Tannin-Based Copolymer Resins: Synthesis and Characterization by Solid State 13C NMR and FT-IR Spectroscopy

In recent years, the interest for bio-sources is rising exponentially and tannins extracts are one of the most interesting, easily-available, phenolic building blocks. The condensed tannins or proanthocyanidins are already known for their polymerization chemistry, which is the basis for several natural-based materials (e.g., adhesives, foams). In the present work we aim to observe the behavior of the extract of Acacia Mimosa (Acacia mearnsii) when reacted with several possible co-monomers at different relative amount, pH and temperature conditions. The more insoluble copolymers obtained with formaldehyde, hexamine, glyoxal, maleic anhydride, furfural and furfuryl alcohol were analyzed through solid state C-13 NMR (Nuclear magnetic resonance) and FT-IR (Fourier Transform-Infrared) spectroscopy. The C-13 NMR afforded the opportunity to detect: (i) aromatic substitutions and consequent poly-condensations for the majority of the hardeners studied; (ii) acylation for the maleic anhydride and also some; (iii) Diels-Alder arrangements for the furanic co-monomers; the FT-IR spectroscopy suggested that the formaldehyde and hexamine copolymers present a higher cross-linking degree.