Perfluoromethyl Groups Research Articles

Synthesis and structures of three new pyridine-containing oxazoline ligands of complexes for asymmetric catalysis.

Three new chiral pyridine-containing oxazoline derivatives with fluorine and perfluoromethyl groups, namely, 2-({2-[(4S)-4-phenyl-4,5-dihydro-1,3-oxazol-2-yl]phenyl}amino)-5-(trifluoromethyl)pyridine, C21H16F3N3O, 2-({5-fluoro-2-[(4S)-4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl]phenyl}amino)-5-(trifluoromethyl)pyridine, C18H17F4N3O, and 2-({2-[(3aR,8aS)-8,8a-dihydro-3aH-indeno[1,2-d]oxazol-2-yl]phenyl}amino)-5-(trifluoromethyl)pyridine, C22H16F3N3O, as chiral ligands in metal-catalysed asymmetric reactions, were synthesized and characterized by spectral and X-ray diffraction methods. The conformation of the molecules is influenced by strong N-H...N hydrogen bonding and weak C-H...X (X= O and N) interactions. There are no intermolecular hydrogen bonds in the crystal structures of the analysed compounds. Hirshfeld surface analysis showed that the H...H contacts constitute a high percentage of the intermolecular interactions. The conformational analysis was performed by theoretical calculations using the density functional theory (DFT) method. The mechanism of complex formation in terms of the electron-withdrawing effect of the substituents on the oxazoline ring and the ligand conformation is discussed.

Preparation and Properties of Vesicles Made of Nonpolar/Polar/Nonpolar Fullerene Amphiphiles

Twenty potassium complexes of penta-[(4-substituted)phenyl][60]fullerene anions were synthesized and examined for their ability to form bilayer vesicles in water. The 4-substituents include alkyl groups ranging from methyl to icosanyl groups and perfluoromethyl, perfluorobutyl, and perfluorooctyl groups. The overall structure of the amphiphiles can be described as a nonpolar/polar/nonpolar (n-p-n') motif as opposed to the usual polar/nonpolar motif of lipid amphiphiles. Despite the hydrophobicity of the fullerene moiety (n-part) and alkyl/perfluoroalkyl chains (n'-part), all compounds except for the one with perfluoromethyl groups were soluble in water because of the centrally located fullerene cyclopentadienide (p-part) and spontaneously formed a vesicle of 25- to 60-nm diameter with a narrow unimodal size distribution. The vesicles are stable upon heating to 90 °C or standing over one year in air, as well as on a solid substrate in air or in vacuum, maintaining their spherical form. The vesicle membrane consists of an interdigitated bilayer of the amphiphile molecules, in which the fullerene n-part is inside and the n'-side is exposed to water. These vesicles, in particular the one bearing icosanyl chains, exhibit the smallest water permeability coefficient ever found for a self-assembled membrane in water.

Surface Induced Tilt Propagation in Thin Films of Semifluorinated Liquid Crystalline Side Chain Block Copolymers

The supramolecular self-assembly within a liquid crystalline block copolymer thin film with mesogenic semifluorinated alkyl side groups was studied using both grazing incidence X-ray diffraction and small angle scattering. Previous studies employing near-edge X-ray absorption fine structure spectroscopy indicated that mesogens at the film surface are tilted relative to the surface-normal. This tilt may arise from the interplay between the low surface energy of perfluoromethyl groups and the entropic degrees of freedom of each side chain (constrained by neighboring mesogens in the smectic layer and the alkyl linker attachment to the polymer backbone). Here, we show that the mesogen tilt at the surface propagates over several smectic layers into the film interior. We propose that the high grafting density of side chains in combination with a head-to-head arrangement of side chain free ends plays a significant role in transmitting mesogen tilt from the surface to the adjacent smectic layers within the film interior. In addition to scattering from individual mesogens, we observed characteristic scattering patterns in the plane of incidence produced by the horizontal smectic layers. The amorphous polystyrene block formed vertical domains interspersed in the liquid crystalline matrix, resulting in out-of-plane Bragg rods.

