6533b85afe1ef96bd12b89d2

RESEARCH PRODUCT

Ion-Induced Stretching of Low Generation Dendronized Polymers with Crown Ether Branching Units

subject

description

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 °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 19F NMR and 1H−19F 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, lk, from lk = 8 to 19 nm and from lk = 19 to 45 nm for the...