Bobert put a magnet in me and is now lowering me into this slime. He said the slime is a polymer and that it is also magnetic! I don’t know what all that means but I guess Dr. Smith is going to show you how to make this stuff. Ahhh! I’m sinking!!!!………..
What do all these objects have in common? They are all polymers! voice: what is a polymer? good question! A polymer consists of EXTREMELY long molecules. Think of a polymer as a bunch of chains that are all in the same range of lengths. Each link in each chain is identical and each link consists of a short molecule. These links in the chain or short molecules are called monomers. When chemical bonds are formed between identical monomers to form polymers the chemical reaction that occurs is called polymerization. Polymers fall into two categories and you are likely familiar with one form: —plastics. Plastics fall in the category of thermoplastics because when heated they soften and can be molded into different forms. The second category of polymers is called thermoset polymers which can be heated and molded only once.
balloons and plastic bags are made of highly flexible polymers. It is surprising just how much you can get these polymers to stretch. This balloon is made of a polymer called latex. We call it rubber more often than we do latex. Dr. Smith is first blowing up the balloon to roughly the length of a wood scewar. He lubricates the wood scewar by dipping it in vegetable oil then spreading the oil over the entire scewar. He locates the two spots where the rubber is the thickest on the balloon and slides the scewar completely through the balloon at these locations. Notice what happens when he tries to insert the scewar in a thin region of the balloon!
You can also insert a skewar through a plastic bag filled with water! Plastic bags are made of polyethylene.
Chemists love polymers because they can control the properties of the polymer. They do this first by first selecting the type of link or monomer in the polymer that they want to synthesize. They also modify the polymer’s properties by controlling the degree of cross-linking that occurs within the polymer. voice: Cross-linking? What’s that? Recall that a polymer consists of a range of chain lengths….. If you place several chains together in a bucket, the chains get intertwined and mixed around. This is just what happens to polymers. A polymer with no cross-linking is just like this bucket of individual chains. However, a polymer with cross-linking has its individual chains or polymer molecules pemanently linked together! This is called cross-linking. Cross-linking greatly strengthens the rigidity of the polymer. So through selection of the monomer and controlling the amount of cross-linking, chemists can choose and pick the properties of polymers they synthesize and also come up with new polymers never before created!
Dr. Smith is going to cross-link a polymer to make magnetic slime. Check this out! Typical white glue is a thermoplastic called polyvinylacetate. He first adds a total of 8 ounces of glue to a mixing container. He then adds water to one of the glue bottles and shakes the bottle to remove the rest of the glue. He adds the entire rinsing to the mixing container. He then repeats for the second bottle of glue again adding the rinsing to the mixing container. He is now adding one tablespoon of iron filings for each ounce of glue, so he is adding a total of 8 tablespoons of iron filings. If you do not have iron filings you can try something like staples. He is now preparing the cross-linking agent….borax by adding 1 tsp of borax to ½ cup of water. After mixing he adds the borax solution to the mixing container. The borax is the “crosslinking agent” it makes the solution basic and causes the long polyvinyl acetate molecules to cross-link. you can see that the thickening and gelling of the glue is becoming quite apparent rather quickly.
Dr. Smith is keeping his neodynium magnet clean by first wrapping it inside a balloon. He placed the magnet very near a lump of the slime to see what would happen over time.
– there are two categories of polymers: thermoset and thermoplastics, the latter being what we simply call plastics
– polymers are long chain like molecules consisting of individual links or monomers that are identical short molecules.
– polymer properties are controlled by selection of the monomer and degree of cross-linking that occurs within the – polymer chains