Self-Assembly of Heteroleptic [Cu(dipyrrinato)(hfacac)] Complexes Directed by Fluorine−Fluorine Interactions

Heteroleptic copper(II) complexes were synthesized from three different meso-substituted pyridyl- and quinoline-dipyrrinato ligands (3-pyrdpm, 3-quindpm, and 4-quindpm). Metal complexes were prepared with both acetylacetonate (acac) and hexafluoroacetylactonate (hfacac) ancillary ligands. The complexes undergo a self-complementary self-assembly process upon crystallization to generate a range of solid-state topologies including one-dimensional coordination polymers and discrete hexameric rings. The self-assembly of these molecular aggregates is driven by metal-ligand bonding, but is also modulated by fluorine-fluorine interactions. Perfluorination of the spectator ligand tends to generate more compact structures, which is attributed to aggregation of the perfluoromethyl groups. The results presented here demonstrate that fluorine-fluorine contacts can be used to modulate supramolecular structures in the solid state.

Hot Embossing Lithography: Release Layer Characterization by Chemical Force Microscopy

AbstractHot embossing lithography is a powerful method of replicating three-dimensional micro-and nano-structures (see Figure 1) using a stamp that is pressed into a heat-softened polymer resin. Cooling below the glass-transition temperature (Tg) of the polymer cures the motifs and the stamp and substrate are then separated. Successful replication is therefore contingent on interfacial interactions during the embossing phase and most importantly during the separation or release phase. Various organo- and perfluoro-silane release layers have been proposed and studied.We have employed variable temperature chemical force microscopy (VT-CFM) using tips silanized with four different SAMs interacting with a thin-film of poly(cyclic olefin), (PCO). The silanized-tip/polymer interaction was studied over a temperature range spanning the Tg of the PCO (∼373 K). Adhesion between a saturated hydrocarbon-decorated tip (OTS) and PCO was comparatively strong (170 nN) 30 K above the Tg of the polymer. Adhesion among the perfluorinated tips was 20 to 50 nN lower at 373 K with a relative increase in perfluoromethyl groups (w/w).

Distinct Demonstration of Methylene Insertion into the Metal−Carbon Bond on Ag(111)

We provide a clear demonstration of the migratory insertion of methylene into the metal−carbon bond on a silver single-crystal surface. The insertion reaction is characterized by the interaction between methylene and perfluoromethyl groups coadsorbed on Ag(111). The CH2 insertion into the Ag−CF3 bond followed by β-fluoride elimination produces CH2CF2, which is our experimental evidence for the insertion mechanism. Our observations confirm the step concerning the propagation of the carbon chain in the Fischer−Tropsch processes.

ChemInform Abstract: Preparation of the First Thione S‐Imides with Perfluoromethyl Groups by the Use of Sodium Hexamethyldisilazanide as a Mild Dehydrohalogenation Reagent.

AbstractFrom the reaction of the sulfenyl chloride (I) with the monosilylated amines (II) the sulfenamides (III) are obtained.

A study of novel heat‐resistant polymers: Preparation of photosensitive fluorinated polybenzoxazole precursors and physical properties of polybenzoxazoles derived from the precursors

AbstractA series of novel photosensitive polybenzoxazole precursors were prepared from polycondensation of 2,2‐bis(3,3′‐amino‐4,4′‐hydroxyphenyl)hexafluoropropane with photosensitive dicarboxylic acid chlorides such as p‐phenylenediacryloyl chloride and benzophenone‐4,4′‐dicarboxylic chloride. The precursors are soluble in common organic solvents owing to the presence of perfluoromethyl groups in the chain structure, and insolubilized in the solvents on irradiation with the light. Polybenzoxazole patterns with high resolution as well as high aspect ratio were reproduced by baking the precursor patterns at 300°C. The pattern shrinkage on the conversion to polybenzoxazole was slight. The polybenzoxazole films offered good heat‐resistance up to 400°C in addition to good electrical properties.

