Microporous Organic Polymers: Synthesis, Characterization, and Applications

The presence of a certain degree of porosity in polymers is a feature that provides them with unique properties and with opportunities to be exploited in a number of technologically important applications. Depending on the size and chemical nature of the pores, they may be exploited for selective adsorption and/or storage of specific molecules; the pores may host catalytically active species or have catalytic activity themselves; they may host probes that act as sensors; pores may also provide reservoirs for controlled release of previously absorbed species; and finally, they may simply provide a selective and preferential pathway for the transport of gases, liquids, or solutes. Within this context, microporous organic polymers represent a rapidly expanding class of amorphous porous materials, composed of fully covalently bound organic building blocks. Depending on the appropriate choice of monomers, functionality, and polymerisation method, they can be prepared both as solution processable or as insoluble networked materials. Typical features of microporous organic polymers (MOPs) are pore diameters of less than 2 nm, high internal surface areas, and elevated thermal stability [1]. At the borderline between microporous and macroporous polymers we can find systems prepared by phase separation or other techniques. Typical challenges in this field are related to polymer synthesis (where the polymer type can be ladder-type polymers of intrinsic microporosity (PIMs), thermally rearrangeable (TR) polymers, or porous organic networks), to the structural characterization of the polymers and/or to the modelling of their structure and properties, and to different application types (e.g., gas sorption and storage, gas permeation, catalysis, heavy metal sorption, energy storage) and operation principles. In this special issue, we report some of the latest advances in the field of synthesis, characterisation and applications of porous or microporous organic polymers, with a total of 11 articles, two of which are reviews. The first group represents solution-processable MOPs. These polymers may be synthesized via different routes, but the key factor is that they consist of highly contorted and rigid polymer backbones, which guarantees on the one hand an enhanced solubility in common organic solvents, and on the other hand very poor packing of the polymer in its solid state, resulting in a high free volume. This is the fundamental principle of PIMs, a novel class of polymers introduced in 2004 by Budd and co-workers [2] that, since then has become the subject of numerous studies [3]. Based on this principle, Genduso et al. report the synthesis and characterization of a novel triptycene-based solution-processable polyamide obtained via polycondensation reaction [4]. The trigonal shape of the triptycene grants an enhanced internal free volume, but the amide bond still provides a certain degree of mobility compared to other much stiffer PIMs, resulting in moderately high gas sorption capacity and gas permeability, but significantly higher selectivity than similar polyimides. Alternatively, Esposito et al. report the performance of the true polymer of intrinsic microporosity PIM-EA(H2)-TB, pristine and blended with Matrimid® [5]. The two polymers showed good compatibility, allowing tailoring of the properties of the blend and increasing the permeability of the pure Matrimid® by some orders of magnitude. This is a convenient alternative to the development of completely novel polymers. Dujardin et al. discuss the characteristics of a class of chemically and thermally robust norbornene based polymer membranes, crosslinked with vinylnorbornene (VNB) comonomer units [6]. Here, the permselective properties could be tailored by the VNB content in the pol