Pyranine Based Ion-Paired Complex as a Mechanophore in Polyurethanes

Area of Science:

• Polymer Science
• Materials Chemistry
• Supramolecular Chemistry

Background:

• Polyurethane thermoplastic elastomers (TPUs) are versatile materials with broad applications.
• Developing novel mechanophores is crucial for creating smart materials with tunable properties.
• Ion-paired complexes offer unique opportunities for designing responsive materials.

Purpose of the Study:

• To develop a new mechanophore for TPUs based on ion-paired complexes.
• To investigate the aggregation behavior of the developed mechanophore in different media.
• To explore the mechanochromic properties of the new material.

Main Methods:

• Incorporation of 8-(2-hydroxyethoxy)pyrene-1,3,6-trisulfonate (HEPTS) as an end-capper in polyurethanes.
• Solvent polarity and concentration-dependent studies of HEPTS aggregation in solution.
• Investigation of fluorescence emission shifts upon addition of dimethylformamide (DMF) to tetrahydrofuran (THF) solutions.
• Mechanical testing of solid polymer samples to induce strain and measure stress-strain relationships.
• Correlation of fluorescence changes with applied strain and stress.

Main Results:

• HEPTS aggregates in apolar media, with aggregation dependent on concentration and solvent polarity.
• Addition of DMF to THF solutions induced a yellow-to-blue fluorescence shift, indicating aggregate dissociation.
• Stretching solid polymer samples above 1 strain and 7.5 MPa stress caused a similar fluorescence shift.
• Strain-induced dissociation of non-attached HEPTS aggregates resulted in less reproducible fluorescence changes.

Conclusions:

• A novel ion-paired complex-based mechanophore (HEPTS) was successfully developed for TPUs.
• The mechanophore exhibits concentration, solvent polarity, and strain-dependent fluorescence changes.
• The material shows potential as a fluorescent strain sensor for TPUs, with tunable mechanochromic properties.