Before performing this demonstration, carefully read the MSDS (Material Safety Data Sheets) for toluene diisocyanate. This reaction
must be performed in a large, well-ventilated area with qualified supervision and faculty approval. Do not attempt to modify the
procedure or increase the scale of this reaction. Be sure to wear safety goggles, gloves, and a lab coat during ALL stages of this
When two viscous liquids are mixed, a rigid foam is produced whose volume is 20-30 times that of the original mixture.
- lab coat, rubber gloves, and approved safety goggles
- 40 mL Part A and 40 mL Part B of a two-component polyurethane foam system
- heat-resistant transite board, approximately 1 m square
- 200-mL disposable cup
- gloves, plastic or rubber
- 250-mL beakers or paper cups
- food-coloring dye (optional)
Put on a lab coat and an approved pair of safety goggles. Place the 200-mL disposable cup in the center of a heat-resistant
transite board. Wearing gloves, mix equal amounts of Parts A and B in the disposable cup. A few drops of a food-coloring dye can be
added to the lighter-colored component. When the foam begins to expand, stop stirring. As the mixture foams, it rises out of the cup,
overflows, and forms a bell-shaped solid.
Because the freshly prepared foam usually contains unreacted isocyanate, it should not be handled until it has cured several
hours in a well-ventilated area and washed with water.
- Isocyanates are irritants to the skin, eyes, and respiratory system. Toluene 2,4-diisocyanate, which has been used in many
polyurethane systems, is reported to cause skin irritation, allergic reactions, and bronchial asthma. The foam product should be
allowed to cure several hours in a well-ventilated area before handling.
- ALL CHEMICALS: In case of contact, immediately flush eyes or skin with copious amounts of water for at least 15 minutes while
removing contaminated clothing and shoes. If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is
difficult, give oxygen. If swallowed, wash out mouth with water provided person is conscious. Call a physician. Remove and wash
contaminated clothing promptly.
Since the individual components are soluble in acetone, they can be dissolved and the solutions flushed down the drain with
water. The rigid foam, when cured, should be discarded in an appropriately labeled waste container.
The fully cured polyurethane is soluble in solvents such as dimethylformamide. Before it is fully cured, the foam can be
removed from the container by using a spatula and small amounts of acetone.
The polyurethane foam system used in this demonstration consists of two viscous liquids. Part A, light amber in color,
contains a polyether polyol, a blowing agent, a silicone surfactant, and a catalyst. Part B, which is dark, contains a polyfunctional
A polyurethane foam is formed by producing a polyurethane (polycarbamate) polymer in the presence of a fluorocarbon
blowing agent. The polymer is formed by the reaction of a polyester polyol, HO-R-OH (whose probable molecular weight range is
400-4000), with a polyfunctional isocyanate, OCN-R'-NCO [for example, methylene bis(4-phenylisocyanate)]. Amine compounds or
metal salts are used as catalysts.
The polyfunctional character of the reactants results in a high degree of cross-linking in the product, forming a rigid foam.
Shakhashiri, Bassam Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry,
Madison, Wisconsin: University of Wisconsin Press, 1983, pp. 216-218.