i><sub>g</sub>≈1×10<sup>−4</sup> K<sup>−1</sup> below <i>T</i><sub>g</sub> to almost zero (≈0.2×10<sup>−4</sup> K<sup>−1</sup>) above <i>T</i><sub>g</sub> and (ii) the isothermal compressibility of the occupied volume at zero pressure below <i>T</i><sub>g</sub> is rather high, <i>κ</i><sub>occ</sub>≈2.5×10<sup>−4</sup> MPa<sup>−1</sup>, and decreases only slightly at <i>T</i><sub>g</sub> to about 2×10<sup>−4</sup> MPa<sup>−1</sup> above <i>T</i><sub>g</sub>. The variation of total, occupied, and free volume parameters with the composition of the SMA copolymers is discussed.
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Publisher
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Polymer
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Wikidata
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Citation
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Polymer 46 (2005) 859-868
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DOI
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https://doi.org/10.1016/j.polymer.2004.11.083
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