Polymerization of styrene in an electrodeless glow discharge

The polymerization (polymer deposition) rate of styrene in an electrodeless glow discharge from styrene vapor and a mixture of styrene vapor and gas (H₂, He, A, and N₂) was investigated. The rate of polymerization, R, was found to be independent of the discharge power. The rate of polymerization of the pure monomer was found to be proportional to the square of monomer pressure p_M. The addition of gas increased the rate of polymerization depending upon the partial pressure of the gas, p_x, and R can be generally expressed by R = a[p_M]²{1 + b[p_x]}. The value of b is dependent of the type of gas and follows the order of N₂, > A > He > H₂. The distribution of polymer deposition was found to be nearly independent of the partial pressure of the gas and of the discharge power with N₂ and H₂ as plasma gas; however, with He and A, the distribution is highly dependent on the partial pressure of the gas and on the discharge power. The study strongly suggests that polymerization occurs in the vapor phase and that the growing polymer radicals deposit on the surface of the discharge vessel, yielding highly crosslinked polymer deposition.     

Polymerization of organic compounds in an electrodeless glow discharge. XI. Pressure in glow discharge

The pressure of a steady-state flow of monomer, p₀, changes to a new steady-state flow pressure, p_g, in glow discharge. The value of p_g is dependent on the flow rate of monomer, the pumping-out rate of the vacuum system for the product gas (which is hydrogen in many cases of plasma polymerization of hydrocarbons), and the characteristic hydrogen yield of a monomer associated with plasma polymerization. The relationships between these factors were established and examined for plasma polymerizations of acetylene, ethylene, and acrylonitrile.     

Polymerization in an electrodeless glow discharge. III. Organic compounds without olefinic doublebond

The rates of polymer deposition from various organic compounds which do not contain an olefinic doublebond in an electrodeless glow discharge were studied. The polymerization rates of these unconventional monomers are by and large similar to those of olefinic monomers reported in the previous study (part II). The rate of polymer deposition R₀ from pure monomer flow can be characterized, according to the analysis used in part II, by R_o = apM² and R₀ = kF_w, where pM is the vapor pressure of the monomer, F_w is the weight basis flow rate of the monomer. Type A monomers which predominantly polymerize and type B monomers which decompose in a glow discharge were also found with these unconventional monomers. The effects of structural factors on the values of a amd k and on the classification of types A and B were examined. These structures and groups—aromatic, heteroaromatic, nitrogen-containing (e.g., >NH,? NH₂,? CN), Si-containing, and olefinic doublebond—favor the polymerization. These structures and groups—oxygen-containing chlorine, aliphatic hydrocarbon chains, and cyclic hydrocarbon chains—favor the decomposition of the monomer in a glow discharge. It is postulated that the polymerization of organic compounds proceed by the recombination of excited species (probably free radicals) created by glow discharge and reexcitation followed by further recombinations in the vapor phase and at the interface.     

Polymerization of organic compounds in an electrodeless glow discharge. V. Amines and nitriles

Polymerizations of amines and nitriles in a glow discharge generated by inductive coupling of 13.5-MHz radio frequency are investigated by employing the measurement of closed-system pressure change. It is found that nitrogen in those compounds are incorporated into polymer in a nearly stoichiometric manner and that the polymerization of those compounds are very much similar to that of hydrocarbons. Hydrogen detachments, opening of double bond and/or cyclic structure, opening of triple bond including C?N, and opening of aromatic and heteroaromatic structures contribute to polymerization of amines and nitriles.     

Polymerization of organic compounds in an electrodeless glow discharge. VI. Acetylene with unusual comonomers

Polymerizations of acetylene with nonpolymerizing gases and vapors such as H₂O, N₂, and CO in a plasma generated by inductive coupling of 13.5 MHz radio frequency are investigated. It is found that acetylene copolymerizes with those comonomers and that properties of copolymers are distinctly different from that of plasma polymer of acetylene. The copolymerization with H₂O has a significant effect in reducing the trapped free radicals in the plasma polymer (to a nonexistent level). Infrared and electron spin resonance (ESR) spectroscopies and elemental analysis of polymers are used to investigate the incorporation of H₂O, N₂, and CO into the plasma polymers.     

