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.

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.

Radical copolymerization of vinyl monomers and cyclic monomers is a versatile approach to degradable vinyl plastics. Despite recent advances, a class of "universal" cyclic monomers that possess broad reactivities with various types of vinyl monomers remains elusive. Herein, we report a general method for the organocatalyzed photocontrolled radical ring-opening cascade copolymerization (rROCCP) of macrocyclic allylic sulfone and various types of vinyl monomers, including acrylates, acrylamides, styrene, and methacrylate. Catalyzed by Eosin Y under visible light irradiation, the copolymerization of macrocyclic allylic sulfone and acrylic monomers displayed near unity comonomer reactivity ratios by fitting the copolymer composition to the Beckingham− Sanoya−Lynd integrated model. Macrocyclic allylic sulfone was also successfully copolymerized with styrene (r 1 = 3.02 and r St = 0.35) or methyl methacrylate (r 1 = 0.18 and r MMA = 5.81) to generate degradable polystyrene and poly(methyl methacrylate). These degradable vinyl copolymers exhibited tunable thermal properties correlated with the incorporation of the degradable main-chain diester motif. The unprecedented reactivities that macrocyclic allylic sulfone demonstrated in the organocatalyzed photocontrolled rROCCP provide a general approach to the wide range of degradable vinyl plastics with various structures and functions.

Hydrogels are deployed widely in all areas of regenerative medicine, including bioprinting. The transport and mechanical properties exhibited by hydrogel assemblies are controlled by their organization and hierarchical assembly. This paper points out the role of nanoscale size and ordering of hydrophobic crosslinked domains on the mechanical and degradation properties of 3D printed amphiphilic hydrogels. A series of six poly(propylene fumarate)-block-poly(ethylene glycol)-block-poly(propylene fumarate) (PPF-b-PEG-b-PPF) ABA triblock copolymers were synthesized by varying both the water-soluble PEG block and the crosslinkable hydrophobic terminal PPF block lengths. Self-assembled hydrogels were formed by dissolving these amphiphilic PPF-b-PEG-b-PPF copolymers in water and covalently crosslinking the PPF units via digital light processing (DLP) additive manufacturing. Differential scanning calorimetry (DSC), in situ diffuse reflectance infrared spectroscopy (DRIFTS-IR) measurements, small-angle neutron scattering (SANS) and compressive measurements highlight how structural properties correlate with mechanical properties within this hydrogel system. Finally, swelling and in vitro degradation tests showed the influence of the nanoscale ordering on the degradation timescale.

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