The process where wood is impregnated by furfuryl alcohol and catalyst and subsequently heated has previously been proposed to be a chemical modification method. But when furfuryl alcohol polymerizes in situ and permanently swells the cell walls, does the reaction indeed generate chemical bonds between the polymer and one or more wood constituents such as lignin, hemicellulose and cellulose? Although indirect observations that support this hypothesis exist, definite proof of such bonding is not yet available. As a first step towards demonstrating the presence of such bonds, we have investigated two liquid model solutions with model compounds (2-methoxy-4-methylphenol and 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol) that chemically resemble principal repeating units of lignin. The selected methods are NMR spectroscopic ones. 2D COSY spectroscopy reveals atoms that are connected through covalent bonds. NMR diffusion experiments give translational self-diffusion coefficients, which are identical for chemically bonded entities. We find that a fraction of the model molecules formed covalent bonds with poly(furfuryl alcohol). These results indicate that the furan polymer in furfurylated wood is grafted to the wood lignin.