Mechanically activated, catalyst-free polyhydroxyurethane vitrimers.

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Chemistry

Background:

• Vitrimers are dynamic polymer networks with catalyst-induced cross-link exchange, enabling reprocessing.
• Traditional thermosets offer high performance but lack recyclability.
• Polyhydroxyurethanes (PHUs) are typically formed from isocyanates and polyols, posing safety concerns.

Purpose of the Study:

• To develop a new class of vitrimers based on polyhydroxyurethanes (PHUs) from cyclic carbonates and amines.
• To investigate the reprocessing capabilities and mechanical properties of these novel PHU vitrimers.
• To elucidate the mechanism of stress relaxation and catalyst-free repair in PHU vitrimers.

Main Methods:

• Synthesis of PHU networks from six-membered cyclic carbonates and amines.
• Mechanical testing (tensile properties) of as-synthesized and reprocessed networks.
• Stress relaxation measurements and kinetic analysis (Arrhenius activation energy).
• Density Functional Theory (DFT) calculations to investigate the mechanism of transcarbamoylation.

Main Results:

• PHU vitrimers exhibit tensile properties comparable to leading thermosets.
• Networks can be reprocessed at elevated temperature and pressure without an external catalyst.
• Reprocessed PHU vitrimers recover approximately 75% of their original mechanical properties.
• Stress relaxation occurs via associative transcarbamoylation with a lower activation energy (111 ± 10 kJ/mol) than model compounds.
• DFT calculations suggest mechanical stress activates transcarbamoylation by disrupting N lone pair conjugation.

Conclusions:

• PHU vitrimers represent a promising new class of repairable and recyclable polymer networks.
• These materials offer excellent mechanical performance without the need for toxic isocyanate monomers.
• The catalyst-free reprocessing and repair capabilities highlight their potential for sustainable material applications.