The yellow-colored poly(phenylacetylene), Poly(Y), is obtained from phenylacetylene using a [Rh(nbd)Cl](2)-NEt3 catalyst in ethanol at 25 degrees 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 stretchedcis-transoid and contractedcis-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 angstrom for Poly(R) and Poly(B). Moreover, information regarding the size and ordering of the vacant space within each polymer is estimated by using Xe-129 NMR technique. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 752-759