Stereochemistry-Tuned Hydrogen-Bonding Synergistic Covalent Adaptable Networks: Towards Recycled Elastomers with...

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Chemistry

Background:

• Covalent adaptable networks (CANs) present opportunities for thermoset polymer recycling.
• Balancing reprocessing ease and creep resistance in CANs is a significant challenge.
• Polyurethanes (PUs) are a key class of thermosets with potential for recyclability.

Purpose of the Study:

• To design and synthesize polyurethane materials with tunable properties by controlling diamine chain extender stereochemistry.
• To investigate the impact of cis- and trans-diamine configurations on mechanical properties, creep resistance, and recyclability.
• To establish structure-property relationships for high-performance, recyclable PUs.

Main Methods:

• Synthesis of polyurethane materials using cis- and trans-configured diamine chain extenders.
• Mechanical testing to evaluate properties like creep resistance and elasticity.
• Recycling studies using hot pressing and solvothermal methods via urea bond exchange.
• Density Functional Theory (DFT) calculations to analyze hydrogen bonding interactions.

Main Results:

• Trans-configured PUs (R,R-DAC-PU, S,S-DAC-PU) demonstrated superior creep resistance and mechanical strength due to dense hydrogen bonding.
• Cis-configured PUs (Cis-DAC-PU) exhibited enhanced processability and elasticity.
• R,R-DAC-PU showed minimal strain change (3.5%) under stress (0.1 MPa) at elevated temperature (170°C) over 60 minutes.
• Both PU configurations were successfully recycled through urea bond exchange reactions.
• DFT calculations confirmed stronger, shorter hydrogen bonds in trans-segments compared to cis-segments.

Conclusions:

• Stereochemistry of diamine chain extenders is crucial for tailoring PU properties.
• Trans-stereochemistry leads to enhanced mechanical performance and creep resistance.
• Cis-stereochemistry improves processability and elasticity.
• The developed PUs are recyclable, offering sustainable solutions for thermoset materials.