Synthesis of Thermoresponsive Core-Shell Microgels Cross-Linked with Acryloyloxyethylaminopolysuccinimide

Abstract

Utilizing a biodegradable cross-linker, acryloyloxyethylaminopolysuccinimide (AEA-PSI), poly(N-isopropylacrylamide) (PNIPAAm) microgels and core-shell structure microgels were prepared via free-radical precipitation polymerization and their phase transition behaviour, phase transition temperature (PTT), hydrodynamic diameters and size distributions (polydispersity indexes, PDI) were investigated. To prepare small-sized and lower PDI PNIPAAm microgels, the optimum parameters should be selected as the concentrations of AEA-PSI, Nisopropylacrylamide (NIPAAm), ammonium peroxodisulfate (APS) and sodium dodecyl sulfate (SDS) were 1.34, 7.56, 0.152 and 0.18 g/L and the hydrodynamic diameter of the microgels was 353.8 nm (PDI, 0.24). All the microgels dispersions exhibited thermoresponsive phase transition at 30.0-32.5 ºC. Using microgels as seeds, the core-shell PNIPAAm microgels were prepared. With increasing the weight ratio of the NIPAAm/AEA-PSI from 1.3:1 to 3:1 and 5:1 in the shell materials, the hydrodynamic diameter of the core-shell microgels increases from 376.4 to 432.5 and 472.3 nm at 25 ºC, respectively. The morphologies of the microgels particles were also investigated by the atomic force microscopy (AFM). The AFM images illuminated that the core-shell microgels particles had symmetrical sizes and non-aggregation, indicating better stability. Compared with the core microgels, the shell-core microgels appear a smoother and denser surface.