Effects of Polyethylene Glycol Molecular Weight and Content on the Properties of PEG ‐Block‐Modified Epoxy Resins

ABSTRACT Waterborne epoxies toughened with polyethylene glycol (PEG) are cleaner than conventional epoxies, yet how PEG's molecular weight and content affect cured coatings remains unclear. Herein, zero‐VOC waterborne epoxy resins were prepared through PEG block modification. The effects of PEG molecular weight (1000–6000 Da) and content (5–20 wt%) on the structures, morphologies, mechanical properties, and corrosion resistances of formed waterborne epoxy resins were examined. Comprehensive characterization by FTIR, 1 H NMR, epoxy equivalent weight (EEW), coating adhesion/impact resistance, and SEM of free‐standing film cross‐sections confirmed successful grafting of PEG. The modified system exhibited uniformly dispersed PEG nanospheres (diameter ≈200 nm) within the epoxy matrix, with interfacial bonding strength governed by the PEG molecular weight and content. The coating modified with 10 wt% (abbreviated PEG‐2000) exhibited optimal integrated performance, with significantly increased dimple density, low‐frequency impedance (2.86 × 10 6 Ω·cm 2 ) after 3‐day salt spray. No substrate corrosion was observed after 10‐day salt spray testing, attributed to the compromised coating densification at low PEG molecular weights (1000 Da), where insufficient hydrogen bonding occurred versus phase separation at high molecular weights (4000 Da). PEG‐2000 achieved balanced compatibility with the epoxy matrix to form a dense crosslinked network, effectively impeding the permeation of corrosive species (O 2 , Cl − ).