| Abstrakt: |
We synthesized two optically active helical polysilanes, poly[(S)‐3,7‐dimethyloctyl‐3‐phenylpropylsilane] (PS1) and poly[(R)‐3,7‐dimethyloctyl‐3‐phenylpropylsilane] (PS2), bearing a flexible and rodlike silicon main chain and enantiopure alkyl side chains with (S)‐ and (R)‐chiral centers, respectively, at the γ‐positions. PS1 and PS2 underwent a thermodriven helix–helix transition at 10 °C in isooctane. Circular dichroism (CD) and UV studies demonstrated the transition characteristics, such as the transition temperature, population of right‐ and left‐handed helical motifs, global shape, and screw pitch. At −80 °C, the dissymmetry ratio suggested that a preferential right‐handed or left‐handed screw sense was present in the polymer chains of PS1 and PS2, respectively. However, above the transition temperature, the appearance of a bisignate cotton band in the CD spectra suggested that both right‐handed screw‐sense, tight helical segments and left‐handed screw‐sense, loose helical segments coexisted in the same chains of PS1 and PS2. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4518–4527, 2004 |
Plný text