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

• We prepared a series of β-nucleated iPP with varying molar masses.
• We tuned their melt structures by controlling heating temperature and studied their crystallization behavior.
• We explored the influences of iPP molar mass on crystallization of β-iPP with different melt structures.
• We studied the thermal stability of the ordered structures with β-nucleation efficiency and the role of molar mass.

To elucidate influence of molecular weight on crystallization behavior of β-nucleated isotactic polypropylene (β-nucleated iPP) with different melt structures, a series of β-nucleated iPP with varying molecular weights were prepared. Results revealed that higher iPP molecular weight was more favorable for formation of high β-phase proportion (βc). By tuning heating temperature (Tf), the melt structure (content of ordered structures within melt) of β-nucleated iPP was controlled. It was found that for all samples, βc evidently elevated with decrease of Tf, indicating occurrence of synergetic effect between ordered structures and β-NA (ordered structure effect, OSE); with decrease of iPP molecular weight, βc triggered by OSE increased gradually and Tf temperature range for occurrence of OSE gradually decreased. Moreover, as holding time at Tf 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.