Gel point

In polymer chemistry, the gel point is an abrupt change in the viscosity of a solution containing polymerizable components. At the gel point, a solution undergoes gelation, as reflected in a loss in fluidity. Gelation is characteristic of polymerizations that include crosslinkers that can form 2- or 3-dimensional networks. For example, the condensation of a dicarboxylic acid and a triol will give rise to a gel whereas the same dicarboxylic acid and a diol will not. The gel is often a small percentage of the mixture, even though it greatly influences the properties of the bulk.[1]

Not to be confused with Gel point (petroleum).

Mathematical definition

An infinite polymer network appears at the gel point. Assuming that it is possible to measure the extent of reaction, , defined as the fraction of monomers that appear in cross-links, the gel point can be determined.[2] 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, , , and :[3]

See also

References
  1. R.J. Young; P. A. Lovell (1991). Introduction to Polymers, 2nd Edition. London: Chapman & Hall. ISBN 0-412-30640-9.
  2. Paul, Hiemenz C., and Lodge P. Timothy. Polymer Chemistry. Second ed. Boca Raton: CRC P, 2007. 381-389
  3. Pinner, S.H. (1956). "Functionality of non-equivalent mixtures". Journal of Polymer Science. XXI (97): 153–157. Bibcode:1956JPoSc..21..153P. doi:10.1002/pol.1956.120219718.

Further reading
  • Rudin, Alfred; Choi, Phillip (2012). The Elements of Polymer Science and Engineering, 3rd Edition. Elsevier Science. p. 410. ISBN 978-0-12-382178-2.
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