Effect of polymer complex formation on the cloud-point of poly( N-isopropylacrylamide) (PNIPAAm) in the poly(NIPAAm- co-acrylic acid): polyelectrolyte complex between poly(acrylic acid) and poly( L-lysine)

Abstract

Random copolymers of acrylic acid (AAc) and N-isopropylacrylamide (NIPAAm) were synthesized by free-radical polymerization. The copolymers were characterized for their temperature- and pH-responsive behaviour by cloud-point experiments. The influence of polyelectrolyte between poly(allyl amine) (PAA) and poly( L-lysine) (PLL) on the lower critical solution temperature (LCST) of a pH/temperature sensitive polymer was compared in the range of pH 2–12. A polyelectrolyte complex was prepared by mixing poly(NIPAAm- co-AAc) and PLL solutions as anionic and cationic polyelectrolytes, respectively. The LCSTs of PNIPAAm/water in the copolymers were strongly affected by the pH, the presence of polyelectrolyte solute and AAc content in the poly(NIPAAm- co-AAc). The influence of more hydrophobic PLL as polyelectrolyte on the cloud-point of PNIPAAm/water in the copolymer was stronger than that of PAA. It is thought that as the side chain length increases from C 1 for PAA to C 4 for PLL, the hydrophobicity of polyelectolyte complex increases, indicating that much more dehydration occurs around PNIPAAm.