Transformational kinetics in liquid crystal polymers and differential scanning calorimetry calibration

Abstract

Liquid crystalline polymers (LCPs) are defined by their instantaneous liquid crystal phase transitions, as compared with set heating/cooling rates in differential scanning calorimetry (DSC). This is well accepted for the case of main-chain (MC) LCPs. It is confirmed here for the case of two side-group (SG) LCPs as well. The DSC temperature calibration is usually based on melting of metals like indium and zinc and hence only possible on heating. Being instantaneous, LC transitions are as such very appropriate for DSC temperature calibration. This is demonstrated for the case of two SG-LCPs: one with a side group including an ester group, and one with a nitrostilbene side group. Transition kinetics were studied upon heating and cooling with DSC rates in the range of 2.5–50 K min⁻¹. After room temperature storage, the SG-LCPs studied showed considerable thermal effects due to physical ageing. These endothermic effects could easily be discerned from the instantaneous LC transitions and appeared to be thermally activated, with apparent activation energies depending on the amount of preceding physical ageing: on reheating after melting and cooling about 475 kJ mol⁻¹, while after long-time storage at room temperature 280 kJ mol⁻¹ is obtained.

Keywords:

• temperature calibration
• differential calorimetry
• kinetics
• liquid crystalline polymer

Acknowledgements

C.T.J. Wreesmann and P.P. de Wit (at former Akzo Nobel Corporate Research) are acknowledged for making available samples of these liquid crystalline polymers. Prof. dr. T.J. Dingemans (Delft University of Technology) made available the structure schemes of HNSPE and MPBPET. S. Kuiper, from the Section NanoStructured Materials at Faculty of Applied Sciences of Delft University of Technology, performed the optical polarisation microscopy. One of the authors (PvM) acknowledges the great hospitality provided by Faculty of Applied Sciences of Delft University of Technology, Section NanoStructured Materials during this study.