Molecular Design of Fluorocarbon Film Architecture by Pulsed Plasma Enhanced and Pyrolytic Chemical Vapor Deposition

Pulsed plasma enhanced chemical vapor deposition (pulsed PECVD) and pyrolytic chemical vapor deposition (pyrolyric CVD) of fluorocarbon films from hexafluoropropylene oxide (HFPO) have demonstrated the ability to molecularly design film architecture. Film structures ranging from highly amorphous crosslinked matrices to linear perfluoroalkyl chain crystallites can be established by reducing the modulation frequency of plasma discharge in plasma activated deposition and by eventually shifting mechanistically from an electrically activated to a thermally activated process. X-ray photoelectron spectroscopy (XPS) showed CF₂ content increasing from 39–65 mol%. Fourier transform infrared spectroscopy (FTIR) showed an increasing resolution between the symmetric and asymmetric CF₂ stretches, and a reduction in the intensity of the amorphous PTFE and CF₃ bands. High-resolution solid-state ¹⁹F nuclear magnetic resonance spectroscopy (NMR) revealed an increasing CF₂CF₂CF₂ character, with the pyrolytic CVD film much like bulk poly(tetrafluoroethylene) (PTFE). X-ray diffraction (XRD) patterns evidenced an increase in crystallinity, with the pyrolytic CVD film showing a characteristic peak at 2 = 18° representing the (100) plane of the hexagonal structure of crystalline PTFE above 19°C.     

Novel organosoluble and colorless poly(ether imide)s based on 1,1-bis[4-(3,4-dicarboxyphenoxy)phenyl]cyclohexane dianhydride and trifluoromethyl-substituted aromatic bis(ether amine)s

A series of novel fluorinated poly(ether imide)s (IV) having inherent viscosities of 0.70-1.08 dL/g were prepared from 1,1-bis[4-(3,4-dicarboxyphenoxy)phenyl]cyclohexane dianhydride (I) and various trifluoromethyl (CF₃)-substituted aromatic bis(ether amine)s II_a-g by a standard two-step process with thermal and chemical imidization of poly(amic acid) precursors. These poly(ether imide)s showed excellent solubility in many organic solvents and could be solution-cast into transparent, flexible, and tough films. These films were essentially colorless, with an ultraviolet-visible absorption edge of 375-380 nm and a very low b^∗ value (a yellowness index) of 5.5-7.3. They also showed good thermal stability with glass-transition temperatures of 207-269 °C, 10% weight loss temperatures in excess of 474 °C, and char yields at 800 °C in nitrogen more than 62%. In comparison with analogous V series poly(ether imide)s without the -CF₃ substituents, the IV series polymers showed better solubility, lower color intensity, and lower dielectric constants.     

Low-energy electron and X-ray degradation of biomedical plasma-fluoropolymer

Plasma-deposited thin films of fluoropolymer on metallic substrates were degraded by low-energy (1-100 eV) electrons and X-ray irradiation to simulate irradiation conditions of implanted coated stents in the human body during diagnostic procedures using high energy radiation. The desorption of anions and cations from the surface of the films induced by 1-100 eV electrons was recorded by mass spectrometry. The electron energy dependence of the emission of F⁻ exhibited a resonant peak at 12.9 ± 0.4 eV, showing the formation of a transient excited anion and a monotonic rise at higher energies, associated to dipolar dissociation. In the positive ion mode, the fragments F⁺, CF⁺, CF₂⁺, CF₃⁺, C₃F₃⁺, C₂F₄⁺ and C₂F₅⁺ were observed. Emission thresholds were measured and laid above 25 eV. The shape of the cation emission curves versus electron energy showed no resonant process. X-ray degradation was studied by X-ray photoelectron spectroscopy for different exposure times. Loss of fluorine in -CF₂ groups was observed and damage mechanisms were proposed.     

Highly fluorinated graphite prepared from graphite fluoride formed using BF3 catalyst

Fluorinated graphites (CF_0.47) were obtained by reaction at room temperature of fluorine gas with graphite in the presence of boron trifluoride and hydrogen fluoride as catalysts. Their thermal treatments under fluorine at temperatures up to 600 °C lead to a progressive increase of the fluorine level resulting in an highly fluorinated graphite (CF_1.02). Whatever the fluorination level, a stage one fluorine-graphite intercalation compound is obtained. The sp² carbon hybridization is maintained for treatment temperature below 300 °C and two types of structure coexist for T_T in the range 350-550 °C. Finally, above 550 °C, carbon hybridization is sp³.The resulting materials were studied by ¹¹B, ¹H, and ¹⁹F NMR and EPR at different experimental temperatures giving informations about the intercalated fluoride species, the temperature of their removal from the host fluorocarbon matrix, as well as their mobility.     

