Boron–boron bonds: boldly breaking boundaries towards amine- and peroxide-free 2K radical polymerization

Abstract

Free radical polymerization (FRP) is one of the most important tools for the production of polymer materials. Many applications of such materials require a convenient polymerization process at room temperature and ambient atmosphere, which is where two-component (2K) systems based on redox initiated radical polymerization truly stand out. However, these radical polymerization systems (RPSs) often require toxic amines and thermally labile (explosive) peroxides as redox pairs. In order to surpass these hazardous limitations, a new RPS for 2K polymerization of industrially implemented methacrylic monomers was developed. The use of diboranes as labile bonds and copper complexes that catalyze their cleavage was found to be a very efficient radical initiation system. High reactivity towards radical polymerization is presented by different combinations of these compounds, and the influence of steric and electrochemical effects is investigated in this context. Furthermore, thermomechanical and mechanical testing of polymer materials was conducted. The obtained polymer networks were found to possess a highly homogeneous structure and furthermore properties that are strongly influenced by the RPS, including the possibility of thermal post-curing reaching T_g's > 150 °C.