Synthesis and chiroptical properties of L-valine-containing poly(phenylacetylene)s with (A)chiral pendant terminal groups

Poly(phenylacetylene)s containing L-valine residues (P1) with (a)chiral pendant terminal groups R-(*()) [-(HC=C(C6H4CONHCH[CH(CH3)(2)]COO-R-(*())})(n)-]; R-(*()) = 1-octyl (P1o), (1S,2R,5S)-(+)-menthyl [P1(+)], (1R,2S,5R)-(-)-menthyl [P1(-)] are designed and synthesized. The polymers are prepared by organorhodium catalysts in high yields (yield up to 88%) with high molecular weights (M-w up to similar to 6.4 x 10(5)). Their structures and properties are characterized by NMR, IR, TGA, UV, and circular dichroism analyses. All the polymers are thermally fairly stable (T-d >= 320 degrees C). The chiral moieties induce the poly(phenylacetylene) chains to helically rotate in a preferred direction. The chirality of the pendant terminal groups affects little the helicity of the polymers but their bulkiness stabilizes the helical conformation against solvent perturbation. The backbone conjugation and chain helicity of the polymers can be modulated continuously and reversibly by acid. (c) 2006 Wiley Periodicals, Inc.