Preparation of Polymers

This is a fun lab in which students prepare three polymers to take home that illustrate the chemistry behind addition and condensation polymers and polymer crosslinking. Addition polymerization is illustrated by formation of a polystyrene cast; students are encouraged to bring something of interest to embed. Condensation polymerization is illustrated by synthesis of nylon. To illustrate the effects of polymer crosslinking on physical properties, students prepare slime form polyvinyl alcohol and sodium borate.

Polystyrene: Casts are prepared in polyethylene scoops like those used to measure coffee or Kool-Aid. Styrene monomer free of inhibitors and catalyst (containing methyl ethyl ketone peroxide) come from Iasco. Eight drops of catalyst are mixed with 13 g of styrene in a 3-oz. paper cup (we use Dixie bathroom cups). Because the styrene is so thick and messy, we measure it out for the students using a top-loading balance protected from drips by a sheet of glass or plastic. You should use something disposable when handling it, because you can never clean it up. The mixture is poured into the polyethylene mold. When it is sufficiently firm, a second batch of styrene is mixed and a few drops are added to the mold. The item being embedded is added gently and the rest of the mixture is poured into the mold, which is allowed to cure in the student's drawer for a week. A little rolling and tapping easily dislodges the final cast.

Nylon: Students put 6 mL of 1,6-diaminohexane solution (0.5 M in water) into a 20-mL beaker. Then they carefully add 6 mL of adipoyl chloride solution (0.2 M in petroleum ether or hexane). Formation of a film is evident at the interface. They grasp the film with forceps, lift it straight out, and drape it over a test tube. The test tube is used as a spool to roll out a length of nylon. The crude nylon is rinsed for at least ten minutes in running water before handling. Other diamines or acyl chlorides would probably work as well. I haven't tested other nonpolar solvents for the acid chloride, but I am told they work as well (e.g. methylene chloride), though be sure the denser solution is added to the beaker first to prevent unwanted mixing.

Slime: Students examine separately 10 mL of 4% polyvinyl alcohol and 4 mL of 4% sodium borate. They may add food color to the polyvinyl alcohol for effect. The borate is poured into the polyvinyl alcohol and the solution is mixed thoroughly. It quickly sets to a clear gel which may be manipulated safely by hand. It is stored in a resealable sandwich bag.

Students are to show their products to their instructor and then asked a couple questions about the chemistry of addition and condensation polymerization, and to explain the molecular basis for the change in physical properties when the slime is made.

Revised 8/31/06