Sigmatropic Rearrangements of Polymer Backbones: Vinyl Polymers from Polyesters in One Step

Architectural Editing of Polyesters and Polyurethanes via Palladium(II)-Catalyzed [3,3]-Sigmatropic Oxo-Rearrangements

Architecture underlies the thermomechanical properties of polymers. Yet, few strategies are available to tune a polymer's architecture after it is prepared without altering its chemical composition. The ability to edit the architecture of a polymer would dramatically expand the accessible architecture-property space of polymeric materials. Herein, we disclose a backbone rearrangement approach to tune the short-chain branching of polymers. Specifically, we demonstrate that palladium(II)-catalyzed [3,3]-sigmatropic oxo-rearrangements can transform branched polyesters and polyurethanes to their linear counterparts. While the effects on materials properties are generally subtle in the case of polyesters, more dramatic changes are observed in the case of polyurethanes: two polyurethanes undergo a soluble-to-insoluble transition, and one exhibits a dramatic increase in both strain at break and toughness after rearrangement. Additionally, the incorporation of alkenes in the polymer backbone through the rearrangement enables facile deconstruction via ethenolysis. In all, we disclose a powerful and broad-scope strategy to edit the architecture of polymer backbones and thereby tune their physical and chemical properties.

Synthesis of Novel Polymers with Biodegradability by Main-Chain Editing of Chiral Polyketones

Although the use of biodegradable plastics is suitable for unrecoverable, single-use plastic, their high production cost and much lower variety compared to commodity plastics limit their application. In this study, we developed a new polymer with potential biodegradability, poly(ketone/ester), synthesized from propylene and carbon monoxide. Propylene and carbon monoxide are easily available at low costs from fossil resources, and they can also be derived from biomass. Using an atom insertion reaction to the main chain of the polymer, the main-chain editing of the polymer molecule proceeded with up to 89% selectivity for atom insertion over main-chain cleavage.

Access to Functionalized Materials by Metal-Free Ring-Opening Metathesis Polymerization of Active Esters and Divergent Postpolymerization Modification

Metal-free ring-opening metathesis polymerization (MF-ROMP) is an emerging polymerization strategy that provides access to ROMP materials by using organic initiators and photoredox catalysts. Unlike metal-mediated ROMP, MF-ROMP is not highly tolerant toward functionalized monomers. Herein, we report that pentafluorophenyl esters are polymerizable under MF-ROMP conditions to produce homopolymers, statistical copolymers, and block copolymers. Amine coupling agents were then used to install a range of functional groups via acyl substitution including alkynes, amino acid derivatives, fluorophores, and redox active moieties. Overall, these findings provide a framework to prepare functionalized ROMP polymers without the risk of metal contamination.

Click to Self-immolation: A "Click" Functionalization Strategy towards Triggerable Self-Immolative Homopolymers and Block Copolymers

Self-immolative polymers (SIPs) are a class of degradable macromolecules that undergo stimuli-triggered head-to-tail depolymerization. However, a general approach to readily end-functionalize SIP precursors for programmed degradation remains elusive, restricting access to complex, functional SIP-based materials. Here we present a "click to self-immolation" strategy based on aroyl azide-capped SIP precursors, enabling the facile construction of diverse SIPs with different trigger units through a Curtius rearrangement and alcohol/thiol-isocyanate "click" reaction. This strategy is also applied to polymer-polymer coupling to access fully depolymerizable block copolymer amphiphiles, even combining different SIP backbones. Our results demonstrate that the depolymerization can be actuated efficiently under physiologically-relevant conditions by the removal of the trigger units and ensuing self-immolation of the p-aminobenzyl carbonate linkage, indicating promise for controlled release applications involving nanoparticles and hydrogels.

Editing of polymer backbones

Polymers are at the epicentre of modern technological progress and the associated environmental pollution. Considerations of both polymer functionality and lifecycle are crucial in these contexts, and the polymer backbone - the core of a polymer - is at the root of these considerations. Just as the meaning of a sentence can be altered by editing its words, the function and sustainability of a polymer can also be transformed via the chemical modification of its backbone. Yet, polymer modification has primarily been focused on the polymer periphery. In this Review, we focus on the transformations of the polymer backbone by defining some concepts fundamental to this topic (for example, 'polymer backbone' and 'backbone editing') and by collecting and categorizing examples of backbone editing scattered throughout a century's worth of chemical literature, and outline critical directions for further research. In so doing, we lay the foundation for the field of polymer backbone editing and hope to accelerate its development.

Advances in the application of named reactions in polymer synthesis

With the development of polymer science, more and more named reactions have been applied to synthesizing polymers. Introducing new reactions into polymer synthesis is undoubtedly an excellent expansion for monomer and polymer libraries. In this review, the named reactions employed in polymer-chain synthesis were divided into seven types: electrophilic reactions, nucleophilic reactions, transition metal-mediated cross-coupling reactions, free radical reactions, pericyclic reactions, multi-component reactions and rearrangement reactions. The discussion was mainly focused on the progress in the utilization of these named reactions in polymer synthesis, which could be a valuable reference for researchers in the polymer field.

Tunable and recyclable polyesters from CO2 and butadiene

Carbon dioxide is inexpensive and abundant, and its prevalence as waste makes it attractive as a sustainable chemical feedstock. Although there are examples of copolymerizations of CO₂ with high-energy monomers, the direct copolymerization of CO₂ with olefins has not been reported. Here an alternative route to functionalizable, recyclable polyesters derived from CO₂, butadiene and hydrogen via an intermediary lactone, 3-ethyl-6-vinyltetrahydro-2H-pyran-2-one, is described. Catalytic ring-opening polymerization of the lactone by 1,5,7-triazabicyclo[4.4.0]dec-5-ene yields polyesters with molar masses up to 13.6 kg mol^-1 and pendent vinyl side chains that can undergo post-polymerization functionalization. The polymer has a low ceiling temperature of 138 °C, allowing for facile chemical recycling, and is inherently biodegradable under aerobic aqueous conditions (OECD-301B protocol). These results show that a well-defined polyester can be derived from CO₂, olefins and hydrogen, expanding access to new polymer feedstocks that were once considered unfeasible.

Advancing the Logic of Polymer Synthesis via Skeletal Rearrangements

Polymers are ubiquitous materials that have driven technological innovation since the middle of the 20th century. As such, the logic that guides polymer synthesis merit considerable attention. Thus far, this logic has often been ‘forward-synthetic’, which constrains the accessible structures of polymer materials. In this article, we emphasize the benefits of ‘retrosynthetic’ logic and posit that the development of skeletal rearrangements of polymer backbones is central to the realization of this logic. To illustrate this point, we discuss two recent examples from our laboratory – Brook and Ireland–Claisen rearrangements of polymer backbones – and contextualize them in prior reports of sigmatropic rearrangements and skeletal rearrangements of polymers. We envision that further development of skeletal rearrangements of polymers will enable advances in not only the chemistry of such rearrangements and the logic of polymer synthesis, but also polymer re- and upcycling.