| pubmed-article:20178364 | pubmed:abstractText | 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). | lld:pubmed |
