含胆酸高分子化合物的制备和特性*

胆酸是哺乳动物体内合成的一种天然化合物,具有特殊的分子结构和优良的生物适应性。由胆酸合成的高分子化合物保持了胆酸的部分性质,如双亲性、手性、侧基反应活性和自组装性能等。在化学和药学领域,含胆酸高分子材料具有重要的应用价值。本文从自由基聚合形成的含胆酸高分子化合物、胆酸修饰的高分子化合物和胆酸聚合物等几个方面综述了含胆酸高分子化合物的制备和特性,并对胆酸在高分子材料方面的新用途作了展望。     

1,3,5,5-tetraphenyl-Δ3-1,2,4-triazolin-2-yl radical–properties in the controlled radical polymerization of poly(methyl methacrylate) and polystyrene

The triazoline derivative 1 was used as an additive in the chain-growth controlled radical polymerization of vinylic monomers to afford narrowly distributed polymers. This new system is applicable to styrene as well as to methacrylates. The monomer consumption and the variation of the molar mass were monitored with time. Thermal properties of the obtained polymers were also studied. After isolation of the polymers, the growth of the chains was re-initiated in the presence of a second monomer and yielded block copolymers.     

Effects of stereochemistry and β-substituents on the rates of vinylic SN2 reaction of hypervalent vinyl(phenyl)-λ-iodanes with tetrabutylammonium halides

Both stereoisomers of β-(2-phenylethoxy)vinyl-λ³-iodane and (Z)-β-aroyloxyvinyl-λ³-iodane were prepared stereoselectively. These substituted vinyl-λ³-iodanes undergo nucleophilic vinylic substitutions with n-Bu₄NX (X=Cl, Br, I) under mild conditions, yielding vinyl halides. The observed inversion of configuration at the ipso vinylic carbon atom is compatible with a concerted vinylic S_N2 mechanism. Kinetic measurements indicated that the rates for vinylic S_N2 reaction of (Z)-vinyl-λ³-iodane are greater than those of the E-isomer, probably because of the higher ground state energy of the Z-isomer. Electronic effects of β-substituents of vinyl-λ³-iodanes in the vinylic S_N2 reaction are also discussed.     

A novel synthesis of functionalized 1,1-difluoro-1-alkenes via isolable 2,2-difluorovinylsilanes

Various 1,1-difluoro-1-alkenes such as monosubstituted 1,1-difluoro-1-alkenes, 2-bromo-1,1-difluoro-1-alkenes, and 1,1-difluoro-3-hydroxy-1-alkenes are prepared in two simple steps from 1-trifluoromethylvinylsilane: (i) its S_N2′ reaction with nucleophiles to construct 2,2-difluorovinylsilanes and (ii) the subsequent substitution of electrophiles for the vinylic silyl group.     

Synthesis of hetero- and carbocycles by nucleophilic substitution at sp carbon

Vinylic halides having alcohol, sulfonamide, active methine, and thiol moieties as nucleophiles cyclize to hetero- and carbocycles by intramolecular nucleophilic substitution at the sp² carbon centers. The density functional theory calculations suggest that the cyclization proceeds through S_N2-type substitution (the in-plane vinylic nucleophilic substitution, S_NVσ), when vinyl halides are substituted with oxygen, nitrogen, and carbon nucleophiles. The substitution with sulfur nucleophiles, in contrast, proceeds through both routes of S_NVσ and out-of-plane vinylic nucleophilic substitution (S_NVπ).     

Versatile Supramolecular Cross‐Linker: A Rotaxane Cross‐Linker That Directly Endows Vinyl Polymers with Movable Cross‐Links

A supramolecular cross‐linked cross‐linker, capable of introducing rotaxane cross‐links to vinyl polymers, has been developed for the rational synthesis of polyrotaxane networks. The experimental results reveal that the combination of an oligocyclodextrin (OCD) and a terminal bulky group‐tethering macromonomer (TBM) forms a polymer‐network structure having polymerizable moieties through supramolecular cross‐linking. Radical polymerization of a variety of typical vinyl monomers in the presence of the vinylic supramolecular cross‐linker (VSC) afforded the corresponding vinyl polymers cross‐linked through the rotaxane cross‐links (RCP) as transparent stable films in high yields under both photoinitiated and thermal polymerization conditions. A poly(N,N‐dimethylacrylamide)‐based hydrogel synthesized by using VSC, RCP_DMAAm, displayed a unique mechanical property. The small‐angle X‐ray scattering (SAXS) results, indicating patterns characteristic of a polyrotaxane network, clearly suggested the presence and role of the rotaxane cross‐links. The confirmation of the introduction of rotaxane‐cross‐links into vinyl polymers strongly reveals the significant usefulness of VSC.     

