Stereoregular poly(methyl methacrylate) (PMMA)-silica nanocomposites were prepared using stereocomplex formation between i-PMMA and s-PMMA by an in situ method. The methodology adopted here is the simultaneous formation of organic gel and inorganic gel, the so-called interpenetrating polymer network (IPN) formation. The gelation of i- and s-PMMA were performed by stereocomplex formation with the associated segments forming the crosslinking points in the presence of tetramethoxysilane (TMOS). The effects of the i/s-ratio, PMMA concentration, molecular weight, and solvent nature on the hybrid materials formation were addressed. The presence of the stereocomplex in the silica matrix was confirmed by DSC and solvent extraction methods. (C) 2003 Wiley Periodicals, Inc.