Photoluminescence properties of BaMoO4 amorphous thin films

BaMoO₄ amorphous and crystalline thin films were prepared from polymeric precursors. The BaMoO₄ was deposited onto Si wafers by means of the spinning technique. The structure and optical properties of the resulting films were characterized by FTIR reflectance spectra, X-ray diffraction (XRD), atomic force microscopy (AFM) and optical reflectance. The bond Mo-O present in BaMoO₄ was confirmed by FTIR reflectance spectra. XRD characterization showed that thin films heat-treated at 600 and 200 °C presented the scheelite-type crystalline phase and amorphous, respectively. AFM analyses showed a considerable variation in surface morphology by comparing samples heat-treated at 200 and 600 °C. The reflectivity spectra showed two bands, positioned at 3.38 and 4.37 eV that were attributed to the excitonic state of Ba²⁺ and electronic transitions within MoO²⁻₄, respectively. The optical band gaps of BaMoO₄ were 3.38 and 2.19 eV, for crystalline (600 °C/2 h) and amorphous (200 °C/8 h) films, respectively. The room-temperature luminescence spectra revealed an intense single-emission band in the visible region. The PL intensity of these materials was increased upon heat-treatment. The excellent optical properties observed for BaMoO₄ amorphous thin films suggested that this material is a highly promising candidate for photoluminescent applications.     

Molecular engineering. Part 9: Enhanced binding ability and selectivity of C2v cavitands

Two new C_2v cavitands with protective side chains were synthesized and their binding properties for small molecules were studied. Cavitand 7 having benzyl side chains binds ethanol most strongly with K_a = 1508 M⁻¹ at 20 °C in CDCl₃, which was driven entropically. Cavitand 8 having coumarinyl side chains showed weaker binding due to its steric hindrance. ¹H NMR spectra show that carceroisomers of ethanol or acetonitrile@cavitand 7 exist in 3:1 ratio at 20 °C. The binding tendencies of the guest molecules were increased in nonpolar solvent media.     

Can mono- or di-butyltin chlorides produce tributyltin chloride at elevated temperatures? Implications for applications in chemical vapour deposition

The thermolysis of the butyltin chlorides at 200-300 °C in the liquid phase has been investigated by ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. The stabilities follow the order: Bu₂SnCl₂ > Bu₃SnCl > BuSnCl₃. Only tributyltin chloride showed any evidence of redistribution, giving dibutyltin dichloride, together with metallic tin, butane, and but-1-ene, which would be formed by decomposition of tetrabutyltin. Dibutyltin dichloride decomposed to give mainly butane with no other apparent liquid organotin compound. Butyltin trichloride gave butane, some butene, and metallic tin, and showed no evidence of forming tributyltin chloride by the redistribution reaction, which would have environmental implications for its use in the CVD coating of glass.     

Isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Isothermal crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated by means of differential scanning calorimetry and polarized optical microscopy (POM). The Avrami analysis can be used successfully to describe the isothermal crystallization kinetics of PHBV, which indicates that the Avrami exponent n=3 is good for all the temperatures investigated. The spherulitic growth rate, G, was determined by POM. The result shows that the G has a maximum value at about 353 K. Using the equilibrium melting temperature (448 K) determined by the Flory equation for melting point depression together with U∗=1500 cal mol⁻¹, T_∞=30 K and T_g=278 K, the nucleation parameter K_g was determined, which was found to be 3.14 ± 0.07 × 10⁵ (K²), lower than that for pure PHB. The surface-free energy σ=2.55×10⁻² J m⁻² and σ_e=2.70±0.06×10⁻² J m⁻² were estimated and the work of chain-folding (q=12.5±0.2 kJ mol⁻¹) was derived from σ_e, and found to be lower than that for PHB. This implies that the chains of PHBV are more flexible than that of PHB.     

Bis(trifluoromethyl)dicarbonate, CF3OC(O)OC(O)OCF3

The synthesis of the new compound, bis(trifluoromethyl)dicarbonate, CF₃OC(O)OC(O)OCF₃, is carried out by reduction of bis(trifluoromethyl)trioxidicarbonate with excess of CO at 0 °C. The product is characterized by IR, Raman, ¹³C and ¹⁹F NMR spectroscopy and its properties are compared with those of the other members of the series CF₃OC(O)O_xC(O)OCF₃, x = 0-3. Single crystals are grown at −25 °C and the X-ray diffraction analysis shows the packing of syn-syn rotamers exhibiting C₂ symmetry. DFT calculations predict this rotamer as the most stable one and also structural and vibrational data are predicted reasonably well.     

