PLAYCHEM experiment


You will weigh the glue you will use.
Given the weight % of polymer in the original glue,  calculate the amount of polymer you actually used.
Given the molecular weight of the polymer and the polymer's density, calculate the polymer's molar concentration in the original glue.  Calculate concentration in   milliMolarity,  mM. Why?
What percentage of the mass of the final ("crosslinked") polymer is due to the  original polymer used.   What is most of the rest?

     This experiment involves three chemicals one of which is "free". the other two items can readily be purchased at a hardware store and/or a supermarket. Their individual stories are are amazing enough, but when mixed together they produce something truly amazing!

     More amazing yet is the fact that the principles on which this experiment is based are used in a number of commercial products, some silly, some serious.

     Borax is a hydrate of sodium tetraborate. It occurs in desert playas where it is shoveled up, cleaned and packaged. It is a water soluble, relatively nontoxic chemical which forms a precipitate with calcium ions. Calcium ions interfere with the action of soap in laundry by precipitating the soap as a sludge, thus destroying its emulsifying properties. Since removing calcium ions improves soap utilization, Borax or chemicals such as sodium phosphate or sodium carbonate which also precipitate calcium ions are frequently added in laundry to act as water softeners or "boosters" or "builders", boosting or building the effect of the soap or detergent.

     Elmer's Glue and similar products are polymers which can be emulsified in water. The chemical structure involves long chains of carbon atoms, 10,000 or more hooked together in a row, with half the carbons (approximately every other one) having either a hydroxyl (-OH ) group or an acetoxy (-OCOCH3) group attached. The remaining carbon valences are satisfied by hydrogen atoms.
     This species is referred to on the label as partially hydrolyzed polyvinylacetate.
This polymer is in one sense similar to polyethylene, the material used to make squeeze bottles and plastic wrap. But whereas polyethylene has only carbon and hydrogen atoms and therefore repels water, this glue is emulsified by water. The difference is the presence of the large number of hydroxy groups on the glue molecule which hydrogen bond with water molecules to produce the water emulsion sold as glue. When the water evaporates, the remaining glue molecules form a tough plastic which is particularly good at holding together wood and paper.

     So with this background, you will add the two together and try to visualize on a molecular level, how to account for the observed changes.

     Oh, by the way, have you figured out the the identity of the "third chemical" mentioned at the beginning? Actually its involvement in this experiment is the basis of some of the more serious applications of the principle involved here.


     Other hydroxy containing polymers can be crosslinked with borax to produce polymers with different properties.  An example of this is guar gum,  a polymer containing the sugar mannose hooked together through oxygen (hemiacetal) links to form the backbone and side chains of the sugar galactose.
Mannose, a disaccharide carbohydrate,  has two glucose molecules chemically joined with one of the oxygens through the hemiacetal linkage.   C12H22O11 .
Galactose is a monosaccharide C6H12O6 .





    Guar gum, a nontoxic polymeric carbohydrate, is soluble in water and used as a thickener for shampoos, salad dressings etc.  It is used in ice cream to make it less "runny" and it also prevents the formation of ice crystals.  Its solutions are extremely viscous but they can be made even more viscous by crosslinking the guar gum chains with borax (or calcium ion).


    In addition to simply making polymers from Glue or Guar Gum you can make polymers containing both.  These are called block copolymers.  The polymers can thus be fine tuned to provide different properties... more "putty"-like or more "slime"-like. 

R.W. Kluiber 1/14/2000    9/28/2008