Some aspects of plasma polymerization of fluorine-containing organic compounds

The polymerization of perfluorocarbons and fluorohydrocarbons was investigated by using both continuous and pulsed rf discharge (100 μsec on and 900 μsec off). Plasma polymerization of perfluorocarbons is generally slower than that of hydrocarbons, which seems to be due to the absence of contribution of fluorine detachment to the plasma polymerization. Presence of multiple bond(s) or cyclic structure in a monomer is necessary to obtain high enough polymerization; however, the plasma polymerization mechanism postulated to plasma polymerization of hydrocarbons is still valid to these monomers. Cyclic structure is very effective to enhance the plasma polymerization capability of perfluorocarbons. Saturated straight-chain perfluorocarbons do not polymerize well in plasma, but the grafting of fluorine-containing functions on the surface of polymeric substrate can be achieved by the plasma of these compounds. The effect of pulse on the plasma polymerization was found to be similar to that found for hydrocarbons.     

Distribution of polymer deposition in plasma polymerization. II. Effect of reactor design

The effects of relative positions of the monomer inlet and the r.f. coil, and of the inlet and outlet, on the distribution of polymer deposition in plasma polymerization of ethylene were investigated using an electrodeless glow discharge by a 13.5-MHz radiofrequency source. The diffusional transport of active species created under the r.f. coil, diffusional transport of polymer forming species, and flow of gas in the system are important factors that determine the distributions of polymer deposition observed in plasma polymerization of ethylene. The mechanisms of polymer deposition are discussed in conjunction with postulated plasma polymerization mechanisms.     

Plasma for Modification of Polymers

The effect of nonpolymer-forming plasma (e.g., plasma of hydrogen, helium, argon, nitrogen) can be viewed as the following two reactions: 1) reaction of active species with polymer, and 2) formation of free radicals in polymer which is mainly due to the UV emitted by the plasma. The incorporation of nitrogen into the polymer surface by N₂ plasma and the surface oxidation by O₂ plasma are typical examples of the first effect. The latter effect generally leads to incorporation of oxygen in the form of carbonyl and hydroxyl and to some degree of cross-linking depending on the type of substrate; however, the degradation of polymer at the surface manifested by weight loss occurs in nearly all cases when polymers are exposed to plasma for a prolonged period of time. The effects of polymer-forming plasma is predominated by the deposition of polymer (plasma polymer); however, with some plasma-susceptible polymer substrates the effect of UV emission from polymer-forming plasma cannot be neglected. The mechanism of polymer formation can be explained by the stepwise reaction of active species and/or of an active specie with a molecule, and the chain addition polymerization of some organic compounds (e.g., vinyl monomers) is not the main route of polymer formation.

Plasma polymers contain appreciable amount of trapped free radicals; however, the concentration is highly dependent on the chemical structure of the monomer. In plasma polymerization, 1) triple bond and/or aromatic structure, 2) double bond and/or cyclic structure, and 3) saturated structure are three major functions which determine the rate of polymer formation and the properties of plasma polymers. The changes of some properties of plasma polymers with time are directly related to the concentration of trapped free radicals in plasma polymers. The amount of trapped free radicals in a plasma polymer is also influenced by the conditions of discharge; however, the UV irradiation from the polymer-forming plasma is not the main cause of these free radicals. Excess amount of free radicals are trapped during the process of polymer formation (rather than forming free radicals in the deposited polymer by UV irradiation). The properties of a plasma polymer is generally different from what one might expect from the chemical structure of the monomer, due to the fragmentation of atoms and/or functions during the polymerization process. This is another important factor to be considered for the modification of polymer surfaces by plasma polymerization.     

