Phase behavior and structure formation for diblock copolymers composed of side-chain liquid crystalline and glassy amorphous components

Phase behavior and structure formation in liquid crystallization of a side-chain liquid crystalline (LC) block copolymers composed of poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PA11OCB) and polystyrene (PSt) were investigated by using a time-resolved small-angle X-ray scattering technique (SAXS), differential scanning calorimetry and polarizing optical microscopy. PA11OCB homopolymer formed smectic (Sm) liquid crystal. Liquid crystallization behavior of the block copolymers depended on the molecular weight and the block composition. When molecular weight was relatively low, order-disorder transition (ODT) was observed. In cooling of such block copolymers, liquid crystallization seemed to wait for the formation of LC-rich microphase by ODT. For the block copolymers with relatively high molecular weight, liquid crystallization slightly enlarged the domain spacing without changing the microphase separation structure in the melt. The order of the LC phase was lowered with decreasing dimensionality of the LC microdomains, that is, the LC blocks formed smectic liquid crystal in the matrix or lamellar microphase while liquid crystallization in the cylindrical microdomains did not show smectic but maybe nematic liquid crystal. Moreover, the LC blocks within the spherical microdomains did not liquid crystallize. From the 2-D SAXS with applying shear flow, the Sm layers were orientated perpendicularly to the interface of the microphase separation. The relation between the layer thickness of the LC phase and the molecular weight suggested that the main chain was extended normally to the interface of the microphase separation.