Micropore Analysis of Polymer Networks by Gas Sorption and ¹²⁹Xe NMR Spectroscopy: Toward a Better Understanding of Intrinsic Microporosity

Abstract

The microporosity of two microporous polymer networks is investigated in detail. Both networks are based on a central spirobifluorene motif but have different linker groups, namely, imide and thiophene units. The microporosity of the networks is based on the "polymers of intrinsic microporosity (PIM)" design strategy. Nitrogen, argon, and carbon dioxide were used as sorbates in order to analyze the microporosity in greater detail. The gas sorption data was analyzed with respect to important parameters such as specific surface area, pore volume, and pore size (distribution). It is shown that the results can be strongly model dependent and swelling effects have to be regarded. (129)Xe NMR was used as an independent technique for the estimation of the average pore size of the polymer networks. The results indicate that both networks are mainly ultramicroporous (pore sizes < 0.8 nm) in the dry state, which was not expected based on the molecular design. Phase separation and network defects might influence the overall network morphology strongly. Finally, the observed swelling indicates that this "soft" microporous matter might have a different micropore size in the solvent swollen/filled state that in the dry state.

Porous Organic Polymers in Catalysis: Opportunities and Challenges

“…Furthermore, the degree of applicability and reliability of other isotherm analyses, such as NLDFT (nonlinear density functional theory), while clearly showing promise, 106,107 has yet to be fully established for these types of materials. 24,108 As mentioned in section 2, while gasderived surface area measurements can provide guidance regarding the porosity of POP-based materials, these may not be directly Scheme 14. Synthesis of 1,3,5-Triethylnylbenzene Containing CMPs via SonogashiraÀHagihara Coupling and the Subsequent Impregnation with Palladium Nanoparticles Using Pd(hfacac) 2 and scCO 2 as Reaction Medium a a Only the formation of nanoparticles inside the pores is predicted.…”

Towards Chiral Microporous Soluble Polymers—Binaphthalene‐Based Polyimides

“…This hysteresis might be explained by a kinetic effect, [22] or the 'dual mode sorption', i.e., the swelling of the polymer matrix by argon or nitrogen after all initial micropores have been filled. [23,24] These two effects raise doubts about the applicability of nitrogen sorption for the porosity analysis of flexible polymers. In order to obtain complementary results, hydrogen and carbon dioxide sorption measurements were therefore performed.…”

“…In order to obtain complementary results, hydrogen and carbon dioxide sorption measurements were therefore performed. These two methods are selective for micropores and swelling effects are less pronounced compared to N 2 sorption at 77 K. [22,[24][25][26][27][28][29] The chiral (þ)BINAM-PMDA polymer adsorbs significant amounts of hydrogen (0.78 wt.-% at 1 bar and 77 K) and carbon dioxide (8.3 wt.-% at 1 bar and 273 K). It is possible to calculate specific surface areas from the H 2 and CO 2 sorption measurements using a Langmuir approach or by application of molecular models such as density functional theory (DFT) or Monte-Carlo (MC) methods.…”

129Xenon NMR: Review of recent insights into porous materials

“…Weber et al analysed the porosity of several polymers (specific surface area, pore size and pore volume) by adsorption experiments of different gas (N 2 , Ar, CO 2 ) using various models and compared the results to that obtained with 129 Xe NMR [174]. The latter give average pore sizes in good agreement with those obtained by gas adsorption.…”