Nanocomposites of exfoliated montmorillonite in polyethylene were obtained using a combination of 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine-dichloro-nickel(II), montmorillonite, and methylalumoxane (MAO) or trimethylaluminum (TMA) to polymerize ethylene. The properties of the polymers were strongly influenced by the amount of clay they contained. The addition of 2.5% commercial montmorillonite (KSF or Cloisite 15A) enhanced the storage modulus from 5 to 878 MPa. Transmission electron microscopy (TEM) analyses provided evidence of exfoliation of the montmorillonite with the formation of a polyethylene nanocomposite. The enhanced mechanical properties were explained as a consequence of the reinforcement due to the presence of nanoscale layers formed from exfoliation of the clay included in the polyethylene matrix. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2159-2165, 2011