Nonpolymerizable gases in plasma polymers

Another important and unique feature of plasma polymerization is the incorporation of gases that do not form polymer or solid deposits in plasma by themselves during polymer formation of organic molecules in plasma. This incorporation of gases is plasma copolymerization and not the trapping of gas molecules in plasma polymers. 

There is a significant difference between copolymerization and codeposition. An example of codeposition is the simultaneous deposition of parylene or a plasma polymer and an evaporated metal, in which each component can be deposited regardless of whether or not the other component is being deposited. Plasma polymerization of a mixture of two hydrocarbons, e.g., CH4 and C2H4, is essentially codeposition of the respective plasma polymers. In contrast, plasma polymerization of gases occurs only in the presence of polymer-forming plasma. This is similar to the copolymerization of maleic anhydride, which does not polymerize, with other vinyl monomers. 

An example of plasma copolymerization of gases is the incorporation of N2 in the plasma polymer of styrene. N2 mixed with styrene was consumed in plasma polymerization [12]. In a closed-system experiment, pressure measurement is a very useful tool for investigating plasma polymerization, particularly when the monomer used does not produce gaseous by-products. The pressure changes observed in a closed-system plasma reactor with mixtures of N2 and styrene are shown in 

The incorporation of N2, CO, and H2O in the plasma polymer of acetylene is evident from the results of elemental analysis as well as from infrared (IR) spectra 

Monomer (pressure, ggHg) c (%) H (%) N (%) 0 (%) Empirical formula Color 

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