An optimized and high-performance Monte Carlo simulation is developed to take thorough account of four different cases of termination in styrene ATRP. According to the simulation results

the bimolecular termination rate constant sharply drops throughout the polymerization when either chain-length dependency of termination rate constant

gel effect

or both together is applied to the simulation. In addition

as expected

the initiator is quickly decomposed at the early stages of the polymerization. The concentration of the catalyst in lower oxidation state decreases at first and then plateaus at higher conversion; furthermore

the steady concentration of MtnY/L in the polymerization is the highest when the chain-length-dependent diffusion-controlled termination rate constant is employed in the simulation. The rates of deactivation and chain end degradation reactions are also smaller in this case. Therefore

the fraction of dormant chains is higher throughout the reaction and consequently the portion of dead polymers decreases. Besides

molecular weight increases linearly with conversion; however

when neither gel effect nor chain-length dependency of termination rate constant is considered

the molecular weight deviates from linearity at the end of the reaction. The peak of chain length distribution shifts toward higher molecular weight too during the reaction. Finally

the molecular weight distribution broadens at higher conversion; however

the chain length distribution of polymers produced under conditions of applying chain-length-dependent diffusion-controlled termination rate constant is narrower.