Structural Characterization of Plasma-Polymerized Hydrocarbons

Oils and films were produced by passage of ethylene, acetylene, and butadiene gases as well as benzene vapor through a radio-frequency electric discharge. The hydrocarbon oils produced in the plasma were dissolved in carbon tetrachloride and were analyzed by infrared and nuclear magnetic resonance spectroscopy. Based on these analyses, concentrations of characteristic functional groups were determined and used to propose molecular structures. The hydrocarbon oils are postulated to consist of irregular sequences of highly branched and incompletely crosslinked aliphatic backbone chains with pendant aromatic rings. Double bonds are interspersed along the chains. Hydrogen/carbon ratios in the proposed structures are consistent with the results from elemental analyses. Products from py-rolysis mass spectrometry can also be interpreted on the basis of the proposed structures. Similar techniques are used to analyze the structures of insoluble plasma polymerized films obtained from the same hydrocarbons. The major distinguishing feature in the films is the very high degree of crosslinking; of the order of one crosslink per six to ten chain carbon atoms.