Chemical Recycling of Poly(bisphenol A carbonate) by Glycolysis under 1,8-Diazabicyclo[5.4.0]undec-7-ene Catalysis

Abstract

The glycolysis reaction of poly(bisphenol A carbonate) (PC) has been explored under 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) catalysis as a potential route to valorize PC wastes by chemical recycling. The amidine base is an active catalyst of PC glycolysis and, under suitable conditions, promotes effectively and selectively the depolymerization of the polymeric material with 1,2-propanediol or glycerol to give the monomer bisphenol A (BPA) and the relevant cyclic carbonate. The depolymerization process has been investigated under solventless conditions, using diol/triol as the reagent and reaction medium, and also in an auxiliary solvent such as tetrahydrofuran (THF) that is able to dissolve the polymer. The influence of a few experimental parameters (temperature, catalyst load, and reaction time) on the selectivity to cyclic carbonate has been studied. High selectivity to cyclic carbonate has been attained by carrying out the depolymerization reaction in THF and using mild temperature conditions and a stoichiometric amount of polyol. The catalyst can be recovered from the reaction mixture as a BPA/DBU adduct and effectively recycled in a successive run.

100th Anniversary of Macromolecular Science Viewpoint: Toward Catalytic Chemical Recycling of Waste (and Future) Plastics

“…ILs − and organic bases − have also been well studied for depolymerizations of bisphenol A (BPA)-PC waste . The monomers obtained from alcoholysis often yield BPA and small carbonates that can be polymerized directly back to PC, however, carbon dioxide can be eliminated by hydrolysis, precluding the return to an original material.…”

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“…[844][845][846] Alkali halide, heterogeneous, ionic liquid, and organic base catalysts have also been employed to increase yield and selectivity for BPA under milder conditions. [847][848][849][850][851][852][853][854][855] The aminolysis of PCs provides value-added ureas and BPA as products. The yield of monomeric products is increased when a diamine is used to form a stable cyclic urea.…”

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“…Interestingly, when BPA-PC was depolymerized with 1,2-propanediol or glycerol in the presence of DBU the reaction yielded BPA and the corresponding cyclic carbonate with very high selectivity. 145 Under solventless conditions (using polyol as both the reagent and reaction medium), yields of the cyclic carbonate (up to 87%) were obtained at 180 °C. Addition of THF, a co-solvent in which BPA-PC is soluble, resulted in nearly quantitative carbonate yields at mild reaction conditions (near room temperature and a stoichiometric amount of polyol).…”