The Gel point in polymer chemistry is the point at which an infinite polymer network first appears. Assuming that it is possible to measure the extent of reaction, p, defined as the fraction of monomers that appear in cross-links, the gel point can be determined. The critical extent of reaction for the gel point to be formed is given by:
For example, a polymer with N≈200 is able to reach the gel point with only 0.5% of monomers reacting. This shows the ease at which polymers are able to form infinite networks. The critical extent of reaction for gelation can be determined as a function of the properties of the monomer mixture, r, ρ, and f:
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“In philosophical inquiry, the human spirit, imitating the movement of the stars, must follow a curve which brings it back to its point of departure. To conclude is to close a circle.”
—Charles Baudelaire (1821–1867)