By using the periodically sampling approach and UV spectrophotometry the conversion of acrylamide and the content of the photoinitiator 2-hydroxy-2-methyl-1-[4-(2-hydroxyeth-oxy)phenyl]-1-acetone in the polymerization process were measured.There are three stages in the photo-polymerization process of acrylanide

according to the acrylamide conversion rate and the corresponding initiator content.A three-stage model of polymerization process was established by the photoinitiator consumption

and the polymerization process was divided into the initial period of polymerization

the polymerization period and the later period of polymerization.The decomposition kinetics of photoinitiator was investigated with a homemade photopolymerization instrument.The initiator decomposition rate constant (kd) was calculated under different conditions.The results show that

photoinitiator decomposition rate constants kd within 4.00×10-4 s-1 can be regulated under the experimental conditions

and there is a best kd combination in the three-stage model

that is

the kd of a first stage was 4.00×10-4 s-1

the kd of the second stage was 1.90×10-4 s-1

the kd of the third stage was 1.90×10-4 s-1.The optimal free radicals concentration of synthesis of polyacrylamide (PAM) is 10.82×10-8~12.56×10-8 mol ·L-1s-1.Photoinitiator initial concentration[I]0 should be controlled at 100~110 mg/L.