Polymerization of organic compounds in an electrodeless glow discharge. IV. Hydrocarbons in a closed system

The polymerization of hydrocarbons was investigated by measuring the hydrogen yield during the glow discharge polymerization in a closed system. It was found that the pressure change in the glow discharge polymerization of hydrocarbons was mainly due to the production of hydrogen and to the loss of vapor phase monomer by polymerization. The opening of triple or double bonds and cyclic structures plays an important role in the polymerization of hydrocarbons; however, these are not exclusive mechanisms. The major polymerization mechanism for saturated normal hydrocarbons seems to be by the formation of free radicals due to hydrogen abstraction and the recombination of these primary radicals. The polymerization due to this mechanism also seems to occur concurrently during the polymerization of hydrocarbons with multiple bond and/or cyclic structures. Aromatic hydrocarbons polymerize with very low hydrogen production, indicating that the utilization of an aromatic double bond is the major mechanism of polymerization.     

Polymerization of organic compounds in an electrodeless glow discharge. X. Internal stress in plasma polymers

Owing to the unique mechanisms operative in plasma polymerization, a thin layer of plasma polymer deposited on the surface of a substrate shows a tendency to expand, indicating an internal stress in the layer. This stress, σ_s, has been estimated from the observed curling of composite membranes in which the thickness of the plasma coating, d, is much smaller than the thickness of a flexible substrate, D, according to the relation where R is the radius of the roll into which the composite films curl up and E is the modulus of the substrate polymer. The stress σ_s is found to depend on the kind of monomer used and to be of the order of magnitude 10⁸–10⁹ dynes/cm² with most of the monomers here employed.     

Polymerization of organic compounds in an electrodeless glow discharge. VIII. Dependence of plasma polymerization of acrylonitrile on glow characteristic

The effects of experimental conditions (i.e., flow rate, pressure, discharge wattage, and glow characteristics) on the plasma polymerization of acrylonitrile were investigated. It was found that the glow characteristic is highly dependent on both flow rate and discharge wattage and that the plasma polymerization depends strongly on the glow characteristic. However, when experimental conditions are selected to maintain a fully developed glow in the tail flame portion of rf discharge, plasma polymerization is independent of discharge wattage and pressure. The polymer deposition rate is linearly proportional to the monomer flow rate. The deviations from this ideal situation are generally attributable to incomplete glow or partial glow under conditions which caused the deviation. The “character” of the glow largely determines the chemistry of the system. Consequently, the properties of polymers formed under different glow characteristics are also different.     

Effect of electrodeless glow discharge on polymers

The effects of gas plasma generated by electrodeless (inductive coupling) glow discharge on polymers were investigated as functions of gas pressure, discharge power, exposure time, and type of plasma gas. A remarkable similarity between the plasma susceptibilities of low molecular weight organic compounds and polymers was observed; i.e., polymers which have ether, carbonyl, ester, or carboxylic acid attached to a nonaromatic structure are very susceptible to plasma. The weight loss was proportional to the exposure time and exposed area. The discharge power and type of gas were found to have a great influence on both the rate of weight loss and the morphology of the exposed surface. The predominant effect of plasma on polymers was found to be degradation (manifested by weight loss). The crosslinking effect was found to be marginal with many polymers; however, significant crosslinking was observed with double bond-containing polymers. The crosslinking was examined by swelling the treated films. With copolymers of styrene–butadiene, 4-vinylpyridine–butadiene, methacrylic acid-butadiene, and acrylic acid–butadiene, the crosslinking was greatly dependent on the discharge power, the butadiene content of the copolymers, and the exposure time. Both degradation and crosslinking by gas plasma were generally limited to the exposed surface; however, the propagation of crosslinking in the direction of thickness was observed with copolymers of styrene–butadiene. The plasma of organic vapor also cause degradation of plasma-susceptible polymers, particularly at high wattage, although the deposition of polymer occurs simultaneously.     

