MALDI-TOF and 13C NMR analysis of flexible films and lacquers derived from tannin

•Highly flexible films were prepared from aminated tannin and furfuryl alcohol with a plasticiser such as glycerol.•Strongly adhering surface finishes were prepared from aminated tannin and furfuryl alcohol with polyethylene imine.•13C NMR and MALDI-TOF showed oligomers of furfuryl alcohol coreacted with non-aminated and aminated tannin flavonoids.•Self-condensation of furfuryl alcohol led to linear methylene–furanic chains also linked to flavonoid reactive sites.•Rearrangement of methylene ether to methylene bridges freed formaldehyde reacting with the flavonoid and furane rings.

Highly flexible films and strongly adhering surface finishes were prepared by reacting partially aminated polyflavonoid tannins with furfuryl alcohol in the presence of plasticisers such as glycerol or polyethylene imine. 13C NMR analysis showed partial amination of the tannin under the conditions used and even the formation of some N bridges between flavonoids, although these were shown to be rare. MALDI-TOF analysis showed the presence of oligomers produced by the reaction of furfuryl alcohol with the flavonoids and the simultaneous self-condensation of furfuryl alcohol. Thus linear methylene–furanic chains were also found to be linked to flavonoid reactive sites. Furthermore, side condensation reactions of furfuryl alcohol lead to the formation of methylene ether bridges between furanic nuclei, followed by rearrangement to methylene bridges with liberation of formaldehyde. This latter reacts with both the reactive sites of the flavonoid and of the furane rings to yield CH2OH and CH2+ groups and methylene bridges.