Patent ID: 8813675

Claim:
A time-temperature indicator comprising: a crystallized diacetylenic compound capable of polymerizing in the solid state to provide an irreversible appearance change in an environmental condition indicator; and a substrate onto which the crystallized diacetylenic compound is applied; wherein a change in appearance of the crystallized diacetylenic compound is detectable in a manner that is useful to indicate a time-temperature condition; wherein the crystallized diacetylenic compound is symmetrically substituted and having the structural formula: R 3 NHCONH—R 4 —C≡C═C≡C—R 4 —NHCONHR 3 wherein R 4 is methylene, ethylene, propylene or butylene, R 3 is ethyl or propyl, the crystallized diacetylenic compound having a crystal structure wherein the crystallized diacetylenic compound molecules have a center-to-center separation, referring to the geometric centers of diacetylene units in adjacent molecules, of less than 4.7 Å, the center-to-center separation being in a direction wherein solid-state polymerization can occur.