An apparatus for measuring the PVT properties of polymers using a metal bellows was developed for pressures up to 200MPa and temperatures from 313K to 473K. The relationship between the volume of the sample cell and the displacement of the bellows was determined measuring the PVT properties of water for temperatures up to 473K and pressures up to 200MPa with an accuracy of ±0.1%. The PVT data for mercury measured with the apparatus showed good agreement with literature values. The PVT relationship for polystyrene was measured in the same ranges of temperature and pressure. The estimated uncertainty in data was less than ±0.0053cm3/g. The PVT data in the rubbery state were correlated with three equations of state. The Simha-Somcynsky equation of state showed the best agreement with experimental values.