Darstellung der ersten Sulfin‐imide (Thion‐S‐imide) mit Perfluormethylgruppen unter Verwendung von Natrium‐hexamethyldisilazanid als schonendes Dehydrohalogenierungsreagenz

Preparation of the First Thione S‐Imides with Perfluoromethyl Groups by the Use of Sodium Hexamethyldisilazanide as a Mild Dehydrohalogenation ReagentFrom the reaction of the sulfenyl chloride 1 with the monosilylated amines 2a, b the sulfenamides 3a, b are obtained in good yields. 1,3‐Dehydrohalogenation of 3a, b with sodium hexamethyldisilazanide yields the thione S‐imides 5a, b. Imide 5a reacts with norbornene (6) to produce the isothiazolidine derivative 7. The structures of 5b and 7 are confirmed by X‐ray analyses.

Fluorine‐containing photoreactive polyimide. II. Preparation and properties of self‐sensitized polyimide precursors

AbstractTwo series of polyimide precursors that have benzophenone(BP) segments in addition to methacryloyl groups and perfluoromethyl groups in the main chain are described. These fluorinated polyimide precursors offered remarkable improvement in solubility in common organic solvents and self‐sensitivity at 365‐nm light (i‐line). It was also found that the sensitivity is extremely enhanced by the aid of a small amount of photoinitiators, and the effective initiators for sensitivity enhancement were different for each series of the precursors. These self‐sensitized polyimide precursors offered high resolution with good pattern profile of aspect ratio over 1.5. The temperatures for 10% weight loss of the imidized films were nearly 500°C from thermogravimetry analysis (TGA), indicating high thermal stability.

Raman and infrared spectra, conformational stability and vibrational assignment for 1,1,1,3,3,3‐hexafluoro‐2‐methoxypropane

AbstractThe Raman spectra of gaseous, liquid and solid 1,1,1,3,3,3‐hexafluoro‐2‐methoxypropane, (CF3)2 CHOCH3, and the corresponding methoxy‐d3 isotope, (CF3)2 CHOCD3, together with the infrared spectra of the gases and solids, have been recorded from 3500 to 30 cm−1. A comparison of the vibrational spectra obtained for the fluid phases with those obtained for the amorphous and annealed solids indicates the predominance of a single conformer at ambient temperature in the fluid phases with the same conformer present in the solid state. Based on the lack of depolarized Raman lines in the fluid phases, and a predominance of nondescript infrared band contours, it is concluded that the stable conformer is the gauche form which has the methoxy group rotated approximately 60° from eclipsing the secondary carbonhydrogen bond. Thirty‐eight of the 39 normal modes have been assigned based on group frequencies, isotopic shifts, depolarization values and infrared band contours. There appears to be coupling of the CF3 and methoxy torsional modes. Utilizing a coupled‐top barrier calculation, the barrier to internal rotation of the perfluoromethyl groups is estimated to be 2858 ± 100 cm−1 (8.2 ± 0.3 kcal mol−1) based on the torsional frequencies of 107 and 64 cm−1 observed in the solid phase. Several of the fundamentals appear as doublets in the spectra of the solids, which indicates that there are at least two molecules per primitive cell. These results are compared with similar data for some corresponding molecules.

Surface tension of polytrifluoropropylmethylsiloxane

AbstractSurface tension studies of the most common fluorosilicone, poly(3,3,3‐trifluoropropylmethylsiloxane) (PTFPMS), give unexpected results. Compared to polydimethylsiloxane (PDMS), the liquid surface tension is higher, the critical surface tension of wetting similar, and the solid surface tension, determined by water and methylene iodide contact angles and the method of Owens and Wendt, considerably lower. As the outermost surface of the lowest energy materials are comprised of close‐packed perfluoromethyl groups and as a flexible polymer backbone should aid in the adoption of the lowest surface energy configuration, fluorosilicones could in principle be the lowest surface energy polymers. In practice, other groups such as the ethylene link between the perfluoromethyl group and the siloxane backbone in PTFPMS are required to produce a stable material. This introduces factors such as bulkiness of side chains, unresolved fluorocarbon/hydrocarbon dipoles, and fluorine/silicon coordination effects. The results are discussed in these terms and compared with PDMS and two fluoropolymers, polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE). PTFE shows similar trends to PTFPMS whereas PCTFE behaves rather like PDMS.

