Acrylamide (AM) and diallyldimethyl ammonium chloride (DADMAC) block copolymer P(AM-b-DADMAC) was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization method. The successful polymerization of controlled composition and polydispersity index of the block copolymer was confirmed by FTIR, H-1-NMR, and size exclusion chromatography analyses. Differential scanning calorimetry and thermal gravimetric analysis further confirmed the interaction between the trithioester groups of RAFT agent and alkenyl groups of AM and DADMAC in the final product. With turbidity, chemical oxygen demand and focused beam reflectance measurement measurements, the block copolymer was proved to be effective at fixing dissolved and colloidal substances onto papermaking fibers, thus removing these substances from the water phase where they have a tendency to aggregate and form troublesome deposits. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4040-4046, 2013