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 na rrow-molecular-weight samples have been studied by X-ray diffraction. Depen ding on the degree of polymerization the polymer shows nematic smectic A(d) , re-entrant nematic and new phase with two-dimensional (2D) periodicity. S uch behaviour is implicit to so-called frustrated systems. However, the mes ogenic side chains are nonpolar and thus the origin of frustration is diffe rent from that in conventional polar liquid crystals. We found that this ph enomenon is steric (entropic) in nature and depends on the length of the po lymer backbone. The phase transformations of mesogen side chain polyacrylat es are discussed in terms of coupling between the smectic ordering of the s ide groups and the polymer backbone conformations.