含氟液晶研究进展

本文简述了含氟液晶的研究进展。根据小分子含氟液晶中氟原子或含氟基团的位置不同,将其分为3类：末端是氟原子或含氟基团的液晶、苯环上氢原子被氟原子取代的液晶、中心桥键上的氢原子被氟原子取代的液晶。根据小分子含氟液晶特点,归纳了氟原子或含氟基团对液晶分子物理性质的影响。同时对高分子含氟液晶的研究进展也做了介绍。     

New fluorinated aromatic poly(ether-amide)s derived from 2,2′-bis(3,4,5-trifluorophenyl)-4,4′-diaminodiphenyl ether and various dicarboxylic acids

A new class of highly fluorinated aromatic poly(ether-amide)s was prepared through triphenyl phosphite-activated polycondensation of 2,2′-bis(3,4,5-trifluorophenyl)-4,4′-diaminodiphenyl ether (FPAPE) and four dicarboxylic acid comonomers. All the resulting polymers were thoroughly characterized by FT-IR, UV, and NMR spectroscopic methods. The effects of the fluorine atoms directly linked to the lateral phenyl rings as well as fluoro-containing phenyl groups attached to the macromolecular chains on some properties of the polymers were investigated by comparing with poly(ether-amide)s prepared from 4,4′-oxydianiline (4,4′-ODA) and 2,2′-diphenyl-4,4′-diaminodiphenyl ether (PAPE). The FPAPE-derived polymers exhibited excellent solubility in a variety of organic solvents. Results obtained from X-ray studies showed that the presence of the bulky fluoro-containing phenyl groups attached to the chains disrupts their structural order in a great amount, and leads to a decrease in crystallinity extent of the macromolecules. Furthermore, the highly fluorinated polymeric chains showed a significant enhancement in organo-solubility, heat-stability and T_g values when compared to their non-fluorinated counterparts.     

Rearrangement routes to selectively fluorinated compounds

Fluoroallylic alcohols are easy to synthesise by a variety of routes using one or two carbon fluorinated building blocks. Sigmatropic rearrangement then transforms these intermediates into species in which the fluorine atom (or atoms) is borne on an sp³-hybridised carbon. Alternatively, allylic alcohols can be transformed into fluorinated vinyl ether derivatives; rearrangement then affords products in which the fluorine atoms occupy a different and complementary location with respect to a carbonyl function.     

Morphology of the surface layer of polymers modified by gaseous fluorine

A change in the surface structure of low-density polyethylene films upon chemical modification by gaseous fluorine has been studied by scanning electron microcopy and X-ray spectral analysis. It has been demonstrated that this treatment leads to formation of the wavy surface; its characteristics depend on the method of polymer synthesis and the initial structure of the test sample. A possible mechanism for structural changes in the surface layer of the polymer during fluorination is considered. It is suggested that the molar volume and the configuration of polymer macromolecules change in the course of replacement of hydrogen atoms with fluorine atoms. Mathematical modeling has been performed for the formation of the fluorinated layer with due regard for chemical transformations of macromolecules and structural heterogeneity of the polymers. The isosurfaces of the polymer with various degrees of fluorination calculated within the framework of the above model indicate that the fluorinated layer being formed is characterized by unequal thickness due to different rates of fluorine diffusion in amorphous and crystalline regions. It has been shown that the degree of fluorination of the polymer is dependent on the duration of treatment. This relationship is in satisfactory agreement with the previous experimental data.     

Systematic Studies on the Effect of Fluorine Atoms in Fluorinated Tolanes on Their Photophysical Properties

In this study, we synthesized a series of fluorinated and non-fluorinated tolanes, in which one or more fluorine atoms were systematically introduced into one aromatic ring of a tolane scaffold, and systematically evaluated their photophysical properties. All the tolanes with or without fluorine substituents were found to have poor photoluminescence (PL) in tetrahydrofuran (THF) solutions. On the other hand, in the crystalline state, non-fluorinated and fluorinated tolanes with one or four fluorine atoms were less emissive, whereas fluorinated tolanes with three or five fluorine atoms exhibited high PL efficiencies (Ф_PL) up to 0.51. X-ray crystallographic analyses of the emissive fluorinated tolanes revealed that the position of the fluorine substituent played a key role in achieving a high Ф_PL. Fluorine substituents at the ortho (2/6) and para (4) positions led to tight and rigid packing due to plural π–π stacking and/or hydrogen bonding interactions, resulting in enhanced Ф_PL caused by the suppression of non-radiative deactivation. Additionally, fluorinated tolanes with three fluorine atoms exhibited notable aggregation-induced PL emission enhancement in THF/water mixed solvents. This demonstrates that the PL characteristics of small PL materials can be tuned depending on the usage requirements.     

