The iterative learning control under periodic operation is used to control molecular weight distribution(MWD)in semi-batch polymerization process in this work.Firstly

the effect of periodic control on the MWD of the semi-batch polymerization reactor is analyzed.Simulation results show that the broadening of molecular weight distribution is achieved through periodic operation

therefore the performance of polymerization is improved.Then the optimal control strategy based on particle swarm optimization(PSO)with an improved performance index is used to control the shape of MWD

in which the control variable is duty cycle of the periodic feeding.In simulation experiment

the control inputs can reach to the optimal values from batch to batch in the presence of model plant mismatches

and the MWD of the polymer approximate the desired MWD gradually

thus the effectiveness of the periodic operation controlling method on MWD is verified.