Fun with polymers..
Today students had a fun time learning about polymers. The students learned how important polymers are in their lives, since polymers include starches (pasta, potatoes), cellulose (wood, plants), proteins, plastics, fabrics both natural (cotton, wool) and manufactured (rayon, nylon). What is a polymer? Polymers are molecules made of linked chains of individual units, or monomers, just as long chains of a bike chain consists of individual links. Students saw how monomers form chains to create polymers, and that chains of polymers can be cross-linked together to get even different properties. Students also learned that plastics were substances named for their ability to be pliable, malleable, and form-able. We discussed three different plastics,which were all made with polymers consisting of the same monomer, but different chain lengths. Students made connections between the flexibility and malleability of a plastic bag to short polymer chain composition and the hardness of a milk jug to long polymers. We discussed a plastic called “PEX”, which consisted of very long polyethylene polymer chains that are cross-linked. Because of this chemical cross-linking, PEX is a very stiff material.
We also discussed the process of cross-linking, which causes polymers to link together. As an experiment we took existing polymers (school-type gel glue and white glue, or polyvinyl acetate to make Glubber) and mixed them with a cross-link solution, tetrahydroxyborate (Borax) in water. Students observed that Glubber started off as a slimy, sticky glue that transformed into a rubbery, dry substance that could be stretched, formed into a ball, broken sharply apart, and bounced, with the addition of a chemical cross-linker. We call this material “Glubber,” and it is easy and safe to make at home under adult supervision.