Crystallization and melting behaviors of the beta-nucleated isotactic polypropylene with different melt structures - The role of molecular weight

摘要

To elucidate influence of molecular weight on crystallization behavior of beta-nucleated isotactic polypropylene (beta-nucleated iPP) with different melt structures, a series of beta-nucleated iPP with varying molecular weights were prepared. Results revealed that higher iPP molecular weight was more favorable for formation of high beta-phase proportion (beta(c)). By tuning heating temperature (T-f), the melt structure (content of ordered structures within melt) of beta-nucleated iPP was controlled. It was found that for all samples, beta(c) evidently elevated with decrease of T-f, indicating occurrence of synergetic effect between ordered structures and beta-NA (ordered structure effect, OSE); with decrease of iPP molecular weight, beta(c), triggered by OSE increased gradually and T-f temperature range for occurrence of OSE gradually decreased. Moreover, as holding time at T-f increased from 1 to 120 min, subsequent melting curves of samples stayed unchanged, reflecting very high thermal stability of the ordered structures, being independent to iPP molecular weight. (C) 2014 Elsevier B.V. All rights reserved.