Melting and chemical behaviors of isothermally crystallized gamma-irradiated syndiotactic polystyrene

Isothermal crystallization kinetics of syndiotactic polystyrene exposed to gamma radiation in vacuum

“…The reasons for melting peak temperatures T 1 , T 2 , and T 3 attributed to b, a, and b9 forms, respectively, were explained in detail by Woo and Wu 33 and Liu et al 29 using DSC and x-ray analyses. DSC thermograms in the different crystallization temperatures for nonirradiated, vacuum-irradiated, and air-irradiated sPS were displayed by Liu et al 29 They elaborated the effect of irradiation environment on crystallization without kinetics. For a sPS sample crystallized at a given temperature and time, the heat flow and corresponding temperature change as a function of time, respectively, in the region of endothermic peak were obtained from DSC thermograms.…”

“…The diffraction angles, diffraction planes, and the corresponding diffraction peaks have been reported previously and are listed in Table IX. 29 A mixture of a and b crystalline forms exists in the gamma-irradiated sPS regardless of the irradiation environment. This is consistent with the DSC melting enthalpy data.…”

“…Note that the melting enthalpy curve at 250°C is shown in the inset because its crystallization time is much longer than those at lower T c s. A general S shape was observed, and these results are similar to those of nonirradiated and air gamma-irradiated sPS samples. 27,29 The induction time (defined as the time between t 5 0 and the onset of a steep rise in melting enthalpy), the rate of H change with crystallization time, and the time required to complete crystallization increased significantly with increasing crystallization temperature. Obviously, the driving force for crystallization is proportional to the difference between the melting temperature and T c .…”

“…29 In this study, XRD was used to confirm the relative changes of the a and b crystalline forms with crystallization time in vacuum irradiated sPS at different doses. Figure 7 displays the XRD patterns for t 5 7 and 50 min at a dose of 800 kGy followed by isothermal crystallization at 240°C.…”

“…Liu et al 29 illustrated that gamma irradiation has a significant effect on the chemical properties and microstructure of sPS. Onyiriuka et al 7 believed that some of the radicals formed in sPS during radiation react with oxygen to form peroxide and then degrade the main chain.…”