Effect of salt and temperature on molecular aggregation behavior of acrylamide polymer

Three kinds of acrylamide copolymers were synthesized in this paper, acrylamide (AM) homopolymer, acrylamide/acrylic acid (AA) copolymer and acrylamide/2-acrylamide-2-methylpropanesulfonic acid (AMPS) copolymer by free radical polymerization. The aggregation behaviours of these polymers in salts water solution were studied. The molecular chains of homopolymer were stretched in salt water solutions, since it did not undergo hydrolysis and there were no charges in the backbone and side chains. Therefore, the conformation of homopolymer was hard to be attacked by salt ions. However, the copolymers synthesized from these monomers had large number of anionic groups. These anions were easily attracted by cations from salt solutions forming ionic bonds, which led to changes in molecular conformation. The viscosity of copolymer decreased since the molecular chains were crimped. The viscosity of copolymer decreased distinctly according to the temperature of different salt solutions, as temperature had great impact on the viscosity of copolymer. The interaction mechanism of polymers exhibited great difference in salts solutions, comparing to temperature. High temperature reduced the entanglement between molecular chains, whereas salt ions neutralized the negative charges on the molecular chains causing curling of molecular chains.