Highly efficient preparation of hyperbranched epoxy resins by UV-initiated thiol-ene click reaction

Hyperbranched epoxy resins (HEPs) attract an increasingly interest due to their remarkably reinforcing and toughening properties on thermoset. A major challenge for HEPs is the serious environmental pollution resulted from the large amount of organic solvents used during tedious synthetic procedure. Another challenge is low yield and low epoxy content of HEPs, resulting in low crosslinking density and impairing mechanical strength and compatibility with matrix. Here we report a fast and environmentally friendly approach to addressing these challenges using a UV-initiated thiol-ene click reaction. The new synthesis process has been used to prepare not only hyperbranched epoxides with high epoxy content, and also many kinds of glycidyl ether epoxy resins (mono-epoxide, di-epoxides, tri-epoxides) based on thiols precursors and allylglycidyl ether. Their chemical structures and molecular weights were characterized by FT-IR, H-1 NMR, electrospray ionization mass spectrometry (ESI-MS) and GPC spectra. All the click reactions took only 5-10 min of UV radiation at room temperature and show very high yields between 98.1 and 99.8%, and epoxy equivalent weight of all the epoxy resins is very close to its theoretical value. This fast and environmentally friendly process may open a new avenue for the design and synthesis of HEPs as well as common epoxy resins. (C) 2016 Elsevier B.V. All rights reserved.