25.4 Slime

Chemical Concept Demonstrated: Cross-linking between polymer chains

Demonstration:

The poly(vinyl alcohol) and borax solution are vigorously mixed together in a cup.
  • Poly(vinyl alcohol) dissolved in warm water.
  • Borax dissolved in water.

Observations:

    A polymer "slime" is produced.

Explanation:

    Poly(vinyl alcohol) is an addition polymer with an average molecular weight of about 100,000 daltons.  Borax reacts with water to form a B4O72+/HB4O7- buffer solution with a pH of about 9.  The borate ions form hydrogen bonds to the -OH groups on the PVA backbone that weakly cross-link this polymer.  Cross-links either weaker or stronger than this would produce materials with very different properties.