Slimy polymer forms when borax solution is added to poly(vinyl alcohol) solution. The polymer can be stretched without breaking if is stretching slowly. This is so called non-Newtonian fluid which under low stress, such as slowly pulling on the material, flows and stretches. However, when pulling sharply, the polymer breaks. We can explain the polymer nature by considering its structure.
Sodium tetraborate (Na2B4O7) is widely known as borax. In borax molecule there are two four-coordinated boron atoms, which have tetrahedral structure as shown below:
The liquid-like nature of the produced polymer is a consequence of hydrogen bonding (crosslinking) between the oxygen atom of the hydroxyl group attached to boron atom, and hydrogen atom of the hydroxyl group of poly(vinyl alcohol), as well as hydrogen bonding of the hydrogen atom of the hydroxyl group attached to boron and oxygen atom of the hydroxyl group of poly(vinyl alcohol). During stretching of this polymer hydrogen bond cleavage occurs within it, so by this experiment the small intensity of hydrogen bonding can be demonstrated, in comparison to covalent or ionic bonds.