Thermodynamic and structure investigations of new side-chain liquid crystal polymer

Bis [(omega-(4'-cyanobiphenyl)-4-yl)oxy-n-alkyl]norborn-5-ene-2,3-dicarboxylate was polymerised via ring opening metathesis polymerisation (ROMP). Two disubstituted polynorbornene derivatives, both of cis configuration, with different length of side-chain were studied. The influence of thermal history on the smectic phase stabilisation, position and shape of the glass transition with temperature and on the relaxation process is shown. Glass transition temperatures (T-g), enthalpies of isotropisation (Delta H-i) and average layer spacing (d) were calculated. Although, the rather flexible spacer (methylene groups) between the mesogenic group and the main chain seems to be sufficient to partially decouple the mobility of the main chain from that of the mesogenic group, the influence of a backbone chain structure is still significant for polymer properties, especially in bulk. The measured layer spacing does not correspond to double length of the side chain (with mesogenic groups and CN substituent) which suggests that either the side chains are not fully extended or some overlapping of CN tails occurs.