The precise effect of degree of branching of epoxy-ended hyperbranched polymers on intrinsic property and performance

Epoxy-ended hyperbranched polymers (EHPs) are increasingly used in toughening and reinforcing diglycidyl ether of bisphenol-A (DGEBA). Synthesis of EHPs with a precise degree of branching (DB) and the effect of DB on the property of EHPs are still a challenge. Here we report the synthesis and properties of nitrogen-phosphor skeleton epoxy-ended hyperbranched polymers (NPEHP-n) with a controlled degree of branching. The particle sizes, rheological properties, mechanical and thermal properties of NPEHP-n/DGEBA composites were studied in detail and compared with those of pure DGEBA. The particle sizes, viscosities, storage modulus and loss modulus of NPEHP-n/DGEBA blends decrease with an increase in DB and content of NPEHP-n, indicating excellent flowability of NPEHP-n with high DB and disentangled function of NPEHP-n. The mechanical performances of the cured NPEHP-n/DGEBA composites increase distinctly with the increase of the DBs and content of NPEHP-n, including the tensile, flexural and impact strength, showing a maximum value at about 9 wt% of NPEHP-n. The improvements on the tensile, flexural, and impact strengths are 31.7-42.8%, 56.4-76.4%, and 172.0-198.3%, respectively. The results will supply available route for disentangling DGEBA chain to obtain low viscosity epoxy resins and solvent-free coatings.