Evidence for increased chain stiffness of polydiacetylene in solution

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Abstract
Evidence has been found of increased chain stiffness of isolated polydiacetylene molecules in solution, associated to an increased side-group interaction, and in at least one case, to an increased and more temperature dependent electronic conjugation length: Bromoform solutions of poly-3BCMU (3B) and poly-4BCMU (4B) were studied by visible and IR absorption spectroscopy and by small angle neutron scattering. The polymers are more rigid than in other solvents: for 3B, b>600 Å at 45 °C and for 4B, b=420±40 Å at 25 °C. Hydrogen bonding between neighboring side groups is observed, decreasing upon increasing temperature. For 3B, the visible absorption spectrum is slightly red shifted, the more so the lower the temperature, indicating an influence of chain stiffness on electronic conjugation length.