Plasma polymerization of tetrafluoroethylene. I. Inductive radio frequency discharge

The plasma polymerization of tetrafluoroethylene in an inductively coupled radio frequency glow discharge, using a flow system, was studied. A simple long tube reactor, with the coupling coil placed at the middle of the tube and gas entrance and exit at the respective ends, was used. Deposition rates and the chemical nature of the polymer (as revealed by ESCA spectra and surface energy studies) are obtained as a function of location in the reactor tube with respect to the coupling coil and of applied energy per unit mass of tetrafluoroethylene (W/FM). It was found that a fluorinepoor polymer, containing considerable carbon–oxygen bonds (after contact with air), is obtained at all locations at high W/FM. When a low W/FM is utilized, such a fluorine-poor polymer is also obtained at locations downstream from the coupling coil (the location of the highest energy density) in the reactor. In the latter case a fluorine-rich polymer containing very little oxygen is formed upstream from the coil. The polymer deposition rate distribution is also considerably broader in a high W/FM plasma than when low W/FM is used. These results are in agreement with earlier studies indicating that fluorine abstraction and decomposition due to fluorine etching occur when the energy density, as expressed by W/FM, is high.     

Plasma polymerization of tetrafluoroethylene. III. Capacitive audio frequency (10 kHz) and AC discharge

The plasma polymerization of tetrafluoroethylene (TFE) is studied in a capacitively coupled system with internal electrodes using a 10 kHz (af) and a 60 Hz (ac) source. The emphasis is on identifying conditions that are compatible with continuous coating of plasma polymer on a substrate moving through the center of the interelectrode gap. Operation at a pressure below 100 mTorr is most favorable for deposition of a substantial portion of the plasma polymer on this substrate. Plasma polymer deposited in this way is characterized by ESCA and by deposition rate data and compared to that deposited using rf power in both capacitively and inductively coupled systems. The polymers found in all systems are broadly similar and completely different from conventional poly(TFE). The distribution of power density in the various systems has been identified and compared. This is accomplished by using the known susceptibility of fluorine-containing polymers (including plasma polymer) to a high-power plasma as a probe of plasma power density within the interelectrode gap in the capacitively coupled system. The most active zone of the af or ac plasma is close to the electrode at a plasma pressure of approximately 40 mTorr. The use of a magnetic field leads to an intense localized glow such that etching by active fluorine atoms occurs at a specific locus on the electrode. By contrast, the low-pressure rf capacitively coupled glow discharge is the mildest of those investigated, and its most active zone is further from the electrode and much more diffusely localized by a magnetic field.     

Plasma polymerization of tetrafluoroethylene

The plasma polymerization of C₂F₄ was carried out in both continuous wave and pulsed rf discharges to establish the effects of reaction conditions on the kinetics of polymer deposition and the polymer structure. ESCA spectra of the polymer show evidence for ? CF₃, ? CF₂, and ? CH₂? groups. Under conditions favoring low deposition rates, the dominant functional group is ? CF₂? . At higher deposition rates the concentration of ? CF₂? groups is reduced and a more crosslinked polymer is produced. Both polymer deposition rates and polymer structures were essentially identical when using continuous wave and pulsed rf discharges.     

Plasma polymerization of tetrafluoroethylene in a field-free zone

Plasma polymerization of tetrafluoroethylene by itself and mixed with inert gases has been studied in the field free zone inside a Faraday cage. The chemical structure was analyzed by ESCA, revealing both linear and branched products. Linear products are formed by less energetic plasmas and at low monomer residence times. Lower energy plasmas result from the use of lower powers and lower percentages of helium in the feed. Production of linear products under these conditions is probably due to lower rates of free radical and metastable formation in the plasma. Through a combination of kinetic and mass transfer effects, shorter monomer residence times under high flow rates and within short distances from the front edge of the electrode give rise to a lower concentration of free radicals at the electrode surface, producing a more linear polymer. Linear products were also formed at very high powers. This latter result is quite unexpected and is probably due to rapid gas phase polymerization. The chemical structure was not affected significantly by the substrate temperature or by hydrodynamics in this work. All of the evidence indicates that the gases were well mixed in the reaction zone for the range of process variables and for the gases studied. The deposition rate was also studied as a function of the reaction conditions. It was affected by the concentration of free radicals, the concentration of the monomer, and the substrate temperature. The observed deposition rate profile across the electrode is consistent with mass transfer and kinetic considerations governing free radical and monomer concentrations on the electrode surface. The deposition rate is greater at the lower substrate temperature used, probably due to enhanced adsorption process.     

