Gel content determination

Lee S (1993) Gel-content determination of polymers using thermal field-flow fractionation. In Provder T (ed) Chromatography of polymers characterization by SEC and FFF. American Chemical Society, Washington, DC, pp 77-88... 

Gel Fractions. Weighed samples were placed in 300 mesh stainless steel baskets and extracted I6 hours in a vapor-jacketed Soxhlet extractor with p-xylene. The insoluble fraction was dried in a vacuum oven with a nitrogen bleed at 80 C overnight and the gel content determined from the initial and final welgpits. 

Lee, A. Gel content determination of polymer using thermal field flow fractionation. Chapter 6. In Chromatography of Polymers Characterization by SEC and FFF Provder, T., Ed. ACS Publications Washington, DC, 1993 77-88. 

As part of our continuing study of the peroxide-catalyzed reactions of MAH with saturated polyolefins, the present investigation was undertaken to determine the extent of crosslinking and/or degradation which accompanies the EPR-MAH reaction. The gel content, presumably indicative of crosslinking, was determined by extraction with cyclohexane at room temperature (22 C) for 60 hr. 

As with many other polymer molecular characteristics, we cannot precisely determine the molecular structure of crosslinked polymers. In practice, we can measure a crosslinked polymer s gel content and its average crosslink density. Each of these analyses provides a single value that represents a complex situation. 

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. 

A determination of the surface hydroxyl groups was made by Noll et al. (183). The total water content was determined by heating to 1100°. The content ofmolecular water was titrated by the Karl Fischer method. Silanol groups react with this reagent only very slowly. Good agreement was observed with silanol contents determined independently by other methods. With silica gel, 5.2 silanol groups were found per 100 A. ... 

The impact strength increases almost linearly with gel content and thus with the degree of crosslinking (17). Figure 9.3 shows the increase of the molecular mobility with the impact strength for ABS. For HIPS it is claimed that the situation is quite similar. The molecular mobility of the soft phase particles is determined by nuclear magnetic-resonance spectroscopy relaxation measurements (16). 

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... 

Testing procedure A standardized procedure which requires choice of solvent for extraction. In PE determinations, xylene was used as a solvent." A more complex procedure was used to determine the gel content in radiation crosslinked PVC filled with calcium carbonate. The compound was extracted with tetrahydrofuran, and non-dissolved residue was determined. This residue was then used for determination of chlorine by the Schoniger method. From the amount of chlorine, the concentration of polymer was established. The remainder of the gel content was a filler embedded by gel. " ... 

Moisture content (me) determination moisture content of starch gels was determined by vacuum oven drying (AOAC, 2002) at 60°C for 24 h. At least duplicate moisture content analyses were carried out for each gel. 

Structural characterization. The content of insoluble material (gel) was determined by soxhlet extraction with p-xylene for 20 h under nitrogen. 

Gel Fraction Determinations. The irradiated polyethylene samples were measured for gel content by extraction with boiling xylene for 72 h. Only one sample, NBS 1475 irradiated to 8.0 Mrad in vacuum at 300 K, showed a measurable gel content. 

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