Noncatalytic Hydrolysis of Epoxidized Castor Oil: A Sustainable Route to Diol‐Rich Polyols and Recyclable Polyboronates

The shift from fossil-based to biobased feedstocks is paramount for sustainable chemical production. This work presents an efficient, catalyst-free method for synthesizing a diol-rich polyol from epoxidized castor oil. Unlike conventional acid-catalyzed methods, the presented approach minimizes undesirable side reactions, yielding a polyol with a high hydroxyl number of 6.5 per triglyceride (370 mg KOH/g) and a low oligomer content. By performing the reaction at 130°C in an overheated water-dioxane mixture, we achieved full epoxide conversion in 24 h, making the process competitive with acid-catalyzed systems. This resulting polyol, characterized by a high content of adjacent diols, was utilized to prepare novel, recyclable polyboronates with 1,4-phenylenediboronic acid. Based on NMR analysis, the stoichiometry of the reaction between the synthesized polyol and phenylboronic acid was determined. Additionally, a regioselective preference for the formation of six-membered cyclic esters with 9,10,12-trihydroxyoctadecanoates, which constitute the main fraction in the synthesized polyol, was revealed. The polymers exhibit properties of low-cross-linking-density elastomers. The dynamic covalent nature of the boronate linkages was confirmed through DMTA and stress relaxation experiments. This research establishes hydroxylated castor oil as a robust and sustainable building block for polymer materials.