Qingrong Fan

The Study of Stress-Yielding of Aged Atactic Polystyrene (a-PS) by Differential Scanning Calorimetry

Full Paper: The stress-yielding mechanism of aged atactic polystyrene (a-PS) was studied by differential scanning calorimetry (DSC) and solvent-swelling measurements and the viewpoint of cohesional entanglement (CE) was applied to interpret the observations. The results indicated that the yielding, as well as the solvent- swelling of aged a-PS, were in essence the processes to break the CE points, generated by the aging at temperatures below aPS’s Tg. In these cases, the break up of CE was manifested by the decrease or disappearance of the stress-induced yielding peak in the stress-strain curve (r-e curve) and that of the endothermic peak near the Tg temperature range of DSC scanning.

Polycarbonate films in the state of high global chain orientation but nearly random segmental orientation

Abstract The polycarbonate (PC) films in the high global chain orientation but nearly random segmental orientation (GOLR) state have been prepared by being uniaxially drawn at temperatures ∼20–30°C above their glass transition temperature, T g, and then the isotropy and anisotropy in some properties of the obtained films have been studied. Experimental results presented show that this kind of amorphous state, the GOLR state, is nearly isotropic in optical birefringence, IR-dichroism and X-ray diffraction pattern, while it is very remarkably anisotropic in behaviors of thermal expansion, solvent-swelling and stress-strain.