CORRELATED ELECTRON-SPIN-RESONANCE AND INFRARED SPECTROSCOPIC STUDY OF THE POSTFORMATION AUTOXIDATION PHENOMENON IN PLASMA-POLYMERIZED 4-VINYL PYRIDINE FILMS

Plasma polymerization of 4-vinyl pyridine (4-VP) proceeds through a ga s-phase free radical mechanism to yield a film that retains much of th e organic functionality of the monomer. During the deposition process, free radicals, which have been shown to quickly react with oxygen, ar e trapped to yield a film with a nascent peroxy radical density of 2.9 X 10(18) spins/g as quantified by electron spin resonance (ESR) spect roscopy. In air at room temperature, peroxy radicals in the film react to produce carbonyl, hydroxyl, and ether structures in the polymer th at was monitored using infrared (IR) spectroscopy. The free radical po pulation was found to decay rapidly at first and then reach an apparen t steady state after 30 hr. As the spin density decreases, a concomita nt growth of vibrational modes associated with oxygen-containing funct ional groups was observed in the IR spectrum of the film. The relative population of oxygen-containing groups continued to increase even aft er the free radical population reached steady state. This slow, auto-o xidative effect may be attributed, in part, to free radical centers th at are anchored to the polymer chain in regions of high crosslinking. In such regions, limited segmental mobility may limit the rate of radi cal-radical recombination (termination) processes relative to oxidativ e radical-center. (C) 1996 John Wiley & Sons, Inc.