Mutual conversion between stretched and contracted helices accompanied by a drastic change in color and spatial structure of poly(phenylacetylene) prepared with a [Rh(nbd)Cl]2-amine catalyst

ABSTRACT The yellow‐colored poly(phenylacetylene), Poly(Y), is obtained from phenylacetylene using a [Rh(nbd)Cl]2‐NEt3 catalyst in ethanol at 25 °C. The color of Poly(Y) drastically changes into red Poly(R) or reddish‐black Poly(B) by immersion in acetylacetone or exposure to chloroform vapor, respectively. Poly(R) is also created from Poly(B) by contact with acetylacetone. Poly(Y) is regenerated from both Poly(R) and Poly(B) by reprecipitation from their chloroform solution into methanol. Wide‐angle X‐ray scattering (WAXS) patterns of Poly(Y) and Poly(R) correspond to a pseudohexagonal crystal called a columnar as stretched cis‐transoid and contracted cis‐cisoid helices, respectively. These helical diameters and pitch widths obtained from the WAXS measurements are agreed with those of MMFF94 calculation models. The smallest helical pitch width is 3.3 Å for Poly(R) and Poly(B). Moreover, information regarding the size and ordering of the vacant space within each polymer is estimated by using 129Xe NMR technique. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 752–759 A stretched helix of polyphenylacetylene is prepared as a fine yellow powder, Poly(Y), using the [Rh(norbornadiene)Cl]2‐NEt3 catalyst in EtOH. Poly(Y) is interconverted to two contracted helix polymers, red Poly(R) or reddish‐black Poly(B), by contact with the acetylacetone (acac) solvent or chloroform (CHCl3) vapors, respectively. Inverse interconversions from Poly(R) or Poly(B) to Poly(Y) occur by reprecipitation from CHCl3 into methanol. Poly(B) is interconverted to the Poly(R) by the acac solvent, but the inverse transformation does not occur by CHCl3 vapors.