Polymerization of p-n-hexyloxyphenylacetylene (pHPA) by using a [Rh(norbornadine)Cl]2-triethylamine catalyst was carried out at room temperature to afford stereoregular helical poly(p-n-hexyloxyphenylacetylene)s (PpHPAs). When ethanol and n-hexane were used as polymerization solvents, a bright yellow PpHPAs, poly(Y) with Mn = 8.5 x 104 and its purple red polymer, poly(R) with Mn = 5.3 x 104 were obtained in 95% yields and 84% yields, respectively. Diffuse reflective UVvis spectra of poly(Y) and poly(R) in solid phase showed different broad absorption peaks at 445 and 575 nm, respectively. X-Ray diffraction patterns of poly(Y) and poly(R) showed typical columnar structures assignable to cis-transoid and cis-cisoid structures, respectively, which were also supported by molecule mechanics calculation. Poly(Y) was irreversibly transformed to a reddish-black polymer, poly(Y-B), which columnar diameter was nearly the same as that of poly(R). Further, poly(Y) showed an exothermic peak in the differential scanning calorimetry trace at 80 degrees C for 1 h in N2 gas. Thus, these findings suggest a thermally irreversible rearrangement from an unstable cis-transoid form, poly(Y) with a stretched cis-transoid helix to a stable cis-cisoid form, poly(R), with a contracted cis-cisoid helix in the solid phase to give poly(Y?B) with the cis-cisoid form. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012