Addition Polymers
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Introduction: Polymers are long chain giant organic molecules are assembled from many smaller molecules called monomers. Polymers consist of many repeating monomer units in long chains. A polymer is analogous to a necklace made from many small beads (monomers). Many monomers are alkenes which react by additionto their unsaturated double bonds. The formation of polyethylene from ethylene (ethene) may be illustrated in the graphic on the left as follows: The electrons in the double bond are used to bond two monomer molecules together. This is represented by the red arrows moving from one molecule to the space between two molecules where a new bond is to form. Note that in the complete polymer, all of the double bonds have been turned into single bonds. No atoms have been lost and you can see that the monomers have just been joined in the process of addition. A simple representation is -[A-A-A-A-A]-. Polyethylene is used in plastic bags, bottles, toys, and electrical insulation. LDPE - Low Density Polyethylene: The first commercial polyethylene process used peroxide catalysts at a temperature of 500 C and 1000 atomspheres of pressure. This yields a transparent polymer with highly branched chanis which do not pack together well and is low in density. Today most LDPE is used for blow-molding of films for packaging and trash bags. HDPE - High Density Polyethylene: An alternate method is to use Ziegler-Natta aluminum titanium catalysts to make HDPE which has very little branching, allows the strands to pack closely, and thus is high density. It is 3 times stronger than LDPE and more opaque. About 45% of the LDPE is blow molded in milk and squeezable bottles.
OtherTypes of Addition Polymers: PVC (polyvinyl chloride) which is found in plastic wrap, simulated leather, water pipes, and garden hoses, is formed from vinyl chloride (H2C=CHCl). The reaction is shown in the graphic on the left. Notice how every other carbon must have a chlorine attached. Link to Polyvinylchloride - with Chime molecule - Macrogalleria at U. Southern Mississippi Polypropylene: The reaction to make polypropylene (H2C=CHCH3) is illustrated in the middle reaction of the graphic. Notice that the polymer bonds are always through the carbons of the double bond. Carbon #3 already has saturated bonds and cannot participate in any new bonds. A methyl group is on every other carbon. Link to Polypropylene - with Chime molecule - Macrogalleria at U. Southern Mississippi Polystyrene: The reaction is the same for polystrene where everyother carbon has a benzene ring attached.
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OtherTypes of Addition Polymers: Links to various polymers with Chime molecule - Macrogalleria at U. Southern Mississippi
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Addition type Polymers
Demonstrations with Polymers
Silly Putty - polyvinyl acetate
Ghostbusters - polyvinyl alcohol
Ghosbusters Slime - Polyguar gum
Peanut Race - polystyrene
Disappearing Cup - polystyrene
Solid Water - sodium polyacrylate