Reducing the formation of six-membered ring ester during thermal degradation of biodegradable PHBV to enhance its thermal stability

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has attracted the attention of academia and industry because of its biodegradability, biocompatibility, thermoplasticity and plastic-like properties. However, PHBV is unstable above 160 °C during melt processing at a temperature above the melting temperature, which restricts practical applications as a commodity material. It is widely believed that thermal degradation of PHBV occurs almost exclusively via a random chain scission mechanism involving a six-membered ring transition state. Here, 2,2′-bis(2-oxazoline) (BOX) was selected to modify PHBV to control the formation of six-membered ring ester during thermal degradation. The resulting hydroxyl-terminated PHBVs (HT-PHBVs) had improved thermal stability due to a decrease in the negative inductive effect of the neighboring group of methylene groups at the β-position to the ester oxygen, and a decrease in the electron-denoting effect of substituent group of carbon atoms at α-position to the ester oxygen. The optimal reaction temperature and time were determined to be 95 °C and 6 h, respectively. Compared with those of original PHBV, the temperature determined at 5% weight loss (T_5%), the initial decomposition temperature (T₀), the maximum decomposition temperature (T_max), the complete decomposition temperature (T_f) of HT-PHBV prepared under the optimal conditions increased by 31, 24, 19 and 19.1 °C, respectively.     

A new catalytic system for the copolymerization of dicyclopentadiene with CO: PdCl2/phen/M(CF3SO3)n

A new three-component catalytic system, PdCl₂/phen/M(CF₃SO₃)_n, was studied in the copolymerization of dicyclopentadiene (DCPD) with CO. It was found that the PdCl₂/phen/CF₃SO₃H catalytic system gave a very low catalytic activity, and the PdCl₂/phen/M(CF₃SO₃)_n catalytic system exhibited high activity when M(CF₃SO₃)_n was introduced instead of CF₃SO₃H. The resultant cooligomer was analyzed using various techniques such as FT-IR, ¹H NMR, ¹³C NMR, DSC and TGA. The results indicated that the copolymer was a polyspiroketal (PS) of CO and DCPD. Due to the tension of the ring of DCPD, the degree of copolymerization is low and the degree of crystallinity is also not high. The effects of ligands, M(CF₃SO₃)_n, solvents, 1,4-benzoquinone/PdCl₂ molar ratio, and temperatures on the copolymerization have been discussed in detail. The results showed that this novel catalytic system exhibited highly efficient activity, especially when 1,10-phenanthroline (phen) was used as ligand and Cu(CF₃SO₃)₂ was used as cocatalyst. The corresponding reaction rate was 49 000 g PS/molPd h when the reaction was carried out at 60 °C and 3.0 MPa of CO. The weight average molecular weight (M_w) and the number average molecular weight (M_n) of the resultant cooligomer were 1180 g/mol and 564 g/mol, respectively.     

Synthesis and properties of organosoluble polyimides based on novel perfluorinated monomer hexafluoro-2,4-toluenediamine

New highly fluorinated aromatic polyimides based on hexafluoro-2,4-toluenediamine and commercially available dianhydrides (6FDA and ODPA) were synthesized by one-pot high temperature polycondensation in benzoic acid melt. Owing to the CF₃ group and fluorine atoms in the meta-linked phenylenediamine fragment, these polyimides combine good solubility in organic solvents including such a low boiling point solvent as chloroform with high glass transition temperatures (330-345 °C), thermal and thermooxidative stability (T₅ is >500 °C). The highly fluorinated polyimide films (hydrogen content is ≤1%) exhibit good dielectric properties and low water absorption as well as excellent optical transparency in the UV-vis region (cut-off wavelength is 311 nm for 6FDA-based and 357 nm for ODPA-based polyimides), which is very important for optoelectronic materials.     

New fluorinated polymers bearing pendant phosphonic groups for fuel cell membranes: Part 1 synthesis and characterizations of the fluorinated polymeric backbone

Radical copolymerizations of chlorotrifluoroethylene (CTFE) with vinyl ethers such as 2-chloroethyl vinyl ether (CEVE) and ethyl vinyl ether (EVE) were performed at 75 °C in the presence of peroxide initiator. Three copolymers were obtained and characterized by means of both NMR and elemental analysis. Then, the chlorine atoms in the side chains were converted into iodine atoms by nucleophilic substitution, which was monitored by ¹H NMR spectroscopy. A series of five copolymers with different amounts of iodine atoms in the side chains were thus obtained. These copolymers exhibited molecular weight values of about 25,000 g mol⁻¹, and the thermal analysis of the copolymers showed a starting degradation from about 220 °C. The T_g values were in the range of 34-41 °C and showed a linear dependence versus the content of iodine atoms.     