Comparing Long‐Chain Branching Mechanisms for Ethylene Polymerization with Metallocenes and Other Single‐Site Catalysts: What Simulated Microstructures Can Teach Us

Three different long‐chain branch (LCB) formation mechanisms for ethylene polymerization with metallocenes in solution polymerization semi‐batch and continuous stirred‐tank reactors are modeled to predict the microstructure of the resulting polymer. The three mechanisms are terminal branching, C–H bond activation, and intramolecular random incorporation. Selected polymerization parameters are varied to observe how each mechanism affects polymer microstructure. Increasing the ethylene concentration during semi‐batch polymerization reduces the LCB frequency of polymers made with the terminal branching and intramolecular mechanisms, but has no effect on those made with the C–H bond activation mechanism, which disagrees with most previous data published in the literature. The intramolecular mechanism predicts that LCB frequencies hardly depend on polymerization time or ethylene conversion, which also disagrees with the published experimental data for these systems. For continuous polymerization reactors, experimental data relating polydispersity to LCB frequency can be well described with the terminal branching mechanism, but both C–H bond activation and intramolecular models fail to describe this experimental relationship. Therefore, detailed simulations confirm that the terminal branching mechanism is indeed the most likely mechanism for LCB formation when ethylene is polymerized with single‐site coordination catalysts such as metallocenes in solution polymerization reactors.     

Critical evaluation of conditions of plasma polymerization

Under conditions of plasma polymerization, we are dealing with the “reactive” or “self-exhausting” rather than the “nonreactive” or “non-self-exhausting” gas phase (plasma). Therefore, many parameters that define the gas phase, such as system pressure and monomer flow rate, which are measured in the nonplasma state (before glow discharge is initiated), do not apply to a steady state of plasma, the conditions under which most of the studies on plasma polymerization are carried out. Consequently, information based on: (1) the polymer deposition rate measured at a fixed flow rate and discharge power, (2) the dependence of deposition rate on flow rate at fixed discharge power, or (3) the dependence of deposition rate on discharge power at fixed flow rate, does not provide meaningful data that can be used to compare the characteristic nature of various organic compounds in plasma polymerization. The significance and true meaning of experimental parameters applicable to conditions of plasma polymerization are discussed. The most important feature is that plasma polymerizations of various organic compounds should be compared at comparable levels of composite discharge power parameter W/FM, where W is discharge power, F is the monomer flow rate (given in moles), and M is the molecular weight of a monomer.     

Effects of cold plasma and UV-C radiation on isotonic solution

The possibility of hypochlorite formation by treating a 0.9% NaCl aqueous solution (isotonic solution) with pulsed UV-C radiation from a weakly ionized plasma of air spark discharge, continuous UV-C radiation from a low-pressure mercury lamp, or cold plasma of flash corona discharge has been explored in flow and batch modes. The mechanisms of reverse reactions in which the product hypochlorite is consumed have been analyzed. It has been shown that the reverse reaction is interrupted in the case of short-term contact of the processed liquid with flash discharge plasma; as a result, hypochlorite accumulates.     

Hydrogen Peroxide Formation by Electric Discharge with Fine Bubbles

Pulsed discharge plasma is typical oxidation technology for disposing organic compounds in aqueous solutions. When this electrical discharge plasma was applied in water, it may produce hydrogen peroxide (H₂O₂) without any catalyst or chemical agent. In order to increase H₂O₂ production by electrical discharge plasma in water, fine bubbles were introduced into the electrical discharge plasma in this experiment. Bipolar pulsed voltages were applied to cylindrical electrodes in the water while Ar or O₂ bubbles were introduced, generating a pulsed discharge plasma. The introduction of the bubbles seemed to enhance the dissociation of water molecules and increased H₂O₂ formation, especially with O₂ bubbling. Dissolved oxygen in the water contributed to H₂O₂ formation by pulsed discharge plasma with the bubbles, while dissociation of water molecules was the cause of H₂O₂ formation by pulsed discharge plasma without bubbles. More H₂O₂ was formed by pulsed discharge plasma with O₂ bubbles, because the amount of dissolved oxygen in the water increased upon bubbling with O₂.     

