Structures of amphiphilic block copolymers in their liquid and solid states

Abstract

Block copolymers are macromolecules comprising two or more chemically different chains joined together by covalent bonds. The development of this field originated with the discovery of termination-free anionic polymerization, which remains the best method for producing monodisperse block copolymers. A variety of molecular architectures are possible, for example, AB diblock, ABA triblock, and starblock copolymers. Current theories deal almost exclusively with diblock and starblock copolymers, with diblocks receiving the most comprehensive treatment. The different component chains in block copolymers usually mix endothermically, and while short blocks may mix at high temperatures, long blocks are incompatible (that is, thermodynamically immiscible). Consequently, the material (bulk) properties of many block copolymers are dominated by their tendency to spontaneously separate into microphases when the temperature is lowered. Similar effects are found in concentrated solutions of block copolymers. The chapter introduces the theory of phase separation in block copolymers, then describes experimental developments in the microphase structures and behaviors of block copolymer melts, particularly recent work on ImSn and EmBn. Finally, the phase behavior of crystallizable block copolymers is briefly reviewed, with an emphasis on EmBn.