Plasma induced polymerization

Plasma can be utilized in the polymerization of monomer liquid. In this case, no substrate is employed, and monomers are typically organic compounds with an olefinic double bond (monomer for chain growth polymerizations). In a typical case, the vapor phase of a monomer liquid in a sealed tube is used to create plasma. The duration of plasma is generally very short (on the order of a few seconds). After plasma exposure, the tube is shaken to mix plasma-induced reactive species with the monomer and is kept at a constant temperature (polymerization temperature) for a prolonged period. 

Plasma-induced species act as initiator of polymerization. Polymerization characteristics and properties of polymers formed by plasma-induced polymerization strongly resemble those of the thermal polymerization of the corresponding monomer [2-12]. Results indicate that plasma-induced polymerization is a free radical addition polymerization initiated by difunctional free radicals created by plasma. The molecular weight of polymer increases with the polymerization time, which is distinctively different from the initiator-initiated free radical addition polymerization. 

After a long reaction time, polymers with exceptionally high molecular weight can be synthesized by plasma-induced polymerization. Since only brief contact with luminous gas phase is involved, plasma-induced polymerization is not considered to be LCVD. However, it is important to recognize that the luminous gas phase can produce chemically reactive species that trigger conventional free radical addition polymerization. This mode of material formation could occur in LCVD depending on the processing conditions of LCVD, e.g., if the substrate surface is cooled to the extent that causes the condensation of monomer vapor. 

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Plasma Polymerization. Plasma-induced polymerization (24) of vinyl monomer from inorganic particles is also employed for polymer grafting. The conventional reactors for liquid-phase polymerization of vinyl compounds after generation of plasma on inorganic particles or powders have been recently invented by Ikeda et al. (25). Haraguchi et al. (26) have also prepared polymer-modified silica by plasma-induced polymerization of glycidyl methaciylate. 

These apparent contradictions can be rationalized in terms of a model which incorporates plasma-induced polymerization along with depolymerization. PBS has long been known to exhibit a marked temperature-dependent etch rate in a variety of plasmas. This is clearly seen in the previously published Arrhenius plots (3,7) for two different plasma conditions (Figure 1). This dependence is characteristic of an etch rate that is dominated by an activated material loss as would occur with polymer depolymerization. The latter also greatly accelerates the rate of material loss from the film. Bowmer et al. (10-13) have shown in fact that poly(butene-l sulfone) is thermally unstable and degrades by a depolymerization pathway. A similar mechanism had been proposed by Bowden and Thompson (1) to explain dry-development (also called vapor-development) under electron-beam irradiation. 

Plasma-induced polymerization is essentially conventional (molecular) polymerization that is triggered by a reactive species created in an electric discharge. In order for one to form polymers by plasma-induced polymerization, the starting material must contain polymerizable structures, such as olefinic double bonds, triple bonds, or cyclic structures. 

In plasma state polymerization, the polymer is formed by the repeated stepwise reaction described above. It should be noted that plasma-induced polymerization does not produce a gas phase by-product, because the polymerization proceeds via the utilization of a polymerizable structure. The process can be schematically represented by tiie following chain propagation mechanism ... 

It should be emphasized that polymerization in a glow discharge consists of both plasma-induced polymerization and plasma state polymerization. Which of these two mechanisms plays the predominant role depends not only on the chemical structure of the starting material but on the condition of the discharge. 

The polymer formation and properties of polymers formed by glow discharge polymerization are controlled by the balance among plasma-induced-polymerization, plasma state polymerization, and ablation. 

If a polymer is formed throu plasma-induced polymerization from tetrafluoroethylene, the ESCA Cls spectrum should be identical to that of Teflon. Therefore, the fact that the ESCA Cls peaks are significantly different from those in the spectrum of Teflon indicates that a major portion of the glow discharge polymerization is not plasma-induced polymerization. How the balance between plasma state polymerization and plasma-induced polymerization is influenced by the conditions of glow discharge and the location of polymer deposition within a reactor can be seen by comparing the ESCA Cls spectra shown in Figures 2-4. 

Because polymer formation can proceed through more than one major type of reaction, i. e., plasma-induced polymerization and plasma state polymerization, depending on the chemical structure of the monomer and also on the conditions of discharge, such as discharge wattage, flow rate, type of discharge, and geometrical factors of the reactor, the balance between polymer formation (polymerization) and ablation is for most cases extremely complicated. 

The monomer chosen is hexafluoroethane, which cannot be polymerized by plasma-induced polymerization and which cannot be polymerized in a glow discharge imder ordinary conditions presumably because the ablation process associated with the glow discharge is excessive. Attempts have been made to supress the ablation process and to shift the balance between plasma state polymerization, which is assumed to be present, and ablation. However, it has been observed that polymer formation for hexafluoroethane does occur when polyethylene is used as substrate. On the other hand, no polymer formation can be observed either with ESCA or by surface energy analysis when glass is used as a substrate. 

This indicates that ablation is no loiter dominant, and polymer formation prevails. This phenomenon can be explained by postulating that Hg reacts with F atoms emanating from the fluorine containing compound in the glow discharge and forms the more stable HF, which reduces the ablation in a dramatic manner. Because hexafluoroethane does not form a polymer by plasma-induced polymerization, the overall effect can be explained by the balance between plasma state polymerization and ablation. 

A. Tiwari, R. Kumar, M. Prabaharan, R. R. Pandey, P. Kumari, A. Chaturvedi, and A. K. Mishra, Nanofibrous polyaniUne thin film prepared by plasma-induced polymerization technique for detection of NO2 gas, Polym. Adv. Technol., n Press, doi 10.1002/ pat. 1470. 

Wavhal DS and Fisher ER, Membrane surface modification by plasma-induced polymerization of acrylamide for improved surface properties and reduced protein fouling, Langmuir 2003,19, 79-85. 

Styrene have been grafted to Nafion using supercritical CO2 for polymer impregnation [160], or grafted to Nafion surface via plasma-induced polymerization [161]. Recently a poly(glycidyl methacrylate) was grafted to Nafion using a simple chemical initiation system [162]. 

A plasma polymerization is a gas plasma initiated and/or propagated conversion of a low-molar-mass compound into a polymer. The plasma-initiated polymerization has also been called a plasma-induced polymerization and the plasma propagated polymerization is sometimes named a plasma state polymerization. The mechanism of the former is a conven-... 

Kim, S.O.Y., Kanamori, T. and Shinbo, T. 2002b. Preparation of thermal-responsive poly(propylene) membranes grafted with n-isopropylacrylamide by plasma-induced polymerization and their water permeation. 

Lopez-Perez, P.M., Marques, A.P., da SUva, R.M.P., Pashkuleva, I. and Reis, R.L. 2007. Effect of chitosan membrane surface modification via plasma induced polymerization on the adhesion of osteoblast-like cells. 

Z. Song, J. Tang, J. Li, and H. Xiao. Plasma-induced polymerization for enhancing paper hydrophobicity. Carbohydr. Polym. 92(1), 928-933 (2013). 

Thin composite films are formed by simultaneous polymerization of compounds during the vacuum evaporation of metals. Modifications have been reported using different modes of preparation and introducing nanoparticles. One version includes simultaneous evaporation of a monomer and metal from different sources, while another relies on the combination of plasma polymerization and metal evaporation." Plasma-induced graft polymerization of traditional monomers (e.g., vinylim-idazole on a capron film) " was carried out during metal evaporation. The plasma polymerization of organometallic compoimds is of special interest." For example, plasma-induced polymerization of diethylberyllimn is remarkable for the simplicity of the equipment required. "... 

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