Aging of 1,3-diaminopropane plasma-deposited polymer films: Mechanisms andreaction pathways

In the course of plasma deposition of organic-polymeric thin films, radical s are incorporated into the growing film. These radicals initiate spontaneo us oxidation reactions that continue over many weeks when the plasma polyme rs are stored in air. These reactions and their products have been previous ly studied in detail for spectroscopically simple, hydrocarbon-based plasma polymers. In this investigation, the aging of 1,3-diaminopropane (DAP) pla sma polymer samples was monitored by XPS and FTIR in order to study how the oxidative reaction pathways might differ in a plasma-deposited material th at is initially rich in amine groups. The freshly deposited DAP plasma poly mer consisted of a random hydrocarbon network with a considerable amount of unsaturation and a high concentration of nitrogen-containing functional gr oups, mainly primary/secondary amines and imines. These groups strongly inf luenced the aging reactions: in contrast to hydrocarbon-based material wher e hydrogen abstraction and reaction of carbon-centered radicals with in-dif fusing oxygen result in a wide range of oxidative products, both XPS and FT IR identified a rather narrow range of products (mainly amides and similar groups) in DAP plasma polymers even after extensive aging for more than 2 y ears. Reaction routes based on oxidation and/or hydrolysis of nitrogen func tional groups, and involving primary as well as secondary reactions, are pr oposed to account for the spectroscopic data. The structure of the aged DAP plasma polymer appeared to be stable, and did not undergo more extensive o xidation, in contrast to hydrocarbon plasma polymers. In particular, carbox ylic acid groups and carbamates were not detected. (C) 1999 John Wiley & So ns, Inc. J Polym Sci A: Polym Chem 37: 2191-2206, 1999.