Thermal effects on the optical properties of single crystals and solution-cast films of urethane substituted polydiacetylenes

Abstract

The optical properties of single crystals and solution‐cast films of two polydiacetylenes, poly3BCMU and poly4BCMU where the substituent group is– (CH₂)_3.4OCONHCH₄COOC₄H₉, are characterized. Visible absorption and reflection spectra for the polymer crystals are typical of those observed for other urethane substituted polydiacetylenes. The optical properties of the polymer films are controlled primarily by intramolecular hydrogen bonding between the N–H and C=O of the urethane functionalities on adjacent substituent groups. Hydrogen bonding stabilizes the planar, fully conjugated conformation of the individual polymer chains in the films. Increased temperature causes a disruption of the hydrogen bond network and a destabilization of the planar polymer conformation. Dramatic color changes result because of the sensitivity of the optical properties to backbone conformation.