A MECHANOCHROMIC SMART MATERIAL

A mechanochromic polyurethane elastomer was synthesized and demonstrat ed. Azobenzene chromophores were introduced into a copolyamide oligome r to provide conformational latches which stabilized the cis-azobenzen es by the formation of intramolecular hydrogen bonds. The copolyamide oligomer was chemically inserted into a polyurethane copolymer. The ch romophores in the resulting copolymer were transformed to the cis-form by ultraviolet (UV) irradiation (lambda = 365 nm) and then succesivel y stretched and relaxed to strains of 100 %, 200 %, and 300 %. After 1 00 % strain and relaxation, the absorbance of polyurethane copolymer a t lambda = 380 nm, which indicates transformation to the trans form, w as not significantly increased. However, the absorbance increased with 200 % and 300 % tensile strain followed by relaxation. A mechanochrom ic relationship between absorbance increase at lambda = 380 nm in the relaxed sample and the maximum strain to which the sample was subjecte d was thus demonstrated.