Influence of Grafted Block Copolymer Structure onThermoresponsiveness of Superparamagnetic Core–Shell Nanoparticles

摘要

The morphology and topology of thermoresponsive polymers have a strong impact on their responsive properties. Grafting onto spherical particles has been shown to reduce responsiveness and transition temperatures; grafting of block copolymers has shown that switchable or retained wettability of a surface or particle during desolvation of one block can take place. Here, doubly thermoresponsive block copolymers were grafted onto spherical, monodisperse, and superparamagnetic iron oxide nanoparticles to investigate the effect of thermal desolvation on spherical brushes of block copolymers. By inverting the block order, the influence of core proximity on the responsive properties of the individual blocks could be studied as well as their relative influence on the nanoparticle colloidal stability. The inner block was shown to experience a stronger reduction in transition temperature and transition enthalpy compared to the outer block. Still, the outer block also experiences a significant reduction in responsiveness due to the restricted environment in the nanoparticle shell compared to that of the freepolymer state. The demonstrated pronounced distance dependence importantlyimplies the possibility, but also the necessity, to radially tailorpolymer hydration transitions for applications such as drug delivery,hyperthermia, and biotechnological separation for which thermallyresponsive nanoparticles are being developed.