The synthesis of polyethylene thermoplastic elastomers via α-diimine-nickel-catalyzed ethylene polymerization using polymerization conditions of elevated temperatures and alkane solvents is highly desirable in industrial production. In this contribution, we constructed a series of highly sterically demanding α-diimine Ni(II) catalysts with abundant tBu substituents for this purpose. These nickel catalysts were examined for ethylene polymerization in hexanes at elevated temperatures (up to 90°C) and proved to be thermally robust at temperatures as high as 90°C. Generally, these nickel catalysts can generate highly branched (ca. 70–80/1000°C) polyethylenes with very high molecular weight (Mn up to 55.79 × 104 g/mol) and the resultant polyethylenes displayed characteristics of thermoplastic elastomers with excellent elastic recovery (SR up to 84%). Compared with some similar α-diimine Ni(II) catalysts, it is shown that the presence of axial remote tBu substituents not only facilitates the dissolution of the catalyst in alkanes, but also improves the elastic recovery value of the obtained polyethylene. 相似文献
Ring-opening copolymerization (ROCP) of benzylsulfonyl macroheterocyclosiloxane (BSM) and five different cyclosiloxanes was systematically investigated. A general approach for the synthesis of benzylsulfonyl-containing silicone copolymers with various substituents, including methyl, vinyl, ethyl, and phenyl, was developed herein. A series of copolymers with variable incorporation (from 6 % to 82 %) of BSM were obtained by modifying the comonomer feed ratio and using KOH as the catalyst in a mixed solvent of dimethylformamide and toluene. The obtained copolymers exhibited various composition-dependent properties and unique viscoelasticity. Notably, the surface and fluorescent characteristics as well as the glass transition temperatures of the copolymers could be tailored by varying the amount of BSM. Unlike typical sulfone-containing polymers, such as poly(olefin sulfone)s, the prepared copolymers displayed excellent thermal and hydrolytic stability. The universal strategy developed in the present study provides a platform for the design of innovative silicone copolymers with adjustable structures and performance. 相似文献
To tune purposefully the electronic structures of poly(carbosilylsilanes), a theory study has been investigated using the
density functional theory combined with AM1 method. Attentions were paid to the dependence of molecular geometries and absorption
spectra on the backbone conformation and the various substituting groups. The strong electronegative substituents can more
effectively tune the geometries and spectra of the polysilanes than the alkyl ones. Their main-chain substitutions can induce
the great red-shift of the absorption spectra, and the side-chain substitutions can induce the blue-shift. The length of methylene
chain in the carbosilyl groups exerts the small effect on the absorption spectra, but with the lengthening of side chain,
poly(carbosilylsilanes) have a preference for the all-trans conformation with the loose helix backbone. Different from the
alkyl side chain in poly(alkylsilanes), the lengthening of carbosilyl chain leads to the decrease of the positive charges
of silicon backbone. 相似文献
Two kinds of bismuth tungsten oxide nanocrystals were prepared by microwave hydrothermal method. The morphology modulation of nanocrystals synthesized with precursor suspension's pH varied from 0.25 (strong acid) to 10.05 (base) was studied. The 3D flower like aggregation of Bi2WO6 nanoflakes was synthesized in acid precursor suspension and the nanooctahedron crystals of Bi3.84W0.16O6.24 were synthesized in alkalescent precursor. The dominant crystal is changed from Bi2WO6 to Bi3.84W0.16O6.24 when the precursor suspension changes from acid to alkalescence. The growth mechanisms of Bi2WO6 and Bi3.84W0.16O6.24 were attributed to the different solubility of WO42− and [Bi2O2]2+ in precursor suspensions with various pH. For the decomposition of Rhodamine B (RhB) under visible light irradiation (λ>400 nm), different morphology of Bi2WO6 crystal samples obtained by microwavesolvothermal process showed different photocatalytic activity. 相似文献
Commercial PEG‐amine is of unreliable quality, and conventional PEG functionalization relies on esterification and etherification steps, suffering from incomplete conversion, harsh reaction conditions, and functional‐group incompatibility. To solve these challenges, we propose an efficient strategy for PEG functionalization with carbamate linkages. By fine‐tuning terminal amine basicity, stable and high‐fidelity PEG‐amine with carbamate linkage was obtained, as seen from the clean MALDI‐TOF MS pattern. The carbamate strategy was further applied to the synthesis of high‐fidelity multi‐functionalized PEG with varying reactive groups. Compared to with an ester linkage, amphiphilic PEG‐PS block copolymers bearing carbamate junction linkage exhibits preferential self‐assembly tendency into vesicles. Moreover, nanoparticles of the latter demonstrate higher drug loading efficiency, encapsulation stability against enzymatic hydrolysis, and improved in vivo retention at the tumor region. 相似文献
Cross‐linked silicone elastomers constructed with dynamic‐covalent boronic esters are first synthesized by photoinitiated radical thiol−ene “click” chemistry. The resultant samples can be cut with a sharp knife into two pieces and then healed via the reversibility of the boronic ester cross‐linkages to restore the original silicone sample within 30 min. Regulation of luminescent properties is achieved by incorporating organic dye into the elastomers through a “one‐pot” thiol–ene reaction. The proposed synthesis procedure demonstrates a new strategy to produce boronic acid silicone materials capable of self‐healing without external forces.