Hydrophobic and hydrophilic modification of hierarchically porous monolithic polyimide derivatives as functional liquid absorbers

Abstract

A cost-effective and facile method was developed for the fabrication of two polyimide-based (PI-based) monoliths (pure PI monolith and hybrid PI monolith) with a hierarchically porous structure that avoids the shortcomings of traditional methods. In this case, the thermally induced phase separation (TIPS) method was used to prepare polyamic acid (PAA) monoliths for the first time, then PI-based monoliths were fabricated by thermal imidization. Through the introduction of octakis(glycidyldimethylsiloxy)octasilsesquioxane into the PAA prepared from 4,4′-oxydianiline and pyromellitic dianhydride, both the hydrophobicity and mechanical strengths of the PI-based monoliths were improved. Moreover, the resulting PI-based monoliths exhibited suitable permeability, homogeneous morphologies, and superior thermal stability. Adsorption tests demonstrated that the resulting hybrid PI monoliths exhibited better adsorption performance for organic solvents and silicone oil than the pure PI monolith. Furthermore, the surface of a polyhedral oligomeric silsesquioxane (POSS) hybridized PI (PI-co-POSS) monolith can be modified into a hydrophilic layer by reaction between the hydrophilic polymer and epoxy groups exposed on the surface. This indicates that PI-co-POSS monoliths have potential in liquid diode application to achieve oil–water separation.