Influence of Salt Doping on the Entropy-Driven Lower Disorder-to-Order Transition Behavior of Poly(ethylene oxide)-b-Poly(4-vinylpyridine)

Poly(ethylene oxide)-b-poly(4-vinylpyridine) (PEO-b-P4VP) block copolymers (BCPs) exhibiting lower disorder-to-order transition (LDOT) phase behavior are doped with different salts (LiCl, CuCl2, and FeCl3), in which both blocks can competitively associate with the metal ions. It is found that the entropy-driven LDOT phase behavior of PEO-b-P4VP can be bi-directionally adjusted by enthalpic interactions, depending on the complexation selectivity of metal ions toward two blocks and doping ratio (r). At low rs, Li+ ions preferentially interact with PEO block, leading to a decreased disorder-to-order transition temperature (T-DOT). Cu2+ ions selectively complex with the P4VP block, and the T-DOT first increases with increasing r, followed by a decrease. By contrast, Fe3+ ions interact strongly with both blocks, resulting in increase of T-DOT. At high rs, the complexation selectivity becomes weaker, leading to reduced immiscibility and increased T-DOT, as compared with the hybrids with low rs. The effects of metal cation and r on the LDOT phase behavior are qualitatively explained by the change of the Flory-Huggins parameter.

Automated summary

The complexation selectivity of metal ions towards the two blocks and the doping ratio significantly affect the entropy-driven LDOT phase behavior of PEO-b-P4VP block copolymers.