(227i) Controlled depolymerization as a novel strategy for the chemical recycling of poly(bisphenol A carbonate) waste materials

The amount of waste derived from non-renewable sources is increasing annually becoming a serious environmental problem [1]. In particular, poly(bisphenol A carbonate) (PC-BPA) has a growing annual worldwide production that exceeds 6 million tons [2]. The controlled depolymerization of PC-BPA with polyhydroxylic-alcohols (polyols) allows not only the recovery of BPA, but also the generation of new compounds with carbonate functionality. The structure of the compounds obtained is determined by the depolymerizing agent used (Figure 1).

Objectives

The mail goal of this work is to study the controlled depolymerization of PC-BPA using a poly-alcohol derived from renewable sources as depolymerizing agent for the production of BPA and cyclic carbonates.

Materials and Methods

Pieces of PC-BPA waste were reacted at 90°C for 2 h in a 15 mL round-bottomed flask equipped with a magnetic stir bar, using an organic solvent with a renewable poly-alcohol and an organic base as catalyst. The volatile compounds were recovered by distillation under reduced pressure. Both polymeric precursors (BPA and cyclic carbonate) were obtained as white powders and characterized by 1H-NMR.

Results and Discussion

The depolymerization of PC-BPA waste was studied using a poly-alcohol derived from renewable sources as the depolymerizing agent. The reaction was carried out using different organic solvents and varying the reagents molar ratio in order to maximize the yield of the cyclocarbonate compound. The reaction products were isolated and structurally characterized by spectroscopic techniques (Figure 2). The process allowed the recovery of BPA, and the polymeric precursor with cyclocarbonate functionality (70%) could be used to obtain new polymers, such as others PC and polyhurethanes. In this way, the recovery of BPA would prevent its disposal in landfills and, therefore, its arrival to aqueous sources.

Conclusions

The controlled depolymerization of PC-BPA waste was carried out successfully using a polyhydroxylic-alcohol derived from renewable sources as the depolymerizing agent. Moreover, BPA and cyclic carbonates were obtained with excellent yield avoiding the use of phosgene and its derivatives. The reaction involves only moderate temperature and a single purification stage. In addition, the depolymerization can be carried out by varying the depolymerizing agents in order to obtain different tailor-made polymeric precursors with cyclocarbonate functionality for the synthesis of new materials.

References

1. Coates, G.W., & Getzler, Y.D. (2020). Nat. Rev. Mat., 5(7), 501-516.

2. Do, T., Baral, E.R., & Kim, J.G. (2018). Polymer, 143, 106-114.