Frustrated Behavior of a Side-Chain Liquid Crystalline Polyacrylate

Polyacrylate with phenyl benzoate mesogenic side groups was synthesized and fractionated into narrow fractions. Structure and phase behavior of the narrow-molecular-weight samples have been studied by X-ray diffraction. Depending on the degree of polymerization the polymer shows nematic, smectic Ad, re-entrant nematic and new phase with two-dimensional (2D) periodicity. Such behaviour is implicit to so-called frustrated systems. However, the mesogenic side chains are nonpolar and thus the origin of frustration is different from that in conventional polar liquid crystals. We found that this phenomenon is steric (entropic) in nature and depends on the length of the polymer backbone. The phase transformations of mesogen side chain polyacrylates are discussed in terms of coupling between the smectic ordering of the side groups and the polymer backbone conformations.