Peroxidase-catalyzed copolymerization of syringaldehyde and bisphenol A

Syringaldehyde, one of the major derivatives of lignin, was copolymerized with bisphenol A via a CiP (Coprinus cinereus peroxidase)-catalyzed reaction. Although syringaldehyde was not polymerized to a solid polymer, the copolymer with bisphenol A was obtained as a dark brown powdery precipitate. The relatively hydrophobic solvent, 2-propanol, gave a better yield (yield = 95%) than hydrophilic solvents, such as methanol, ethanol or acetone. Characteristic signals corresponding to the aldehyde group of syringaldehyde in the copolymer were detected in the FT-IR and 13C NMR spectrum. The ratio of syringaldehyde incorporated into the copolymer was estimated by measuring the amount of monomers consumed (syringaldehyde and bisphenol A), which proportionally increased up to 80 mol% on increasing the initial ratio of syringaldehyde to bisphenol A. TGA (thermogravimetric analysis) showed that the thermally crosslinked copolymer (syringaldehyde:bisphenol A = 1:1, w/w) had a much higher thermal resistance to thermal degradation than poly(bisphenol A); 36% residue still remained under a nitrogen atmosphere, even over 800 °C. This implies that the copolymer of syringaldehyde and bisphenol A could be a new thermally stable material originating from renewable resources.