Free volume in two differently plasticized poly(vinyl chloride)s: a positron lifetime and PVT study

The temperature dependence of the specific volume, V, and of the mean size of local free volumes (holes), vh, of poly(vinyl chloride) containing 10 wt% (PVC-h) and 30 wt% (PVC-s) of the plasticizer di-n-butyl phthalate (DBP) were studied by pressure–volume–temperature (PVT) and positron annihilation lifetime spectroscopy (PALS) experiments. Using the Simha–Somcynsky equation-of-state, the hole fraction h was calculated from the PVT data. It was found that the thermal expansivity of the specific volume V, the specific free volume Vf=hV, and vh increase with the content of plasticizer. From the comparison of V and Vf with vh the hole number per gram N′h is estimated. Other than vh, N′h does not depend on the temperature nor on the content of plasticizer.