Pyranine Based Ion-Paired Complex as a Mechanophore in Polyurethanes

A new mechanophore for polyurethane thermoplastic elastomers based on ion-paired complexes is developed. 8-(2-hydroxyethoxy)pyrene-1,3,6-trisulfonate (HEPTS) is incorporated into polyurethanes as an end-capper and aggregates in apolar media. Aggregation of the ionic HEPTS end groups in solution depends on concentration solvent polarity. The addition of dimethylformamide to a tetrahydrofuran solution of the polymer results in the dissociation of the aggregates and a significant shift in fluorescence emission from yellow to blue. The same shift in fluorescence emission is induced by stretching the solid polymer at strains larger than 1 and stresses above 7.5 MPa, with a clear increase above 12.5 MPa. Strain induced dissociation of HEPTS aggregates not attached to the polymer chain leads to fluorescence changes that are much less reproducible.