Torsional Strain Enabled Ring-Opening Polymerization towards Axially Chiral Semiaromatic Polyesters with Chemical Recyclability.

The development of new chemically recyclable polymers via monomer design would provide a transformative strategy to address the energy crisis and plastic pollution problem. Biaryl-fused cyclic esters were targeted to generate axially chiral polymers, which would impart new material performance. To overcome the non-polymerizability of the biaryl-fused monomer DBO, a cyclic ester Me-DBO installed with dimethyl substitution was prepared to enable its polymerizability via enhancing torsional strain. Impressively, Me-DBO readily went through well-controlled ring-opening polymerization, producing polymer P(Me-DBO) with high glass transition temperature (Tg >100 °C). Intriguingly, mixing these complementary enantiopure polymers containing axial chirality promoted a transformation from amorphous to crystalline material, affording a semicrystalline stereocomplex with a melting transition temperature more than 300 °C. P(Me-DBO) were capable of depolymerizing back to Me-DBO in high efficiency, highlighting an excellent recyclability.

Highly Reactive Cyclic Carbonates with a Fused Ring toward Functionalizable and Recyclable Polycarbonates.

Monomer design plays an important role in the development of polymers with desired thermal properties and chemical recyclability. Here we prepared a class of seven-membered ring carbonates containing trans-cyclohexyl fused rings. These monomers showed excellent activity for ring-opening polymerization (ROP) with turnover frequency (TOF) up to 6 × 105 h-1 and catalyst loading down to 50 ppm, which yielded high-molecular-weight polycarbonates (Mn up to 673 kg/mol) with great thermostability (Td > 300 °C). Ultimately, the resulting polycarbonates can completely depolymerize into their corresponding cyclic dimers that can repolymerize to synthesize the starting polymers in moderate yields, demonstrating a potential route to achieve chemical recycling. Postfunctionalization of the unsaturated polycarbonate was conducted through cross-linking reaction and "click" reaction under UV irradiation.

Light Runs Across Iron Catalysts in Organic Transformations.

Over the past decades, organometallic complexes with precious elements, such as ruthenium and iridium, are widely used as visible-light photoredox catalysts. Recently, more and more complexes based on earth-abundant and inexpensive elements have been used as sensitizers in photochemistry. Although the photoexcited state lifetimes of iron complexes are typically shorter than those of traditional photosensitizers, the utilization of iron catalysts in photochemistry has sprung up owing to their abundance, low price, nontoxicity, and novel properties, including exhibiting ligand to metal charge transfer states. This concept focuses on recent advances in light-driven iron catalysis in organic transformations, including iron/photoredox dual catalysis, light-induced iron photoredox catalysis and light-induced generation of active iron catalysts. The prospect for the future of this field is also discussed.