Novel ABC₂-type liquid-crystalline block copolymers with azobenzene moieties prepared by atom transfer radical polymerization

A series of novel ABC₂-type liquid-crystalline block copolymers with azobenzene moieties in the side chains were prepared by combination of atom transfer radical polymerization (ATRP) and the chemical modification reaction. First, the bromine-terminated diblock copolymer poly(ethylene oxide) monomethyl ether-block-polystyrene (MPEO-PS-Br) was prepared by ATRP of styrene initiated with macroinitiator MPEO-Br, which was obtained from the esterification of MPEO and 2-bromoisobutyryl bromide. Then, the bromo end groups of the resulting MPEO-PS-Br were derivatized into twice as many bromoisobutyrates by the chain end modification reaction to obtain ω,ω′-bis(bromo)-PS-MPEO (MPEO-PS-Br₂). The azobenzene-containing blocks of poly[6-(4-methoxy-azobenzene-4′-oxy) hexyl methacrylate] (PMMAZO) with different molecular weights were introduced into the derivative diblock copolymer by a second ATRP to synthesize the novel ABC₂-type liquid-crystalline block copolymers poly(ethylene oxide) monomethyl ether-block-polystyrene-block-{poly[6-(4-methoxy-azobenzene-4′-oxy) hexyl methacrylate]}₂ [MPEO-PS-(PMMAZO)₂].