Plasma fluorination of polystyrene

ESCA and contact-angle measurements were used to characterize the surfaces of polystyrene films exposed to SF₆, CF₄, and C₂F₆ plasmas. SF₆ plasmas cause loss of aromaticity in the polystyrene surface region via saturation of the phenyl ring and/or carbon-bond breakage and subsequent fluorination. C₂F₆ plasmas graft CF_x radicals directly to the polystyrene surface without necessarily destroying the aromaticity of the polymer. CF₄ plasmas appear to be intermediate in character between SF₆ and C₂F₆ plasmas.     

Plasma fluorination of organosilicon polymeric films for gas separation applications

SF₆ plasma treatment using an RF discharge was carried out for the surface fluorination of polytrimethylsilylpropyne (PTMSP) and polyvinyltrimethylsilane (PVTMS) films. Gas permeation of the fluorinated and untreated films for O₂, N₂, He, H₂, CH₄ and CO₂ gases has been measured. Plasma fluorination increases the ideal selectivities of the PTMSP films decreasing their permeances for all the gases measured, and does not affect the permeances and selectivities of the PVTMS films. The composition and chemical structure of the fluorinated polymer surface were investigated using X-ray photoelectron spectroscopy (XPS) and ¹⁹F nuclear magnetic resonance (NMR) spectroscopy. Within the range of the treatment parameters studied, permselectivity and surface composition of the fluorinated PTMSP films depend slightly on the treatment time and the density of the fluorine atom flux on the modified surface. The trimethylsilyl substituents are detached and carbon atoms are partially fluorinated during modification. The structure of the fluorinated layer contains crosslinks and unsaturated bonds.     

Epitaxy of helical polyolefins

The structural rules which govern the epitaxial crystallisation of polymers - and especially polyolefins - on organic substrates are established. Illustrative examples involve isotactic and syndiotactic polypropylenes and poly( l-butene). Investigation of the film structure by electron microscopy, electron diffraction and atomic force microscopy reveals some unprecedented features, including in particular the selection of the contact plane according to the chirality of its constituent helices, and direct observation of both right and left hands of polyolefin helices.     

Post-polymerization functionalization of polyolefins

Polyolefins are macromolecular alkanes and include the most familiar and most commercially produced plastic, polyethylene. The low cost of these materials combined with their diverse and desirable property profiles drive such large-scale production. One property that renders polyolefins so attractive is their resistance to harsh chemical environments. However, this attribute becomes a severe limitation when attempting to chemically convert these plastics into value-added materials. Functionalization of polymers is a useful methodology for the generation of new materials with wide ranging applications, and this tutorial review describes both new and established methods for the post-polymerization modification of polyolefins.     

Catalytic degradation of polyolefins

Silica, alumina, silica-aluminas and zeolites were screened as catalysts for polyolefins degradation. The degradations were carried out at temperatures from 200°C till to 600°C under vacuum. The degradation products were analyzed using gas chromatography-mass spectrometry (GC-MS). The comparison between these products and those obtained by thermal degradation in the absence of catalyst gives us many informations about the different mechanisms of the two degradation reactions. Kinetic measurements and thermogravimetry provided further useful data for screening the catalysts, finding the best operating conditions.     

Electrochemical fluorination of sulfones

Conclusions Perflurodiethylsulfone and perfluoroethanesulfonyl fluoride are obtained during electrochemical fluorination of diethylsulfone. In the case of tetramethylenesulfone one C — S bond is broken and perfluorobutanesulfonyl fluoride is formed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 945–947, April, 1969.     

Electrophilic aromatic fluorination with fluorine: meta-Directed fluorination of anilines

Anilines are mainly or selectively fluorinated in the meta-position with F₂ when dissolved in triflic acid, sometimes in the presence of small quantities of antimony pentafluoride. The regioselectivity is increased when an electron-donating substituent is present at the para-position.     

Anodic fluorination of azobenzene

Electrolysis of azobenzene (I) in the system of Et₄NF · 3HF, MeCN results in predominant fluorination of the products of polymerization of I formed in the course of electrolysis. Also, m-fluoroazobenzene (II) and o-fluoroazobenzene (III) (II: III = 4: 1) were obtained with a low yield. Anomalously high content of m-isomer II is probably related to redistribution of localization of electron-deficient centers in cation-radical I as a result of its protonation by acidic electrolyte.     

Direct fluorination of polyamide

Direct fluorination of polyamides imparts improved wetting property to the surface of the polymer. The acid content and fluorine content are compared to the wetting property of the treated polymer. The results indicate there is a favorable ratio of acid content and fluorine content that allows for best wetting property. The effect of added oxygen to the fluorinating medium is to reduce the wetting property imparted to the polymer.     

