温度,压力对多省并醌类聚合物导电性能的影响

以氯化锌为催化剂，利用多环芳烃蒽，芘等的不同酸酐如１，２，４，５－均苯四甲酸二酐，四氯苯酐等，在３０６℃逐步聚合得到多省并醌类聚合物，仔细纯化后在不同温度，压力下对其他电导率进行了测量，研究了温度，压力对其电导率的影响。     

γ′‐Selective Functionalization of Cyclic Enones: Construction of a Chiral Quaternary Carbon Center by [4+2] Cycloaddition/Retro‐Mannich Reaction with 3‐Substituted Maleimides

The first example of organocatalyzed γ′‐selective functionalization of cyclic enones with 3‐substituted maleimides results in the stereoselective construction quaternary carbon center is presented. The reactions provided γ′‐functionalized cyclic enones and β‐functionalized cyclopentenones in good to excellent yields with excellent diastereo‐ and enantioselectivities. DFT calculations indicated that the reaction might proceed as a [4+2] cycloaddition/retro‐Mannich reaction which could explain the unexpected product with a chiral quaternary carbon center and the excellent stereoselectivity.     

Change of adsorption modes of dyes on fluorinated TiO2 and its effect on photocatalytic degradation of dyes under visible irradiation

Surface-fluorinated TiO2 (F-TiO2) particles were prepared via the HF etching method. The surface characteristics of fluorinated TiO2, the adsorption modes of dyes, and the reaction pathways for the photocatalytic degradation of dye pollutants under visible light irradiation were investigated. It was found that, in the treatment of TiO2 by HF etching, F(-) not only displaces surface HO(-) but also substitutes some surface lattice oxygen. Using zwitterionic Rhodamine B (RhB) dye as a model, the change of the adsorption mode of RhB on F-TiO2 relative to that on pure TiO2 was validated by adsorption isotherms, X-ray photoelectron spectroscopy (XPS), and IR techniques for the first time. RhB preferentially anchors on pure TiO2 through the carboxylic (-COOH) group, while its adsorption group is switched to the cationic moiety (-NEt 2 group) on F-TiO2. Both the photocatalytic degradation kinetics and mechanisms were drastically changed after surface fluorination. Dyes with positively charged nitrogen-alkyl groups such as methylene blue (MB), malachite green (MG), Rhodamine 6G (Rh6G), and RhB all underwent a rapid N-dealkylation process on F-TiO2, while on pure TiO2 direct cleavage of dye chromophore ring structures predominated. The relationship between surface fluorination and the degradation rate/pathway of dyes under visible irradiation was also discussed in terms of the effect of fluorination on the surface adsorption of dyes and on the energy band structure of TiO2.     

Single-Atom Nickel on Carbon Nitride Photocatalyst Achieves Semihydrogenation of Alkynes with Water Protons via Monovalent Nickel

Prospects in light-driven water activation have prompted rapid progress in hydrogenation reactions. We describe a Ni²⁺−N₄ site built on carbon nitride for catalyzed semihydrogenation of alkynes, with water supplying protons, powered by visible-light irradiation. Importantly, the photocatalytic approach developed here enabled access to diverse deuterated alkenes in D₂O with excellent deuterium incorporation. Under visible-light irradiation, evolution of a four-coordinate Ni²⁺ species into a three-coordinate Ni⁺ species was spectroscopically identified. In combination with theoretical calculations, the photo-evolved Ni⁺ is posited as HO−Ni⁺−N₂ with an uncoordinated, protonated pyridinic nitrogen, formed by coupled Ni²⁺ reduction and water dissociation. The paired Ni−N prompts hydrogen liberation from water, and it renders desorption of alkene preferred over further hydrogenation to alkane, ensuring excellent semihydrogenation selectivity.     

Inverse Kinetic Solvent Isotope Effect in TiO2 Photocatalytic Dehalogenation of Non‐adsorbable Aromatic Halides: A Proton‐Induced Pathway

An efficient redox reaction between organic substrates in solution and photoinduced h⁺_vb/e^?_cb on the surface of photocatalysts requires the substrates or solvent to be adsorbed onto the surface, and is consequentially marked by a normal kinetic solvent isotope effect (KSIE≥1). Reported herein is a universal inverse KSIE (0.6–0.8 at 298 K) for the reductive dehalogenation of aromatic halides which cannot adsorb onto TiO₂ in a [D₀]methanol/[D₄]methanol solution. Combined with in situ ATR‐FTIR spectroscopy investigations, a previously unknown pathway for the transformation of these aromatic halides in TiO₂ photocatalysis was identified: a proton adduct intermediate, induced by released H⁺/D⁺ from solvent oxidation, accompanies a change in hybridization from sp² to sp³ at a carbon atom of the aromatic halides. The protonation event leads these aromatic halides to adsorb onto the TiO₂ surface and an ET reaction to form dehalogenated products follows.     

