Versatile procedure for site-specific grafting of polymer brushes on patchy particles via atom transfer radical polymerization (ATRP)

We report the preparation of chemically anisotropic colloidal dumbbells of which one lobe is functionalized with chemical handles in the form of chlorine groups. The chlorines are easily converted to azides and subsequently to active initiators for Atom Transfer Radical Polymerization (ATRP) by Click Chemistry. These initiators are exploited for site-specific grafting of poly(N-isopropylacrylamide) (p(NIPAM)) brushes on the reactive patches. The geometric ratio between the grafted and non-grafted lobe is tunable by the shape of the initial dumbbell and the polymer grafting time. Furthermore, the versatility of our synthesis protocol is underlined by extending it to colloids with multiple reactive patches. The partially grafted dumbbell-shaped particles are employed as building blocks for finite-sized colloidal clusters. A directional interaction between the non-grafted lobes is easily introduced by dispersing the partially grafted dumbbels in a high ionic strength medium. Finally, we briefly explore the potency of this system of forming stimuli-responsive colloidal clusters by exploiting the strongly temperature dependent properties of the grafted polymers.