A MECHANOCHROMIC SMART MATERIAL

A mechanochromic polyurethane elastomer was synthesized and demonstrated. Azobenzene chromophores were introduced into a copolyamide oligomer to provide conformational latches which stabilized the cis-azobenzenes by the formation of intramolecular hydrogen bonds. The copolyamide oligomer was chemically inserted into a polyurethane copolymer. The chromophores in the resulting copolymer were transformed to the cis-form by ultraviolet (UV) irradiation (lambda = 365 nm) and then succesively stretched and relaxed to strains of 100 %, 200 %, and 300 %. After 100 % strain and relaxation, the absorbance of polyurethane copolymer at lambda = 380 nm, which indicates transformation to the trans form, was not significantly increased. However, the absorbance increased with 200 % and 300 % tensile strain followed by relaxation. A mechanochromic relationship between absorbance increase at lambda = 380 nm in the relaxed sample and the maximum strain to which the sample was subjected was thus demonstrated.