A typical atom transfer radical polymerization (ATRP) system for preparing a novel flocculant polyacrylamide with low polydispersity and tacticity was studied in this paper. Lewis acids Y(OTf)

3

and AlCl

3

were introduced respectively as stereospecific reagent in the ATRP of acrylamide with chloroacetic acid as initiator and CuCl/TMEDA as catalyst. The influence of certain amount of the added Lewis acids on the rate and controllability of polymerization was studied. The participation of the Lewis acid AlCl

3

in the polymerization afforded the resultant polyacrylamides with lower polydispersity index 1. 03 and well-controlled tacticity with

meso

content 76% under the optimum reaction condition used. Kinetic experiments also revealed the polymerization of acrylamide in presence of Lewis acid proceeded with an ATRP process. Furthermore

the obtained flocculants were introduced in the flocculation experiments to testify their flocculation efficiency

which indicated that the flocculation efficiency of the polymer flocculants were dependent upon molecular weight (

M

n

)

polydispersity index (PDI) and

meso

content (

m

) of the polymer flocculants. The molecular weight of the flocculants played a critical role in influencing on flocculation efficiency

on the other hand

the narrower of PDI and the higher meso content of the polymer would be beneficial to improving the flocculation efficiency.