Thermothickening Behavior of Graft Copolymers Containing Poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) Side Chains in Aqueous Solution

Abstract

Thermoassociative graft copolymers poly(sodium acrylate)-graft-poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide), PAA/P(NIPA-co-DMAA) have been recently synthesized through a two-step route. The primary structure of the graft copolymers is constituted of a weak polyelectrolyte (PAA) backbone and thermosensitive side chains containing NIPA and DMAA. Taking advantage of this well-controlled synthesis, the side chains length and composition have been selectively modified by changing the initial concentration of the initiators and by introducing the more hydrophilic comonomers, respectively. The thermothickening behavior of the graft copolymers was studied by the viscosity measurements and the results obtained suggested that the association temperature and the sharpness of the thermothickening curve can be selectively controlled by varying the concentration, side chains composition and length of the graft copolymers and by adding NaCl. In the meantime, the thermoassociative behavior was also illustrated with the fluorescence measurements from a microscopic point of view.

Keywords:

• thermoassociative polymers
• graft copolymers
• poly(N-isopropylacrylamide-co-dimethylacrylamide)
• thermothickening
• structure-property relations