The kinetics of the bulk polymerization of methyl methacrylate (MMA) in the presence of montmorillonite (MMT) were studied. The effect of MMT on the radical polymerization of MMA was researched by determining the polymerization rate dilatometrically. It was assumed that there were both bimolecular and monomolecular termination processes involved in the termination of the radicals in the polymerization. It was found that a lower benzoyl peroxide (BPO) concentration promotes a higher fraction of monomolecular mode in chain termination. The results show that there is an optimal ratio of MMT to initiator that increases the bulk polymerization rate of MMA. The X-ray results show that the layer structure of the formed PMMA-MMT composites was also affected by the BPO concentration. With lower initiator concentration, less pronounced layer structure will be observed. (C) 2003 Wiley Periodicals, Inc.