Versatile Chemical Recycling Strategies: Value-Added Chemicals from Polyester and Polycarbonate Waste

Area of Science:

• Coordination Chemistry
• Polymer Chemistry
• Green Chemistry

Background:

• Chemical upcycling of waste polymers like polycarbonates and polyesters is crucial for sustainable materials management.
• Existing methods often require harsh conditions or lack efficiency and selectivity.
• Development of mild and effective catalysts for polymer degradation and monomer recovery is an ongoing challenge.

Purpose of the Study:

• To explore the efficacy of Zn(II)-half-salen complexes in the chemical upcycling of commercial polyesters and polycarbonates.
• To report the first instance of discrete metal-mediated poly(bisphenol A carbonate) (BPA-PC) methanolysis at room temperature.
• To demonstrate a circular economy approach by converting plastic waste into valuable renewable materials.

Main Methods:

• Synthesis and characterization of Zn(II)-half-salen complexes.
• Methanolysis of poly(bisphenol A carbonate) (BPA-PC) using Zn(II) catalysts in 2-Me-THF at room temperature.
• Kinetic analysis to determine reaction rates (k_app).
• Upcycling of poly(ethylene terephthalate) (PET) waste into renewable poly(ester-amide)s (PEAs).

Main Results:

• Zn(II) complexes demonstrated high activity, achieving complete BPA-PC consumption within 12-18 minutes.
• High yields of bisphenol A (BPA) (85-91%) were obtained within 2-4 hours.
• Catalysts exhibited high apparent rate constants (k_app) of 0.28±0.040 and 0.47±0.049 min⁻¹.
• Renewable poly(ester-amide)s (PEAs) with excellent thermal properties were synthesized from PET-derived monomers.

Conclusions:

• Zn(II)-half-salen complexes are highly effective catalysts for the mild and selective chemical upcycling of BPA-PC.
• The developed method represents a significant advancement in room-temperature polymer degradation and monomer recovery.
• This work establishes a viable pathway for the circular upcycling of plastic waste into high-value materials.