The formation, structure and properties of urethane-diacetylene copolymers as optical strain-sensitive surface coatings

Abstract

Segmented copolyurethanes comprising ductile polyether-urethane (PE-U) and rigid diacetylene-urethane (DA-U) phases, have been prepared via a one-shot, bulk polymerisation process. Subsequent thermal treatment (100 °C/40 h) of the as-prepared linear copolymers effected solid-state topochemical reactions within the DA-U phase, producing crosslinked and intensely coloured materials. The cross-polymerised copolymers had values of T g between −32°C and 70°C depending on composition, and were elastically isotropic with tensile moduli and strengths ranging, respectively, from 20–1800 MPa, and 8–67 MPa. The copolymers exhibited optical properties similar to those of polydiacetylene single crystals, and produced intense resonance Raman spectra. In particular, the CC triple bond stretching Raman band at ~ 2080 cm −1 was well defined and shifted to lower frequency under the application of tensile stress/strain. The copolyurethanes may be readily applied as surface coatings to various substrates, and their use as optically stress/strain-sensitive materials (optical strain sensors) is demonstrated.