Surface properties of fluorinated single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) were fluorinated at several different temperatures. The change of atomic and electronic structures of fluorinated SWCNTs was investigated using X-ray photoelectron spectroscopy (XPS), electrical resistivity measurements and transmission electron microscopy (TEM). The amount of doped fluorine increases with increasing doping temperature, and the fluorine atoms are covalently attached to the side-wall of the SWCNTs. From Raman spectra and HRTEM study, the strong fluorination on the SWCNTs leads to the breaking of carbon–carbon bonds and the disintegration of tube structure. Several intermediate phases of fluorinated SWCNTs are observed during e-beam irradiation in HRTEM.     

Fluorinated Rings: Conformation and Application

The introduction of fluorine atoms into molecules and materials across many fields of academic and industrial research is now commonplace, owing to their unique properties. A particularly interesting feature is the impact of fluorine substitution on the relative orientation of a C−F bond when incorporated into organic molecules. In this Review, we will be discussing the conformational behavior of fluorinated aliphatic carbo- and heterocyclic systems. The conformational preference of each system is associated with various interactions introduced by fluorine substitution such as charge-dipole, dipole-dipole, and hyperconjugative interactions. The contribution of each interaction on the stabilization of the fluorinated alicyclic system, which manifests itself in low conformations, will be discussed in detail. The novelty of this feature will be demonstrated by presenting the most recent applications.     

Surface tension of fluoroalkanes in a liquid phase

The parachor assigned to fluorine atoms in fluorinated alkanes was examined. The values vary systematically with the number of fluorine atoms in the molecule. Partially fluorinated alkanes show large values, while perfluoroalkanes give a smaller value which is constant for all the perfluoroalkanes examined in this work. The molecular structure seems to be important for the intermolecular interaction of this series of compounds, and may be responsible for the deviation from the parachor additivity rule.     

聚(对亚苯基-1,3,4-噁二唑)纤维表面氟化处理研究

采用氟气(F2)对聚(对亚苯基-1,3,4-噁二唑)(p-POD)纤维表面进行直接氟化处理.衰减全反射红外光谱(ATR-FTIR)和表面电子能谱(XPS)的结果显示,通过直接氟化处理,p-POD纤维较易与F2发生反应,表面大分子链上引入了大量C—F键,表面氟元素含量高达28.2%,且F原子以—CF/C O、—CFH及—CF2形式存在,表明在表面氟化过程中,既有取代反应,也有加成反应.热失重(TGA)结果表明氟化前后p-POD纤维的耐高温性能没有受到影响,X射线衍射图谱(XRD)表明氟化后纤维的聚集态有序性略微增加.氟化前后纤维的断裂强度基本无变化,在体积分数为20%的硫酸溶液中的人工加速酸老化条件下,氟化后纤维在老化120 h后的断裂强力保留率在80%以上,相比氟化前的纤维提高了约90%,即耐酸性得到明显改善.推测表面氟化处理改善p-POD纤维耐酸性的机理是氟化后p-POD纤维表面N元素含量降低,抑制了溶剂化过程;纤维表面致密程度得到提高以及F原子与酸液形成氢键,从而阻止噁二唑环的质子化,延缓了老化进程.     

氟取代聚芳醚酮低温合成及其结构研究

通过傅克酰基化反应合成4,4'-二(4-氟苯甲酰基)二苯醚、4,4'-二(五氟苯甲酰基)二苯醚、4,4'-二(4-氟苯甲酰基)二苯硫醚以及4,4'-二(五氟苯甲酰基)二苯醚4种长链双卤单体,并进一步制备了含二氮杂萘酮聚芳醚酮聚合物.通过多氟取代双卤单体在含二氮杂萘酮聚芳醚酮聚合物主链中引入氟原子.多氟取代双卤单体具有多...     

