| As two kinds of potential engineering plastics, syndiotactic polystyrene (s-PS) and syndiotactic polypropylene (s-PP) have enjoyed intense industrial and academic interest, due to their good performance and complex polymorphic behavior. In the past, the work in structure of s-PS demonstrated that four different crystalline forms is possible by different processing behavior: a, P, i~ and 6. The crystalline Q and P forms are characterized by chains in the trans planar conformation with an identity period of c=0.Slnm, can be obtained from the melt or the glassy state of s-PS under different thermal condition, whereas the crystalline Y and 6 forms have chains in the S(2/1)2 helical conformation with an identity period of c=0.78nm, are formed under condition where solvents are in vol ~Ted. s-PP presents polymorphism in the solid state, too. It can be divided as four kind of crystalline forms that were named as form I . II , III and IV, respectively. Both form I and II were characterized by chains in helical (TTGG)~ conformation, crystalline form III have chains in trans- planar conformation, and form IV presents chains in a (T6G2T2G2)~ conformation which intermediate between the helical (TTGG)~ and the trans-planar conformation. The research on the crystal of s-PS and s-PP have made progress these years but still need step further in some fields. In this paper, the crystal structure, crystal form transition, melting, morphology and -lx- kinetics was studied by WAXD, DSC, successive WAXD, PLM, SEM and TG, respectively. Based on WAXD diffraction patterns of isothermal melt crystallization, the conclusion that s-PS crystallized from melt contain a and P s-PS. The increasing of T~ and degree of syndiotacticity is benefit to the formation of P and a s-PS, respectively. Crystal plane distance (d) and crystallite dimension is influenced by T~ greatly. The decreasing of cooling rate (a) benefit to the formation of P s-PS. The relation of cool crystallization time (ta) of quenched s-PS and heating rate (R) is calculated as t~12l5.6R0843. The crystal formed within cool crystallization could be only a s-PS, and the melt of it is company with re-crystallization. Two kind of solvent-induced s-PS: v and 6 s-PS was prepared by a new simple way. Corresponding to successive WAXD patterns during heating at 10K/mm of Y and 6 s-PS, y s-PS transform to a s-PS within 190-2100C before melt. 6 s-PS transform to y s-PS at 180-200 憕C and transform continue to a form at 200-2150C. 6 - y and y - a transition is endothermal and exothermal process, respectively. To the nonisothermal crystallization of s-PS, the nucleation mechanism of earlier and later stage is different. The mechanism of earlier stage is influenced by cooling rate greatly, by that Qf later stage is heterogeneous nucleation and three-dimension growing. Energy of nonisothermal and cool crystallization is 382KJ/mol and 158.2KJ/mol, respectively. The m7orphology of melting-crystallization s-PS which has different content of a and P forms was observed by PLM and SEM. There are eight kinds of spherulite formed as crystalline temperature (Ta) changed from 220 0C to Tm. Four-sectional spherulite and eight-sectional spherulites can be obtained when crystallized in higher temperature (T~>2400C). The spherulite is feathered and lamellae structure is bulking As T~ low... |
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