Studies on thermotropic liquid crystalline polyphosphates containing photoreactive dual mesogens

Abstract

A series of thermotropic liquid crystalline polyphosphates, containing photochromic molecules of stilbene in the backbone and substituted azobenzene in the side chain, were synthesized respectively. The inherent viscosity measurements were determined for all the polymers. The stability and char yield, T_g, T_m and T_i were investigated by thermal analysis. Polarizing optical microscopy of all the polymers exhibited birefringent melts with liquid crystalline behaviour. Variable temperature powder X‐ray diffraction techniques were performed for confirmation of textures. UV‐visible photolysis studies investigated the simultaneous behaviour of reactivity rates of crosslinking of stilbene units and isomerization, caused by azobenzene units in the main chain/side chain LCPs. Photoisomerization kinetics demonstrated the switching time rates for the trans‐cis conversion of the azobenzene unit. A model polymer was synthesized and compared for the effect of stilbene in the main chain. Dipole moment values were calculated for the simulated low molecular mass of the pendant substituents to predict the polarity using MOPAC 3D Pro.

Acknowledgement

The authors thank the University Grants Commission, India (UGC No.F.12‐113/2001, New Delhi, India) for financial support of this work. We are also grateful to Sophisticated Regional Instrumentation Center, Indian Institute of Technology, Chennai, India for spectral analysis.