Shape-directed assembly of a "macromolecular barb" into nanofibers: stereospecific cyclopolymerization of isopropylidene diallylmalonate.
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).
Miyamura
Yasunao
Y
Department of Chemistry and Biotechnology, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Kinbara
Kazushi
K
Yamamoto
Yohei
Y
Praveen
Vakayil K
VK
Kato
Kenichi
K
Takata
Masaki
M
Takano
Atsushi
A
Matsushita
Yushu
Y
Lee
Eunji
E
Lee
Myongsoo
M
Aida
Takuzo
T