Segmented Polyurethane Elastomers with Mechanochromic and Self-Strengthening Functions.

Area of Science:

• Polymer Science
• Materials Chemistry
• Mechanochemistry

Background:

• Mechanochromic materials change color in response to mechanical force.
• Existing mechanochromic polymers often require specific functional groups or external stimuli.
• Force-induced cross-linking in bulk elastomers remains a significant challenge.

Purpose of the Study:

• To synthesize and characterize novel mechanochromic elastomers.
• To investigate force-induced cross-linking reactions in bulk polymers.
• To demonstrate the potential for damage detection in elastomers.

Main Methods:

• Synthesis of segmented polyurethanes (SPUs) incorporating difluorenylsuccinonitrile (DFSN) mechanophores.
• Mechanical testing (compression and extension) to induce DFSN dissociation and radical formation.
• Spectroscopic analysis to monitor color changes and radical generation.
• Solubility tests to assess cross-linking and changes in mechanical properties.

Main Results:

• The synthesized SPUs exhibited a distinct color change (pink) upon mechanical stress due to DFSN dissociation into cyanofluorene (CF) radicals.
• Mechanical stimulation led to radical polymerization of methacrylate side chains, resulting in cross-linking and insolubility of the elastomers.
• An SPU variant also displayed sensitive mechanofluorescence, indicating potential for optical damage sensing.
• This study demonstrates, for the first time, bulk elastomer property changes and damage detection via simple compression or extension.

Conclusions:

• Novel mechanochromic elastomers capable of force-induced cross-linking have been developed.
• The materials exhibit visible color changes and altered mechanical properties upon stress, enabling self-reporting of mechanical events.
• These findings open new avenues for designing smart materials with integrated damage detection capabilities.