Plasma polymerization of trimethylsilane in cascade arc discharge

Plasma polymerization of trimethylsilane (TMS) in cascade arc discharge was experimentally investigated. It was found that the deposition rates of methane and TMS plasma polymer were dependent on plasma parameters, and the surface characteristics of plasma polymer were also dependent on plasma variables. The following plasma variables were studied: arc current, argon flow rate, TMS flow rate, chamber pressure, substrate axial, and radial positions. Carbon, silicon, and oxygen were the main elements observed in TMS polymer films obtained by x-ray photoelectron spectroscopy (XPS). Powder-like TMS polymer films were observed by scanning electron microscopy (SEM). The size distribution of the powder-like particles was strongly dependent on deposition parameters. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1653–1665, 1997     

Radiation-induced emulsion polymerization of tetrafluoroethylene

The radiation-induced emulsion polymerization of tetrafluoroethylene was carried out with the use of ammonium perfluorooctanoate as an emulsifier at an initial pressure of ca. 30–35 Kg/cm². The polymerization rate was shown to be proportinal to about the 0.8 power of the dose rate in the range of 2 × 10⁴ to 10⁵ R/hr and to be almost independent of emulsifier concentration. The molecular weight of the polymer lies in the range of 10⁴ to 10⁵, increases with reaction time at the initial stage, and decreases with emulsifier concentration, but is independent of the dose rate from 2 × 10⁴ to 6 × 10⁴ R/hr. If the emulsifier is not used, a polymer with a molecular weight as high as 1.8 × 10⁶ to 2 × 10⁷ is obtained. Apparently, the emulsifier and its radiolysis products act as chain transfer agents. Postirradiation polymerization was found to take place with the formation of products with increased molecular weight.     

Plasma polymerization of ethylene in an atmospheric pressure-pulsed discharge

The polymerization of ethylene in an atmospheric pressure-pulsed discharge has been studied. Partial pressures of ethylene up to 4 kN/m² were used with helium as a diluent. Deposition rates (on glass slides) were the same throughout the discharge volume over a wide range of operating conditions. These rates were in the 1–2 Å/sec range. The films were clear, soft, and showed good adhesion to the glass substrates. Oligomers large enough to visibly scatter 637.8-nm light were observed in the gas phase under all conditions in which film deposition occurred. The experimental results suggest that Brownian diffusion of these oligomers was the rate-limiting step in the film deposition process.     

Plasma polymerization of organoisothiocyanates. II. Structure of polymer film

Methyl-, n-propyl-, allyl-, and phenyl isothiocyanates (MITC, PITC, AITC, and PHITC respectively) were polymerized in an RF (13.56 MHz) plasma electrodeless flow system. The plasma produced polymers were characterized using IR, GPC, GC/MS, and direct pyrolysis mass spectrometry (DPMS) techniques. The solubility tests and chromatographic examinations of the polymers revealed a small soluble fraction which contained a mixture of oligomers with a predominance of dimers and trimers. Molecular structure of the components of these fractions, identified by GC/MS, suggests fragmentation of the monomers to reactive fragments: $$ ^ \cdot {\rm RSCN},^ \cdot {\rm RCN},{\rm R}^ \cdot ,^ \cdot {\rm CN} $$ (in the case of MITC, PITC, AITC) and $ ^ \cdot {\rm ArNCS},{\rm PhS}^ \cdot ,{\rm Ph}^ \cdot ,^ \cdot {\rm CN} $ (in the case of PHITC). The DPMS data, being generally consistent with IR and GS/MS results, proved the presence in the polymers of sulfide, polysulfide, thiocarbonyl (–CS–S–and–S–CS–S–) groups, and molecular sulfur S₈. Elementary plasma reactions involved in the formation of the observed structural units are proposed.     

