Ordering in a nematic side-chain polymer. A proton and deuterium nuclear magnetic resonance study

Abstract

 The aim of this work is to study in detail the orientational structure of liquid-crystalline polymers with different molecular weight. The advantage of our approach is the use of broad-band ¹H and ²H NMR spectroscopy for the analysis of the orientational order of the main-chain and mesogenic groups in conjunction with small-angle neutron scattering results. Investigations of a series of partially deuterated side-chain polymers with methoxybenzylbenzoate mesogenic groups have been carried out. The deuteration of the main chain enables separate access to order and orientation effects of the side chain and the main chain. The molecular orientation of the substances investigated can be frozen in its nematic phase below the glass-transition temperature. It is independent of the molecular weight, whereas the dynamics of the director reorientation (rotational viscosity) in the nematic phase strongly depends on the molecular weight. The main-chain deuterons provide powder spectra after orientation of the polymer in magnetic fields, indicating a very weak or lacking orientational anisotropy. A complete decoupling of the main and the side group can be deduced.