Zinc-Catalyzed Chemical Recycling of Poly(ϵ-caprolactone) Applying Transesterification Reactions

The chemical recycling of poly(ϵ-caprolactone) (PCL) was explored based on depolymerization and polymerization. The concept bases on the zinc-catalyzed depolymerization via methanolysis to produce methyl 6-hydroxyhexanoate, which is polymerized in a zinc-catalyzed condensation reaction to generate new PCL and close the cycle. In more detail, with zinc(II) acetate as catalyst, PCL was depolymerized with turnover frequencies of up to 468 h⁻¹ using microwave heating. On the other hand zinc(II) acetate was also able to catalyze the polymer formation using the monomer methyl 6-hydroxyhexanoate. PCL was obtained in good yield and M_n ∼1729 g/mol and M_w ∼5823 g/mol were achieved.