Order and dynamics of a series of side chain liquid crystal copolymers through 2H NMR spectroscopy

The order and dynamics of the mesogenic groups in a series of side chain liquid crystal copolymers were investigated in their nematic phase through H-2 NMR. The main chain is built with a variable content of randomly distributed acrylic and methacrylic units, while the mesogenic groups are based on a phenyl benzoate moiety which is labeled on one phenyl ring. The analysis of the orientational order together with the spectral densities J(1)(w(0)) and J(2)(2w(0)) revealed a certain degree of heterogeneity concerning both the order of the mesogens a and m respectively bound to the acrylic and the methacrylic nonomers and their dynamics. In fact, mesogens m are more ordered than a and characterized by slower motions. The processes mainly contributing to relaxation proved to be the rotation of the phenyl ring about its para-axis and the spinning of the whole mesogenic unit.