25.4. Organic Reactions http://www.ck12.org
Addition Polymers
Anaddition polymeris a polymer formed by addition reactions between monomers that contain a double bond.
Molecules of ethene can polymerize with each other under the right conditions to form a polymer called polyethy-
lene.
nCH 2 =CH 2 →( CH 2 -CH 2 )nThe letternstands for the number of monomers that are joined in repeated fashion to make the polymer and can
have a value in the hundreds or even thousands.
Polyethylene can have different properties depending on the length of the polymer chains and on how efficiently they
pack together. Some common products made from different forms of polyethylene include plastic bottles, plastic
bags, and harder plastic objects such as pipes.
Several other kinds of unsaturated monomers can be polymerized and find use in common household products.
Polypropylene is stiffer than polyethylene and is used in plastic utensils and some other kinds of containers. Polystyrene
is used in insulation and in molded items such as coffee cups. Polyvinyl chloride (PVC) is extensively used for
plumbing pipes. Polyisoprene is a polymer of isoprene and is better known as rubber. It is produced naturally by
rubber trees, but several variants have been developed which demonstrate improvements on the properties of natural
rubber.
Condensation Polymers
Acondensation polymeris a polymer formed by condensation reactions. Monomers of condensation polymers
must contain two functional groups so that each monomer can link up with two other monomers. One type of a
condensation polymer is called a polyamide. An amide is characterized by the functional group shown below, where
the carbon of a carbonyl group is bonded to the nitrogen of an amine.
One pair of monomers that can form a polyamide is adipic acid and hexanediamine. Adipic acid is a carboxylic
acid with two carboxyl groups on either end of the molecule. Hexanediamine has amino groups on either end of
a six-carbon chain. When these molecules react with each other, a molecule of water is eliminated, making it a
condensation reaction (Figure25.23).
The polymer that results from the repetition of the condensation reaction is a polyamide called nylon-66. Nylon-66
was first invented in 1935 and has been used for all sorts of products. It and other polyamides are commonly found
in fibers, clothing, fishing line, carpeting, and many other products (Figure25.24).
Polyester is another common type of condensation polymer. Recall that esters are formed from the reaction of an
alcohol with a carboxylic acid. When both the acid and alcohol have two functional groups, the ester is capable
of being polymerized. One such polyester is called polyethylene terephthalate (PET), which is formed from the
reaction of ethylene glycol with terephthalic acid. The structure of PET is shown below (Figure25.25).