Side-chain liquid crystal block copolymers with well-defined structures prepared by living anionic polymerization I. Thermotropic phase behavior and structures of liquid crystal segment in lamellar type of microphase domain

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-n 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 (S-A) 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 S-A 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 S-A temperatures. It gradually decreases from the value of crystal phase to that of isotropic phase. The reduction is around 20-25%, which can be explained in terms of the change in main-chain conformation of the LC block.