Multiple Force-Triggered Downconverted and Upconverted Emission in Polymers Containing Diels-Alder Adducts

Area of Science:

• Polymer Science
• Materials Science
• Chemical Engineering

Background:

• Fluorescent mechanophores are crucial for monitoring polymer deformation and damage.
• Developing mechanophores with multi-responsive capabilities is a key research area.

Purpose of the Study:

• To incorporate Diels-Alder (DA) adducts as mechanophores into poly(methyl acrylate) (PMA-BA) and poly(hexyl methacrylate) (PHMA) polymers.
• To investigate the multi-triggered response of these DA mechanophores to various mechanical stresses, including ultrasound, freezing, and compression.
• To evaluate the potential of these mechanophores for detecting microscale fractures and damage in polymeric materials.

Main Methods:

• Incorporation of DA adducts into linear PMA-BA and network PHMA polymers.
• Application of pulsed ultrasonication, freezing, and compression to induce mechanical stress.
• Quantification of DA mechanophore dissociation using absorption spectra and 1H NMR.
• Measurement of molecular weight changes via gel permeation chromatography.
• Assessment of photon upconversion responses using PtOEP and PdTPTBP sensitizers.

Main Results:

• DA mechanophores in PMA-BA and PHMA exhibited cyan fluorescence upon mechanical stress, indicating damage.
• Ultrasonication of PMA-BA solution resulted in a 52% DA mechanophore dissociation.
• The rate constant for mechanical cleavage was determined to be 1.2×10⁻⁴ min⁻¹⋅kDa⁻¹.
• Freezing and compression of PHMA samples revealed microscale fractures through mechanophore activation.
• Photon upconversion responses were observed in both polymer solutions and bulk samples under various force stimuli.

Conclusions:

• DA adducts serve as effective fluorescent mechanophores for detecting mechanical stress and damage in polymers.
• The developed mechanophores demonstrate a multi-triggered response to ultrasound, freezing, and compression.
• These mechanophores show promise for real-time monitoring of polymer integrity and microscale fracture detection.