GC/MS and PGC/MS analyses of plasma polymerization for benzaldehyde

Abstract

SYNOPSISGas chromatography/mass spectrometry studies of gas condensates in plasma and pyrolysis products of plasma polymer for benzaldehyde were made. Both products' analyses indicate the significant presence of benzyl and carbonyl groups in plasma polymer samples. Infrared measurements were also used to correlate the structures suggested by GC/MS results. A radical mechanism, which involved hydrogen abstraction, aldehyde group abstraction, and benzyl fragmentation under plasma activation, was proposed. The highly crosslinked and branched structures of the plasma polymer were attributed to the subsequent reactivity of free radicals, formed as a result of the scission of the chemical bonds in the benzaldehyde molecules.

Pulsed Plasma Polymerization of Benzaldehyde for Retention of the Aldehyde Functional Group

“…Additional supporting evidence for processes such as Scheme during plasma polymerization can be obtained from the work of Zhao et al , First, the CH aldehyde bond is considered extremely labile, especially in plasmas, primarily because it is the weakest bond in benzaldehyde . Second, complete conversion of aldehyde to ketone functional groups has been observed by Zhao et al in the films produced by CW plasma polymerization of benzaldehyde. , Finally, the neutral effluent from the benzaldehyde plasma using a hyphenated GC/MS technique showed significant generation of benzene, diphenyl ketone, and smaller unsaturated compounds at CW powers of 60 W . The authors proposed that the formation of diphenyl ketone was through gas-phase reactions of benzoyl radicals (I) (Scheme ), resulting in ketone functional groups in the deposited film.…”

“…Moreover, optical emission spectroscopy (OES) data of CW benzaldehyde plasmas in our laboratory show strong signals from both excited-state CO and R-H emission at all powers. 21 Additional supporting evidence for processes such as Scheme 1 during plasma polymerization can be obtained from the work of Zhao et al 10,11 First, the CH aldehyde bond is considered extremely labile, 22 especially in plasmas, 4 primarily because it is the weakest bond in benzaldehyde. 12 Second, complete conversion of aldehyde to ketone functional groups has been observed by Zhao et al in the films produced by CW plasma polymerization of benzaldehyde.…”

“…Use of pulsed sources reduces trapped radicals in the film, lowers deposition surface temperatures, decreases high-energy ion bombardment and UV flux to the surface, and provides greater control over the resulting film chemistry . We have previously reported the use of pulsed rf plasmas to produce a variety of organic films with a high degree of controllability over film composition. , Additional work in this area has concentrated on inorganic materials such as amorphous hydrogenated silicon carbide (a-Si 1 - x C x :H). , …”

“…The main goal is to explore pulsed plasma conditions that result in retention of the aldehyde functional group on the surface of the deposited polymeric film . Zhao et al have performed CW plasma polymerization using benzaldehyde but found little retention of the aldehyde functional group in their films using infrared spectroscopy, thermogravimetric analysis, contact angle goniometry, and gas chromatography−mass spectrometry (GC-MS). , Instead, an abundance of ketone functional groups was observed, suggesting that the terminal hydrogen of the aldehyde group was extremely labile during plasma polymerization. This seems reasonable, as the C−H bond on the aldehyde group is the weakest bond in the monomer ( D 0 ∼ 78 kcal/mol) .…”

“…3,5 Additional work in this area has concentrated on inorganic materials such as amorphous hydrogenated silicon carbide (a-Si 1-x C x :H). 8,10 In the present work, benzaldehyde is used as the monomer in a series of pulsed plasma polymerizations. The main goal is to explore pulsed plasma conditions that result in retention of the aldehyde functional group on the surface of the deposited polymeric film.…”