Preparation and Properties of Castor Oil-Based Dual Cross-Linked Polymer Networks with Polyurethane and Polyoxazolidinone Structures

Dual cross-linked polymer networks (DCPNs) are novel copolymers containing two different cross-linking polymers with superior comprehensive properties. The aim of this study was to explore the feasibility of preparation of novel castor oil-based DCPNs material. First, two novel biobased reactive monomers of epoxidized castor oil (ECO) and ricinoleic acid epoxy (RAE), containing both hydroxy and epoxy groups, were synthesized from castor oil (CO). Their chemical structures were characterized by Fourier transforminfrared spectroscopy (FTIR) and 1H-nuclear magnetic resonance (1H NMR) analysis. Both hydroxy and epoxy groups can react with the isocyanate groups of toluene-2,4-diisocyanate (TDI), and then two renewable resource-based DCPNs of RAE/TDI and ECO/TDI, containing both polyurethane (PU) and polyoxazolidinone (POXDN) molecular structures, were designed and prepared. The tensile properties, gel content (GC), hardness, fractured surface morphologies, thermostabilities, and dynamic mechanical and thermal properties of these renewable resource-based copolymers were all investigated. Results show that the tensile properties, GC, hardness, and glass transition temperature (Tg) of the fabricated DCPNs were superior to those of the pure CO/TDI copolymerized system. The fabricated DCPNs, particularly RAE/TDI, were found to have good tensile strength of 12.47 MPa and the highest elongation at break of 154.99%, and its thermostability was also increased greatly compared with that of the pure CO/TDI copolymerized system.