Enhancement of Moisture-Resistant Performance of Epoxy Resins via Introduction of Hydrophobic and Flexible Chains

The introduction of long and flexible polyether chains in epoxy resins is an effective method to improve their toughness. However, using the hydrophilicity/hydrophobicity of polyether chains to tune their moisture resistance has been overlooked currently. In this work, two types of polyether-based diglycidyl ethers with hydrophilic poly(oxyethylene) (DGEPOE) and relatively hydrophobic poly(oxybutylene) segments (DGEPOB) are synthesized and then binary-cured with commercial diglycidyl ether of bisphenol A (DGEBA), respectively, yielding the corresponding DGEPOE:DGEBA-m:ns and DGEPOB:DGEBA-m:ns based on various ratios. For comparison, pure DGEPOEr, DGEPOBr, and DGEBAr resins are also prepared. Results show that the equilibrium water uptake of DGEPOB:DGEBA-m:ns is at least less than one-fifth of that of DGEPOE:DGEBA-m:ns; meanwhile, the diffusion coefficients of water molecules in DGEPOB:DGEBA-m:ns are also 1-2 orders of magnitude lower than those in DGEPOE:DGEBA-m:ns, demonstrating that the incorporation of hydrophobic POB chains can significantly reduce the hygroscopicity of resins. Moreover, DGEPOB:DGEBA-m:ns not only exhibit superior flexibility and ductility relative to pure DGEBAr, but display exceptional strength and toughness in comparison with pure DGEPOBr. These findings suggest that tuning the hydrophilicity/hydrophobicity of building units of epoxy monomers offers a promising strategy for developing high-performance epoxy materials, especially suitable for humid environments. Binary-cured epoxy networks are prepared via mixing hydrophilic diglycidyl ether of poly(oxyethylene) or relatively hydrophobic diglycidyl ether of poly(oxybutylene) with diglycidyl ether of bisphenol A. POE-based networks display high hygroscopicity since POE segments offer high hydrophilicity. In contrast, POB-based networks significantly improve moisture-resistant performance and reduce water uptake due to POB segments having relative hydrophobicity. image