Gel content analysis

We use gel content analysis to determine the weight fraction of a crosslinked polymer that is bound into an insoluble network. We immerse a stainless steel mesh basket containing a known weight of the crosslinked polymer in a suitable solvent (which may be heated to facilitate dissolution). If necessary, we can slice or grind the sample to increase its surface area. After 24 hours or more, we remove the basket from the solvent and dry it to constant weight. We calculate the gel content from Eq. 5.6. 

The essence of all gel content analysis procedures is to extract virtually all... 

The calculation of cross-link density is applicable only to samples from which the insoluble portion has been extracted. A standard procedure whereby this measurement can be made in combination with gel content analysis is found in ASTM method D 2765. 

Lipids, relatively nonpolar chemical substances found in plant, bacterial, and animal cells, are among the most ubiquitous of biomolecules. In this experiment, a lipid extract of ground nutmeg will be purified by chromatography on a silica gel column. Analysis of the lipid extract by thin-layer chromatography will provide the classification of the components in the extract. The unknown lipids will be further characterized by saponification and analysis of the fatty acid content by gas chromatography. For an abbreviated experiment, students may be provided samples of natural oils and fats that can be analyzed by saponification and gas chromatography. 

Sol-gel analysis is an important tool for distinguishing between polymers that can be cross-linked by irradiation and polymers that are not cross-linkable by radiation techniques. These experiments are typically done for wall-to-wall gels and offer the possibility to determine the irradiation conditions for microgel formation. Charlesby and Pinner first obtained a simple expression relating the soluble part of a polymer sample, the sol fraction (5) or sol content (in contrast to the insoluble part, the gel fraction (g) or gel content) to the absorbed dose D of radiation [10, 12],... 

Gel content measurements ASTM D2765 Compression tests ASTM D2990 Specific gravity determination Dynamic mechanical analysis (DMA) Ultrasonics... 

Fig. 9 Sol-gel analysis of PVP gel. (a) Gel content versus radiation dose (e-beam) (b) Charlesby-Pinner plot (with regression line).The gelation dose is determined to Dg = 94 kGy from the intercept follows po/ijo = 103. Reprinted from Burkert et al. (2007a), p. 1326. Copyright (2007), with permission from Elsevier...

Quartz substrates were used for UV-visible spectroscopic analysis, as well as for gel content and weight loss measurements. Salt (NaCl) flats were used as substrates for FTIR analysis. 

After purification, polymers are typically characterized by a standard set of techniques that can include amino acid content analysis, mass spectrometry, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and immu-noblotting. These methods are intended to verify the identity of the polymer. Depending on the type of polymer being... 

Since the ATR-FTIR for the chemical composition analysis is limited to the surface of the membranes, a gel test was carried out on the cross-linked membranes. In this study, the gel contents of the cross-linked membranes were measured by soaking the membranes in THF for 2 days at 25°C. The gel contents increased with the cross-linker concentrations (Table 11.4). This indicates that the degree of cross-linking increased with the cross-linker concentrations, which supports the FTIR results. 

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