The simple solvent-free synthesis of 1H-quinazoline-2,4-diones using supercritical carbon dioxide and catalytic amount of base

Only supercritical carbon dioxide (scCO₂) as a reactant and a solvent, and catalytic amount of base (DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), DBN (1,5-diazabicyclo[4.3.0]non-5-ene), Dabco^® (1,4-diazabicyclo[2.2.2]octane), and triethylamine) afforded 1H-quinazoline-2,4-diones in good to excellent yields from 2-aminobenzonitriles. 6,7-Dimethoxy-1H-quinazoline-2,4-dione, which is a key intermediate of medicines (Prazosin, Bunazosin, and Doxazosin) was synthesized successfully in a 97% yield, using 0.1 equiv of DBU under scCO₂ (10 MPa) at 80 °C.     

Synthesis of α, ω perfluoropolyether iodides

Perfluoropolyether (PFPE) diacyl halides of formula XCOCF₂O[(CF₂O)_n(CF₂CF₂O)_m]_pCF₂COX, with X = Cl, F and molecular weight (MW) 400-4000 g mol⁻¹ are smoothly converted in high yields to the corresponding α, ω diiodides in the absence of solvent, employing KI or LiI at 210 °C with extrusion of CO. During the reactions, β-elimination of COF₂ from the terminal difluoromethylene oxide units (CF₂O, C₁ unit) occurs to some extent until a tetrafluoroethylene oxide unit (OCF₂CF₂, C₂ unit) is encountered yielding a OCF₂CF₂I terminus. This considerably alters the MW distribution of the final diiodide especially for low MW PFPEs. Operating in supercritical conditions of CO (scCO) or both scCO and CO₂ (scCO₂) on low (<600 g mol⁻¹) MW diacyl halides, lowers β-elimination from 95 to 52 mol% if KI is used or from 43 to 30 mol% if LiI is used. With higher MW (>600 g mol⁻¹) β-elimination is lowered from 15 to <1 mol% in scCO conditions employing KI.     

Environmental assessment of CFC alternatives: Rate constants for the reactions of OH radicals with fluorinated compounds

The rate constants for the reactions of OH radicals with CF₃OCHFCF₃, and CF₃CHFCF₃ have been measured over the temperature range 250-430 K. Kinetic measurements have been carried out using the flash photolysis, and laser photolysis methods combined, respectively, with the laser induced fluorescence technique. The influence of impurities in the samples has been investigated by using gas chromatography. No sizable effect of impurities was found on the measured rate constants of these fluorinated compounds, if the purified samples were used in the measurements. The following Arrhenius expressions were determined: k(CF₃OCHFCF₃) = (4.39 ± 1.38) × 10⁻¹³ exp[−(1780 ± 100)/T] cm³ molecule⁻¹ s⁻¹, and k(CF₃CHFCF₃) = (6.19 ± 2.07) × 10⁻¹³ exp[−(1830 ± 100)/T] cm³ molecule⁻¹ s⁻¹.     

Synthesis and characterization of fluorous (S)- and (R)-1-phenylethylamines that effect heat facilitated resolution of (±)-2-(8-carboxy-1-naphthylsulfinyl)benzoic acid via diastereomeric salt formation and study of their circular dichroism

Perfluoroalkyl- or nonafluoro-tert-butoxy-alkyl-substituted enantiopure amines having the structure PhCHCH₃(NR¹R²) [R¹ = H, CH₃; R² = (CH₂)₃C₈F₁₇, (CH₂)₂OC(CF₃)₃; R¹ = R² = (CH₂)₃C₈F₁₇, (CH₂)₂OC(CF₃)₃] are obtained in high yields, when (S)-(−)-1-phenylethylamine is reacted with readily accessible alkylating reagents or fluorous 2° amines (R¹ = H; R² = (CH₂)₃C₈F₁₇, (CH₂)₂OC(CF₃)₃) are methylated in a Leuckart-Wallach reaction. The solubility patterns of these novel chiral amines and their hydrochlorides are qualitatively described for a broad spectrum of solvents and the fluorous partition coefficients of the free bases are determined by GC. A novel method for the resolution of enantiomers is disclosed here, which involves the use a half-equivalent of the selected resolving agent in solvent water that displays low solubility for the crystalline diastereomeric salt(s) formed even at temperatures near to its boiling point. Compound (S)-(−)-PhCHCH₃[NH(CH₂)₃C₈F₁₇] is found to satisfy all the latter conditions and successfully used for the heat facilitated resolution of the title racemic acid. The circular dichroism (CD) spectra of six novel fluorous (S)-(−)-1-phenylethylamine derivatives are measured in ethanol, trifluoroethanol and hexafluoropropan-2-ol and discussed in detail.     

