Sodium montmorillonite (Na-MMT) absorbed a radical initiator, potassium persulfate (KPS), by way of hydrogen bonding between hydroxyl groups in the Na-MMT lattice and the sulfonic anions of KPS. FT-IR absorbance bands of hydroxyl groups in the Na-MMT lattice and the sulfonic anions of KPS shifted to lower wavenumber regions, compared with the free silicate and the initiator. The amounts of initiator adsorbed on the silicate were determined by using thermogravimetric analysis. The initiator adsorbed on silicate (IAS) commenced the polymerization of acrylonitrile (AN), delaminating silicate layers in polyacrylonitrile (PAN)/silicate nanocomposites. Molecular weights of PANs extracted from the nanocomposites decreased as the amount of initiator in IAS increased. Heterogeneous nucleation, polymerization in the basal spacing of the silicate layers, was analyzed by high performance liquid chromatograph. Storage moduli, E' of the nanocomposites were enhanced with the molecular weights of PAN matrixes. Glass temperatures, T-g, of the nanocomposites were dependent on the molecular weights of the PAN matrixes and the contents of the 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) charged. (C) 2004 Elsevier Ltd. All rights reserved.