Polymers from natural occurring phenols as novel bioinspired antioxidants

Polymers of natural polyphenols have so far received little attention as bioavailable, biocompatible antioxidants for several applications e.g. in packaging and related technologies. Expected advantages with respect to the monomers would include greater chemical stability under processing conditions and lower tendency to be released into the contact medium (food, water, etc.) with reduced adverse effects. As an example we have recently found that a polymer obtained by oxidation of caffeic acid methyl ester is highly efficient in stabilizing polyethylene against oxidative degradation.1 We have also observed that acid treatment significantly improves the antioxidant properties of natural phenolic pigments.2 Herein we report the results of a systematic investigation of the reducing and free radical scavenging properties of bioinspired polymers prepared by horseradish/H2O2 oxidation of a series of natural phenolic compounds (e.g. ferulic acid, caffeic acid and pyrogallol) and of the effects of acid treatment on these properties.3 Both 2,2-diphenylpicrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays indicated a significant increase (up to 230 times) in the antioxidant properties of almost all the phenolic polymers investigated. Details on the structural modifications induced by the acid treatment as deduced by electron paramagnetic resonance (EPR), UV-vis spectroscopy and solid state CPMAS NMR will be reported. This study furnishes important information to tailor synthetic phenolic polymers as novel easily accessible materials for use in packaging and biomedical applications.