The glass transition temperature of polystyrene - Results of a round robin test

A round robin test was performed to determine the reliability of values for the glass transition temperature T-g as determined by DTA on polymers. Ten different instruments were involved. The test material was high molecular weight polystyrene. Values for T, (midpoint) were reported in the range 107 degrees C+/-2 K. The respective heat flow curves differed considerably in shape. In the literature a T-g of 100 degrees C is often given for polystyrene. The discrepancy between this value and the value of 107 degrees C found in the round robin test is due to three differences: the thermal history of the sample, the evaluation of the heat flow curves, and the effect of finite sample size.