Chain Folding in Main-Chain Liquid Crystalline Polyester with Strong π–π Interaction: An Efficient β-Nucleating Agent for Isotactic Polypropylene

Abstract

The influence of the main-chain liquid crystalline polyester (PBDPS) on the crystallization and melting behaviors of isotactic polypropylene (iPP) has been investigated by differential scanning calorimetry (DSC), X-ray diffraction (WAXD), and polarized optical microscopy (POM). The results suggested that PBDPS is an efficient β-nucleating agent for iPP. The melting crystallization temperature as well as β-crystal of iPP increased with increasing of PBDPS content. The relative content of β-iPP crystals (kβ) can reach 96.6% while adding 4% PBDPS during isothermal crystallization at 135 °C. The increased β-nucleation efficiency was ascribed to the adjacent phenyl rings in side groups of PBDPS stacked well together even when the temperature was higher than its clearing point (Ti). Moreover, the distance between stacked phenyls is 0.32 nm, which is half of the unit cell parameter in the c-direction of β-iPP, indicating a lattice match between β-iPP and PBDPS.