Direct Catalytic Asymmetric Doubly Vinylogous Michael Addition of α,β‐Unsaturated γ‐Butyrolactams to Dienones

An asymmetric doubly vinylogous Michael addition (DVMA) of α,β‐unsaturated γ‐butyrolactams to sterically congested β‐substituted cyclic dienones with high site‐, diastereo‐, and enantioselectivity has been achieved. An unprecedented DVMA/vinylogous Michael addition/isomerization cascade reaction affords chiral fused tricyclic γ‐lactams with four newly formed stereocenters.     

Solid–Liquid Phase Equilibria in the Ternary Systems (LiBO 2 + NaBO 2 + H 2 O) and (LiBO 2 + KBO 2 + H 2 O) at 288.15 K and 0.1 MPa

Solid–liquid phase equilibria for the two aqueous systems (LiBO2 + NaBO2 + H2O) and (LiBO2 + KBO2 + H2O) at T = 288.15 K and p = 0.1 MPa were determined using the isothermal dissolution equilibrium method. The experimental results show that the phase diagrams consist of one two-salt co-saturated invariant point, two univariant solubility isotherms, and three crystallization fields. The two systems belong to simple co-saturated type, and neither double salt nor solid solution were found. The densities change regularly as the sodium metaborate (potassium metaborate) concentration increases in solution, and reach their maximum values at the invariant point. Based on the Pitzer and its extended Harvie–Møller–Weare (HMW) model, the solubilities for the ternary systems at 288.15 K were represented, and the calculated results agree well with the experimental values.     

Synthesis of high‐impact biodegradable multiblock copolymers comprising of poly(butylene succinate) and poly(1,2‐propylene succinate) with hexamethylene diisocyanate as chain extender

Block copolymers demonstrate excellent thermal and mechanical properties superior to their corresponding random copolymers and homopolymers. However, it is difficult to synthesize block copolymers comprising of different polyester segments by copolycondensation due to the serious transesterification reaction. In this study, multiblock copolymers comprising of two different polyester segments, i.e. crystallizable poly(butylene succinate) (PBS) and amorphous poly(1,2‐propylene succinate) (PPSu), were synthesized by chain‐extension with hexamethylene diisocyanate (HDI). Amorphous PPSu segment was incorporated to improve the impact strength of PBS. The copolymers were characterized by GPC, laser light scattering (LLS), NMR, DSC, and mechanical testing. The results of ¹³C NMR spectra suggest that multiblock copolymers with regular sequential structure have been successfully synthesized. The data of DSC and mechanical testing indicate that block copolymers possess excellent thermal and mechanical properties with satisfactory tensile strength and extraordinary impact strength achieving upto 1900% of pure PBS. The influence of PPSu ratio and chain length of both the segments on the thermal and mechanical properties was investigated. The incorporation of an amorphous soft segment PPSu imparts high‐impact resistance to the copolymers without obviously decreasing the melting point (T_m). The favorable mechanical and thermal properties of the copolymers also depend on their regular sequential structure. At the same time, the introduction of amorphous PPSu segment enhances the enzymatic degradation rate of the multiblock copolymers. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrophoresis of Bottle‐Brush Polyelectrolytes in an Attractive Nanochannel

A molecular dynamics study of the electrophoresis of bottle‐brush polyelectrolytes (BPEs) through nanochannels is reported. The BPE molecules consist of a neutral backbone with charged side chains. For strong attractive interactions between the BPE and the wall, the BPE is being trapped on the channel surface. A stretching–shrinking migration of the BPE in a channel of radius 6σ is observed at relatively strong electric fields. The stretching–shrinking transition is periodic for intermediate electric fields but not for stronger electric fields. The BPE also shows a transverse migration toward the wall at weak electric fields, while toward the center with further enhancing the electric field. For a channel with larger radius 12σ, the BPE does not migrate in the stretching–shrinking manner.