Tailored Acid Carrier Acidity for the Controlled C═C Peracid Epoxidation of Cardanol-Based Materials with Different Polarities

In this paper, the controlled C═C peracid epoxidations of cardanol derivatives with different polarities including cardol glycidyl ether (Cardol-GE), cardanol, cardol, and cardanol polyoxyethylene ether ammonium sulfate have been achieved by tailoring the acidities of the acid carriers. Various peracid carriers with different acidities (including formic acid, acetic acid, and nonanoic acid) have been utilized. The epoxidation structure has been characterized using Fourier transform infrared, nuclear magnetic resonance, epoxy equivalent titration, and liquid chromatography. It was demonstrated that the epoxy ring-opening reaction occurs due to the presence of the peracid. The proportion of the ring openings is closely related to the acidity, reaction temperature, and reaction time. By tailoring the acidity of the acid carriers, the epoxy ring-opening rate can be significantly reduced while maintaining a high degree of epoxidation degree. Interestingly, it is found that the peracid carrier with higher acidity is needed for Cardol-GE with a lower functional group polarity, and this is explained by the two-phase nature of the peracid epoxidation reaction. The mechanical strength of the composites using Cardol-GE was improved by 83% after side-chain epoxidation. Moreover, it was found that the epoxidation rate was not directly proportional to the number of C═C bonds in their side chains; this is explained by the different reactivities of different C═C bonds. This article gives a deeper understanding of the correlation between the polarity of the cardanol-based materials and their C═C bond epoxidation and may serve as a guide for the controllable epoxidation of all cardanol-based materials.