Thermoelastic and photoelastic properties of crosslinked liquid‐crystalline side chain polymers

Measurements of stress and birefringence of crosslinked liquid‐crystalline side chain polymers are reported. The results are compared with those obtained for conventional elastomers. It is found that the thermoelastic behaviour in the nematic state completely differs from that observed for common polymer networks due to the anistropic ordering of the mesogenic side chains. The retractive force in the nematic state is found to be independent of path, indicating that the nematic phase is a homogeneous phase. Photoelastic investigations prove the propotionality of stress and birefringence above the clearing temperature Tc which is similar to common elastomers. The stress‐optical coefficient, however, strongly depends on temperature in the pretransformation region. X‐ray measurements show a uniform orientation of the mesogenic side groups in the nematic state. The diffraction patterns observed contain many more reflexes than observed for common nematics.