Phase Behavior of New Side Chain Smectic C* Liquid Crystalline Block Copolymers

Abstract

The liquid crystalline and microphase behavior of new chiral side chain liquid crystalline diblock copolymers is described. The materials, which contain a smectic C* mesogen, are block copolymers of polystyrene and methacrylates containing (s)-2-methyl-1-butyl-4‘-(((4-hydroxyphenyl)carbonyl)oxy)-1,1‘-biphenyl-4-carboxylate mesogens. The influences of the liquid crystalline (LC) mesophase on block copolymer ordering and of the block copolymer morphology on LC properties as a function of molecular weight and block copolymer composition are discussed. Microphase segregated structures were observed for blcok copolymers ranging from 24 to 63% w/w LC block. The lamellar domains of the block copolymers stabilize the layered smectic mesophase, particularly the smectic C* phase. The length of the polystyrene block, as well as the LC block, affected LC phase transition temperatures, probably due to phase mixing and the nature of the block copolymer interface. When the molecular weight is low, and the liquid crystal block content is high, the order−disorder transition temperature, at which block copolymer phase segregation is observed, and the LC clearing point occur at the same temperature; this correlation between LC order and the ODT has not been reported before for LC side chain block copolymers. The block copolymer morphology in these cases is arranged to accommodate the focal conic superstructure seen in optical micrographs of this LC block copolymer.