|Fundamental Studies and Recent Advances in Anionic Polymerization
5. Assembly and Self-organization of Macromolecules with Hetero-phase Structures
Polymeric and Organic Materials Department, Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan
Nippon Gomu Kyokaishi,(2007),80(7),266-272 General Review in Japanese
Morphological studies of well-defined polymers with heterophase structures including AB diblock copolymers, ABC triblock terpolymers, and 3-arm asymmetric ABC star-branched polymers are reviewed. Among them, ABC triblock terpolymers and asymmetric ABC star-branched polymers have been recently synthesized by means of living anionic polymerization. It has been well established as Molau's rule for a long time that the microphase-separated structures observed for AB diblock copolymers are successively changed from spherical, cylindrical, gyroid, to lamellar, depending on the composition f and combination parameter N where and N are the segment-segment interaction energy and the degree of polymerization, respectively. On the other hand, in ABC triblock terpolymers, there are additional several parameters ( AB, AC, BC , fA, fB, N) that can be varied by the sequential order (ABC, ACB, and BAC). Their morphologies are dependent on the relative magnitude of three segment-segment interaction parameters: a lamellar morphology that minimizes both interfacial contact energy and chain stretching with
AB = BC< AC, a core-shell cylindrical morphology that reduces the overall free energy with AB<BC< AC, and a cylinder-at-the-wall and a sphere-at-the-wall that accommodate the most energetically favorable contact with AB = BC>> AC. Moreover, 3-arm asymmetric ABC star-branched polymers potentially develop several super lattice structures including tricontinuous gyroid ones based on the arm length ratios and interaction parameters. Such characteristic morphologies are of particularly interest to produce novel and unique self-organized nano architectures potentially applicable to nano-devices.
Living Anionic Polymerization, AB Block Copolymer, ABA Triblock Copolymer, ABC Triblock Terpolymer, ABC Star-branched Polymer, Microphase Separation, Self-organization, Hetero-phase Structure