Iodomethane oxidative addition to β-diketonatobis(triphenylphosphite)rhodium(I) complexes: A synthetic, kinetic and computational study

New rhodium(I)- and rhodium(III)-β-diketonato complexes of the type [Rh(FcCOCHCOR)(P(OPh)₃)₂] and [Rh(FcCOCHCOR)(P(OPh)₃)₂(CH₃)(I)], with Fc = ferrocenyl and R = Fc, CH₃ and CF₃, have been synthesized. The reactivity of complexes of the type [Rh(β-diketonato)(P(OPh)₃)₂] increase in the order: β-diketonato = (CF₃COCHCOCF₃)⁻ < (CF₃COCHCOPh)⁻ < (CF₃COCHCOCH₃)⁻ < (PhCOCHCOPh)⁻ < (CF₃COCHCOFc)⁻ < (CH₃COCHCOPh)⁻ < (CH₃COCHCOCH₃)⁻ < (CH₃COCHCOFc)⁻ < (FcCOCHCOFc)⁻, giving linear relationships between the kinetic parameter ln k₂ and the parameters that are related to the electron density on the rhodium centre; the sum of the group electronegativities of the β-diketonato side groups (χ_R + χ_R′) and the pK_a of the uncoordinated β-diketone RCOCH₂COR′. The large negative values of the volume and entropy of activation indicated a mechanism which occurs via a polar transition state. A density functional theory study, at the PW91/TZP level of theory, indicates that oxidative addition of iodo methane to [Rh(FcCOCHCOCF₃)(P(OCH₃)₃)₂] occurs via a two-step mechanism. This mechanism involves a nucleophilic attack by the metal on the methyl carbon to displace iodide to form a metal-carbon bond and the coordination of iodide to the five-coordinated intermediate to give a six-coordinated trans alkyl product.     

X-ray diffraction study on the thermal expansion behavior of cellulose Iβ and its high-temperature phase

Oriented films of cellulose prepared from algal cellulose were hydrothermally treated to convert them into highly crystalline cellulose Iβ. The lateral thermal expansion behavior of the prepared cellulose Iβ films was investigated using X-ray diffraction at temperatures from 20 to 300 °C. Cellulose Iβ was transformed into the high-temperature phase when the temperature was above 230 °C, allowing the lateral thermal expansion coefficient of cellulose Iβ and its high-temperature phase to be measured. For cellulose Iβ, the thermal expansion coefficients (TECs) of the a- and b-axes were α_a = 9.8 × 10⁻⁵ °C⁻¹ and α_b = 1.2 × 10⁻⁵ °C⁻¹, respectively. This anisotropic thermal expansion behavior in the lateral direction is ascribed to the crystal structure and to the hydrogen-bonding system of cellulose Iβ. For the high-temperature phase, the anisotropy was more conspicuous, and the TECs of the a- and b-axes were α_a = 19.8 × 10⁻⁵ °C⁻¹ and α_b = −1.6 × 10⁻⁵ °C⁻¹, respectively. Synchrotron X-ray fiber diffraction diagrams of the high-temperature phase were also recorded at 250 °C. The cellulose high-temperature phase is composed of a two-chain monoclinic unit cell, a = 0.819 nm, b = 0.818 nm, c (fiber repeat) = 1.037 nm, and γ = 96.4°, with space group = P2₁. The volume of this cell is 4.6% larger than that of cellulose Iβ at 30 °C.     

Mechanism of degradation induced embrittlement in polyethylene

The thermal oxidation of polyethylene films in air at 80 °C and 90 °C has been studied by tensile testing, IR spectrophotometry and molar mass determination from rheometric measurements. In the conditions under study, the polymer predominantly undergoes chain scission and embrittles suddenly when the weight average molar mass reaches a critical value (90 kg mol⁻¹), far before significant damage of the entanglement network (M_e = 1.9 kg mol⁻¹) in the amorphous phase.The following embrittlement mechanism is proposed: chain scission in the amorphous phase induces chemicrystallization. The thickness of the interlamellar amorphous layer (l_a) decreases until a critical value of the order of 6-7 nm, below which plasticity cannot be activated and the polymer behaves in a brittle manner, as previously shown for virgin polyethylene. Using (l_a, M_W) maps, it is possible to explain the differences observed in the embrittlement behaviour of semi-crystalline polymers predominantly undergoing chain scission.