Explosion of tetrafluoroethylene during nonisothermal polymerization

On the basis of dimerization kinetics and experimental data on thermal explosion we determine conditions for ignition of tetrafluoroethylene on a hot wall. A mathematical model of nonisothermal polymerization on a plane wall and in a cavity which takes into account heat removal to the wall and to the gas phase is proposed. The conditions for explosion hazard situations are established and expressions for the induction time are obtained. Saint Peterburg. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 5, pp. 56–62, September–October, 1993.     

Radiation-induced seeded copolymerization of tetrafluoroethylene with propylene. II. Kinetic analysis

The radiation-induced seeded copolymerization of tetrafluoroethylene with propylene was kinetically analyzed by assuming that growing radical in polymer particle is deactivated by degradative chain transfer to propylene and/or by recombination with newly entered radical which grows for a while before recombination. Apparent rate constant of initiation is 2.6 × 10^?9 mole/liter rad independent of the monomer composition in polymer particles. Apparent rate constant of propagation lies in the range of 10⁵ hr^?1 increasing with tetrafluoroethylene fraction. Change in apparent rate constant of chain transfer with propylene fraction suggests that first-order termination by radical occlusion or radical escape to aqueous phase may occur simultaneously with the degradative chain transfer. Average number of radical in a particle is found to increase with dose rate and levelled off at the value of 0.9. The higher value above 0.5 is explained by Trommsdorff effect. The dose rate exponent of average number of radical changes from 1 to 0 with increasing dose rate. This change is consistent with the dose rate effect on the polymerization rate under the constant number of polymer particles.     

The effects of hydrogen on the plasma polymerization of tetrafluoroethylene

A study was made of the effects of hydrogen containing additives on the polymerization of tetrafluoroethylene in a radiofrequency low pressure plasma. The addition of ethylene and molecular hydrogen were found, under certain circumstances, to significantly increase the rate of polymer deposition. This effect is ascribed to the release of hydrogen atoms from the additive, which enhance the formation of fluorocarbon-free radicals and scavenges fluorine atoms. ESCA (electron spectroscopy for chemical analysis) spectra of the deposited films show that upon addition of hydrogen to the monomer, the F/C ratio of the film decreases and the H/C ratio rises. Hydrogen addition also influences the extent of crosslinking—a decrease being observed at low discharge power and an increase being observed at high discharge power.     

Plasma polymerization of hexamethyldisiloxane in the gas phase. II. Formulation of various selected parameters affecting rate of polymerization and their optimization

Formulation of three selected operational parameters (flow rate of monomer, radio frequency power applied, and reactor tube pressure) affecting rate of polymerization of HMDS by plasma at 13.56 MHz is made by use of rotatable central composite (RCC) statistical design. The flow rate is found to be the most important parameter in determining deposition rate, followed by power and pressure; optimum values of these three to yield maximum deposition rate are also evaluated.     

Emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. IV. Effects of additives on polymer molecular weight

Poly(tetrafluoroethylene) (PTFE) of high molecular weight, 4.5 × 10⁷, was incidentally obtained at earlier study of an emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. In order to clarify this phenomenon, the effects of additives, in particular radical scavengers, on the molecular weight of PTFE and its polymerization behavior were studied. It was found that the molecular weight of PTFE is increased by the addition of hydroquinone, benzoquinone, α-pinene, dl-limonene, and ethylenediamine but is decreased by oxygen and triethylamine. A PTFE latex with molecular weight higher than 2 × 10⁷ was obtained in the presence of hydroquinone. It is concluded that additives such as hydroquinone and benzoquinone, which rapidly scavenge the primary radicals (OH·, H·, and e_aq^?) in the aqueous phase but not the growing polymer radicals in PTFE particles, are most effective in increasing the molecular weight.     

Application of radio frequency glow discharge plasma for enhancing adhesion bonds in polymer/polymer joints

It was found in this study, that air radio frequency glow discharge (rfGD) plasma is increasing surface roughness and is enhancing wettability of poly(propylene) (PP), poly(ethylene) (PE), and poly(carbonate) (PC). As an addition, the increased surface microhardness of PP and PE was found. Results indicate that rfGD air plasma treatment is very effective tool for improvement of adhesive properties of studied polymers as tested on single lap and double lap joints. The value of maximum load rise from 107 to 1926 N (approximately 18‐fold increase) for 20‐min‐treated PE and from 314 to 834 N (approximately three‐fold increase) for PP. Artificial accelerated ageing rapidly decreased the quality of adhesive joint. The value of maximum load decreased from 1926 to 221 N (approximately nine‐fold decrease) in the case of 20‐min‐treated PE. This result indicates that the ageing of the adhesive joint of plasma treated polymers can be a limitation factor in the possible application of the final component because of the extremely high loss of its initially‐enhanced mechanical properties. However, the strength of the thus prepared joints was higher in comparison to the plasma nontreated virgin samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1827–1833, 2006     

