Stimuli-responsive polymer brushes are smart materials for the design of bio-interactive and responsive interfaces. The "grafting-to" approach is a convenient preparation procedure that allows the modification of surfaces with preformed and most notably well-defined functionalized macromolecules. However, the shortcoming of this approach is an intrinsic limitation of the grafting density, which in turn affects the stimuli-responsive properties of the brush system. Here, a general strategy to overcome this limitation and to simultaneously improve the switching behavior of a temperature-responsive poly(N-isopropylacrylamide) (PNiPAAm) brush is reported. A technically simple processing step is used in combination with the thermal azide-alkyne cycloaddition to perform the chain extension of alkyne-functionalized PNiPAAm brushes with azide-functionalized PNiPAAm molecules.