Investigate the Glass Transition Temperature of Hyperbranched Copolymers with Segmented Monomer Sequence

Hyperbranched copolymers with segmented structures were synthesized using a chain-growth copper-catalyzed azide–alkyne cycloaddition (CuAAC) polymerization via sequential monomer addition in one pot. Three AB₂-type monomers that contained one alkynyl group (A), two azido groups (B), and one dangling group, either benzyl or oligo­(ethylene oxide) (EO_<i>x</i>, <i>x</i> = 3 and 7.5), were used in these CuAAC reactions. Varying the addition sequences and feed ratios of the monomers produced a variety of hyperbranched copolymers with tunable compositions, molecular weights, segmented structures, and consequently glass transition temperature (<i>T</i>_g). It was found that the <i>T</i>_g of hyperbranched copolymers was little affected by the polymer molecular weights when <i>M</i>_n ≥ 5000. However, the values of <i>T</i>_g were significantly determined by the compositions of the terminal groups and the outermost segment of the hyperbranched copolymers. The last added AB₂ monomer in the polymerization formed an outermost “shell” and shielded the contribution of inner segments to the glass transition of the copolymers, reflecting a chain sequence effect of hyperbranched polymers on the thermal properties

Isomerism in Au–Ag Alloy Nanoclusters: Structure Determination and Enantioseparation of [Au₉Ag₁₂(SR)₄(dppm)₆X₆]³⁺

Revealing structural isomerism in a nanocluster remains significant but challenging. Herein, we have obtained a pair of structural isomers, [Au₉­Ag₁₂­(SR)₄­(dppm)₆­X₆]³⁺-C and [Au₉­Ag₁₂­(SR)₄­(dppm)₆­X₆]³⁺-Ac [dppm = bis­(diphenyphosphino)­methane; HSR = 1-adamantanethiol/<i>tert</i>-butylmercaptan; X = Br/Cl; C stands for one of the structural isomers being chiral; Ac stands for another being achiral], that show different structures as well as different chiralities. These structures are determined by single-crystal X-ray diffraction and further confirmed by high-resolution electrospray ionization mass spectrometry. On the basis of the isomeric structures, the most important finding is the different arrangements of the Au₅Ag₈@Au₄ metal core, leading to changes in the overall shape of the cluster, which is responsible for structural isomerism. Meanwhile, the two enantiomers of [Au₉­Ag₁₂­(SR)₄­(dppm)₆­X₆]³⁺-C are separated by high-performance liquid chromatography. Our work will contribute to a deeper understanding of the structural isomerism in noble-metal nanoclusters and enrich the chiral nanocluster