Zn-catalyzed coordination-insertion depolymerization strategy of poly(3-hydroxybutyrate) under bulk conditions

Poly(3-hydroxybutyrate) (PHB), as a bio-based polyester material, is considered to be one of the most promising alternatives to conventional plastics. With the mass production and spread in application of PHB, the recycling of end-of-life PHB will be crucial. Compared to slow biodegradation, chemical recycling can rapidly provide monomers and profitable platform chemicals and maintain the value and usefulness of PHB materials. In this work, the Zn-catalyzed coordination-insertion depolymerization of PHB to alkyl 3-hydroxybutanoate via an alcoholysis strategy was explored in detail. Zinc bis[bis(trimethylsilyl)amide] (Zn(HMDS)2), as an environmentally friendly and versatile transesterification catalyst, could facilitate depolymerization of PHB smoothly under mild and solvent-free conditions, providing the degradation product alkyl 3-hydroxybutanoate with high yield and purity. Additionally, the influence of reaction conditions such as temperature, molar equivalents of alcoholysis reagents, and polymer tacticity on the depolymerization process was explored and optimized. In this way, the depolymerization of PHB through a coordination-insertion depolymerization mechanism was achieved for the first time. This work enriches the options for the chemical upcycling of PHB plastics.