Electrophilic fluorination of organosilanes

The fluorination of organosilanes with the silyl groups directly attached or adjacent to an aryl or alkenyl group has been only very recently examined despite the fact that the corresponding fluorinated products are synthetically useful building blocks. In these reactions, the silyl group enhances the reactivity of the pi-nucleophile and controls the sense of regiochemistry upon addition of the electrophilic source of fluorine. These reactions take advantage of the beta effect of the silicon-carbon bond and recent results from the literature revealed that this chemistry allows for the preparation of a variety of novel fluorinated building blocks including enantio-enriched derivatives.     

Controlled fluorination of clays

The fluorination of clays by a mild fluorinating reagent, HPF₆ was investigated using a sample of bentonite. The reaction resulted in the fluorination at the aluminum sites to form octahedral aluminum oxyfluoride species. This led to considerable modification of the surface characteristics such as surface area, porosity and particle size of nano-clay particles. The fluorinated clay was characterized by X-ray powder diffraction, XPS, SEM, EDS, infrared spectroscopy and solid-state NMR.     

Cross metathesis functionalization of polyolefins

A cross metathesis strategy is reported for the post-polymerization functionalization of the pendant vinyl groups present in a range of polyolefin architectures. This represents a general strategy for the synthesis of tailored random and block copolymers as well as homopolymers.     

Adhesion mechanisms of grafted polyolefins

By comparing surface properties assessed by wettability measurements with polymer-metal adhesion strength determined by peeling for different grafted polyolefins (acrylic acid grafted polyethylene, acrylic acid and maleic anhydride grafted poly(ethylene-vinyl acetate), maleic anhydride grafted polypropylene), a general adhesion mechanism can be proposed. The surface polarity is not the main determining parameter for adhesion. Polyolefin-aluminium adhesion is obtained through chemical bonding of acid groups grafted in the polymer bulk and basic groups present on the aluminium.     

Site selectivities in fluorination

In the synthesis of bio-active compounds, fluorinated compounds play a prominent role. However, the site-selective fluorination of organic molecules is often challenging, because activation of a reaction site using a fluorinating reagent can be difficult in a substrate possessing many functional groups. This digest introduces recent examples of site-selective fluorination reactions.     

Progress in fullerene fluorination

Fluorofullerenes hold the promise of being useful synthetic intermediates, because of the ease with which they undergo nucleophilic substitution. However, the progress in this field has been hampered by the difficulty in controlling fluorination for the preparation of fluorofullerenes of either low, or specific fluorine content. In this paper, previous work is described together with the latest developments involving the use of metal fluorides as fluorinating species. The availability of specific fluorofullerenes has made it possible to make the first detailed studies of the nucleophilic substitution reactions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 852–861, May, 1998.     

Catalytic enantioselective fluorination of oxindoles

We have developed a highly efficient catalytic enantioselective fluorination of oxindole derivatives. In the presence of a catalytic amount of chiral Pd complex 2 (2.5 mol %), various substrates, including aryl- and alkyl-substituted oxindoles, were fluorinated in a highly enantioselective manner (up to 96% ee). In addition, when R was a hydrogen atom, enantioselective fluorination followed by solvolysis gave a monofluorinated ester with up to 93% ee. To our knowledge, this is the first example of catalytic enantioselective fluorination of oxindoles.     

Ring-opening fluorination of bicyclic azaarenes

We have discovered a ring-opening fluorination of bicyclic azaarenes. Upon treatment of bicyclic azaarenes such as pyrazolo[1,5-a]pyridines with electrophilic fluorinating agents, fluorination of the aromatic ring is followed by a ring-opening reaction. Although this overall transformation can be classified as an electrophilic fluorination of an aromatic ring, it is a novel type of fluorination that results in construction of tertiary carbon–fluorine bonds. The present protocol can be applied to a range of bicyclic azaarenes, tolerating azines and a variety of functional groups. Additionally, mechanistic studies and enantioselective fluorination have been examined.

A ring-opening fluorination of bicyclic azaarenes was developed. Although this overall transformation can be classified as an electrophilic fluorination of aromatics, it is a novel type of fluorination that results in construction of tert-C–F bonds.     

Palladium-catalyzed fluorination of carbon-hydrogen bonds

This communication describes the development of a new Pd-catalyzed method for the fluorination of carbon-hydrogen bonds. A key step of these transformations involves palladium-mediated carbon-fluorine coupling-a much sought after, but previously unprecedented, transformation. These reactions were successfully achieved under oxidative conditions using electrophilic N-fluoropyridinium reagents. Microwave irradiation in the presence of catalytic palladium acetate served as optimal conditions for the fluorination of C-H bonds in a variety of substituted 2-arylpyridine and 8-methylquinoline derivatives.