Melting and solid phase transitions of isothermally crystallized copolymers of tetrafluoroethylene and hexafluoropropylene

The melting and the solid-solid transition behaviours of isothermally crystallized samples of FEP copolymers of various compositions are described. The results suggest that a significant contribution to the increases of the melting and transition temperatures, observed upon isothermal crystallization, is due to a reduction of the concentration of the perfluoromethyl groups in the crystallites, with partial segregation of them in the melt. Nevertheless a suitable extrapolation of the experimental melting temperatures leads to a reasonable value for the equilibrium melting temperature of poly(tetrafluoroethylene).

Formation of stable radicals in the radiolysis of fluoroorganic compounds

The existence of anomally long-living radicals (life time in liquid more than 100 days at 300 K) which arise in the process of radiolysis has been discovered in liquid perfluorocarbons. The ESR spectra analysis has allowed the singling out of two types of radical: (1) the perfluoroalkyl radical in which the unpaired electron stabilization is thought to be connected with the steric isolation of the surrounding perfluoromethyl groups and (2) the perfluoroalkyl radical whose stabilization is connected with the delocalization of the unpaired electron conjugated with the double CC bond. These stable radicals may be employed in the synthesis and modification of fluoropolymers as initiators and regulators, in the dosimetry of reactor irradiation, as well as in medico-biological investigations as spin-labelled compounds.

Surface analysis and adhesive bonding I. Fluoropolymers

Detailed physical and chemical surface characterization of fractured adhesive joints, guided by qualitative fracture mechanics theory, constitutes a semiempirical method to elucidate adhesive bonding phenomena. Inherent flaws, interfacial separation, viscoelastic and plastic responses, and crazing and crack propagation are the main factors governing overall bond strength. Surface analyses (primarily by SEM/EDAX 2 and ESCA 3) provide an estimate of the nature and extent of each mechanism. Results from various fluoropolymer joints are presented and rationalized in terms of the elastic modulus and fracture work in the failure zone. Bond strength on untreated fluoropolymers is negligible, but ESCA shows a small amount of fluorocarbon transfer to the adhesive. Surface treatments increase surface energy via a hydrocarbon layer ∼20 to >500 Å thick, and useful peel strength results. SEM shows fracture relatively deep in the fluoropolymer with pronounced microdeformation. When the surface treatment is depleted by heat or light, bond strength varies with surface composition. Also, copolymers with perfluoropropylvinyl ether side chains in place of perfluoromethyl groups are superior hot melt adhesives. The combination of SEM and ESCA shows cohesive failure in both instances, but the latter separates closer to the interface and with relatively little deformation.

Melting Temperatures of Copolymers

The melting temperatures (532° to 580°K) of copolymers of tetrafluoroethylene and hexafluoropropylene have been measured on a microscope hot stage. The copolymers had concentrations of perfluoromethyl groups between 0.0275 and 0.075 groups per carbon atom and lamella thicknesses which varied from 340 to 500 Å independently of comonomer concentration. An equation based on the concept of inclusion of the groups within the lamellar crystals as defects has been fitted to the data. The constants of fitting yield the equilibrium melting temperature, 616.6°±4.9°K, the surface energy, 4.5×10−13±1.6×10−13 erg/fold, and the perfluoromethyl defect energy, 0.047±0.003 eV/defect. Within the limits of error, these values are shown to be satisfactory by the possible comparisons with previously reported values or with values deduced from physical models. Neglecting the effect of lamella thickness yields a significantly poorer fit of the data.

Inclusion of Perfluoromethyl Groups in the Crystals of Copolymers of Tetrafluoroethylene and Hexafluoropropylene.

