The process of spin-coating to fabricate thin polymer films with high molecular weight can produce samples with entanglement concentrations that are far below the equilibrium value. It is not clear whether or not such low entanglement concentrations are responsible for the depression of the glass temperature in thin polymer films. In this work, we measure the calorimetric glass temperature and viscoelastic response of polystyrenes with molecular weights ranging from 3x10(3) to 43.7x10(6) g/mol, for both bulk material and for samples freeze-dried from dilute solution. We conclude that the reduction of the glass temperature observed in thin polymer films cannot be due to the reduced entanglement concentration in the samples.

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A new piston-cylinder-type pressurizable dilatometer controlled by a stepper motor has been developed to measure the time-dependent bulk modulus and pressure-volume-temperature (PVT) behavior of polymeric materials. The dilatometer can be operated from 35 to 230 degrees C and at pressures of up to 250 MPa. The sample cell, which contains the sample and a fluorinated oil as the confining fluid, is totally submerged into a high precision oil bath to achieve a temperature stability of better than 0.01 degrees C. The instrument is calibrated with mercury and quartz. The total instrument volume is 4.0 cm(3), of which 2.3 cm(3) is the sample cell; the total volume can be measured with an average absolute error of better than 5.0x10(-4) cm(3). To demonstrate the instrument's capabilities, the time-dependent bulk modulus and the PVT behavior of a polystyrene are obtained and compared to the literature.