Carbon-Fluorine Bondings of Fluorinated Fullerene and Graphite

Carbon-fluorine bondings of fluorinated fullerenes and fluorine-graphite intercalation compound C_xF were investigated in detail on the basis of XPS data and the potential model using the charge distribution calculated by semiempirical method. It has been confirmed by the present study that two peaks in the C_1s spectra observed for fluorinated fullerenes are assigned to carbon atoms bonded to fluorine atoms and those unbound to fluorine atoms, and the small difference in charges and Madelung potentials of fluorine atoms in different circumstances well explains the single peak in F_1s spectra of fluorinated fullerenes. In the calculated structures of 1,3-C₆₀F₂ and 1,2-C₆₀F_x (x = 2?6) used as the models of C_xF, three kinds of carbon-fluorine bondings were observed corresponding to nearly ionic, semicovalent and covalent C? F bondings. The calculated result supports that the bi-intercalation structure of stage 1 C_xF consists of nearly ionic and semi-covalent fluorines.     

Some new approaches to modifying aromatic and heteroaromatic compounds by means of fluorine-containing substituents

Modification of physiologically active substances by means of fluorine atoms or fluoroalkyl groups is known in numerous cases to lead to compounds with a markedly higher activity. The optimum change in the properties is considered to be achieved by inserting 1-3 fluorine atoms into the molecule. Therefore modifications of compounds by such groups as CHF₂, CF₃, CH₂F are most frequently used in synthesis of fluorine-containing pharmaceutical and agricultural chemicals.

At the same time, the data obtained in recent years indicate the existence of some others regularities. Thus, in a number of cases highly active drugs have been revealed among highly fluorinated substances containing polar groups of atoms in the molecule. The physiological activity of fluorine-containing compounds seems to be determined not so much by the degree of fluorination as by the relationship between the hydrophobic and the hydrophilic properties. This conclusion is quite justified, since it is the compound's lipophilic-hydrophilic balance that determines its transport in biosystems and the possibility of the interaction with the lipoprotein sites of biomembranes. Moreover, compounds with a heightened fluorine con-     

Recent Advances in the One‐Step Synthesis of Distally Fluorinated Ketones

Fluorinated ketones are intriguing compounds in synthetic chemistry and life science‐related fields. The development of efficient methodologies to obtain these compounds is of significant importance and has therefore attracted considerable attention. This Minireview highlights recent progress made in the synthesis of fluorine‐containing ketones, with an emphasis on those methods in which the construction of carbonyl groups is synergetic with distal (β‐, γ‐, δ‐, etc.) incorporation of fluorine atoms or fluorinated groups.     

Synthesis of gemini surfactants with twelve symmetric fluorine atoms and one singlet F MR signal as novel F MRI agents

A family of fluorinated gemini surfactants derived from perfluoropinacol has been synthesized as novel ¹⁹F magnetic resonance imaging (¹⁹F MRI) agents. These fluorinated surfactants with 12 symmetric fluorine atoms and one singlet ¹⁹F MR peak can be conveniently prepared from perfluoropinacol and oligo(ethylene glycols) on multi-gram scales. Solubility, hydrophilicity (log P), and critical micelle concentration (CMC) measurements of these fluorinated surfactants indicated that high aqueous solubility can be achieved by introducing oligo(ethylene glycols) with appropriate length into perfluoropinacol, i.e., manipulating the fluorine content (F%). One of these fluorinated surfactants with high aqueous solubility and excellent ¹⁹F MR properties has been identified by ¹⁹F MRI phantom experiments as a promising ¹⁹F MRI agent.     

Langmuir monolayers and the transferred films of fluorinated amphiphiles containing vinyl groups

The monolayer behavior of long-chain esters of acrylic and methacrylic acids containing perfluoro or partially fluorinated carbon chains at the air/water interface was studied by surface pressure-area isotherm measurements and Brewster angle microscopy. It has been found that a minor change in the chemical structures of these fluorinated amphiphiles, such as a hydrogen substituted at the omega-position of the hydrophobic fluorocarbon tails instead of a fluorine as well as hydrophilic vinyl ester groups inserted between acrylates and methacrylates, induces a drastic change in the isotherms for the monolayers, suggesting different molecular orientation and packing in the films. The monolayers were transferred by horizontal lifting, Langmuir-Blodgett, and surface-lowering methods to give the X-, Y-, and Z-type films, respectively. These films were characterized by scanning probe microscopy, to clarify the mesoscopic surface structures of the molecular films exposed with the hydrophilic or hydrophobic moieties in air, depending upon the dipping methods. The Z-type films with the outermost surface of the fluorinated substituents were examined in relation to the frictional properties that strongly depend upon the fluorine and the hydrogen atoms at the end of the hydrophobic fluorocarbon chains, which is controllable at the atomic level.     

