title: Shape-directed assembly of a "macromolecular barb" into nanofibers: stereospecific cyclopolymerization of isopropylidene diallylmalonate.
abstract: Cyclopolymerization of isopropylidene diallylmalonate (1) in CH(2)Cl(2) using as the initiator a crystallographically defined alpha-diimine Pd(II) complex with a trans-azobenzene strap (trans-3) proceeds stereospecifically to give a cycloolefinic polymer that is rich in threo-disyndiotactic sequences (st(rich)-2; syndiotactic tetrad content = 60% at -10 to 0 degrees C). Polymer 2, when perfectly threo-disyndiotactic, adopts a "barb"-shaped geometry with its cyclic malonate pendants sticking out alternately up and down along the rigid main chain. Under appropriate conditions, st(rich)-2 regularly self-assembles, not only in the solid state but also in solution, into nanofibers that eventually give rise to physical gelation of halogenated solvents such as CH(2)Cl(2). In sharp contrast, a reference polymer 2 that is rich in threo-diisotactic sequences (it(rich)-2), which likely adopts a helical geometry, has poor self-assembly capability in solution and neither forms nanofibers nor induces physical gelation of CH(2)Cl(2).
authors.affiliation: Department of Chemistry and Biotechnology, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Yasunao
authors.initials: Y
authors.lastname: Miyamura
authors.forename: Kazushi
authors.initials: K
authors.lastname: Kinbara
authors.forename: Yohei
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Vakayil K
authors.initials: VK
authors.lastname: Praveen
authors.forename: Kenichi
authors.initials: K
authors.lastname: Kato
authors.forename: Masaki
authors.initials: M
authors.lastname: Takata
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takano
authors.forename: Yushu
authors.initials: Y
authors.lastname: Matsushita
authors.forename: Eunji
authors.initials: E
authors.lastname: Lee
authors.forename: Myongsoo
authors.initials: M
authors.lastname: Lee
authors.forename: Takuzo
authors.initials: T
authors.lastname: Aida