Abstract
The conformation of a photoresponsive polymer bearing azo units in the main chain, poly(propionaldehyde azine) (PrAz), in tetrahydrofuran was investigated by viscosity measurements before and after trans-to-cis photoisomerization and also by the rotational isomeric state (RIS) model. Before photoisomerization (i.e., in the case of trans-pPrAz), viscosity data indicated that pPrAz took a more extended conformation than did a diene polymer analog poly(butadiene). The RIS model analysis revealed that the extended conformation of pPrAz arose mainly from the difficulty of gauche conformation around the carbon-carbon bond in the main chain. After trans-to-cis photoisomerization (i.e., in the case of pPrAz consisting of trans and cis units), viscosity data indicated that the photoisomerization led to a slight extension of the pPrAz chain. The RIS model analysis explained that the photoisomerization formed preferentially the anti-cis isomer, resulting in a larger characteristic ratio to avoid severe steric hindrance between the ethyl groups on neighboring main-chain carbon atoms.
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Upon trans-to-cis photoisomerization, the syn- and anti-trans units are converted into the anti- and syn-cis units, respectively, while the erythro and threo configurations are maintained. Thus, the fractions of erythro and threo units were fixed at 0.65 and 0.35, respectively, upon calculation of C∞ for pPrAz after photoisomerization.
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Hashidzume, A., Ueno, Y. & Sato, T. Conformational Analysis of Poly(propionaldehyde azine) in Dilute Solution. Polym J 38, 1152–1159 (2006). https://doi.org/10.1295/polymj.PJ2006066
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DOI: https://doi.org/10.1295/polymj.PJ2006066