Temperature and pH dual-responsive behavior of dendritic poly(N-isopropylacrylamide) with a polyoligomeric silsesquioxane core and poly(2-hydroxyethyl methacrylate) shell

Novel temperature and pH dual-responsive dendritic polyoligomeric silsesquioxane (POSS)-poly(N-isopropylacrylamide) (PNIPAm)-poly(2-hydroxyethyl methacrylate) (PHEMA) copolymers are prepared via atom transfer radical polymerization and click reactions. The cloud points (T_c) decrease with decreasing pH from 10.0 to 5.0 due to the weakened inter-molecular interactions and enhanced intra-molecular hydrogen bonding, whereas the T _c exhibits a small increase from pH 5.0 to 4.0 because of the better solvation of PHEMA at highly acidic conditions. The above findings are corroborated by the different sizes of aggregates observed by dynamic light scattering. The encapsulation of a fluorescent dye and stimulated release by temperature and pH changes are also demonstrated. Temperature and pH dual-responsive dendritic poly(N-isopropylacrylamide) with a biocompatible poly(2-hydroxyethyl methacrylate) (PHEMA) shell is successfully synthesized via a combination of ATRP and a click reaction. The solution phase transition behavior of the dendrimer is sensitively affected by pH over a wide range. Encapsulation and controlled release of a fluorescent dye from the dendrimer in response to temperature and pH changes are also demonstrated.