A study on the preparation of microporous polymer papers or sponges and their pore structures

Abstract

Microporous organic polymers are of great interest due to their large surface area, physicochemical stability, and easy modification of their chemical structures. They have potential applications in gas storage, separation, and sensing. However, most porous polymers are obtained as insoluble powders, complicating their use in practical applications. In this study, various microporous polymers were prepared in the form of papers, sponges, or thin films. First, a microporous polymer paper (MPP) was prepared via the Sonogashira coupling reaction of 1,4-diiodotetrafluorobenzene and 1,3,5-triethynylbenzene. MPP was thin, flexible, and foldable, similar to classic paper. It had an interconnected network structure of hollow tubes and polymer showed superhydrophobicity with a water contact angle of 162o. Cryogenic nitrogen adsorption experiments showed that MPP has a microporous structure with a BET surface area of 715 m2g-1. The CO2 and H2 uptake amounts of MPP at 1 bar were 35.5 cm3g-1 at 273 K and 1.26 wt% at 77 K, respectively. The selectivity of CO2 over N2 at room temperature was 17.6. The measured iodine uptake of MPP was found to be 65 wt%. Secondly, compressible monolithic microporous polymer sponges were prepared via the Sonogashira coupling reaction of 1,3,5-triethynyl benzene and 1,4-diiodobenzene (MPS1) or 4,4-diiodobiphenyl (MPS2) at room temperature. SEM and TEM images of these polymers showed bundled hollow tubular microstructures. The sponges completely recovered their initial shapes after 95 % compression. Cryogenic nitrogen adsorption experiments showed that the sponges had high BET surface areas of up to 1090 m2g-1. The CO2 and H2 uptake amounts of MPS1 at 1bar were 49.9 cm3g-1 at 273 K and 1.93 wt% at 77 K, respectively. MPS1 had a high water contact angle of 150o and could remove hydrophobic solvents on water. MPS1 showed good filtration performance for small molecules such as dye molecules or VOC gases. Lastly, a hyperbranched polymer was used as a building block for the synthesis of a microporous organic polymer. Hyperbranched polyphenylenes were prepared from (3,5-dibromophenyl)boronic acid, which contained numerous unreacted bromophenyl end groups. Utilizing metal-catalyzed coupling reactions between these functional groups, cross-linked porous polymers were obtained. Although the hyperbranched polyphenylenes did not show porosity, their cross-linked polymers had highly porous structures with BET surface areas of up to 2030 m2g-1. An insoluble porous thin film was fabricated by the spin casting of a solution containing a hyperbranched polyphenylene followed by a Sonogashira cross-coupling reaction.