CuSO4-catalyzed self-initiated radical polymerization of 2-(N,N-dimethylamino) ethyl methacrylate as an intrinsically reducing inimer

Since tertiary amines (Cα-H) can be oxidized by peroxides and transition metal cations in high oxidation states into Cα· radicals to initiate vinylic polymerizations of methacrylates, Cu2+ and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) form a polymerizable redox initiating pair, in which DMAEMA serves as an intrinsically reducing inimer. CuSO4 -catalyzed aqueous self-initiated radical polymerizations of DMAEMA were successfully performed at ambient temperature via a continuous Cu2+-tertiary amine redox initiation based on catalyst regeneration in the presence of O2 . The polymerization kinetics was monitored by gas chromatography and the structure of PDMAEMA was characterized by gelpermeation chromatography, nuclear magnetic resonance spectroscopy, laser light scattering and online intrinsic-viscosity analysis. Both the monomer conversion and the molecular weight of PDMAEMA increase with the reaction while the molecular weight distribution maintains rather broad, as the Cu2+-DMAEMA redox-initiation leads to linear PDMAEMA chains with terminal methacryloxyl moieties, and the Cu2+-PDMAEMA redox-initiation results in branched chains. The branched topology forms and develops only for the high-MW components of the PDMAEMA. Our results provide a facile strategy to prepare branched polymers from such commercially available intrinsically reducing inimers using a negligible concentration of regenerative air-stable catalysts.     

Programming Photodegradability into Vinylic Polymers via Radical Ring-Opening Polymerization

Incorporation of photolabile moieties into the polymer backbone holds promise to remotely-control polymer degradation. However, suitable synthetic avenues are limited, especially for radical polymerizations. Here we report a strategy to program photodegradability into vinylic polymers by exploiting the wavelength selectivity of photocycloadditions for radical ring-opening polymerization (rROP). Irradiation of coumarin terminated allylic sulfides with UVA light initiated intramolecular [2+2] photocycloaddition producing cyclic macromonomers. Subsequent RAFT-mediated rROP with methyl acrylate yielded copolymers that inherited the photoreactivity of the cyclic parent monomer. Irradiation with UVB initiated efficient photocycloreversion of the coumarin dimers, causing polymer degradation within minutes under UVB light or days under sunlight exposure. Our synthetic strategy may pave the way to insert photolabile linkages into vinylic polymers, tuning degradation for specific wavelengths.     

Controlled macromolecular synthesis by the nucleophile/lewis acid binary systems

Amphiphilic initiator systems consisting of bulky nucleophiles as propagating species and bulky electrophiles (Lewis acids) as monomer activators bring about high-speed living anionic polymerization of polar vinylic and heterocyclic monomers to give narrow molecular weight distribution (MWD) polymers.     

Carboboration-Driven Generation of a Silylium Ion for Vinylic C−F Bond Functionalization by B(C6F5)3 Catalysis

Strong main-group Lewis acids such as silylium ions are known to effectively promote heterolytic C(sp³)−F bond cleavage. However, carrying out the C(sp²)−F bond transformation of vinylic C−F bonds has remained an unmet challenge. Herein, we describe our development of a new and simple strategy for vinylic C−F bond transformation of α-fluorostyrenes with silyl ketene acetals catalyzed by B(C₆F₅)₃ under mild conditions. Our theoretical calculations revealed that a stabilized silylium ion, which is generated from silyl ketene acetals by carboboration, cleaves the C−F bond of α-fluorostyrenes. A comparative study of α-chloro or bromostyrenes demonstrated that our reaction can be applied only to α-fluorostyrenes because the strong silicon-fluorine affinity facilitates an intramolecular interaction of silylium ions with fluorine atom to cleave the C−F bond. A broad range of α-fluorostyrenes as well as a range of silyl ketene acetals underwent this C−F bond transformation.     