Polymerization of organic compounds in an electrodeless glow discharge. IX. Flow-rate dependence of properties of plasma polymers of acetylene and acrylonitrile

Properties (free-radical concentration, gas permeabilities, internal stress, and contact angle of water) of plasma polymers of acetylene and of acrylonitrile were investigated as a function of flow rate of monomer in an electrodeless glow discharge. It was found that the monomer flow rate has a strong influence on free-radical concentration, gas permeabilities, and internal stress but little influence on the contact angle of water. The discharge power has little effect on properties when the full glow is maintained in the reactor. Gas permeabilities decrease with increasing concentration of free radicals in plasma polymers.     

Polymerization of organic compounds in an electrodeless glow discharge. VII. A fluid mechanic aspect of plasma and its effect on the polymer deposition rate

The deposition rate of polymer from plasma of an organic compound is influenced by the fluid mechanical aspect of plasma. Using cylindrical reactors which have constriction of various size, and utilizing the tail-flame portion of inductively coupled r.f. (13.5 MHz) glow discharge, it is demonstrated that the polymer deposition rate is proportional to the ratio of surface area/volume of the reactor tube, which has been often neglected in studies of polymer deposition rate.     

The initiation of in situ polymerization of vinyl monomers in polyester by glow discharge

Glow discharge initiation of in situ polymerization of acrylic acid and other vinyl monomers incorporated in PET films was investigatigated. The influence of glow discharge conditions such as the gas used, plasma power, discharge current, and plasma treatment time on polymerization yield was determined. Though glow discharge effects are limited to the film surface, in situ polymerization of the vinyl monomers took place and the vinyl polymer could be found all through the film cross section. At short plasma treatment time only surface modification took place, while at longer treatment time bulk modification occurred, too. Good polymerization yields were obtained. Gel effect behavior was observed. Mechanical properties of the modified PET film were not changed, while the contact angle with water improved when polar vinyl monomers were used.     

Graft polymerization of hydrophilic monomers onto textile fibers treated by glow discharge plasma

Graft polymerization of vinyl monomers was made onto some natural and synthetic textile fibers that were pretreated by glow discharge plasmas. Among the monomers investigated, 2-hydroxyethyl methacrylate (HEMA) produced the most improved grafting effects. Effects of plasma gas source, exposing time of glow discharge, grafting time, temperature, etc., on grafting were investigated. Postpolymerization in vacuum allowing oxygen shutoff was desirable for improved grafting yield. Air exposure of the plasma pretreated textile fabrics lead to decrease of grafting yield prominently because of the deactivation of radicals by oxidation. Grafting amount was dependent also on the nature of the substrate textile fibers, and cotton was, in general, more reactive. Breaking strength of yarns increased after graft polymerization of HEMA, while the strength decreased by etching of yarns by plasma treatments using nonpolymerizable gas species. Increase of the strength in the grafted yarn is attributed to binding effect of the grafted polymers as revealed from studies of morphology by scanning electron microscopy. © 1996 John Wiley & Sons, Inc.     

Impregnation and polymerization of vinylic monomers in porous media. II. Polymerization in situ

In this work, we have studied the kinetics of polymerization of styrene and of methyl methacrylate in a porous asbestos cement medium initiated by the thermal decomposition of a radical initiator. Our results show that the presence of the porous medium appreciably modifies the rate of polymerization. Two factors have been proposed to explain this effect: a variation of the constant of decomposition of the initiator resulting from the alkalinity of the surface, and a modification of the rate constant of chain propagation related to the electron-releasing or attracting capacity of the double bond of the monomer. Nevertheless, the polymerization remains solely initiated by radicals resulting of the thermal decomposition of the initiator as the rate varies according to the square root of the initiator concentration and tends toward zero for polymerization containing no peroxide.     

Polymerization of linseed oil in an electric discharge

Summary The treatment of linseed oil by the action of electric discharges (voltolization) in a hydrogen atmosphere (80 mm. Hg, 70°C.) is described. It has been known for a long time that voltolization of linseed oil brings about a polymerization of the oil. Now it has been proven that the nature of the polymerization product thus obtained is absolutely different from that of thermally or catalytically polymerized linseed oils. In contrast to the latter, voltolized linseed oils contain only small amounts of cyclic compounds. Their viscosity is relatively low, even at a high polymerization degree, and considerably less than that of thermally polymerized oils of a corresponding degree of polymerization. Atomic hydrogen seems to play an important part in the voltolization process. Coupling of fatty acid chains is made possible by combining radicals, formed primarily by the action of hydrogen atoms. Coupling reaction occurs almost exclusively intermolecularly. The possibility of transforming linseed oil and other drying oils into polymerization products of a completely different chemical structure, depending on the applied polymerization process, opens new possibilities for their manufacture. Compare T. Hoekstra, Thesis, Delft 1958 (in Dutch).     

