Poly(L-lactide)/layered aluminosilicate nanocomposites were synthesized in bulk by ring-opening polymerization in the presence of two organo-modified montmorillonites. When the organo-modifier consisted of an ammonium cation bearing primary hydroxyl groups, polymerization was initiated by the alcohol functions after adequate activation. The growing polymer chains were directly "grafted" onto the clay surface through the hydroxyl-functionalized ammonium cations yielding exfoliated nano-composites with enhanced thermal stability.