Polyflavonoids and lignin from Pinus radiata (D. Don.) biomass were esterified with maleic anhydride by several synthesis pathways (22 °C, 24 h). Influence of the solvent (dimethylformamide (DMF), DMF/H2O, acetone, formamide)-, the catalyst-type (H2SO4, NaHCO3), and the NaHCO3-change (70 and 100 mmol) on the esterification yield, and the degree of substitution (DS) were estimated. The effect of the maleilation on structural features was assessed by spectroscopy (FT-IR, UV–vis, RMN), and molecular exclusion chromatography. FT-IR, and 1H-NMR provide valuable insight regarding the esterification extent. The results show that esterification of high molecular weight polyphenols exhibited reasonable yields (80–95 wt.%). A significant influence of the solvent-, and the catalyst was observed. Synthesis in formamide, as well as by the highest charge of the alkaline catalyst, exhibited the best performance toward the polyphenol´s modification. Maleilation efficiency was strongly influenced by the polyphenol-type. Non-water soluble polyflavonoid derivatives exhibited the highest DS/monomer unit regardless the synthesis conditions. Carboxylated polyphenols from radiata pine may be used as functional co-polymer for new kinds of material applications.