Chemical characterization of polymerized products formed in the reactions of matairesinol and pinoresinol with the stable radical 2,2-diphenyl-1-picrylhydrazyl

Polymerization reactions of the lignans matairesinol and pinoresinol with the stable radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) were studied. The reactions were rapid and almost quantitative. The molecular weight distribution (MWD) of the formed lignan dimers and polymers was determined by high-performance size-exclusion chromatography (HPSEC) combined with evaporative light-scattering detection (ELSD), and the compounds were characterized by HPLC-MS, pyrolysis-GC/MS, NMR, MALDI-ToF-MS, and GC-MS of the monomeric and dimeric units formed by KMnO₄ oxidation. The yield of high-MW polymers is higher for pinoresinol (69%) than for matairesinol (43%). According to the HPSEC-ELSD analyses, the MWD is also broader for the pinoresinol polymers. The latter seem to consist mainly of hepta-hexacontalignans (MW 2.5–21.4 kDa), whereas the matairesinol polymers are mainly penta-pentadecalignans (MW 1.8–5.3 kDa). The polymers seem to contain mainly unmodified lignan units linked by 5-5′ bonds.