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Polyhydroxyalkanoates (PHAs) have attracted increasing interest as sustainable plastics because of their biorenewability and biodegradability in the ambient environment. However, current semicrystalline PHAs face three long-standing challenges to broad commercial implementation and application: lack of melt processability, mechanical brittleness, and unrealized recyclability, the last of which is essential for achieving a circular plastics economy. Here we report a synthetic PHA platform that addresses the origin of thermal instability by eliminating α-hydrogens in the PHA repeat units and thus precluding facile cis-elimination during thermal degradation. This simple α,α-disubstitution in PHAs enhances the thermal stability so substantially that the PHAs become melt-processable. Synergistically, this structural modification also endows the PHAs with the mechanical toughness, intrinsic crystallinity, and closed-loop chemical recyclability.

Geminal disubstitution of cyclic monomers is an effective strategy to enhance the chemical recyclability of their polymers, but it is utilized for that purpose alone and often at the expense of performance properties. Here we present synergistic use of gem-α,α-disubstitution of available at-scale, bio-based δ-valerolactones to yield gem-dialkyl-substituted valerolactones ([Formula: see text]), which generate polymers that solve not only the poor chemical recyclability but also the low melting temperature and mechanical performance of the parent poly(δ-valerolactone); the gem-disubstituted polyesters ([Formula: see text]) therefore not only exhibit complete chemical recyclability but also thermal, mechanical and transport properties that rival or exceed those of polyethylene. Through a fundamental structure-property study that reveals intriguing impacts of the alkyl chain length on materials performance of [Formula: see text], this work establishes a simple circular, high-performance polyester platform based on [Formula: see text] and highlights the importance of synergistic utilization of gem-disubstitution for enhancing both chemical recyclability and materials performance of sustainable polyesters.

Aliphatic polyamides, or nylons, are typically highly crystalline and thermally robust polymers used in high-performance applications. Nylon 6, a high-ceiling-temperature (HCT) polyamide from ε-caprolactam, lacks expedient chemical recyclability, while low-ceiling temperature (LCT) nylon 4 from pyrrolidone exhibits complete chemical recyclability, but it is thermally unstable and not melt-processable. Here, we introduce a hybrid nylon, nylon 4/6, based on a bicyclic lactam composed of both HCT ε-caprolactam and LCT pyrrolidone motifs in a hybridized offspring structure. Hybrid nylon 4/6 overcomes trade-offs in (de)polymerizability and performance properties of the parent nylons, exhibiting both excellent polymerization and facile depolymerization characteristics. This stereoregular polyamide forms nanocrystalline domains, allowing optical clarity and high thermal stability, however, without displaying a melting transition before decomposition. Of a series of statistical copolymers comprising nylon 4/6 and nylon 4, a 50/50 copolymer achieves the greatest synergy in both reactivity and polymer properties of each homopolymer, offering an amorphous nylon with favorable properties, including optical clarity, a high glass transition temperature, melt processability, and full chemical recyclability.

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

Tetrahydropyran (THP) is a five-carbon heterocyclic ether that is non-carcinogenic, non-peroxide forming, biodegradable, and economically competitive with tetrahydrofuran (THF) as a solvent.

Technologically important thermosets face a long-standing end-of-life (EoL) problem of non-reprocessability, a more sustainable solution of which has resolved to nascent vitrimers that can merge the robust material properties of thermosets and the reprocessability of thermoplastics. However, the lifecycle of vitrimers is still finite, as they often suffer from significant deterioration of mechanical performance following multiple reprocessing cycles, analogous to mechanical recycling, and they often show undesired creep under working conditions. To address these two key limitations, we have developed a cross-linked semi-crystalline polythioester with both dynamic covalent bonds and intrinsic crystallinity and chemical recyclability, affording a vitrimeric system that exhibits not only reprocessability and crystallinity-restricted creep but also complete chemical recyclability to initial monomer by catalyzed depolymerization in solution or bulk. Therefore, reported herein is an "infinite" vitrimer system that is empowered with a facile closed-loop EoL option once serial reprocessing deteriorates performance and the material can no longer meet the application requirements. Specifically, the polythioester vitrimer was constructed by copolymerization of a bicyclic thioester with a bis-dithiolane, producing dynamically cross-linked polythioesters with excellent property tunability, from amorphous to semi-crystalline states and melting transition temperatures from 91 to 178 °C.

Activating inert sp

In typical cyclic polymer synthesis via ring-closure, chain growth and cyclization events are competing with each other, thus affording cyclic polymers with uncontrolled molecular weight or ring size and high dispersity. Here we uncover a mechanism by which Lewis pair polymerization (LPP) operates on polar vinyl monomers that allows the control of where and when cyclization takes place, thereby achieving spatial and temporal control to afford precision cyclic vinyl polymers or block copolymers with predictable molecular weight and low dispersity (≈1.03). A combined experimental and theoretical study demonstrates that cyclization occurs only after all monomers have been consumed (when) via conjugate addition of the propagating chain end to the specific site of the initiating chain end (where), allowing the cyclic polymer formation steps to be regulated and executed with precision in space and time.

Chemically recyclable polymers have attracted increasing attention since they are promising materials in a circular economy, but such polymers appropriate for packaging applications are scarce. Here a combined thermal, mechanical, and transport (permeability and sorption) study is presented of a circular polymer system based on biobased trans-hexahydrophthalide which, upon polymerization, can lead to amorphous, homochiral crystalline, and nanocrystalline stereocomplex materials. This study uncovers their largely different transport properties of the same polymer but with different stereochemical arrangements and synergistic or conflicting effects of crystallinity on transport properties versus thermal and mechanical properties. Overall, the homocrystalline chiral polymer shows the best performance with an outstanding barrier character to gases and vapors, outperforming commercial poly(ethylene terephthalate) and polyethylene. The results presented herein show that it is possible to modify the crystalline structure of the same polymer to tune the mechanical and transport properties and generate multiple materials of different barrier characters.

This work utilizes frustrated Lewis pairs consisting of tethered bis-organophosphorus superbases and a bulky organoaluminum to furnish the highly efficient synthesis of well-defined triblock copolymers via one-step block copolymerization of lignin-based syringyl methacrylate and n-butyl acrylate, through di-initiation and compounded sequence control. The resulting thermoplastic elastomers (TPEs) exhibit microphase separation and much superior mechanical properties (elongation at break up to 2091 %, tensile strength up to 11.5 MPa, and elastic recovery up to 95 % after 10 cycles) to those of methyl methacrylate-based TPEs. More impressively, lignin-based tri-BCPs can maintain TPEs properties up to 180 °C, exhibit high transparency and nearly 100 % UV shield, suggesting potential applications in temperature-resistant and optical devices.

The unprecedented growth and socioeconomic impacts of polyolefins clearly outline a major success story in the world of polymer science. Polyolefins revolutionizes industries such as health care, construction, and food packaging. Despite the benefits of polyolefins, there is a rising concern for the environment due to high production volume (i.e., fossil fuel consumption), often short usage time, and problems related to waste management and accumulation in the natural environment. Creating a circular economy for polyolefins through effective recycling technologies has the potential to decrease the environmental impact of these materials. This perspective discusses polyolefins and their impact, existing and emerging recycling/upcycling solutions, and recycle-by-design alternatives that are challenging the status quo.