A promising solution to address the challenges in plastics sustainability is to replace current polymers with chemically recyclable ones that can depolymerise into their constituent monomers for circular use of materials. Despite the progress, few depolymerisable polymers exhibit the excellent thermal stability and strong mechanical properties of traditional polymers. Here we report a series of chemically recyclable polymers that show excellent thermal stability (decomposition temperature > 370 ºC) and tunable mechanical properties. The polymers are formed via ring-opening metathesis polymerisation of cyclooctene with a trans-cyclobutane installed at the 5,6-positions. The additional ring converts the nondepolymerisable polycyclooctene into a depolymerisable polymer by reducing the ring strain energy in the monomer (from 8.2 kcal/mol in unsubstituted cyclooctene to 4.9 kcal/mol in the fused ring). The fusedring monomer enables a broad scope of functionalities to be incorporated, providing access to chemically recyclable elastomers and plastics that show promise as next-generation sustainable materials. Main TextSynthetic polymers, including synthetic rubber and synthetic plastics, have been used in nearly every aspect of our daily lives. The dominance of synthetic polymers is largely driven by their excellent stability and processability as well as their versatile mechanical properties. However, due to their high durability, waste materials composed of these polymers have accumulated in the ocean and have caused serious concerns for marine ecosystems 1 . In addition, since 90% of these polymers are derived from nite fossil feedstocks, the production of these materials is unsustainable if they cannot be recycled and reused 2 .
Polymers that can be chemically recycled to their constituent monomers offer a promising solution to address the challenges in plastics sustainability through a circular use of materials. The design and development of monomers for nextgeneration chemically recyclable polymers require an understanding of the relationships between the structure of the monomers/ polymers and the thermodynamics of polymerization/depolymerization. Here we investigate the structure−polymerization thermodynamics relationships of a series of cyclooctene monomers that contain an additional ring fused at the 5,6-positions, including transcyclobutane, trans-cyclopentane, and trans-five-membered cyclic acetals. The four-and five-membered rings trans-fused to cyclooctene reduce the ring strain energies of the monomer, and the enthalpy changes of polymerizations are found to be in the range of −2.1 to −3.3 kcal mol −1 . Despite the narrow range of enthalpy changes, the ceiling temperatures at 1.0 M span from 330 to 680 °C, due to the low entropy changes, ranging from −2.7 to −5.0 cal mol −1 K −1 . Importantly, geminal substituents on the transfive-membered cyclic acetal fused cyclooctenes are found to reduce the ceiling temperature by ∼300 °C, although they are not directly attached to the cyclooctene. The remote gem-disubstituent effect demonstrated here can be leveraged to promote depolymerization of the corresponding polymers and to tune their thermomechanical properties.
Degradable vinyl polymers by radical ring‐opening polymerization are promising solutions to the challenges caused by non‐degradable vinyl plastics. However, achieving even distributions of labile functional groups in the backbone of degradable vinyl polymers remains challenging. Herein, we report a photocatalytic approach to degradable vinyl random copolymers via radical ring‐opening cascade copolymerization (rROCCP). The rROCCP of macrocyclic allylic sulfones and acrylates or acrylamides mediated by visible light at ambient temperature achieved near‐unity comonomer reactivity ratios over the entire range of the feed compositions. Experimental and computational evidence revealed an unusual reversible inhibition of chain propagation by in situ generated sulfur dioxide (SO2), which was successfully overcome by reducing the solubility of SO2. This study provides a powerful approach to degradable vinyl random copolymers with comparable material properties to non‐degradable vinyl polymers.
Degradable vinyl polymers by radical ring-opening polymerization are promising solutions to the challenges caused by non-degradable vinyl plastics. However, achieving even distributions of labile functional groups in the backbone of degradable vinyl polymers remains challenging. Herein, we report a photocatalytic approach to degradable vinyl random copolymers via radical ring-opening cascade copolymerization (rROCCP). The rROCCP of macrocyclic allylic sulfones and acrylates or acrylamides mediated by visible light at ambient temperature achieved near-unity comonomer reactivity ratios over the entire range of the feed compositions. Experimental and computational evidence revealed an unusual reversible inhibition of chain propagation by in situ generated sulfur dioxide (SO 2 ), which was successfully overcome by reducing the solubility of SO 2 . This study provides a powerful approach to degradable vinyl random copolymers with comparable material properties to non-degradable vinyl polymers.
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