Polyesters with built-in threshold temperature and deformation sensors

The preparation and characterization of blends of polyesters and excimer-forming, photoluminescent 1,4-bis-(alpha-cyano-styryl)-benzenes, which function as built-in deformation or threshold temperature sensors, are described. Binary blends of poly(ethylene terephthalate) (PET) or poly(ethylene terephthalate glycol) (PETG) and small amounts (0.2-2% w/w) of a series of sensor dyes were prepared by melt-processing. The phase behavior of these materials can be controlled via the composition, the nature of solubility-controlling substituents attached to the dyes, and the processing protocol. Subjecting appropriately processed samples to either temperatures above their glass transition or mechanical deformation can significantly change the extent of molecular aggregation of the photoluminescent guest molecules, which in turn leads to a variation of the contributions of monomer and excimer emission. Since the emission maxima associated with these transitions can differ by as much as 138 nm, this change can readily be detected by spectroscopic means and in many cases even by the unassisted eye.