Molecular-weight dependence of phase structure and viscosity in a liquid crystalline polyester with strong π–π interaction

ABSTRACT

In this article, the molecular-weight dependence of the phase structure, rheological behaviour and thermal stability of a main-chain liquid crystalline polyester (PBDPS) with strong π–π interaction was investigated in details by differential scanning calorimetry, polarising optical microscopy, wide-angle X-ray diffraction, dynamic oscillatory rheological measurements and thermogravimetric analysis. While the molecular weight of PBDPS is 5.2k, it shows smectic B and smectic A phases prior to isotropic phase. With increasing molecular weight, smectic B phase of PBDPS gradually disappeared. Moreover, the smecitc B to smectic A (T_lc) and smectic A to isotropic (T_i) phase transition temperatures decreased as increased molecular weight. The rheology results suggested that fluid type of PBDPSs changed from Newtonian fluid to pseudo-plastic fluid as the molecular weight of PBDPS increased. In addition, the zero-shear viscosity (η₀) of PBDPS showed a power law relationship (${\eta }_0\propto M{w}^{4.21\pm 0.16}$) with molecular weight of PBDPS. All the PBDPSs showed good thermal stability with an initial decomposition temperature higher than 360°C.

Graphical Abstract

KEYWORDS:

• Main-chain liquid crystalline polymer
• phase structure
• molecular-weight dependence
• rheological behaviour

Acknowledgement

The authors gratefully acknowledge financial support from the Natural Science Foundation of Jiangsu Province (BK20150257), the Top-notch Academic Programs Project of Jiangsu higher Education Institutions and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. The authors also thank Prof. Li Chen at Sichuan University (China) for his kind assistance with the 2D WAXS tests.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors gratefully acknowledge financial support from the Natural Science Foundation of Jiangsu Province [BK20150257], the Top-notch Academic Programs Project of Jiangsu higher Education Institutions and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.