Ring-Opening Polymerization of a Bicyclic Lactone: Polyesters Derived from Norcamphor with Complete Chemical Recyclability

Abstract

Chemical recycling of polymers is an elegant approach to achieve a circular economy and address the sustainability and endof-life issues of plastics. Herein, we report the ring-opening polymerization of a bicyclic lactone that is easily accessible from norcamphor. High molecular weight polyesters (M n up to 164 kg mol −1 ) are obtained using ZnEt 2 as catalyst, while the polymerizability of the monomer is good even at high temperatures. More importantly, the polymers can be completely depolymerized under thermolysis conditions to selectively recover the pristine monomer. Thus, the monomer design strategy of using ring-fused/hybridized lactones enables an innovative monomer−polymer system that shows both high polymerizability and high depolymerizability.

Advances in the Synthesis of Chemically Recyclable Polymers

“…In 2022, Rieger et al [109] . extended the strategy of using bicyclic lactones with a six‐membered ring core structure in CRM.…”

“…However, polyesters obtained from double‐ring ROP with five‐membered ring as the core structure cannot be chemically recycled. Therefore, the introduction of CH 2 group in the carbonyl α position of PNCL backbone has a huge positive effect, which is helpful for the clean recovery of monomer [109] . Recently, Li [110] reported the ROP of bridged lactone 2‐oxabicyclo[2.2.2]octan‐3‐one ([2.2.2]VL) under trifluoromethanesulfonic acid (TfOH) and n‐butyl lithium ( n BuLi) (Figure 26).…”

“…In 2022, Rieger et al [109] extended the strategy of using bicyclic lactones with a six-membered ring core structure in CRM. Norcamphor lactone (NCL) was synthesized by one-step method using commercially available norcamphor as raw material.…”

“…Therefore, the introduction of CH 2 group in the carbonyl α position of PNCL backbone has a huge positive effect, which is helpful for the clean recovery of monomer. [109] Recently, Li [110] reported the ROP of bridged lactone 2-oxabicyclo[2.2.2]octan-3-one ([2.2.2]VL) under trifluoromethanesulfonic acid (TfOH) and n-butyl lithium ( n BuLi) (Figure 26). The stereoregular P[2.2.2]VLs showed high crystallinity and melting temperatures (233 ~245 °C).…”

Leveraging the monomer structure for high-performance chemically recyclable semiaromatic polyesters

“…4–35 In a pioneering work, poly (γ-butyrolactone) from the ring-opening polymerization (ROP) of “non-polymerizable” butyrolactone was discovered to quantitatively depolymerize into its monomer γ-butyrolactone upon being heated at 220–300 °C for one hour, 4,36 manifesting the potential of its chemical recycling in the circular plastics economy and promoting the development of this field. However, most of the currently studied polymer systems have involved aliphatic polyesters 37–48 and chemically recyclable aromatic polyesters have been less extensively investigated. As one of the most popular thermoplastic polyesters in our daily lives, polyethylene terephthalate (PET) has been widely utilized in fibers, resins, and filming owing to its outstanding properties associated with the aromatic moieties on the polymer backbone.…”