Ethylene plasma-polymerized

A number of typical polymer-forming monomers have been polymerized using plasma polymerization including tetrafluoroethylene, styrene, acrylic acid, methyl methacrylate, isoprene, and ethylene. Polymerization of many nontypical monomers has also occurred including toluene, benzene, and simple hydrocarbons. 

In addition to microelectronic and optical applications, polymers deposited using thermal and plasma assisted CVD are increasingly being used in several biomedical applications as well. For instance, drug particles microencapsulated with parylenes provide effective control release activity. Plasma polymerized tetrafiuoroethylene, parylenes and ethylene/nitrogen mixtures can be used as blood compatible materials. An excellent review of plasma polymers used in biomedical applications can be found in reference 131. 

The facts found with pulsed radio frequency discharge that (1) the largest increase in dangling bonds is observed with ethylene and fluorohydrocarbons (e.g., vinyl fluoride and vinylidene fluoride), (2) the dangling bonds in tetrafluoro-ethylene decrease, and (3) dangling bonds in most perfluorocarbons decrease support a significant difference between the plasma polymerization of hydrocarbons and that of perfluorocarbons summarized above. 

Equation (12.7) relates p to p, but both constants c and d contain parameters for the monomer and the product gas. Therefore, it is anticipated that Eq. (12.7) would hold between p and but that the intercept and the slope of a straight line would depend on the pumping characteristics of the monomer. Figure 12.3 depicts the p -pa relationship for the plasma polymerization of ethylene with and without a liquid N2 trap in the system. Although there exists a relationship given by Eq. (12.7), cannot be uniquely related to / o- In other words, the manipulation of by manipulation of the pumping rate does not control the value of p ... 

Figure 20.7 Distribution of polymer deposition in the plasma polymerization of ethylene with the addition of Freon 12 (CCI2F2) key ( ) ethylene F = 2.5 seem), />g = 44 (Q) Freon 12/Et = 0.10, pg = 43 (A) Freon 12/Et = 0.76, g = 45, (Freon 12/Et denotes the mole ratio of CCI2F2 to ethylene), pg in mtorr.

The rate of plasma polymerization depends on the nature of the monomer gas. In addition, such parameters as flow rate, pressure, power, frequency, electrode gap and reactor configuration also strongly influence the polymerization rate for a given monomer. Generally at low flow rates there is an abundance of reactive species so the polymerization rate is limited only by the availability of monomer supply. At high flow rates, however, there is an overabundance of monomer concentration and the polymerization rate now depends on the residence time. At intermediate flow rates these two competing processes result in a maximum. This behavior is illustrated in Figure 1 for ethane, ethylene, and acetylene (11). These data also demonstrate the effect of increased unsaturation in... 

Figure 1. Rates of plasma polymerization of acetylene, ethylene, and ethane as a function of monomer flow rate (llj...

Figure 5. The rate of plasma polymerization of ethylene as a function of electrode gap (15)...

Journal of Macromolecular Science, Chemistry Figure 9. Characteristic map for the plasma polymerization of ethylene (ISj... 

The morphology of the plasma polymerized films has been examined by electron microscopy by a number of workers ( 3,, 48). Figure 12 shows the replica electron micrograph of plasma polymerized ethylene deposited on chromium substrate at several gas pressures (46). The presence of powder particles is clearly evidenced in Figures 12a-c. The size and density of the powdery products decrease with increasing pressure until at a pressure of 3 torr when the polymer is mainly film and contains very few particles. 

Figure 12. Transmission electron micrographs of plasma-polymerized ethylene on chromium substrate at 80 mL/min, 100 W, and (a) 0.7 torr, (b) 1.5 torr, (c) 3 torr, and (d) substrate alone (46)...

Figures 13 and 14 compare the surface structures of the plasma polymerized ethylene on Teflon, and cleaved mica ( 6). Because of the rougher initial surface on Teflon, there is a greater concentration of powder on that surface. The mica surface is smooth before polymer deposition. The polymer films are also very smooth and featureless, indicating the strong dependence of morphology of plasma polymerized films on the surface roughness of the substrates.

Figure 13. Transmission electron micrographs of plasma-polymerized ethylene on Teflon substrate. Polymerization conditions are the same as in Figure 12 ( 46j.

Figure 16. Postulated model of plasma-polymerized ethylene film (56)...

Figure 17. Fyrolysis/gas chromatography pyrogram of plasma-polymerized ethylene oil (59)...

Stancell et. al. ( 0) reported the possible use of ultrathin films deposited onto relatively permeable substrates as permselective membranes. Ultrathin and highly crosslinked coatings effectively distinguish between molecules of different sizes and increase the permselectivity of the substrate film. Chang et. al. ( ) demonstrated that the permeability coefficient of silicone rubber to oxygen decreased noticeably after depositing a plasma-polymerized ethylene film on the surface. Colter, et. al. (92.93) found similar effects of plasma polymerized films as diffusion barriers in controlled-released drug delivery systems. 

Most studies of plasma polymerization have been conducted in continuous wave rf plasmas. The effects of pulsed mode operation have received only limited attention. In a recent study, Yasuda et al. (1 ) found that while the polymerization rate of most monomers decreased when polymerization was carried out in a pulsed versus continuous plasma, the polymerization rate of a few monomers was enhanced. The present study was undertaken to determine the effects of pulsed operation on the plasma polymerization of ethylene and ethane. These monomers were selected because their behavior in continuous wave plasmas had been examined extensively in previous investigations (2 - ). ... 

As in the case of ethylene and acetylene W, plasma polymerization of benzene produced either a powder or film depending on reaction conditions. A typical condition in which thin film with the required property was produced (the RO membrane condition) is shown in Table 1, coded as Condition B, while that for poor quality film formation is designated A. Conditions for powder formation are designated C and E in the table. Generally speaking, film formation was observed at high benzene flow rates, and powder formation was observed at low pressures and low benzene flow rates, as in the case of ethylene and acetylene ( ). However, the RO membrane conditions do not correspond to either a unique point on the pressure (P) versus benzene flow rate (Q(Bz)) plane nor do they correspond to the conditions in which a lot of polymer was produced. This means that the quality of the film cannot be correlated directly to the macroscopic reaction conditions. 

A scheme for bicyclic dimer formation from HMCTSN under plasma conditions has been proposed in our previous paper (J.) According to this scheme, formation of new Si-N bonds with tertiary nitrogen between trisilazane rings leads to crosslinking of the polymer, and involves the production of hydrocarbons such as methane and ethane. Indeed, gas chromatographic analysis of the gaseous residue after plasma polymerization has shown that it consists mainly of three hydrocarbons methane, ethane and ethylene in the 5 33 4 ratio. 

Our earlier structural studies (15) have shown that in the case of plasma-polymerized HMCTSN and HMCTSO other crosslinking reactions may take place. Ultraviolet radiation emitted by the plasma may cause a hemolytic cleavage of Si-C and C-H bonds in SiCH groups, fo-lowed by crosslinking in the polymer via formation of methylene and ethylene linkages between silicon atoms. 

In order to modify favorably the interaction balance at PE/PS contacts, mica was subjected to LMP treatments using E and S monomers in sequence. In principle, the generation of plasma-polymerized ethylene (PPE) and styrene (PPS) on the mica surface might... 

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