Influences of pre-ordered melt structures on the crystallization behavior and polymorphic composition of β-nucleated isotactic polypropylene with different stereo-defect distribution.

ABSTRACT As part of continuous efforts to understand the surprising synergetic effect between β-nucleating agent and pre-ordered structures of isotactic polypropylene (iPP) in significant enhancement of β-crystallization (Ordered Structure Effect, OSE), two β-nucleated iPP with different uniformities of stereo-defect distribution (WPP-A and WPP-B) were prepared, their crystallization behaviors with variation of melt structures were studied in detail. The results revealed that β-phase can hardly form in WPP-A (whose stereo-defect distribution is less uniform) because of its strong tendency of α-nucleation caused by its less uniform stereo-defect distribution, while WPP-B is more favorable for β-crystallization; As fusion temperature decreases, similar variation trends of crystallization temperature and β-phase proportion can be observed from WPP-A and WPP-B, indicating the occurrence of OSE behavior, which provides unsurpassed β-nucleation efficiency and induces β-crystallization even in WPP-A which is less favorable for β-crystallization; moreover, the upper and lower limiting temperatures of Region II of WPP-A and WPP-B are identical, suggesting the uniformity of stereo-defect distribution has little influence on temperature window for OSE (denoted as Region II). To explore the physical nature of Region II, self-nucleation behavior and equilibrium melting temperature [ABSTRACT FROM AUTHOR]