Surface Modification of Textile Fibers and Cords by Plasma Polymerization

In this paper we report on the treatment of industrial fibers and cords by means of plasma polymerization techniques. Coatings of plasma-polymerized pyrrole or acetylene were deposited on aramid fibers, aramid cords and polyester cords. The equipment was a custom-built semi-continuous reactor operated on a pulsed DC glow discharge. The fibers and cords were tested for adhesion to various polymers such as tire cord skim stock rubber compounds and epoxy adhesives. Standard industrial pull-out force adhesion measurement techniques were used. The deposition conditions of the plasma polymer films were varied within wide limits. It was found that, in general, films deposited under low-power and high-pressure conditions performed better than films prepared under high-power and low-pressure conditions. For some systems pulsing of the discharge power improved the performance further. For all systems studied, the optimized plasma polymer surface modification outperformed current industrial standards. The plasma-polymerized coatings were characterized by various techniques and the excellent performance results are explained in a tentative model based on the molecular structure of the films. This structure was found to be strongly dependent on the discharge conditions.     

Plasma polymerization of tetrafluoroethylene. III. Reproducibility and effects of substrate and reactor materials

Plasma polylmerization occurs in plasmas surrounded by surfaces and polymer formation is one of the complicated interactions that take place between active species and molecules which constitute surfaces and gas phases. Effects of reactor wall, substrate materials, flow rate, and discharge power on polymer formation, and properties of polymer deposits were investigated by ESCA, IR (infrared) spectroscopy, and the measurement of system pressure. The effect of surface is important at the initial stage of plasma polymerization which can be easily detected by the system pressure change; however, integrated properties such as IR spectroscopy and the deposition rate show the effect in a less pronounced manner. ESCA, which reflects the properties of surface (approximately 20 A? in depth), showed the effect of surface in an even less sensitive manner. The amount and properties (including the effects of surfaces) are dependent on plasma polymerization parameter W/FM(W, wattage; F, volume flow rate; and M, molecualar weight of monomer) and the location of deposition within a reactor. IR and ESCA data clearly showed the dependence of polymer properties on W/FM; i.e., increase of W and decrease of M to be equivalent. When all these factors were kept under control, the reproducibility of plasma polymerization was found to be excellent.     

Polymerisation du trans pentadiene-1,3 par un amorceur soluble associant le triethylaluminium et l'orthotitanate de n-butyle—II: Structure et croissance des chaines polymeres

Study of the first compounds resulting from the insertion of trans 1,3 pentadiene into the titanium-carbon bond showed that only a small fraction of these bonds are active in polymerization and also that the geometrical isomerism of the by-products is a function of the ageing time of the catalytic system as for the polymer. Study of the polymer showed that the molecular distribution is wide and bimodal although the polymerization process is of a living type. Stereoregularity of the macromolecules is a growing function of the molecular weight. Long times of polymerization or high concentrations of catalyst lead to the formation of organic gel.     

Immobilized streptavidin gradients as bioconjugation platforms

Surface density gradients of streptavidin (SAV) were created on solid surfaces and demonstrated functionality as a bioconjugation platform. The surface density of immobilized streptavidin steadily increased in one dimension from 0 to 235 ng cm(-2) over a distance of 10 mm. The density of coupled protein was controlled by its immobilization onto a polymer surface bearing a gradient of aldehyde group density, onto which SAV was covalently linked using spontaneous imine bond formation between surface aldehyde functional groups and primary amine groups on the protein. As a control, human serum albumin was immobilized in the same manner. The gradient density of aldehyde groups was created using a method of simultaneous plasma copolymerization of ethanol and propionaldehyde. Control over the surface density of aldehyde groups was achieved by manipulating the flow rates of these vapors while moving a mask across substrates during plasma discharge. Immobilized SAV was able to bind biotinylated probes, indicating that the protein retained its functionality after being immobilized. This plasma polymerization technique conveniently allows virtually any substrate to be equipped with tunable protein gradients and provides a widely applicable method for bioconjugation to study effects arising from controllable surface densities of proteins.     

