MOLECULAR DESIGN, SYNTHESIS, AND CHARACTERIZATION OF LIQUID-CRYSTAL COIL DIBLOCK COPOLYMERS WITH AZOBENZENE SIDE-GROUPS

The synthesis and characterization of a family of well-defined liquid crystal-coil (LC-coil) diblock copolymers have been carried out. The b lock copolymers in this study have been designed to have nearly identi cal molecular weight azobenzene-containing LC blocks in order to elimi nate possible variations in LC behavior caused by the differences in t he LC block molecular weight. Quantitative hydroboration chemistry was used to convert tile pendent double bonds of an isoprene block to hyd roxyl groups to which the mesogenic groups were attached via acid chlo ride coupling. The LC homopolymer and the block copolymers (LC volume fraction from f(LC) = 0.82 to f(LC) = 0.20) all exhibited smectic meso phases with similar clearing transition temperatures. The clearing tra nsition enthalpies strongly depend on the block composition ratio and decrease as the LC block volume fraction decreases. Solvent-casting of a lamellar LC-coil copolymer (SICN5-66/60) resulted in an oriented bu lk film in which both the axes of the mesogenic groups and the lamella r interfaces lie parallel to the film surfaces. A LC cylinder morpholo gy was observed with a f(LC) = 0.22 LC-containing block (SICN5-176/55) using TEM and confirmed by SAXS measurements. This is the first obser vation with the LC block in a cylinder microdomain. Other morphologies (bicontinuous, LC sphere) were observed by TEM while retaining the sm ectic order in the LC microphase.