X-ray diffraction has been used to measure the separation of the molecular axes as a function of temperature, lamella thickness, and comonomer concentration in copolymers of tetrafluoroethylene and hexafluoropropylene. These data show that the increase of separation with increasing concentration of perfluoromethyl groups is a consequence of inclusion of the groups in the crystals and not an artifact associated with lamella thickness or crystal transition temperature. This conclusion is supported by the fact that diffuseness of some of the x-ray reflections in the copolymers indicates the presence of molecular disorder which might be expected from inclusion of the perfluoromethyl groups in the crystals. The lamellas in the copolymers are thinner than those in the typical homopolymer and this aspect of the structure is the primary cause of the lower density in the copolymers. Analysis of the available data indicates that this is also the situation in copolymers of ethylene and propylene. For both copolymer series, the density of the lamellas is apparently increased by the inclusion of the methyl groups in the crystals as defects.

A Copolymer With Lamellar Morphology.

Electron microscopy, together with wide- and small-angle x-ray diffraction studies, indicates that copolymers of tetrafluorocthylene and hexafluoropropylene are lamellar. The lamellar development is extensive; the lamellae can be broad and extend for many microns. The perfluoromethyl groups are incorporated within the lamellae as point defects.

Relaxations in Copolymers of Tetrafluoroethylene and Hexafluoropropylene

The modulus and internal friction of copolymers of tetrafluoroethylene and hexafluoropropylene (HFP) were measured with longitudinal waves at a frequency of 12 Mc between −80° and 260°C. The dielectric dissipation factor was measured at 0.1, 1.0, 10, and 100 kc between −180° and 200°C. Samples included copolymers with compositions ranging from pure polytetrafluoroethylene to pure polyhexafluoropropylene. A relaxation at −10°C (12 Mc) in polytetrafluoroethylene shifts to higher temperatures with increasing HFP content. Data suggest that 5 to 13 main-chain carbon atoms are involved, a size consistent with assigning the relaxation to motions of a small point defect in the crystal lattice. Molecular models indicate that the effects of these defects are reduced by perfluoromethyl groups which enter the lattice as another kind of point defect. Dielectric and mechanical relaxation temperatures agree approximately and yield the same activation parameters. These parameters exhibit no significant variation with HFP content and follow a relation which applies to activated processes in inorganic solids. The relation also obtains for a relaxation at 197°C (12 Mc) in polytetrafluoroethylene. This relaxation shifts to lower temperatures and the activation enthalpy decreases with increasing HFP content. Dielectric data do not exhibit the relaxation, and heating polytetrafluoroethylene near the melting point does not introduce sufficient polar groups to alter this result. Another relaxation observed below −150°C in the dielectric but not in the ultrasonic data is independent of polymer density and HFP content.

The spreading of liquids on low-energy surfaces. V. Perfluorodecanoic acid monolayers

The wettability of more than 90 pure liquids on oriented close-packed monolayers of perfluorodecanoic acid adsorbed on platinum, copper, brass, and glass has been studied. Comparison with results reported earlier for solid polyethylene, oriented monolayers of octadecylamine, and solid polytetrafluoroethylene shows that oriented, close-packed monolayers of perfluorodecanoic acid are the most nonwettable surfaces ever found and that for most liquids in contact with these surfaces the contact angle (θ) decreases in the order θ CF 3 > θ CF 2 > θ CH 3 > θ CH 2. Values of the work of adhesion, the initial and final spreading coefficients, and the free energy decrease on immersion, f SL , were computed from contact angle measurements and surface tensions using the assumption justified by experiment that f SV ∘ = 0. From the values of f SL , it has been possible to estimate the free surface energy of the surfaces prepared from films of perfluorodecanoic acid. Structural differences determining the wetting properties of liquids are presented, and the effect of increase in surface tension of higher members in a homologous series is discussed. Observed modifications of the wetting properties of high-energy solids by adsorption of a single monolayer, demonstrate beyond doubt the short-range nature of the forces involved in wetting. In view of the remarkable resistance to wetting shown by surfaces of close-packed perfluoromethyl groups, surface-active compounds with —CF 3 groups and hydrophilic groups at opposite ends of the molecule should have unusual and valuable properties, and they deserve to be treated as a special class of surface-active compounds.