What is gel?

Gel is a generic term for solvent-insoluble polymers with a three-dimensional network structure and their swollen bodies. Simply put, a gel is a network of numerous chains of macromolecules.
Gels are also an intermediate substance form between solids and liquids, varying from close to a viscous solution to a fairly hard solid, depending on their chemical composition and respective factors.
Gels are found in many familiar places, such as the lens and cornea of the eye, jelly, tofu, contact lenses and air fresheners, and play an important role in many fields.

Polymers and gel fraction

What determines the solubility of polymers is not only the affinity of the polymer chain to the solvent (similarities dissolve well together), but also the following relationships.

Large molecular weight → Small solubility
Good crystallinity → Small solubility
Many branching structures → Large solubility
Many cross-linked structures → Small solubility

Cross-linking, not only radiation cross-linking but also other cross-linking processes, only result in the addition of one polymer chain to another, resulting in the presence of a small number of very large molecular weight polymers, which are not observed as gels. However, as cross-linking progresses and a three-dimensional network structure is formed, they aggregate to form a gel.
This phenomenon is manifested in the relationship between dose and gel fraction, whereby when the gel fraction is measured at different doses, no gel is usually seen in the beginning and gel can only be measured after a certain dose has been exceeded.

Summary

Gel fraction measurement is the most effective way to assess the degree of cross-linking.
To measure the gel fraction measurement of polymers other than polyethylene, it is necessary to select the most suitable solvent and determine the measurement conditions independently with reference to JIS K 6796 / ISO10147.

If you have any questions about how to measure gel fraction, solvent selection, etc., please feel free to contact us.