Side chain liquid crystal polymers of 2,3‐disubstituted norbornenes via ring‐opening metathesis polymerisation, 3. Influence of backbone microstructure and grafting ratio on the thermotropic behaviour

Abstract

AbstractThe ring opening metathesis polymerisation (ROMP) of (±)‐ and (−)‐exo, endo‐bis[(4′‐cyanobiphenyl‐4‐yl)oxyalkyl]norborn‐5‐ene‐2,3‐dicarboxylates using three different Schrock type molybdenum alkylidene complexes ([Mo(NAr)(CH‐t‐Bu)(OR)2] with RC(CH3)3, C(CH32)(CF3) or C(CH3)(CF3)2) resulted in the formation of side chain liquid crystalline polymers (SCLCP's). The different initiators caused changes in the backbone tacticity which were determined by means of NMR techniques. The influence of the type of tacticity on the thermotropic behaviour of the SCLCP's was investigated. The thermal properties were determined by differential scanning calorimetry (DSC). The transition temperatures increased with rising molecular weight up to a degree of polymerisation of about 40. Above this value the thermal properties remained constant with increasing molecular weight. The types of phases for the liquid crystalline polymers were elucidated by polarising optical microscopy (POM). In general, the highly tactic polymers showed a broader thermal range of the LC phase. The kind of initiator used caused changes of the thermal and thermotropic behaviour of the SCLCP's. A grafting ratio model is introduced to explain the findings. From the experimental data a structure/property relationship is developed which might help to predict liquid crystalline properties of unknown polymers.