Graft polymers, owing to their grafted structures, possess unique properties useful for a broad range of applications. Due to the demand for a circular economy, it is desirable to have graft polymers depolymerizable. However, depolymerizable graft polymers are rare, and existing examples of depolymerizable graft polymers lack the rigor in controlling the size and architecture. Herein, we demonstrate a robust method to synthesize depolymerizable graft polymers by leveraging our recent development of chemically recyclable polymers prepared from controlled ring-opening metathesis polymerization of trans-cyclobutane fused trans-cyclooctenes. The superior reactivity of the highly strained trans-cyclooctene allows grafting-through of macromonomers to be successfully conducted, empowering excellent control in backbone length for various types of sidechains, including a poly(ethylene glycol), a polylactide, and an aliphatic chain. Notably, an ultrahigh molecular weight of 14 000 kDa is achieved with high conversion (>90%) and low dispersity (Đ < 1.2). The controlled polymerization enables the synthesis of graft polymers of various architectures, including block and statistical copolymers. Kinetic studies of depolymerization show that the graft polymers depolymerize to the cis-cyclooctene macromonomers through an unzipping mechanism. The versatile synthesis of depolymerizable graft polymers opens the door to sustainable thermoplastics with diverse material properties.

Fluorinated polymers are important functional materials for a broad range of applications, but the recycling of current fluorinated polymers is challenging. We present the first example of semi-fluorinated polymers that...

Polymers with low ceiling temperatures (Tc) are highly desirable as they can depolymerize under mild conditions, but they typically suffer from demanding synthetic conditions and poor stability. We envision that this challenge can be addressed by developing high-Tc polymers that can be converted into low-Tc polymers on demand. Here, we demonstrate the mechanochemical generation of a low-Tc polymer, poly(2,5-dihydrofuran) (PDHF), from an unsaturated polyether that contains cyclobutane-fused THF in each repeat unit. Upon mechanically induced cycloreversion of cyclobutane, each repeat unit generates three repeat units of PDHF. The resulting PDHF completely depolymerizes into 2,5-dihydrofuran in the presence of a ruthenium catalyst. The mechanochemical generation of the otherwise difficult-to-synthesize PDHF highlights the power of polymer mechanochemistry in accessing elusive structures. The concept of mechanochemically regulating the Tc of polymers can be applied to develop next-generation sustainable plastics.

Chemically recyclable polymers offer a promising solution to address the issues associated with the unsustainable use of plastics by converting the traditional linear plastic economy into a circular one. Central to developing chemically recyclable polymers is to identify the appropriate monomers that enable practical conditions for polymerization and depolymerization and ensure useful stability and material properties. Our group has recently demonstrated that transcyclobutane-fused cyclooctene (tCBCO) meets the abovementioned requirements and is a promising candidate for developing chemically recyclable polymers. Herein, encour-aged by the success with tCBCO, we investigate the thermodynamics of polymerization of a relevant system, trans-benzocyclobutene-fused-cyclooctene, which can be viewed as tCBCO with an additional benzene ring. The study shows that introducing an additional benzene ring favors polymerization and disfavors depolymerization, and the effect is predominantly entropic. The benzo-effect can be leveraged to fine-tune the thermodynamics of polymerization and depolymerization to facilitate the chemical recycling of polymers.

Polymers with low ceiling temperatures (Tc) are highly desirable as they can depolymerize under mild conditions, but they typically suffer from demanding synthetic conditions and poor stability. We envision that this challenge can be addressed by developing high-Tc polymers that can be converted into low Tc polymers on demand. Here, we demonstrate the mechanochemical generation of a low-Tc polymer, poly(2,5-dihydrofuran) (PDHF), from an unsaturated polyether that contains cyclobutane-fused THF in each repeat unit. Upon mechanically induced cycloreversion of cyclobutane, each repeat unit generates three repeat units of PDHF. The resulting PDHF completely depolymerizes into 2,5-dihydrofuran in the presence of a ruthenium catalyst. The mechanochemical generation of the otherwise difficult-to-synthesize PDHF highlights the power of polymer mechanochemistry in accessing elusive structures. The concept of mechanochemically regulating Tc of polymers can be applied to develop next-generation sustainable plastics.