GLASS TRANSITION TEMPERATURE OF POLYSTYRENE DETERMINED BY DSC REVISITED
DSC法测定PS玻璃化温度的再研究

The method of reconstruction histograms of glass transition temperature from differential scanning calorimetry (DSC) thermograms proposed by Fevotte was improved,and the temperature related with half rubbery content Tghr was defined as an new parameter for glass transition.The rubbery fraction was obtained by deduction of the heat flow caused by retardant enthalpy recovery from the recorded DSC heat flow.The revisit of the glass transition behavior of polystyrene (PS) by using the modified Fevotte method was described in this paper.It was found that Tghr of PS is about 4 K higher than that obtained by using the widely used half specific heat capacity (Cp) extrapolated method.The reproducibility of Tg acquired by the modified Fevotte method was improved compared with that using the methods provided by the general commercial software.When the effect of annealing time and cooling rate on glass-rubber transition behavior of PS was investigated,the modified Fevotte method shows its superiority.It was found that Tghr of PS increases monotonously with increasing annealing time and decreasing cooling rate.Polymer with different thermal history usually shows different Tg.Tghr of PS was predicted to be in the range of 377.5 K to 390.9 K depending on physical aging extent.Also it is indicated that the physical aging mode has little effect on polymer Tg.