Molecular intermediates in glow discharge polymerization

Mass spectral analysis of gaseous effluents from glow discharge polymerization of propylene confirms the formation of molecular propyne as an intermediate in the polymerization reaction. Observation of oligomeric species of mass number 138 or higher at the lowest monomer feed rate of the study indicates that a certain fraction of polymerization occurs in the gas phase.     

Grafting fluorocarbons to polyethylene in glow discharge

A systematic surface fluorination of high-density polyethylene was carried out using CF₄, CF₃H, CF₃Cl, and CF₃Br, in a radio-frequency glow discharge. Based on ESCA and wettability measurements, all of these compounds provided a fluorocarbon layer on high-density polyethylene surface, but the fluorine to carbon ratio and extractability of the films were strongly dependent on the starting materials and the location of the sample specimen in the reactor chamber as well as the duration of the reaction. The results with vertically held, CF₃H-treated samples showed a high level of nonextractable surface fluorination and very little change in wetting properties before and after extraction with CF₂ClCFCl₂.     

反应器聚合方法制备聚烯烃类热塑性弹性体技术进展

对聚烯烃类热塑性弹性体(o-TPE)这一领域的最新成就作了简要的评述,并对新产品和其应用前景作了介绍。首先描述了1994—1995年间第一个上市的所谓"聚烯烃弹性体",即辛烯含量较高的乙烯/辛烯共聚物。详细讨论了丙烯类的热塑性弹性体。介绍了制取这类弹性体,其微观结构设计的基本原理和实践;含较高立构缺陷和区域缺陷的等规聚丙烯和低立构规整性的间规聚丙烯,以及在近几年中由 ExxonMobil 和 Dow Chemical 公司分别推向市场的两种工业化产品——热塑性弹性体(Vistamaxx 和 Versify)。最后介绍了今年6月份才公布的用所谓"链段穿梭聚合"方法制取的多嵌段烯烃共聚物。     

Enhanced thermionic emission of mayenite electride composites in an Ar glow discharge plasma

Mayenite electride has attracted increasing research interests because of its unique electronic properties. The thermionic emission behavior of the mayenite electride is relatively unknown. Previous studies revealed that mayenite electride exhibited a bare work function ranged from 2.1–2.6 eV when the thermionic emission was tested in vacuum, and enhanced emission currents could be achieved by applying a super-high external electric field. In this paper, the thermionic emission behavior and the corresponding effective work function of two types of mayenite electride based composites, mayenite electride-titanium and mayenite electride-carbon, were investigated in an Ar glow discharge plasma at elevated temperatures (400–1000 K) without applying a high external electric field, which is critical for the application in electric propulsion and other aerospace apparatus, yet never had been done before. During the testing, the thermal equilibrium process and plasma sheath expansion were observed. The effective work function of the two mayenite electride composites were determined as a function of temperature. The Rasor-Warner model was applied to determine the bare work function and adsorption-site density of the mayenite electride based composites. Results suggested that the adsorption of Ar ions led to the enhanced thermionic emission (~30 A/m² at 985 K) and low effective work functions (0.9–2.2 eV) of mayenite electride based composites, without the need of applying high electric fields. Our findings will pave the ways for the application of mayenite electride and its composites as the thrust cathode materials for electric propulsion where plasma is present.     

Effects of functional groups in glow discharge polymerization

Summary Glow discharge polymerizations of allyltrimethylsilane (ATMS) and trimethylvinyloxysilane (TMVOS) were investigated by elemental analysis and infrared spectroscopy. The formed polymers were far different in elemental composition from the starting materials, and possessed high carbon and hydrogen contents. There was less difference in an infrared-spectral sense between the two polymers from ATMS and TMVOS. A polymer-forming process in a discharge state is discussed.