Masayoshi Tabata
Muroran Institure of Technology
Muroran JAPAN
Title: Emerging ï° conjugated Stretched and Contacted Helices of Substituted Polyacetylenes Prepared with an Organo-rhodium Catalyst
Biography
Biography: Masayoshi Tabata
Abstract
The highly stereoregular preparation of mono-substituted polyacetylenes (SPA)s was performed using an [Rh(norbornadiene)Cl]2-triethylamine catalyst to give the π-conjugated helical polymers. Because the SPAs are expected as new advanced materials due to semiconductivity, NLO properties, external stimulus responsibility, enantioselectivity, and oxygen permeability. These properties are strongly related to the geometrical structure, e.g., cis or trans forms and higher-order structure, e.g., p stacking along with the helical main-chain in the solid phase. Therefore, we have investigated whether the geometrical and helical structures of the SPAs can be controlled through molecular design and/or external stimuli. The p-n-hexyloxyphenylacetylene (pPA) monomer was stereoregularly polymerized using the Rh catalyst at 25 °C. When ethanol and n-hexane were used as the polymerization solvents, a yellow P(Y), and its red P(R) were obtained, respectively. The diffuse reflective UV-vis spectra of these polymers showed lmax at 445 and 575 nm, respectively. The WAXS patterns of P(Y) and P(R) exhibited hexagonal columnar structures which were attributed to the stretched and contracted helices, respectively. Additionally, P(Y) was irreversibly transformed into a reddish-black P(YâžžB), whose columnar diameter was identical to that of P(R) when heated at 80 °C for 1 h. These findings suggest a thermally irreversible rearrangement from a thermally unstable P(Y) with a stretched helix to a stable P(YâžžB) with a contracted helix. In the case of aliphatic polyacetylene ester the mutual helical oscillation between the contacted and stretched helices was found in the solution1