Poly (ethylene oxide) grafted multiwalled carbon nanotube (PEO‐graft‐MWCNT) was successfully prepared by a ring‐opening polymerization of ethylene oxide. Thermogravimetric analysis results indicated that the amount of the grafted PEO polymer was about 40.0 wt %. Rigid polyurethane foams (PUF) filled with MWCNT and PEO‐graft‐MWCNT were also fabricated to investigate the influence of grafted PEO interfacial layer on the foaming process, morphology and mechanical properties of PUF.