Synthesis and application of epoxy-ended hyperbranched polymers

Epoxy-ended hyperbranched polymers (EHPs), as important type of functional thermosetting hyperbranched polymers, have attracted broad and continuing interest from both academic and industrial researchers. Benefiting from their high-crosslinking ability, void-containing topological structure and very low viscosity, EHPs have been widely applied in reinforcing and toughening diglycidyl ether of bisphenol-A (DGEBA) and in solvent-free or environmentally-friendly coatings. Therefore, the design and synthesis of EHPs provide a robust tool for controlling the interfacial interaction between EHPs and DGEBA to finally gain excellent comprehensive performance. In this review, the perspectives and recent advances of preparation methods, performance control and promising applications of various EHPs have been comprehensively summarized. In addition, a single toughening function, a simultaneously reinforcing and toughening function and the mechanism of DGEBA by EHPs are also discussed and investigated by integrating molecular simulations, dynamic mechanical analysis (DMA) and scanning electron microscope (SEM) technologies. EHPs with high contents of epoxy group show simultaneous reinforcing and toughening in DGEBA, regardless of their aliphatic and aromatic structures, and whether there is phase-separation or homogenous structure associated with the fractured surface. The simultaneous reinforcing and toughening mechanism changes the conventional conception of inter-contradiction between the toughening and reinforcing function. It was also found that EHPs with different synthetic strategies and diverse performance have allowed an increasing number of versatile industrial applications.