NMR Investigation of the Main-Chain Orientation in Liquid-Crystalline Side-Chain Polymers

The main-chain orientation in different groups of liquid-crystalline side-chain polymers was investigated using several NMR techniques. For two polyesters the average orientation of the main chain in dependence on the main-chain spacer length could be found from 2D PASS experiments. In polysiloxanes with different mesogenic side groups and different spacer lengths this information could be received from chemical shift anisotropy measurements. Additionally, application of a modified β-echo allowed the separation of the dipolar ²⁹Si-²⁹Si interaction and to characterize the transversal anisotropy of the main-chain segments. Comparison with small angle neutron scattering results gave good agreement, where the different length scale of both methods has to be taken into account.