Elastomeric vitrimers from designer polyhydroxyalkanoates with recyclability and biodegradability

Molecular Reconstruction for the High-Performance Recycled Fluororubbers

To address the challenges associated with the difficult recycling of fluorinated specialty materials and the subpar performance of recycled products, a molecular reconstruction strategy of oxidative degradation, fluorination addition is reported, and end-group transformation, which upcycled waste fluororubber into high-performance, chemically awakenable amino-terminated low-molecular-weight fluoropolymer (ATLF-Boc). Leveraging the chemical properties of the vinylidene fluoride structure in the waste fluororubber, carboxyl-terminated low-molecular-weight fluoropolymer (CTLF) with controlled molecular weight and end-group content are synthesized. Further, the whole chain is structurally strengthened at the molecular scale to achieve higher fluorine content and thermal stability, and saturated carboxyl-terminated low-molecular-weight fluoropolymer (SCTLF) is synthesized. Subsequently, to balance high reactivity and stable storage, high-performance ATLF-Boc is synthesized, realizing the upcycling of waste fluororubber. After upcycling, the awakened ATLF exhibits a high fluorine content (66.95%), and the cured ATLF shows the regulation of surface hydrophilicity and hydrophobicity (between 43° and 114°), a high tensile strength of 13.3 MPa, an excellent thermal stability (T10% = 359 °C). In this study, a novel solution for the upcycling of waste fluororubbers for fabricating functional materials is offered, which is of great significance in the field of fluorinated specialty materials.

Tunable and Degradable Dynamic Thermosets from Compatibilized Polyhydroxyalkanoate Blends

Polyhydroxyalkanoates (PHAs) are versatile, biobased polyesters that are often targeted for use as degradable thermoplastic replacements for polyolefins. Given the substantial chemical diversity of PHA, their potential as cross-linked polymers could also enable similar platforms for reversible, degradable thermosets. In this work, we genetically engineered Pseudomonas putida KT2440 to synthesize poly(3-hydroxybutyrate-co-3-hydroxyundecenoate) (PHBU), which contains both 3-hydroxybutyrate and unsaturated 3-hydroxyundecenoate components. To reduce the brittleness of this polymer, we physically blended PHBU with the soft copolymer poly(3-hydroxydecanonate-co-3-hydroxyundecenoate) in mass ratios of 1:3, 1:1, and 3:1. Upon observing varying degrees of immiscibility by scanning electron microscopy, we installed dynamic boronic ester cross-links via thiol-ene click chemistry, which resulted in compatibilized dynamic thermoset blends ranging in hard, medium, and soft rubber or elastomer thermomechanical profiles. These dynamic thermoset blends were subjected to controlled biological degradation experiments in freshwater conditions, achieving timely mass loss despite the cross-linked architectures. Overall, this work highlights a two-component platform for the production of degradable and reprocessable dynamic thermoset blends suitable for several classes of cross-linked polymer technologies from tailored, biological PHA copolymers.

Access to Polyhydroxyalkanoates with Diverse Syndiotacticity via Polymerization by Spiro-Salen Complexes and Insights into the Stereocontrol Mechanism

Polyhydroxyalkanoates (PHAs) have attracted broad interest as promising sustainable materials to address plastic pollution and resource scarcity. However, the chemical synthesis of stereoregular PHAs via ring-opening polymerization (ROP) has long been an elusive endeavor. In this contribution, we exploited a robust spiro-salen yttrium complex (Y3) as the catalyst to successfully prepare syndiotactic PHAs with diverse pendent groups. Simply altering the ratio of enantiomeric catalysts allowed to access of PHAs with diverse syndiotacticity (Pr=0.5-0.99, from sticky oil to tough materials), delivering tunable thermal properties (glass transition temperature, Tg from -52 to 70 °C and melting transition temperature, Tm from 38 to 223 °C). A combined experimental and computational study suggested a polymeric exchange mechanism could boost the polymerization activity and control the syndioselectivity.

