Fully Recyclable Metastable Polymers and Composites

Fully-cycled depolymerization and repolymerization of a low ceiling temperature polymer, cyclic poly­(phthalaldehyde) (cPPA), yielding high performance structural polymer is demonstrated. The facile conditions for cPPA depolymerization circumvent the extreme conditions required to break down and recycle traditional thermoplastics and thermosets. cPPA depolymerizes in as little as 14 min at 120 °C, with concurrent evaporation and quantitative recovery of the monomer. Polymerization of the recovered monomer produces cPPA with molecular and mechanical properties identical to the original material. Depolymerization of cPPA is also demonstrated in the presence of various carbon fiber reinforcements. Continuous carbon fibers retain 100% of their moduli and tensile strength through multiple generations of recycling, while fully recycled cPPA/carbon nanofiber composites exhibit mechanical properties equivalent to the original composite and show no degradation with cycling.