Novel resveratrol-based hyperbranched epoxy resin suitable for comprehensive modification of epoxy resins

Abstract

Hyperbranched epoxy resins are efficient modifiers for epoxy resins but still require simultaneous improvements in terms of thermomechanical/mechanical properties and thermal stability. Herein, a novel resveratrol-based hyperbranched polyether epoxy resin (HBPEER) was designed for all-purpose epoxy resin modification. To this end, hyperbranched polyether with terminal phenolic hydroxyl groups was first synthesized from commercially available 1,6-dibromohexane (A2-type monomer) and resveratrol (B'B2-type monomer). Surface modification with epichlorohydrin was afterward implemented to produce hyperbranched polyether with terminal epoxy groups (HBPEER). Next, various HBPEER-modified epoxy thermosets were prepared and characterized. The results suggested that compared to the neat diglycidyl ether of bisphenol A (DGEBA) thermoset, the 6 wt% HBPEER-modified epoxy thermoset showed an increase in impact strength, elongation at break, critical stress intensity factor (KIC), critical crack propagation energy release rate (GIC), flexural strength, tensile strength, storage modulus, glass transition temperature (Tg), and initial thermal decomposition temperature (Td5%) by 69.6 %, 87.0 %, 32.0 %, 68.2 %, 29.3 %, 37.0 %, 8.1 %, 3.5 %, and 1.6 % respectively. Moreover, the dielectric constant and loss of 6 wt% HBPEER-modified epoxy thermoset decreased by 16.2 % and 16.5 %, respectively. Such comprehensive performance modifications were caused by the combined effects of crosslink density improvement, efficient intramolecular cavity, rigid stilbene units, and flexible aliphatic backbone of HBPEER.