A study of the oxidative degradation of furfuryl alcohol polycondensates by infrared spectroscopy

Abstract

The oxidative curing and oxidative degradation of cured furfuryl alcohol polycondensates was examined, with infrared spectroscopy, by following the functional group changes occurring in the solid phase of the resin. It has been found that the oxidative degradation of nitrogen‐cured resins initially proceeds through the oxidation of methylene linkages to bifuryl ketonic species activated by adjacent furan rings. The second stage of oxidation is the scission of the bifuryl ketonic chain positions to produce substituted furoic acids. The process is postulated to proceed in a manner analogous to that observed in phenolic resin systems. The curing of furfuryl alcohol resin in air is shown to be a multistep process in which the initial oxidation of methylol groups to carboxylic acids is competitive with further polymerization through methylol condensation at adjacent furan ring alpha hydrogen positions. In addition, the oxidation of already formed methylene linkages to the bifuryl ketones is a competitive process removing methylene linkages after they are produced during further condensation (curing reactions). These routes of degradation are in good agreement with observed oxidations of furfuryl alcohol resins under more drastic conditions and offer a reasonable mechanism for resin degradation consistent with observations in analogous polymer systems.

Poly(furfuryl alcohol) formation in neat furfuryl alcohol and in cymene studied by ATR-IR spectroscopy and density functional theory (B3LYP) prediction of vibrational bands

“…The account given above largely agrees with published assignments of some of the poly(FA) IR bands [11][12][13][14][15][16] and adds significantly more detail. Our results also allow the correction of incorrect assignments, which appear in this literature.…”

“…It is thus clear that the 1675 cm À1 band of the structural models considered can only be assigned to such a perturbation. The possibility remains, however, that this band is caused by a carbonyl side product, where its relatively low frequency suggests interaction of the carbonyl moiety with a conjugated structure [11,12,15].…”

The chemistry of furfuryl alcohol resins

“…The composition of the liquid polymer and the mechanism of polymerization have also been studied by Hachihama and S h~n o .~-'~ Takano examined the products from the initial stages of resinification and isolated two homologs of difurylmethane, 2,2'-methylenebis(5-furfurylfuran) and 2,5-bis(furfurylf~rfuryl)furan.~~-~~ Conley and Metil proposed mechanisms for the oxidative degradation of the polymer by studying changes in the functional groups of the resin revealed by infrared spectroscopy. 18 These workers also isolated a carbonyl compound, 5-hydroxy-3-pentenoic lactone, by fractionating a thermally condensed resin.…”

Surfactant‐Exfoliated Highly Dispersive Pd‐Supported Graphene Oxide Nanocomposite as a Catalyst for Aerobic Aqueous Oxidations of Alcohols

“…Good to excellent product yields were obtained forb enzylic alcohols bearing electron-donating ( www.chemcatchem.org them have been shown to be suitable for the oxidation of hydroxyl groups contained in heterocycles. [40,41] As expected, secondary alcohols were difficult to oxidize. Nevertheless, the conversion of 1-phenylethanol and aliphatic alcohols as secondary alcohols to their corresponding ketones under optimized reactionc onditions could be achieved in excellent yields by increasing the reactiont ime and increasing the catalystl oading to 1mol %u nder basic media (adding 1equiv.ofK 2 CO 3 )t oensure acceptable conversions (Table 2).…”