623927-86-6Relevant academic research and scientific papers
Accordion-like oscillation of contracted and stretched helices of polyacetylenes synchronized with the restricted rotation of side chains
Yoshida, Yoshiaki,Mawatari, Yasuteru,Motoshige, Asahi,Motoshige, Ranko,Hiraoki, Toshifumi,Wagner, Manfred,Muellen, Klaus,Tabata, Masayoshi
, p. 4110 - 4116 (2013)
A chiral substituted acetylene, (s)-2-octyl propiolate, was stereoregularly polymerized using a catalyst, [Rh(nbd)Cl]2, at 40 C in methanol to give the corresponding helical polymer, Ps2OcP. The changes of 1H and 13C NMR spectra in line shapes and splitting patterns were consistently interpreted in terms of restricted rotation around the ester O-*C bond, ～O-*CεHε(R)～, R = a branched CHε3 in the ester side chains rather than the helix inversion with the aid of a 3-site jump model. Three peaks due to the branched methyl Hε proton and its Cη carbon observed at 0 C suggested the formation of three rotamers called A, B, and C, based on the presence of the contracted helix and stretched helix forms that have an intrinsic helical pitch. Furthermore, an accordion-like helix oscillation (HELIOS) along the main chain axis was proposed to explain the temperature dependence spectral changes observed in 1H and 13C NMR, UV-vis, and circular dicromism (CD) spectra. The temperature dependence UV-vis and CD spectra of Ps2OcP corroborate the presence of contracted and stretched one-handed helix sense polymers in solution in which the helical pitches and their persistence lengths depend on the temperature.
