Influence of two liquid crystalline polysiloxanes with different average molecular weight as new β-nucleator on crystallization structure of isotactic polypropylene

Two liquid crystalline polymers (LC-N1 and LC-N2) with different average molecular weight were designed and synthesized as a new beta-nucleator in isotactic polypropylene (iPP). The main aim of this work was to investigate the influence of LC-N1 and LC-N2 on the crystallization structure and beta nucleating activity of the iPP with wide angle X-ray diffraction and polarized optical microscopy. The beta nucleation activity not only depended on the nucleator content, mesogenic molecular structure, and thermal processing history, but also on average molecular weight of the liquid crystalline polymers. LC-N1 or LC-N2 has been found to be an effective beta-nucleator for the iPP. The experimental results indicated the relative content of beta-crystal first increased and then decreased with increasing the nucleator content or crystallization temperature. The addition of LC-N1 or LC-N2 could provide a large number of nuclei, enhance the crystallization rate, reduce the spherulite size, and lead to a more uniform morphology; moreover, the colorful beta-crystal was also induced. In addition, LC-N2 with higher average molecular weight is more effective than LC-N1 in inducing beta heterogeneous nucleation under same crystallization conditions.