depolymerizable-olefinic-polymers-based-on-fused-ring-cyclooctene

Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers

The growing consumption of synthetic polymers and the accumulation of polymer waste have led to a pressing need for new routes to sustainable materials. ...

University of Akron

Though numerous applications require degradable polymers, there are surprisingly few polymer systems that combine superior stability and controllable degradability. Particularly, the degradability of a conventional degradable polymer is typically enabled by cleavable groups on the backbone, which can be attacked by stimuli in ambient conditions, causing undesirable material deterioration. Here we report a general strategy to overcome this issue: "locking" the degradability during handling and use of the polymers and "unlocking" it when degradation is needed. This strategy is demonstrated with a cyclobutane-fused lactone (CBL) polymer. The cyclobutane keeps polymer backbone intact under conditions that hydrolyze the lactone and allows the ester group to be recovered when undesirable hydrolysis occurs. When backbone degradation is needed, the degradability can be unlocked by mechanochemical activation that converts the polyCBL into a linear polyester. The rare combination of two intrinsically conflicting properties, i.e., backbone stability and accessible degradability, can make this polymer a potential option for new sustainable materials.

A Polymer with "Locked" Degradability: Superior Backbone Stability and Accessible Degradability Enabled by Mechanophore Installation.

A promising solution to address the challenges in plastics sustainability is to replace current polymers with chemically recyclable ones that can depolymerize into their constituent monomers to enable the circular use of materials. Despite some progress, few depolymerizable polymers exhibit the desirable 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 °C) and tunable mechanical properties. The polymers are formed through ring-opening metathesis polymerization of cyclooctene with a trans-cyclobutane installed at the 5 and 6 positions. The additional ring converts the non-depolymerizable polycyclooctene into a depolymerizable 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 fused-ring 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.

Olefin metathesis-based chemically recyclable polymers enabled by fused-ring monomers.

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 next-generation 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 -cyclobutane, -cyclopentane, and -five-membered cyclic acetals. The four- and five-membered rings -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. 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 K. Importantly, geminal substituents on the -five-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 -disubstituent effect demonstrated here can be leveraged to promote depolymerization of the corresponding polymers and to tune their thermomechanical properties.

Article	Year
A Polymer with "Locked" Degradability: Superior Backbone Stability and Accessible Degradability Enabled by Mechanophore Installation. Journal of the American Chemical Society\| PubMed ID: 31940198	2020
Olefin metathesis-based chemically recyclable polymers enabled by fused-ring monomers. Nature chemistry\| PubMed ID: 34294914	2021
Understanding the Structure-Polymerization Thermodynamics Relationships of Fused-Ring Cyclooctenes for Developing Chemically Recyclable Polymers. Journal of the American Chemical Society\| PubMed ID: 34985870	2022

Junfeng Zhou

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