'High-Entropy Polymers': A New Mixing Route of Suppressed Phase Separation

Alloys and ceramics of multi-component compositions and hence having high entropy at random solution states recently received focused attentions. The present work emulates the "high-entropy" concept by using a common solvent to prepare polymer blends from a number of polymers, which shows interesting unique phenomena and promising properties. By investigating the heterogeneous domain size (Λ) of thin solid films prepared by spin coating, we found that de-mixing, commonly observed in polymer blends, can be suppressed when the number of polymer species (n) in the blend increased. In binary blends (n=2), de-mixing occurred, manifesting a wide spread of Λ strongly influenced by the inter-segmental enthalpy and chain length. However, as n increased, the Λ distribution shrank sharply by a declining upper edge, indicating significant de-mixing suppression. The suppression is attributable to high mixing entropy and a kinetic steric effect blocking like-polymer aggregation during film formation. The de-mixing suppression was found effective in dispersing poly(9,9'-dioctylfluorene), a conjugated polymer (CP), in the optically inert n=5 blend where the CP molecules remained well separated, as shown spectroscopically, for CP fractions up to 50 wt.%, manifesting excellent efficiency performance.