Photonics of High-Entropy Polymers Revealing Molecular Dispersion via Polymer Mixing.

Abstract

Blending multiple polymers together to form the so-called "high-entropy polymers (HEPs)" can generate the effects of molecular dispersion in addition to suppressing polymer phase separation. We embedded a semiconducting polymer (conjugated polymers, CPs) in an optically inert matrix composed of <i>n</i> polymer species and found that a molecule-level dispersion is attained in HEPs defined as <i>n</i> ≥ 5. In the regime of dilute CP concentrations, the photonic properties vary widely in the <i>n</i> = 1 matrices owing to diverse solubility parameters, but the distribution narrows with <i>n</i>, and the CP starts to exhibit behaviors of molecule-level dispersion at <i>n</i> ≥ 5, where the matrix polymers compete with each other to exert direct influences on the embedded CP. Specifically, for MEH-PPV, increasing <i>n</i> reduces the fluorescence redshift and spectral width from diminishing aggregation. For the rigid PFO molecules, increasing <i>n</i> creates a dilution effect facilitating formation of the low-energy planar β-phase. For the flexible regioregular P3HT-rr, HEPs offer well-dispersed amorphous chains highly susceptible to chain environments, thus influencing η_R's in the quasi-fixed amorphous-crystalline energy transfer landscape. The HEP effects continue for greater CP concentrations, consistent with the matrix dispersing behaviors in the dilute regime. This work demonstrates a molecular-level dispersion by HEPs, offering a method of molecular tailoring for polymer research and applications via simple mixing.