Synthesis, nanostructures, and functionality of amphiphilic liquid crystalline block copolymers with azobenzene moieties

A series of liquid crystalline (LC) homopolymers of poly{11-[4-(4-butylphenylazo)phenoxy]-undecyl methacrylate} containing an azobenzene mesogen with different degrees of polymerization were synthesized by using the atom transfer radical polymerization (ATRP) method. The homopolymers were prepared with a range of number-average molecular weights from 6100 to 23 500 with narrow polydispersities of less than 1.17. Thermal investigation showed that the homopolymers exhibit monolayer smectic A, smectic C, and an unknown smectic X phases. The transition temperatures increase slightly with the increase of the molecular weights and level off at around 21 500. Novel amphiphilic LC-coil diblock copolymers with a defined length of a flexible poly(ethylene glycol) segment as the hydrophilic coil were also prepared by the ATRP method. The LC-coil diblock copolymers exhibit narrow polydispersities of less than 1.11. Morphologies of the thin films of the block copolymers were investigated by using transmission electron microscopy (TEM). Microphase separation with small size in the range of 10-20 nm (nanoseparated structures) was observed. Different photophysical and photochemical behaviors were observed between annealed homopolymer and block copolymer films, which is thought to be caused by the formation of nanostructures of the block copolymers.