等离子体引发丙烯酰胺水溶液聚合

用两种等离子体引发丙烯酰胺水溶液聚合的方法 ,制备了线性超高分子量聚丙烯酰胺 .研究了放电时间、放电功率、单体的初始浓度及溶液的pH值等对聚合产物的影响     

Synthesis and stability of BODIPY‐based fluorescent polymer brushes at different pHs

We report a simple strategy for the grafting of poly(methacrylic acid) [poly(MAA)] brushes from silicon substrate by surface‐initiated RAFT polymerization and the subsequent coupling of BODIPY to these brushes to render them fluorescent. The poly(MAA) brushes were first generated by functionalization of hydrogen‐terminated silicon substrate with methyl‐10‐undecenoate which both leads to the formation of an organic layer covalently linked to the surface via Si? C bonds without detectable reaction of the carboxylate groups and couples to the polymerization initiator, followed by surface‐initiated RAFT polymerization of tert‐butyl methacrylate from these substrate‐bound initiator centers, and finally conversion of tert‐butyl groups to carboxylic acid groups. The poly(MAA) brushes were then made fluorescent by grafting a BODIPY derivative via an ester linkage. The stability of the BODIPY‐based fluorescent polymer brushes in buffer solutions at pH 6.0 to 12.0 with added salt was investigated by ellipsometry, fluorescence microscopy, grazing angle‐Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy. The results of these measurements indicated that the organic molecule‐initiator bond (ester linkage) is unstable and can be hydrolyzed resulting in detaching of the immobilized polymer from the silicon substrate. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3586–3596     

A STUDY OF THE POLYMERIZATION MECHANISM OF ACETONITRILE IN GLOW DISCHARGE

Plasma polymerization of acetonitrile was carried out by a capacitively coupled RF plasma apparatus with external electrodes under some different reaction conditions such as discharge power. By investigating the informations provided by the polymer deposition regularities, IR spectra and elementary analysis results, the polymerization mechanism of acetonitrile in glow discharge have been investigated. The results show that acetonitrile polymerized in glow discharge mainly through hydrogen detachment for initiation at lower energy levels and the role that opening C≡N triple bond played in polymerization became more important at higher energy levels.     

Mechanistic studies of plasma polymerization of allylamine

Plasma polymerization of allylamine is performed both in continuous wave and pulsed mode. Chemical derivatization is applied to determine primary and secondary amine concentration. Primary amines are efficiently formed, but secondary amines are more abundant. A polymerization mechanism is proposed to account for the difference in amine content obtained from comparison between continuous wave and pulsed mode plasma polymerization. The AFM measurements performed on ultrathin (1-10 nm) plasma polymers confirm the continuity of films and that the film growth on silicon occurs via a layer-by-layer mechanism because no islandlike structures were detected.     

Kinetics of DC Discharge Plasma Polymerization of Hexamethyldisiloxane and Pyrrole

This paper investigates DC plasma polymerization kinetics by combining plasma parameters with film deposition rate in different conditions. The monomers hexamethyldisiloxane (HMDSO) and pyrrole were used. Both single and double Langmuir probes were used to measure the plasma parameters in pulsed power and continuous discharges. In order to avoid probe tip contamination, the probe was heated. Plasma density and electron temperature are reported. The electron current wave form is obtained in pulse power conditions. From the data, a plasma polymerization model is proposed. The conclusion is that the monomer molecules and free radicals adsorbed on the substrate surface react with activated sites produced by high energy ions bombarding the film, resulting in polymerization at the film surface.     

