| Popis: |
New polyacetylenes with cholesteryl side-groups with different spacer lengths are polymerized through classical metathesis reaction in solution with the transition metal halides WCl6, MoCl5, and TaCl5. The highest polymerization yield and the best average molecular weight are obtained with the cholesteryl 4-pentynoate (CP5) with the 1 ,4-dioxane/WCl6 couple and the measured values are, respectively, 87% and 15 · 104. All of the other esters, cholesteryl propynoate or cholesteryl 10-undecynoate give low polymerization yields. Poly(CP5) is a red transparent solid; it can be dissolved in common organic solvents and can be cast from solution into films. The solid-state film presents a transition to a thermotropic liquid-crystalline phase at 189°C and a transition to the isotropic phase at 189°C. A progressive decoloration occurs in solution and in the liquid-crystalline phase. The results are interpreted as conformational changes of the polyene planar chain in a less conjugated backbone. The third-order susceptibility χ3 measured by third harmonic generation on the red polymer lies in the range of 10−21 V2·m−2 in accord with the low content of the active part in the molecule and to a moderate length of conjugation of this highly crowded polyacetylenic chain. |
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