Controllability on topological structures and properties of hyperbranched epoxy resins

Hyperbranched epoxy resin (HERs) have attracted increasing attention from scientists and engineers, due to their excellent functionalities in homogenously reinforcing and toughening diglycidyl ether of bisphenol-A (DGEBA) without phase separation. However, it remains a great challenge to control the topological structures of HERs and to discover the effect of microstructure on the properties of epoxy resins. Here, we report the synthesis of NP skeleton epoxy hyperbranched polymer (NMHEP-n) with a controllable degree of branching (DB) and topological structures by a thiol-ene click reaction. The DB of NMHEP-n can be tuned readily with a ratio of designed branched and linear monomers from 0 to 1.0, which can determine the topological structure from linear rod-like chains to ellipsoidal, further to spherical molecular chains. With the increase of DB from 0 to 1.0, a root-mean-square z-average radius of gyration (Rg), hydrodynamic radius (Rh) and shape factor (ρ = Rg/Rh) decrease, being an agreement with the variation from linear to spherical shape. Performance of NMHEP-n/DGEBA composites, including cold resistance, tensile, flexural, and impact strengths, are significantly improved with an increase in DB and content, and the maximum value appears at 12 wt% NMHEP-0.5 in composites. The simultaneous improvement on various properties is attributed to a homogeneous reinforcing and toughening mechanism, which can be rationalized and substantiated by DMA, AFM, SEM, and Raman techniques. These results render an applicable approach to prepare high-performance thermosets and composites.