Syndioselective Ring-Opening Polymerization of β-Lactones Enabled by Dimethylbiphenyl-Salen Yttrium Complexes

Polyhydroxyalkanoates (PHAs) have served as promising alternatives to traditional petroleum-based plastics. Chemical synthesis of stereoregular PHAs via stereocontrolled ring-opening polymerization (ROP) of racemic β-lactones was a desired strategy with a formidable challenge. Herein, we developed a class of DiMeBiPh-salen yttrium complexes that adopted a cis-α configuration for stereoselective ROP of rac-β-butyrolactones (rac-BBL) and rac-β-valerolactone (rac-BVL). Notably, catalyst Y5 promoted robust polymerization with TOF up to 104 h-1 and furnished syndiotactic P3HB, P3HV, and P(3HB)-co-P(3HV) copolymers with Pr values of up to 0.95. Varying the compositions in P(3HB)-co-P(3HV) copolymers offered an intriguing opportunity to fine tune the thermal properties. Our kinetic study supported a polymeryl exchange mechanism. This work demonstrated that the DiMeBiPh-salen system could serve as a new catalytic framework for the stereoselective ROP of β-lactones, which leverages the catalyst design for stereoselective polymerization.

Investigation on Polyether Sulfone Toughening Epoxy Vitrimer: Curing and Dynamic Properties

Diglycidyl ether of bisphenol A crosslinking with glutaric anhydride is used to form the conventional "covalent adaptive network", polyether sulfone (PES) by coiling and aggregating on the adaptive network is used to significantly increase the uncured resin viscosity for improving the processability of epoxy resin, but inevitably affecting the curing reaction and dynamic transesterification reaction. This study investigates the crucial roles of PES in curing dynamics and stress relaxation behavior. The results indicate that although PES does not directly participate in the crosslinking reaction of polyester-based epoxy vitrimers. Moreover, the isothermal curing studies reveal that the addition of PES can greatly bring forward the reaction rate peak from conversion α = 0.6 to α = 0.2, meaning that the curing mechanism transfers from chemical control to diffusion control. Dynamic property analysis shows that the addition of PES significantly accelerates stress relaxation, especially at lower temperatures, leading to low viscous flow activation energy Eτ and relatively insensitive stress relaxation behavior to temperature. Introducing PES into vitrimer resin greatly improves crosslinking density (2.31 × 10⁴ mol m- 3), enhancing glass transition temperature (82.68 °C), tensile strength (68.66 MPa), and fracture toughness (6.25%). Additionally, the modified vitrimer resin exhibits satisfying shape memory performance and reprocessing capability.

Monodisperse polyhydroxyalkanoate nanoparticles as self-sticky and bio-resorbable tissue adhesives

Monodisperse nanoparticles of biodegradable polyhydroxyalkanoates (PHAs) polymers, copolymers of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB), are synthesized using a membrane-assisted emulsion encapsulation and evaporation process for biomedical resorbable adhesives. The precise control over the diameter of these PHA particles, ranging from 100 nm to 8 μm, is achieved by adjusting the diameter of emulsion or the PHA concentration. Mechanical properties of the particles can be tailored based on the 3HB to 4HB ratio and molecular weight, primarily influenced by the level of crystallinity. These monodisperse PHA particles in solution serve as adhesives for hydrogel systems, specifically those based on poly(N, N-dimethylacrylamide) (PDMA). Semi-crystalline PHA nanoparticles exhibit stronger adhesion energy than their amorphous counterparts. Due to their self-adhesiveness, adhesion energy increases even when those PHA nanoparticles form multilayers between hydrogels. Furthermore, as they degrade and are resorbed into the body, the PHA nanoparticles demonstrate efficacy in in vivo wound closure, underscoring their considerable impact on biomedical applications.

Recyclable and (Bio)degradable Polyesters in a Circular Plastics Economy

Polyesters carrying polar main-chain ester linkages exhibit distinct material properties for diverse applications and thus play an important role in today's plastics economy. It is anticipated that they will play an even greater role in tomorrow's circular plastics economy that focuses on sustainability, thanks to the abundant availability of their biosourced building blocks and the presence of the main-chain ester bonds that can be chemically or biologically cleaved on demand by multiple methods and thus bring about more desired end-of-life plastic waste management options. Because of this potential and promise, there have been intense research activities directed at addressing recycling, upcycling or biodegradation of existing legacy polyesters, designing their biorenewable alternatives, and redesigning future polyesters with intrinsic chemical recyclability and tailored performance that can rival today's commodity plastics that are either petroleum based and/or hard to recycle. This review captures these exciting recent developments and outlines future challenges and opportunities. Case studies on the legacy polyesters, poly(lactic acid), poly(3-hydroxyalkanoate)s, poly(ethylene terephthalate), poly(butylene succinate), and poly(butylene-adipate terephthalate), are presented, and emerging chemically recyclable polyesters are comprehensively reviewed.