Chemical Upcycling of Poly(3-hydroxybutyrate) into Bicyclic Ether–Ester Monomers toward Value-Added, Degradable, and Recyclable Poly(ether ester)

The chemical recycling of plastic wastes into value-added products is an attractive strategy to reduce the consumption of fossil fuels and reduce the plastic pollution. We report here the facile upcycling of poly(3-hydroxybutyrate) (P3HB) into value-added polymerizable monomers and subsequent polymerization toward degradable and recyclable polymers. The bicyclic monomer 4-methyloctahydro-2H-benzo[b][1,4]dioxepin-2-one (4-MOHB) was first synthesized from P3HB through efficient steps. The obtained monomers underwent bulk ring-opening polymerization (ROP) catalyzed by stannous octoate (Sn(Oct)2) to give the amorphous materials. With benzyl alcohol (BnOH) as an initiator, Sn(Oct)2 can effectively catalyze the ROP of bicyclic ether–ester monomers in a controllable fashion. Moreover, poly(4-methyloctahydro-2H-benzo[b][1,4]dioxepin-2-one) (P(4-MOHB)) showed a closed-loop recovery property due to the fused bicyclic monomer structure. The selective depolymerization of the P(4-MOHB) homopolymer back to 4-MOHB monomer can be easily realized using p-toluenesulfonic acid (TsOH) or Sn(Oct)2 as a catalyst in solution or in bulk. This strategy to recycle bioplastics into value-added materials has a promising application prospect and is beneficial to extend the life cycle of environment-friendly materials.