Plasma polymerization of phenyl isothiocyanate

Thin polymer films were obtained by plasma polymerization of phenyl isothiocyanate. Polymerizations were carried out in rf (13.56 MHz) glow discharge generated in an electrodeless flow system. It was found that this monomer produces uniform films with a wide range of thicknesses, from hundreds of nanometers to tens of micrometers. The deposition rate appeared to be dependent on the substrate distance from the monomer inlet. The chemical structure of plasma polymer was characterized by using elemental analysis, IR spectroscopy, gas chromatography, and mass spectrometry. Elemental analysis showed that the composition of polymer depends on the substrate position in the reactor. It was observed that sulphur content decreased with increasing the substrate distance from the monomer inlet, whereas nitrogen content appeared to increase. The IR data revealed significant decrease in —NCS groups content in the polymer as compared with the monomer spectrum and indicated for the appearance of new absorption bands corresponding to the ? CN and C? H aliphatic, groups. The results account for a strong fragmentation of monomer in plasma involved in decomposition of isothiocyanate group and phenyl ring. The soluble fraction of polymeric material was examined by gas chromatography and then the separated products were analyzed by mass spectrometry. The soluble fraction was found to be composed of numerous low molecular-weight compounds. Identification of their structure revealed the presence of residual monomer, thiophenol, cyanobenzene, diphenyl, diphenyl sulphide, diphenyl disulphide, phenyl thiocyanate, dicyanobenzene, phenatroline, and some other oligomeric products. Formation of these compounds proves high susceptibility of ? NCS group in the monomer towards different fragmentation reactions. The surface free energy and electrical conductivity of polymer films were evaluated. The surface free energy value was very close to those estimated for plasma polymers deposited from other benzene derivatives. The low electrical conductivity manifested by the investigated polymeric material indicated for its dielectric character. The photoelectrical measurements revealed some photoconductivity effect in this material.     

The effect of positive ion energy on plasma polymerization: a comparison between acrylic and propionic acids

Using a novel RF biasing technique, the energy of positive ions at a depositing substrate is controlled, independently of other parameters. Under bias conditions which gave the maximum and minimum ion energies, plasmas of propionic and acrylic acid were investigated using mass spectrometry, an ion flux probe, quartz crystal microbalance, and X-ray photoelectron spectroscopy (XPS). For both compounds investigated, the ion energy affects the deposition rate but leaves the neutral gas-phase chemistry and positive ion fluxes unchanged. The chemistry of the polymer deposit for acrylic acid is unaffected by the change in ion energy, but the chemistry of the propionic acid plasma polymer changes markedly. We argue that the results presented are consistent with the hypothesis that, under the plasma conditions explored, the carbon-carbon double bond present in acrylic acid plays a significant role in the formation of the polymer. Conversely, the absence of this bond in propionic acid leads us to conclude that positive ions contribute significantly to film formation for this compound.     

PLASMA POLYMERIZATION OF ACETYLENE/CO_2/H_2

A study has been made on the plasma polymerization of acetylene/CO_2/H_2 in a capacitively coupled RF plasma. The monomer mixture yielded a crosslinked film with light brown color. A kinetic study is reported for the plasma polymer ization of acetylene/CO_2/H_2. The effects of discharge power level and reactor geometry on the rate of polymer formation are reported. The structure of the plasma polymer is investigated by IR study.     

Plasma polymerization. IX. A systematic investigation of materials synthesized in inductively coupled plasmas excited in perfluoropyridine

The RF plasma polymerization of perfluoropyridine was investigated for a range of operating parameters. The stoichiometries of the resulting thin films indicated a predominance of rearrangement mechanisms in their formation in which both nitrogen and fluorine were retained at approximately the same level as in the starting monomer. In appropriate cases a comparison was drawn with plasma polymers produced under comparable conditions from perfluoro and pentafluorobenzenes. Although the plasma polymer films from the benzenes have a low critical surface tension, that for the pyridine system changes with time, and the surface becomes completely wettable with water. This is attributed to surface hydrolysis of the plasma polymer films produced from perfluoropyridine.