Developing the Polyimide Glycolysis and Upcycling of the Recovered Valorized Monomers for Low-Dielectric-Loss Poly(ester imides)

Abstract

As next-generation high-frequency communication technologies advance rapidly, microelectronic components require higher processing temperatures and reduced signal loss. Consequently, poly(ester imides) (PEIs) are widely utilized in these fields. However, efficient recycling methodologies for PEIs remain to be established. In this work, we developed a PEI chemical recycling protocol via glycolysis. The proposed system was verified as generally applicable to depolymerizing various types of PEIs. Moreover, the depolymerization process enabled the isolation of aromatic diols: bis(2-hydroxyethyl) terephthalate (BHET) and 5-hydroxy-2-(4-hydroxyphenyl)isoindoline-1,3-dione (HPID). While the recovered BHET established a closed-loop polyester recycling pathway within the glycolysis system, the isolated HPID was converted into aromatic diamine to serve as a precursor for regenerating high-performance PEIs. Among the regenerated samples, a new PEI exhibits a combination of properties, including a 5% thermal decomposition temperature of 414 °C, a high glass transition temperature exceeding 300 °C, a low coefficient of thermal expansion of 18 ppm/°C, and an ultralow dielectric dissipation factor of 0.003 at 10 GHz, compatible with the high-frequency insulation applications of polyimides. Finally, the carbon emission factor was 31.2 kg-CO2/kg-product, comparable to or lower than that of the general monomer precursor for virgin PEIs, which represents an effective strategy to reduce the environmental burden of the PEI glycolysis system. Although glycolysis is primarily used for PEIs rather than the entire polyimide category, PEIs remain an irreplaceable material system for thermally durable and high-frequency insulation applications. In summary, this work establishes a sustainable glycolysis-based upcycling pathway for PEIs. Compared with hydrolysis-, methanolysis-, and aminolysis-based chemical recycling of polyimides, this approach uses ethylene glycol as a low-carbon-footprint, non-toxic solvent to produce valorized chemical products, including recovered BHET and regenerated advanced PEIs.