Three types of seemingly unyielding trade-offs have continued to challenge the rational design for circular polymers with both high chemical recyclability and high-performance properties: depolymerizability/performance, crystallinity/ductility, and stereo-disorder/crystallinity. Here, we introduce a monomer design strategy based on a bridged bicyclic thiolactone that produces stereo-disordered to perfectly stereo-ordered polythiolactones, all exhibiting high crystallinity and full chemical recyclability. These polythioesters defy aforementioned trade-offs by having an unusual set of desired properties, including intrinsic tacticity-independent crystallinity and chemical recyclability, tunable tacticities from stereo-disorder to perfect stereoregularity, as well as combined high-performance properties such as high thermal stability and crystallinity, and high mechanical strength, ductility, and toughness.

Ten years have passed since the conception of what was termed Lewis pair polymerization (LPP) that employs Lewis acid and base in pairs to not only activate monomers but also effect chain initiation, propagation, and transfer events. Compared to other polymerization methodologies, LPP's cooperative and synergistic two-component catalytic mechanism empowers several unique or advantageous features, including extraordinary tunability of catalyst/ initiator systems, compounded thermodynamic and kinetic control over comonomer sequences in one-pot LPP of monomer mixtures for highly resolved block copolymers, complete chemoselectivity in LPP of multifunctional vinyl monomers, independent tuning of polymerization activity and target polymer molecular weight, controlled heat dissipation in bulk polymerization with unactivated monomers functioning as solvent molecules, and coupled selectivity and livingness with immortality of the active species to produce ultrahigh molecular weight polymers and block copolymers with record-number (53) blocks. Focusing on four fundamental attributes of any polymerization methodologymechanism, kinetics, control, and selectivitythis Perspective narrates the growth and development of LPP, tracing each innovation back to fundamental principles so that each concept can be strategically applied, and describes new frontiers fertile for future research.

Precision synthesis of cyclic polymers with predictable molecular weight and low dispersity is a challenging task, particularly concerning cyclic polar vinyl polymers through a rapid chain-growth mechanism and without high dilution. Harder yet is the precision synthesis of cyclic block copolymers (cBCPs), ideally from comonomer mixtures. Here we report that Lewis pair polymerization (LPP) capable of thermodynamically and kinetically compounded sequence control successfully addressed this longstanding challenge. Thus, LPP of acrylate/methacrylate mixtures under ambient temperature and normal concentration conditions rapidly and selectively affords well-defined cBCPs with high molecular weight (M n = 247 kg/mol) and low dispersity (Đ = 1.04) in one step. Such cBCPs have been characterized by multiple techniques, including direct structural observation by imaging.

Two well-known low-ceiling-temperature (LCT) monomers, γ-butyrolactone (γ-BL) toward ring-opening polymerization (ROP) to polyester and cyclohexene toward ring-opening metathesis polymerization (ROMP) to poly­(cyclic olefin), are notoriously “nonpolymerizable”. Here we present a strategy to render not only polymerizability of both the γ-BL and cyclohexene sites, orthogonally, but also complete and orthogonal depolymerization, through creating an LCT/LCT hybrid, bicyclic lactone/olefin (BiL=). This hybrid monomer undergoes orthogonal polymerization between ROP and ROMP, depending on the catalyst employed, affording two totally different classes of polymeric materials from this single monomer: polyester P­(BiL=)ROP via ROP and functionalized poly­(cyclic olefin) P­(BiL=)ROMP via ROMP. Intriguingly, both P­(BiL=)ROP and P­(BiL=)ROMP are thermally robust but chemically recyclable under mild conditions (25–40 °C), in the presence of a catalyst, to recover cleanly the same monomer via chain unzipping and scission, respectively. In the ROP, topological and stereochemical controls have been achieved and the structures characterized. Furthermore, the intact functional group during the orthogonal polymerization (i.e., the double bond in ROP and the lactone in ROMP) is utilized for postfunctionalization for tuning materials’ thermal and mechanical performances. The impressive depolymerization orthogonality further endows selective depolymerization of both the ROP/ROMP copolymer and the physical blend composites into the same starting monomer.

The ability to synthesize well-defined block copolymers (BCPs) from one-pot comonomer mixtures has powerful chemical and practical implications. However, controlling sequences between highly reactive, homologous comonomers such as acrylates during polymerization is challenging. Here we present a Lewis pair polymerization strategy that uniquely utilizes preferential Lewis acid coordination to differentiate between comonomers, distinctive kinetics, and compounded thermodynamic and kinetic differentiation to precisely control sequences and suppress tapering and misincorporation errors, thus achieving well-defined and resolved di- or tri-BCPs of acrylates.