Low-pressure polymerization of ethylene. II

This paper presents the kinetic study of polymerization of ethylene with VOCl₃ and aluminum alkyls such as Et₃Al and Et₂AlCl. The effect of various parameters like the [Al]/[V] ratio, catalyst concentration, reaction time, temperature, solvents, and additives on rate of the reaction, yield, and molecular weight is reported. Each of these parameters has a remarkable effect on the yield and the rate of polymerization for both catalyst systems. Triethylamine is found to increase the catalyst efficiency and the rate. It is also observed that aliphatic hydrocarbons acted as a better polymerization medium than did the aromatic ones.     

Emulsion polymerization of tetrafluoroethylene: effects of reaction conditions on the polymerization rate and polymer molecular weight

The emulsion polymerization of tetrafluoroethylene (TFE) was carried out in a semibatch reactor using a chemical initiator (ammonium persulfate) and a fluorinated surfactant (FC-143). The effects of the reaction condition were investigated though the polymerization rate, molecular weight of polytetrafluoroethylene (PTFE), and stability of the dispersion. The emulsion polymerization of TFE was different from conventional emulsion polymerization. The polymerization rate was suppressed when the polymer particles were significantly coagulated. The polymerization rate increased with operating temperature, surfactant concentration, and agitation speed, due to the enhanced stability of the polymer particles. However, once the parameter value was reached, the rate decreased due to the coagulation of the particles. Stable PTFE dispersion particles were obtained when the surfactant concentration was in the range between 3.48 × 10⁻³ and 32.48 × 10⁻³ mol/liter, which is below critical micelle concentration (CMC). The molecular weight of the PTFE obtained was a function of the surfactant and initiator concentrations, and the polymerization temperature. The molecular weight increased as each parameter decreased. This is against the phenomena observed in a conventional emulsion polymerization. A stable PTFE dispersion polymer having a high molecular weight was obtained by optimizing the reaction conditions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 777–793, 1999     

Plasma polymerization of organosiloxanes

Plasma polymerization of disiloxanes containing various functional groups—hexamethyldisiloxane (HMDSO), tetramethyl-1,3-bis(chloromethyl)-disiloxane (CMDSO), tetramethyl-1,3-bis(hydroxylbutyl)-disiloxane (HBDSO), and tetramethyl-1,3-bis(amino propyl)-disiloxane (APDSO)— was carried out using an inductively coupled electrodeless glow discharge. The monomer polymerization kinetics and the distribution of chemical species deposited showed that monomer reactivity varied among the different siloxanes. Monomers of APDSO and CMDSO possessed higher rates of polymerization. Polymer IR spectra and ESCA analyses indicated that the chemical structures of plasma-polymerized products of HMDSO, HBDSO, and CMDSO resembled that of crosslinked polydimethylsiloxane. The polar hydroxyl and chlorine functionality in the HBDSO and CMDSO monomers was not present in the deposited films. In contrast, the polymerized product of APDSO retained amino functionality and also formed new Si–H bonds.     

Characterization of bis‐(phenoxy)phosphazene polymers using radio frequency glow discharge mass spectrometry

A radio frequency glow discharge mass spectrometry (rf‐GDMS) source is evaluated for future applications in the “fingerprint” characterization of polyphosphazene membranes. The rf‐GDMS spectra of a series of bis(phenoxy)phosphazene polymers contain ions that originate from both the phosphazene backbone and the phenoxy moiety, resulting in signature ions of the polymer family. “Fingerprint” ions from the substituted R‐group on the phenoxy moiety of the different derivatives allows the individual polymers to be distinguished from one another. The ability of the rf‐GDMS source to characterize these materials directly in the solid state will be useful for the continued application of these polymers as separation membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 954–961, 2000