All-Hydrocarbon Polymers with Chemical Recyclability via a Catalyst-Free and Solvent-Free Method

Area of Science:

• Synthetic Chemistry
• Polymer Science
• Sustainable Chemistry

Background:

• Chemically recyclable polymers typically rely on cleavable heteroatom (C-X) bonds.
• Developing recyclable all-hydrocarbon polymers is challenging due to the difficulty in creating reversible carbon-carbon (C-C) bonds.

Purpose of the Study:

• To design and synthesize a chemically recyclable all-hydrocarbon polymer.
• To establish a closed-loop recycling process for all-hydrocarbon polymers using dynamic covalent chemistry.

Main Methods:

• Utilized the dynamic covalent Diels-Alder reaction of cyclopentadienyl (Cp) units.
• Synthesized A2-type Cp2-terminated monomers with alkyl or aryl spacers.
• Employed A2 + A2 Diels-Alder step-growth polycondensation at 100 °C.

Main Results:

• Achieved high molecular weight all-hydrocarbon polymers (up to 245.3 kDa) with tunable glass transition temperatures (-20 to 133 °C).
• Demonstrated thermo-reversible depolymerization via retro-Diels-Alder at 250 °C, yielding a macromonomer.
• Showcased quantitative repolymerization at 100 °C with preserved polymer properties, achieving 100% atom economy.

Conclusions:

• Successfully developed the first chemically recyclable all-hydrocarbon polymer using Diels-Alder dynamic covalent chemistry.
• Established a catalyst-free, solvent-free, and thermo-driven recycling loop for all-hydrocarbon polymers.
• Paved the way for a new class of circular, all-carbon-backbone polymers with significant potential in sustainable materials.