Thermo-reversible hydrogels based on poly(N,N-diethylacrylamide)-block-poly(acrylic acid)-block-poly(N,N-diethylacrylamide) double hydrophilic triblock copolymer

A novel double hydrophilic poly(N,N-diethylacrylamide)-poly(acrylic acid)-poly(N,N-diethylacrylamide) (PDEAAm-PAA-PDEAAm) triblock copolymer was synthesized by sequential anionic polymerization and modification of the poly(tert-butyl acrylate) middle block by selective hydrolysis and neutralization to its ionic functions. Due to the pH-sensitivity of the PAA central block and the thermo-sensitivity of the PDEAAm end-blocks, it exhibits responsive behavior in aqueous media. At low temperatures and high pH, it is molecularly dissolved while at temperatures above the LCST of the PDEAAm end-blocks, a sol-gel transition was observed which should be ascribed to the formation of a three-dimensional transient network comprising PDEAAm hydrophobic physical crosslinks interconnected by PAA negatively charged elastic chains. The sol-gel transition and the rheological properties of the physical gel are strongly influenced by the presence of salt.