The structure of the free volume in poly(styrene-co-acrylonitrile) from positron lifetime and pressure volume temperature (PVT) experiments -: I.: Free volume from the Simha-Somcynsky analysis of PVT experiments

The structure of the free volume and its temperature dependence between 25 and 190 degreesC of styrene with acrylonitrile, SAN (0 to 50 mol-% AN), is studied by pressure volume temperature (PVT) and positron annihilation lifetime spectroscopy this first part of the work, PVT data are reported which were analysed with the Simba-Somcynsky equation of state (S,S eos) to estimate the volume fraction of holes, h, which constitute the excess free volume. The temperature and pressure dependence of the specific volume V, the specific occupied and free volume, V-occ = (1 - h)Vand V-f = hV, and the corres ponding isobaric expansivities and isothermal compressibility for both the rubbery and glassy state, are estimated. We obtained the unexpected results that (i) the occipied volume changes its coefficient of thermal expansion alpha(occ),(g) approximate to 0.5alpha(g) approximate to 1 X 10(-4) K-1 below T-g to almost zero above T-g and (ii) the isothermal compressibility of the occupied volume at zero pressure is rather high 10(-4) MPa-1, and decreases only slightly at T-g. The variation of total, occupied, and free volume paramet composition of the SAN copolymers is discussed.