Another Name For Slime?

I was prompted to comment on the letter by Leiming Li, entitled “Polymers ... or Slime” because the experiment that uses white glue and borax to produce a cross-linked polymer is often used in middle school science classrooms to teach students about polymers (C&EN, Jan. 10, page 3). In my experience, however, the final product is not slime but an elastomer.

For example, in the eighth-grade physical science class that I help teach as a 
RESEED volunteer (www.reseed-sv.org), we ask the students to add 20 mL of a saturated solution of borax (sodium perborate) to 5 mL of Elmer’s glue (polyvinyl acetate) in a small cup and stir with a wooden tongue depressor. After a few minutes, the cross-linked polymer forms a rubberlike mass at the end of the wooden stick. Students then remove the material, squeeze out the excess liquid, and rub it between their palms to form a round “rubber” ball, which they can then bounce off the floor.

Some teachers call this experiment “Rubber from Glue,” but we call it “Glue Ball Chemistry” because this hands-on activity is accompanied by an audiovisual presentation that discusses polymers and cross-linking as well as the chemistry of this multistep process. It’s an entertaining way to introduce students to polymer 
science.

Joseph A. Castellano
San Jose, Calif.