Shape memory polymers with built-in threshold temperature sensors

The design, fabrication and characterization of a new shape memory polymer (SMP) with built-in temperature sensing capabilities are reported. The material was prepared by incorporating a fluorescent, chromogenic oligo(p-phenylene vinylene) dye into a cross-linked poly(cyclooctene) (PCO) matrix via guest diffusion. The dye concentration was chosen to allow for self-assembly of the dye upon drying, resulting in the formation of excimers. Exposure of these phase-separated blends to temperatures above the melting point (T_m) of the PCO leads to dissolution of the dye molecules, and therefore causes a pronounced change of their absorption and fluorescence color. The optical changes are reversible; i.e., the aggregate absorption and emission are restored upon cooling below T_m. The color is dictated by the phase behavior and is independent of the mechanical state of the SMP. Thus the effect allows one to monitor reaching of the set/release temperature of the polymer.