Poly(ionic liquid)s (PIL)s, as a subclass of polyelectrolytes, are composed of polymeric backbones with ionic liquid (IL)-based species in each repeating unit. Recent studies have deepened the understanding of the PIL concept in terms of characteristics, functions and applications in comparison to classical ILs and traditional polyelectrolytes. During the past two decades, PILs have developed themselves into an interdisciplinary subject among various research areas such as polymer science, materials science, catalysis, separation and sensing. Currently, the chemistry and applications of conventional polyelectrolytes are being expanded forward by the PIL concept. 

This PhD thesis deals with PIL-based porous hybrid and composite membranes. It is motivated by the growing demand on functional porous polymer membranes, in particularly, porous polyelectrolyte membranes in both industry and academia. By applying PILs as building blocks in membranes, the as-prepared porous PIL membranes combine certain desirable properties of ILs and common polymers with a wider potential to satisfy this demand. As a step further, the incorporation of functional guest substances on a molecular or nanoscale can enable new functionalities of porous membranes and broaden their application scope. 

The aim of this thesis is to develop synthetic approaches to fabricate porous PIL-based membranes based on hybridization and composition of a cationic PIL and a guest substance, and explore their diverse functions. Herein, fabrication methods based on two mechanisms were proposed and investigated. First, electrostatic complexation between a cationic hydrophobic PIL and a weak poly-/multi-acid. Second, ice-assisted phase separation of a hydrophobic PIL in water when in contact with a multi-acid compound as an ionic crosslinker. In following, task-specific functions were built up in porous PIL membranes via addition of specific metal-containing substances. This thesis content is inherently interdisciplinary, as it combines polymer chemistry and processing, membrane fabrication and materials science to secure its success in implementation, and this thesis advances the design and application scope of porous polyelectrolyte membranes.