Synthesis of the first (G1) and second generation (G2) dendronized macromonomers MG1 and MG2 with the dibenzo-24-crown-8 moiety as branching unit is reported. The corresponding dendronized polymers, the polymethacrylates PG1 and PG2, were synthesized by free radical polymerization using AIBN as initiator at 60-80 degrees C. Static and dynamic light scattering revealed a significant chain expansion upon complexation of these polymers' crown ether side chains with K+ ions. It is concluded that electrostatic repulsion does not significantly contribute to the chain expansion because of excessive counterion binding even well below the Manning limit, as evidenced by F-19 NMR and H-1-F-19 NOE experiments. Rather, the conformational change of the crown ether moieties upon K+-ion binding plus the short-range interaction between ion pairs formed along the chain cause the observed significant increase in chain stiffness in terms of the Kuhn statistical segment length, l(k), from l(k) = 8 to 19 nm and from l(k) = 19 to 45 nm for the PG1 and PG2 polymers, respectively, At full KPF6 loading, the effect is as large as to triple the molar mass of the side chains, as evidenced by the similar values of the Kuhn statistical segment length of the fully complexed PG1 as compared with the noncomplexed PG2 sample. It is thus demonstrated that steric repulsion induced by host-guest interactions is well suitable to control the conformation of polymers with densely grafted side chains.