Synthesis of Cardanol-Based Polyols via Thiol-ene/Thiol-epoxy Dual Click-Reactions and Thermosetting Polyurethanes Therefrom

Abstract

Two novel bio-based polyols were synthesized from cardanol via thiol-ene/thiol-epoxy dual click-reactions. Compared with the cardanol-based polyols synthesized by the thiol-ene reaction, the cardanol-based polyols synthesized by thiol-ene/thiol-epoxy dual reactions have a higher hydroxyl number due to the additional secondary hydroxyl group generated from the thiol-epoxy reaction. The synthesized polyols were formulated with hexamethylene diisocyanate (HDI) trimers to prepare cardanol-based thermosetting polyurethane (PU) films. Thorough thermal and mechanical characterizations of the prepared PU films were carried out to study the structure–property relationship. An UV-aging test was conducted to characterize the color retention of the cardanol-based PU films. The thermal stability of cardanol-based PU films was improved after converting the phenolic hydroxyl to aliphatic hydroxyl. With increasing the hydroxyl number of cardanol-based polyols, the cross-link density, glass transition temperature, elastic modulus, tensile strength, and hardness of cardanol-based PU films were all improved. The results of this work confirmed that the utilization of thiol-ene/thiol-epoxy dual click-reactions is an effective approach to synthesize cardanol-based polyols with a relatively high hydroxyl number. The significance of this work is believed to broaden the usage of cardanol in different PU formulations and applications.