Rapid and Controlled Ring-Opening (Co)Polymerization of Bio-Sourced Alkyl-δ-Lactones To Produce Recyclable (Co)Polyesters and Their Application as Pressure-Sensitive Adhesives

It is attractive to develop chemically recyclable polymers with desirable performances from commercial monomers to avoid the expensive and time-consuming scalable process for completely new monomers. In this contribution, we present the rapid and controlled ring-opening polymerization (ROP) of bio-sourced commercial alkyl-δ-lactones to produce closed-loop recyclable polyesters in the presence of an organophosphazene base (tBu-P2)/urea binary catalyst. The obtained polyesters are capable of recycling back to pristine monomers by simply heating them in bulk in the presence of stannous octanoate (Sn(Oct)2) as the catalyst. The effects of alkyl substituent length on the polymerization kinetics, thermodynamics, as well as the properties of resultant poly(alkyl-δ-lactone)s were investigated. Well-defined triblock copolymers consisting of poly(alkyl-δ-lactone)s as soft middle block and PLLA as hard end block were successfully prepared by one-pot, sequential ROP of alkyl-δ-lactones and l-lactide (l-LA). These triblock copolymers can be used as pressure-sensitive adhesives without the addition of tackifiers or other additives. The chemical recycling of these triblock copolymers to recover ethyl lactate and alkyl-δ-lactones with high yields was achieved by alcoholysis and then distillation under reduced pressure.