Investigation of the Porosity of Poly(sodium methacrylate) Hydrogels by ¹H‐NMR T₂‐Relaxation and Inverse Size‐Exclusion Chromatography

Abstract

A series of poly(sodium methacrylate) hydrogels, also called superabsorbents, having a theoretical degree of neutralization of 100 mol%, and degree of crosslinking varying from 0.6 to 20 mol%, are synthesized via conventional free radical polymerization. The networks are characterized in detail by inverse size‐exclusion chromatography and 1H‐NMR relaxometry in order to place particular emphasis on the investigation of the pore size distribution (PSD) and the chain mobility, respectively. The two previously mentioned parameters are compared to understand the correlation between the elastic chain mobilities and the average pore size of the hydrogel. From the resulting data, a new empirical equation is proposed, which is valid under the given experimental conditions and permits a rough estimation of the average PSD from the relaxation data. Thus, the equation permits to reduce the number of analytical techniques needed for the characterization of complex systems such as polymer networks.

Covalent Adaptable Networks Based on Dynamic Alkoxyamine Bonds

“…Reproduced with permission. [107] Copyright 2020, Wiley-VCH GmbH. a nitroxide-exchange manipulation of the network, which corresponds to the presence of two different nitroxide moieties (illustrated as red and green in Figure 9a), can be precisely monitored in situ with high sensitivity via EPR spectroscopy due to the distinct hyperfine coupling constants of the two nitroxides.…”

“…Reproduced with permission. [ 107 ] Copyright 2020, Wiley‐VCH GmbH. d) Left: Mesh size distribution of three different [2 + 4]‐combination networks determined from ISEC investigations; right: SEC results of the decrosslinked polystyrene from different [2 + 4]‐combination networks.…”

“…[ 10 ] In the inverse mode, namely inverse size‐exclusion chromatography (ISEC), it is possible to determine the mesh‐size distributions of the networks. In this technique, a range of well‐defined polymer standards with known number‐average molecular weights flow through a column constituent of networks of unknown mesh sizes as stationary phase (Figure 9d) [ 107 ] The resulting standard elution volumes are plotted against the molecular weights of polymer standards, which allows for the calculation of the mesh sizes in the examined networks. [ 10 ] For instance, the mesh‐size radius of the three networks similar to what is seen in Figure 9b were determined to be 7.6 ± 1.7 nm ([2+4]P), 4.2 ± 1.1 nm ([2+4]O, and 9.8 ± 2.3 nm ([2+4]E), respectively (Figure 9d).…”

“…A series of polymer standards with known molecular weights were passed through the porous materials stationary phase made of CAN. Reproduced with permission [107]. Copyright 2020, Wiley-VCH GmbH.d) Left: Mesh size distribution of three different [2 + 4]-combination networks determined from ISEC investigations; right: SEC results of the decrosslinked polystyrene from different [2 + 4]-combination networks.…”

Assessment of the effectiveness of liquid hot water and steam explosion pretreatments of fast-growing poplar (Populus trichocarpa) wood

“…To measure the biomass porosity, different methods are used: Simons' stain, Congo red, nitrogen porosimetry or NMR (nuclear magnetic resonance) (Meng et al 2013;Dougherty et al 2014;Karimi and Taherzadeh 2016;Alam et al 2019). Other methods: DSC (differential scanning calorimetry) and ISEC (inverse size exclusion chromatography) are also used, but most often for porosity analysis of silica, naphthalene, soil or hydrogels (Brun et al 1977;Jerabek et al 1993;Guan and Guiochon 1996;Strange et al 2003;Yao and Lenhoff 2004;Kozłowski et al 2010;Charmas and Skubiszewska-Zięba 2017;Pfeifer et al 2021) and pulps, nitrocellulose or thermally modified wood (Berthold and Salmén 1997;Książczak et al 2003;Fahlén and Salmén 2005;Park et al 2006;Zauer et al 2014;Szadkowski and Szadkowska 2020). In the available literature, there is scarce information about using ISEC method for porosity analysis of wood, especially wood of the fast-growing poplars in a context of bioethanol production.…”