FRUSTRATED BILAYER SMECTIC PHASE IN MAIN-CHAIN POLYMERS WITH 2 DIFFERENT SPACERS

We have studied the structural characteristics of the smectic phases f ormed by the main-chain type of polymers in which the mesogenic biphen yl moieties are linked by two different odd-numbered aliphatic spacers in a regularly alternate fashion. The first interesting result of thi s study is that the two different types of layer structures are formed depending on the difference in the lengths of two aliphatic spacers. In the polymers with the two spacers having a small difference in thei r lengths, the single layer structure is formed as a result of the ran dom mixing of the two different spacers. In contrast, if there is a su fficiently large difference in lengths, the two different spacers part icipate into different layers and so the smectic phase appears to have a bilayer character. The second interesting result is that the bilaye r smectic phase pretends the frustrated structure with the unusual den sity modulation in the direction parallel to the layer. This frustrate d structure has been explained as resulting from a two-dimensional esc ape of the spontaneous polarization.