Surface modification. II. Functionalization of solid surfaces with vinylic monomers

A new method to functionalize surfaces of solid substrates such as glass, silicon crystals, and silica microspheres with appropriate vinylic monomers, i.e., methyl vinyl ketone, methyl acrylate, methacrolein, and acrolein, is described. The surface modification process was performed through the following sequence of reactions: (a) derivatization of the surfaces with to-nitrile groups by interacting the substrates with SiCl₃(CH₂)₃CN; (b) subsequent reduction of the a)-nitrile groups with diborane to w-amine groups; (c) binding of the vinylic monomers to the surfaces via the to-amine groups. pK_1/2 of the surface primary amine groups, as determined by contact angle titration, was found to be 2–4 units lower than the pK_1/2 values of primary amine analogous in solution. Methyl vinyl ketone and methyl acrylate were covalently bound to the amine surfaces only under basic conditions via the Michael addition reaction. Methacrolein and acrolein were covalently bound to the amine surfaces under both acidic and basic conditions via two major reactions: the Michael addition reaction and Schiff base bond formation. The concentration of the aldehyde groups of the surfaces obtained by the reaction with methacrolein and acrolein was significantly higher than that obtained using the common, published method in which glutaraldehyde interacts with the amine surfaces.     

Stannylated polynorbornenes as new reagents for a clean Stille reaction

New functionalized polynorbornenes have been obtained in good yields by vinylic copolymerization of norbornene with a (norbornenyl)SnBu(2)Cl monomer, catalyzed by [Ni(C(6)F(5))(2)(SbPh(3))(2)]. Subsequent functionalization produces a wide variety of polymers with different --SnBu(2)R groups (R=aryl, vinyl, alkynyl). The polymers can be used as R-transfer reagents in Stille couplings, thereby providing easy workup and separation of the polymeric tin byproducts from the coupling products. Tin contents of around 0.05 wt % are found in the Stille products. The stannylated polymers can be recycled and reused with good efficiency.     

新型功能性超支化聚酯的合成及表征

近年来 ,树枝状和超支化聚合物的研究受到了广泛重视 ,被视为 2 1世纪聚合物科学发展的重要方向[1] .这两种聚合物都有大量的端基 ,与相同分子量的线型聚合物相比 ,它们具有更低的粘度和更好的溶解性 .树枝状聚合物具有规整的结构 ,但合成困难 ;超支化聚合物的支化结构不完整 ,可以通过简单的一步聚合获得 ,因此 ,后者受到更广泛的重视 ,也最有可能实现工业化 [2 ,3] .通常 ,超支化聚合物是通过 ABx(x≥ 2 )型单体的缩聚合成的 ,通过改变超支化聚合物的组成、结构及对其端基进行功能修饰 ,可以制备多种具有特殊用途的新材料 ,在粘度改性剂…     

Hydride‐Rhodium(III)‐N‐Heterocyclic Carbene Catalysts for Vinyl‐Selective H/D Exchange: A Structure–Activity Study

A series of neutral and cationic Rh^III‐hydride and Rh^III‐ethyl complexes bearing a NHC ligand has been synthesized and evaluated as catalyst precursors for H/D exchange of styrene using CD₃OD as a deuterium source. Various ligands have been examined in order to understand how the stereoelectronic properties can modulate the catalytic activity. Most of these complexes proved to be very active and selective in the vinylic H/D exchange, without deuteration at the aromatic positions, displaying very high selectivity toward the β‐positions. In particular, the cationic complex [RhClH(CH₃CN)₃(IPr)]CF₃SO₃ showed excellent catalytic activity, reaching the maximum attainable degree of β‐vinylic deuteration in only 20 min. By modulation of the catalyst structure, we obtained improved α/β selectivity. Thus, the catalyst [RhClH(κ²‐O,N‐C₉H₆NO)(SIPr)], bearing an 8‐quinolinolate ligand and a bulky and strongly electron‐donating SIPr as the NHC, showed total selectivity for the β‐vinylic positions. This systematic study has shown that increased electron density and steric demand at the metal center can improve both the catalytic activity and selectivity. Complexes bearing ligands with very high steric hindrance, however, proved to be inactive.     

Knitting N‐doped Hierarchical Porous Polymers to Stabilize Ultra‐small Pd Nanoparticles for Solvent‐Free Catalysis

Hierarchical porous polymers with more than one pore size distributions can effectively support noble metal catalysts and circumvent the limitation of the diffusion of the reactants, and thus exhibit both excellent catalytic activity and superior diffusive properties. Herein, we report a simple one‐step Friedel–Crafts reaction to knit a series of benzene heterocycle monomers, such as indane, indoline, indole and tetrahydronaphthalene to obtain hierarchical porous polymers with high surface areas and/or abundant N sites. These polymers can be directly used to immobilize Pd ions, and stabilize Pd nanoparticles during the thermal reduction process to obtain Pd/polymer catalysts. In particular, indoline‐ and indole‐based polymers with high N content up to 7 wt % exhibit outstanding ability to stabilize uniform ultrasmall Pd nanoparticles. The obtained Pd‐polymers exhibit excellent catalytic activity in the solvent‐free oxidation of benzyl alcohol with O₂.     

