A new Monte Carlo simulation model for the kinetics of emulsion polymerization is proposed. Normally, for emulsion polymerizations, each polymer particle consists of less than 10(8) monomeric units; therefore, the kinetic behavior of all polymer molecules in each polymer particle can be simulated easily using the Monte Carlo method with a well-designed algorithm. In the Monte Carlo technique, it is straightforward to account for virtually any kinetic event, such as the desorption of oligomeric radicals and chain length dependence of kinetic parameters, and as a consequence very detailed information such as the full distributions of the dead polymer molecular weights and macroradicals among polymer particles can be obtained. When no chain transfer agents are used, chain transfer to monomer tends to become the dominant chain stoppage mechanism due to the long time interval between radical entry, and this may result in active terminal double bonds on polymer chains depending on the monomer transfer mechanism. If active terminal double bonds are formed and polymerize, the present simulations show that the effect of long-chain branching on the molecular weight distribution is significant with the formation of very high molecular weight chains. Monte Carlo simulations provide greater insight into the complex molecular processes which occur during emulsion polymerization.