Modulation of Thermodynamic and Kinetic Inverted Phase Behavior of Block Copolymers by Inorganic Polyoxometalates
The Keggin polyoxometalates (POM) H3PW12O40 (PW) electrostatically complexed with poly(styrene-block-2-vinyl pyridine) (PS-b-P2VP) in DMF, and ordered microphase separation occurred through solvent evaporation. The phase behaviors of PS-b-P2VP/PW in bulk were systematically investigated by using SAXS and TEM to discover the effect of POM contents and molecular weights of block copolymers. Computational simulation was also performed to reveal the same phase transition sequence as the experimental results. As POM contents increase, the PS-b-P2VP/PW complex with a low molecular weight changed from lamellar phase (LAM) to hexagonal cylindrical phase (HEX), and finally transited into spherical phase (SPH). Unexpectedly PS-b-P2VP/PW complexes with a high molecular weight were inclined to form kinetic-trapped intermediate phase (inverted HEX). The mechanism of formation of inverted phases were proposed based on simulation that asymmetric swelling in the concentrated DMF solution would result in the ultimate kinetic-trapped nanostructure in bulk.