AbstractUsing dithioester as a chain‐transfer agent and azobisisobutyronitrile as an initiator, we synthesized amphiphilic poly(styrene‐block‐acrylamide) [P(St‐b‐Am)] by the reversible addition–fragmentation chain transfer (RAFT) polymerization method. To improve the heat stability of the block polymers, amphiphilic P(St‐b‐Am)/organic montmorillonite (O‐MMT) nanocomposites were successfully prepared by the addition of O‐MMT during the preparation of the block polymer. The nanocomposites were tested by gel permeation chromatography, IR spectroscopy, X‐ray diffraction, transmission electron microscopy, and thermogravimetry. As for polystyrene (PSt)/O‐MMT, RAFT polymerization could control the molecular weight and the molecular weight distribution of PSt. PSt/O‐MMT was used as a macro RAFT agent to conduct the polymerization of acrylamide, and P(St‐b‐Am)/O‐MMT nanocomposites were prepared. Nanosize layers of montmorillonite were dispersed in the block polymer matrix, and exfoliative nanocomposites were formed. Therefore, the P(St‐b‐Am)/O‐MMT nanocomposites had a better heat stability than before. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008