Synthesis, structure, and properties of polyacetylenes possessing chiral spirobifluorene moieties in the side chain

Abstract

Synthesis, property, and structure of a few polyacetylenes having the pendent optically active spirobifluorene moiety as a C2 chiral group are described. Optically inactive achiral monomer 2-ethynyl-9,9′- spirobifluorene was obtained from 2-bromo-9,9′-spirobifluorene, while optically active monomers (R)-2′-ethynyl-9,9′-spirobifluorene-2-ol and (R)-2-acyloxy-2′-ethynyl-9,9′-spirobifluorene were prepared from optically pure 2,2′-dihydroxy-9,9′-spirobifluorene. Polymerizations of these monomers were carried out by a rhodium catalyst system ([Rh(nbd)Cl]2-triethylamine) in THF at room temperature to give polyacetylenes with Mw ca. 25000 in moderate yields. The chemical and thermal properties of polymers were evaluated. The structural characteristics were studied by UV-vis, CD, and Raman spectra in addition to the specific optical rotation. The experimental results suggested the formation of optically active polymers which took the cis-transoidal main chain conformation, while the main chains had helical structures as simulated (P-screwed 16-1 helix in the case of poly(R)-1-OH). The formation of one-handed helical polymers was caused by the introduction of a group with molecular chirality in the side chain. © 2008 The Society of Polymer Science.