This paper describes the synthesis of side-chain liquid crystalline polymers and block copolymers by living anionic polymerization and their thermotropic phase behavior. The polymers were successfully prepared with a narrow distribution of molecular weight. The thermotropic transition behavior between crystal, smectic A, and isotropic phases was examined with a function of the molecular weight. Living anionic polymerization also allowed the preparation of well-defined block copolymers with amorphous polystyrene. In these block copolymers, microphase separation due to liquid crystalline and amorphous blocks was observed by electron microscopy and small-single X-ray methods. Effects of the microphase separation were also examined on the thermotropic phase behavior and structure.

ABSTRACT:We have synthesized the A-B block copolymer with polystyrene as A segment and side-chain liquid crystal (LC) polymer as B segment by a sequential living polymerization. The copolymers were successfully prepared with quantitative yields, possessing the predictable M. values, compositions, and narrow molecular weight distributions. The thermotropic phase behavior and structures were examined for nine copolymers with the fraction of segments around 50 w% and with the various molecular weights ranged from 8000 to 34000. All the polymers exhibit the well-defined lamellar type of segregation and the side-chain LC segment in the microdomain forms crystal, smectic A (SA) and isotropic phases with increasing temperature. The lamellar segregation is maintained over the whole temperature region from crystal to isotropic phases, and the crystal and SA structures are formed with a preferential orientation to the microdomain interface such that the mesogenic side-chain groups lie parallel to the interface. The lamellar thickness depends on the SA temperatures. It gradually decreases from the value of crystal phase to that of isotropic phase. The reduction is around 2(}--25%, which can be explained in terms of the change in main-chain conformation of the LC block.KEY WORDS Block Copolymer I Liquid Crystal I Smectic Phase I Microphase Separation I Lamellar Structure I Living Polymerization I Liquid crystal (LC) polymers with mesogenic groups in the side chains (side-chain LC polymers) have been extensively studied. 1 • 2 More recently, the research interests have focused on a role of the main-chain backbone on liquid crystal structures and properties. The various parameters with respect to the main-chain backbone such as a degree of polymerization, molecular weight distribution, tacticity, and monomer unit distribution in copolymers can be considered. An essential breakthrough can be performed by controlled polymerization such as group-transfer polymerization and living polymerization, since these permit the control of several parameters given above because of the synthesis of welldefined structures. 3 -8 In the previous paper, 9 we succeeded to prepare a series of side-chain LC polymers with a well-controlled structure, by living anionic polymerization. Polymerization was attempted at an elevated temperature of -40oC since precipitation occurs during the polymerization at a usually applied temperature of -78oC. Irrespective of this unusual condition for the living anionic polymerization, the polymers were obtained with unimodal distribution of less than 1, 1 when the molecular weights are less than 12000. Their thermotropic phase behavior and structures were examined as a function of the molecular weight.