Forcing polymers to be semiconductors: In mechanochemistry, the application of force to a polymer is used to pry open specific chemical bonds. Chen et al. leveraged this technique to produce semiconducting blocks of polyacetylene in an insulating precursor. Ring-opening metathesis polymerization tethered together a series of fused four-carbon rings, reminiscent of the unusual ladderane membrane lipids of anaerobic ammonium-oxidizing bacteria. Subsequently, sonication unzipped these strained rings into alternating C=C double bonds, thereby extending π-conjugation along the polymer backbone. Science , this issue p. 475

Membranes have the potential to substantially reduce energy consumption of industrial chemical separations, but their implementation has been limited owing to a performance upper bound—the trade-off between permeability and selectivity. Although recent developments of highly permeable polymer membranes have advanced the upper bounds for various gas pairs, these polymers typically exhibit limited selectivity. We report a class of hydrocarbon ladder polymers that can achieve both high selectivity and high permeability in membrane separations for many industrially relevant gas mixtures. Additionally, their corresponding films exhibit desirable mechanical and thermal properties. Tuning of the ladder polymer backbone configuration was found to have a profound effect on separation performance and aging behavior.

Enol ethers are widely used as quenching reagents for Grubbs catalysts. However, we report the surprisingly effective ring-opening metathesis polymerization (ROMP) of cyclic enol ethers, because the resulting electron-rich ruthenium alkylidene complex remains active towards metathesis of electron-rich olefins, despite its deactivation toward hydrocarbon olefins. We demonstrate the first example of ROMP of cyclic enol ethers, using 2,3-dihydrofuran as the monomer, producing a new type of degradable and depolymerizable poly(enol ether). The pol-ymers exhibited perfect regioregularity and their molecular weights can be regulated using the loading of Grubbs initiators or the use of a linear vinyl ether as the chain transfer agent. We also developed protocols to deactivate the catalyst following metathesis of enol ethers and cleave the catalyst off the result-ing polymers using H2O2 oxidation. The resulting poly(dihydrofuran) can be recycled to monomer via depoly-merization with Grubbs catalyst or degraded to small molecules by hydrolysis under acidic conditions. This work opens exciting opportunities for a new class of ROMP monomers that lead to degradable polymers.

Achieving fast population transfer (FPT) in multiparticle systems based on the cavity quantum electronic dynamics is an outstanding challenge. In this paper, motivated by the quantum Zeno dynamics, a shortcut for performing the FPT of ground states in multiparticle systems with the invariant-based inverse engineering is proposed. Numerical simulation demonstrates that a perfect population transfer of ground states in multiparticle systems can be rapidly achieved in one step, and the FPT is robust to both the cavity decay and atomic spontaneous emission. Additionally, this scheme is not only implemented without requiring extra complex conditions, but also insensitive to variations of the parameters.