Study On Preparation Of Polyacrylamide And Hydrogels By Living Radical Polymerization

Polyacrylamide (PAM) is one of the polymers which have the highest output and the widest application in the current; it is a challenge on how to control the molecular weight and molecular structure of PAM and its derivatives. Atom transfer radical polymerization (ATRP) is a great prospect polymerization method which has a lot of advantages, such as the polymer molecular weight and structure controllable, chain length of polymer more homogeneous. In the paper, the PAM and its hydrogels are preparation by ATRP using the wate as solvent, the main contents and results of the work including the following three parts:In the first part, using cuprous chloride (CuCl) as catalyzer, 2,2'-bipyridyl(bpy) as ligand, 2-chloro-propionamide (CPA) as initiator in water-based system, the atom transfer radical polymerization (ATRP) of acrylamide (AM) was studied. The variations factors such as the monomer concentration, the ratio of the initiator and catalyst concentration ([C]: [I]), and the ratio of the monomer and initiator ([AM]∶[CPA]) were discussed in the paper, which effects on the monomer conversions and molecular weights of the polymers the kinetics of ATRP. The experimental results showed that when the monomer concentration was 40%, [AM]∶[CPA] was 79:1, [C]: [I] was 1:1 and CuCl/bpy was1:3, the molecular weight distribution was less than 1.5, and the molecular weight of polymerization could be controllable well and the living polymerization characteristic was apparently in the polymerization reaction.In the second part, preparation the polyacrylamides (PAM) hydrogels by ATRP was studied. Based on the best preparation conditions of first part, using N,N'- methylene-bisacrylamide (BIS) as crosslinker, the PAM hydrogels were successfully prepared by ATRP. In the ATRP system of AM and BIS, the reaction rate increased with the increasing concentration of BIS. Gel point for the ATRP of AM and BIS was investigated and the result was compared with Flory theory, it was found that the gel point in the ATRP of AM and BIS approached the Flory theoretical value, that indicated the PAM hydrogels with homogeneous network structure.The swelling ratio and the swelling rate of the PAM hydrogels were investigated under the different concentrations of monomers, amount of crosslinker and amount of initiator. The results showed that the monomer concentration was 20%, and the amount of crosslinker is 5% of AM, and the initiator concentration is 3.7%, the PAM hydrogels have a high swelling ratio.In the third part, preparation the poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-AM)) hydrogels by ATRP was studied.. The technology of synthesize the hydrogels was successfully obtained, in which water and dimethylformamide are used as mixture solvent, and pentamethyltriethylenetetramine is used as ligand, and the synthsis technology can prepared the P(NIPAM-co-AM) thermosensitive or intelligent hydrogels by ATRP. The experimental results show that the swelling ratio, swelling rate and LCST (lower critical solution temperature) of the P(AM-co-NIPAM) hydrogels increase with increasing the mole fraction of AM monomer. Compare to radical polymerization, P(AM-co-NIPAM) prepared by ATRP have some characteristic such as a lower LCST, quick swelling rate and high water-retention ratio.