Electrochemical stability and transformations of fluorinated poly(2,6-dimethyl-1,4-phenylene oxide)

Fluorination of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) leads to narrowing of its window of electrochemical stability in a cathodic range of potentials. It is found this is connected with appearance of both perfluorinated and incompletely fluorinated units in the polymer. The former units are liable to electrochemical reduction (at potentials <−2.0 V) followed by elimination of fluorine anions and the latter react with basic products (generated at potentials <−1.8 V) of electrochemical reduction of the background solution. In the both cases this results in appearance of conjugated multiple bonds in the fluorinated macromolecules. Quantities of these units in fluorinated PPO were determined with a help of direct and indirect electrochemical reductive degradation techniques.     

The Design and Synthesis of Highly Branched and Spherically Symmetric Fluorinated Oils and Amphiles

A new surfactant design principle, based on concepts borrowed from protein science, is proposed. Using this principle, a class of highly branched and spherically symmetric fluorinated oils and amphiles has been designed and synthesized, for potential applications in the construction of fluorocarbon nanoparticles. The Mitsunobu reaction was employed as the key step for introducing three perfluoro-tert-butoxyl groups into pentaerythritol derivatives with excellent yields and extremely simple isolation procedures. Due to the symmetric arrangement of the fluorine atoms, each fluorinated oil or amphile molecule gives one sharp singlet ¹⁹F NMR signal.     

Novel Partially Fluorinated Copolymers: Evidence of the Effect of Fluorine on the Reactivity of the Unfluorinated Comonomer Units

Summary: A conventional free‐radical polymerization of vinyl or propenyl ethers with acrylic or methacrylic monomers with fluorine substitution either in the main chain or in the ester groups has permitted us to obtain a series of copolymers with substantially different fluorine contents and distributions to be obtained. Such copolymers were considered as model compounds to offer new valuable insights as to the influence of fluorinated moieties on the overall stability and, more specifically, on their reactivity with atmospheric oxygen under environmental‐like conditions. Depending on the relative position of the fluorine atoms with respect to the common active center of oxidation, the influence ranges from a simple slowing down of the process to a complete redirection towards an otherwise secondary mechanism of oxidation.

FT‐IR spectra of the carbonyl region of three novel fluorinated copolymers after oxidation.     

Preparation and properties of waterborne epoxy resin modified by poly(meth)acrylates containing long fluorinated side chains

Abstract

Two waterborne poly(meth)acrylates containing fluorinated side chains (PALF and PASF) were synthesized by conventional radical copolymerization. Then waterborne epoxy composites with hydrophobic surface were obtained through a phase-inversion emulsion technique, using the PALF and PASF acrylates as reactive surface additives. Contact angle measurements and X-ray photoelectron spectroscope were employed to characterize the surface properties and the results confirmed that the fluorine atoms in the longer fluorinated side chains migrated to the outmost layer more efficiently. The effect of the fluorinated content and the length of the fluorine side chain on thermal and bulk properties of the waterborne epoxy resin was investigated. With increasing the fluorinated content or the length of the fluorine side chain, the contact angles and thermal properties improved while the mechanical properties showed no deterioration.     

BODIPY Dyes Bearing Multibranched Fluorinated Chains: Synthesis,Structural, and Spectroscopic Studies

A small series of boron-dipyrromethene (BODIPY) dyes, characterized by the presence of multibranched fluorinated residues, were designed and synthesized. The dyes differ in both the position (para-perfluoroalkoxy-substituted phenyl ring or boron functionalization) and number of magnetically equivalent fluorine atoms (27 or 54 fluorine atoms per molecule). Photophysical and crystallographic characterization of the synthesized BODIPYs was carried out to evaluate the effect of the presence of highly fluorinated moieties on the optical and morphological properties of such compounds.