Improving colloidal stability and response performances using looped thermal-responsive brushes.

Looped polymer brushes lacking chain terminals exhibited unique topological structures and associated properties. Looped polymer brushes in solution have been extensively studied, although the topology and corresponding performances of the thermal-responsive polymer upon grafting onto nanoparticle surfaces have been hardly reported. In this work, gold nanoparticles (AuNPs) were modified using poly(-isopropyl acrylamide) (PNIPAAm) terminated with one thiol and two thiol groups to prepare linear and looped PNIPAAm brush-coated AuNPs, respectively. The effect of the topology of PNIPAAm brushes on thermal-responsive behavior, colloidal stability and release performances was evaluated in detail. Compared to the linear counterparts, the looped polymer exhibits relatively higher colloidal stability and rapid thermal-responsive behavior during heating-cooling temperature cycling. This resulted in a more pronounced release of dye molecules triggered by the looped one upon temperature change, and even if the release is first saturated at 25 °C, it is triggered again by raising the temperature to 45 °C. In contrast, the linear polymer brushes did not show significant triggering behavior due to chain entanglement. This work demonstrated how the polymer brush topology affected thermal-responsive nanoparticles' stability and temperature-responsive behavior, which may provide new opportunities for surface modification of looped polymer brushes with temperature-sensitive properties.