Influence of Grafted Block Copolymer Structure on\nThermoresponsiveness of Superparamagnetic Core–Shell Nanoparticles

Abstract

The\nmorphology and topology of thermoresponsive polymers have a\nstrong impact on their responsive properties. Grafting onto spherical\nparticles has been shown to reduce responsiveness and transition temperatures;\ngrafting of block copolymers has shown that switchable or retained\nwettability of a surface or particle during desolvation of one block\ncan take place. Here, doubly thermoresponsive block copolymers were\ngrafted onto spherical, monodisperse, and superparamagnetic iron oxide\nnanoparticles to investigate the effect of thermal desolvation on\nspherical brushes of block copolymers. By inverting the block order,\nthe influence of core proximity on the responsive properties of the\nindividual blocks could be studied as well as their relative influence\non the nanoparticle colloidal stability. The inner block was shown\nto experience a stronger reduction in transition temperature and transition\nenthalpy compared to the outer block. Still, the outer block also\nexperiences a significant reduction in responsiveness due to the restricted\nenvironment in the nanoparticle shell compared to that of the free\npolymer state. The demonstrated pronounced distance dependence importantly\nimplies the possibility, but also the necessity, to radially tailor\npolymer hydration transitions for applications such as drug delivery,\nhyperthermia, and biotechnological separation for which thermally\nresponsive nanoparticles are being developed.