Molecular Deformation and Optomechanical Behavior of Glassy Diacetylene-Containing Segmented Block Copolyurethanes

The mechanical and optomechanical behavior of glassy, diacetylene-containing, segmented copolyurethanes has been investigated. The polydiacetylene chains formed via solid-state cross-polymerization in the hard segment domains not only reinforce mechanically the copolymers at the molecular level but also confer on them optical properties similar to those of polydiacetylene single crystals. Resonance Raman spectroscopy is shown to be a powerful technique for structural characterization and as an optical strain probe for the study of copolymer deformation. During deformation, the C≡C triple bond stretching band in the Raman spectra of the diacetylene-containing copolymers was found to shift to lower wavenumbers by over −6 cm⁻¹/%, compared to −20 cm⁻¹/% for polydiacetylene single crystals. The relationship between the Raman band position and overall copolymer strain provides information about the molecular deformation of the polydiacetylene chains in the hard segment domains. Furthermore, it enables the strain in the copolymers to be measured by monitoring the Raman band position. The results clearly demonstrate, in these materials, the achievement of a unique combination of the optical properties of polydiacetylenes with the mechanical behavior and processibility of polyurethanes. These copolymers thus represent a new class of optically stress-strain sensitive, isotropic materials (optical strain sensors) which can be readily processed into and used in a variety of forms including fibers, films, bulk sheets, surface coatings, and composites.