Orientation of the Main Chain in Liquid-Crystalline Side-Chain Polyesters with Variation of Main-Chain Spacer Length

Previous X-ray investigations on liquid-crystalline side chain polyesters with variable spacer length in the side chain as well as in the main chain led to the assumption that the structure will change qualitatively if the main chain spacer length exceeds a certain value. We obtained indications supporting this assumption by applying two-dimensional C-13 NMR. It was shown that for a sample with main chain spacer shorter than the critical length, the main chain segments align perpendicular to the side chains ([P-2] = -0.46), and for spacer length larger than critical length, the main chain segments preferentially orient themselves parallel to the side chain ([P-2] = 0.28).