Cyclopropanation of Terminal Alkenes through Sequential Atom‐Transfer Radical Addition/1,3‐Elimination

An operationally simple method to affect an atom‐transfer radical addition of commercially available ICH₂Bpin to terminal alkenes has been developed. The intermediate iodide can be transformed in a one‐pot process into the corresponding cyclopropane upon treatment with a fluoride source. This method is highly selective for the cyclopropanation of unactivated terminal alkenes over non‐terminal alkenes and electron‐deficient alkenes. Due to the mildness of the procedure, a wide range of functional groups such as esters, amides, alcohols, ketones, and vinylic cyclopropanes are well tolerated.     

Metallocene monomers and polymers. Ferrocenyl and ferrocenylene derivatives

The synthesis and study of some polyenes, polýiminoimides and Schiff polybases with ferrocene obtained by either polymerization or polycondensation are reported.The following monomers were used: ethynylferrocene, 1-chloro-1′-ethynyl-ferrocene, α-chloro-β-formyl-p-ferrocenylstyrene, p-ferrocenylphenylacetylene, p-ferrocenylacetophenone, 1,1′-diacetylferrocene and 1,1′-bis[β-(2-furyl)acryloyl]ferrocene which were characterized by spectral and thermodifferential analyses and Hückel MO calculations. The polymerization was performed in the presence of benzoyl and lauroyl peroxides, triisopropylboron and complex catalysts of [P(C₆H₅)₃]₂ NiX₂ type. The ferrocene derivatives were polycondensed with biuret, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl thioether, 4,4′-diamino-2,2′-dinitrodiphenyl disulphide in the presence of metallic salts and p-toluene sulphonic acid as catalysts.Polymers with either linear or tridimensional structure showing good thermal stability and semiconducting properties have been obtained. Some polymers show catalytical activity in the polymerization of chloroformylated vinylic derivatives.     

Recent Development of Hypercrosslinked Microporous Organic Polymers

Hypercrosslinked polymers (HCPs) are currently receiving great interest due to their easy preparation, high chemical and thermal stability, and low cost. Combined with the lightweight properties and high surface areas HCPs can be considered as promising materials for gas storage and separation, catalysis, and heavy metal ions removal in wastewater treatment. This Feature Article summarizes strategies for the preparation of HCPs, comprising the post‐crosslinking of “Davankov‐type” resins, direct polycondensation of aromatic chloromethyl (or hydroxymethyl) monomers, and knitting aromatic compound polymers (KAPs). The HCPs applications, such as H₂ storage, CO₂ capture, and heterogeneous catalysis, are also discussed throughout in the article. Finally, the outlook of this research area is given.     

High‐Performance Polymers for Membrane CO2/N2 Separation

This Concept examines strategies to design advanced polymers with high CO₂ permeability and high CO₂/N₂ selectivity, which are the key to the success of membrane technology for CO₂ capture from fossil fuel‐fired power plants. Specifically, polymers with enhanced CO₂ solubility and thus CO₂/N₂ selectivity are designed by incorporating CO₂‐philic groups in polymers such as poly(ethylene oxide)‐containing polymers and poly(ionic liquids); polymers with enhanced CO₂ diffusivity and thus CO₂ permeability are designed with contorted rigid polymer chains to obtain high free volume, such as polymers with intrinsic microporosity and thermally rearranged polymers. The underlying rationales for materials design are discussed and polymers with promising CO₂/N₂ separation properties for CO₂ capture from flue gas are highlighted.     

Sonogashira cross-coupling reaction of organotellurium dichlorides with terminal alkynes

The Sonogashira cross-coupling reaction of vinylic and heteroaromatic tellurium dichlorides has been explored, yielding the corresponding enynes and 2-alkynyl substituted heteroaromatic compounds. The reaction was carried out with PdCl₂/CuI as catalysts and triethylamine as base, using methanol as solvent. The reaction proceeded under mild conditions and the cross-coupled products were obtained in good yields and in a stereoconservative manner.