Download Unit 2, Lesson 13: Polymers Polymers are very large organic

Unit 2, Lesson 13: Polymers
Polymers are very large organic molecules that are made by linking together many smaller organic
molecules into long chains. The word “polymer” comes from two Greek words: “poly” meaning “many”
and “mer” meaning “parts”.
The small particles that make up the polymers are called “monomers”, meaning “one part”. The monomers
are attached together into long chains by polymerization reactions. They look like a long string of beads.
Different polymers have different characteristics, depending on:
1. the types of monomers they are made from,
2. the types of bonds that hold the monomers together.
There are many different naturally occurring polymers, including:
• starch, a polymer of glucose molecules
• DNA, a polymer of nucleotides
• protein, a polymer of amino acids
• cellulose (wood and paper), a polymer of glucose molecules
• wool, hair, fingernails, silk etc.
One of the most useful achievements of modern chemistry has been the development of techniques for
synthesizing polymers from non-biological sources such as petroleum derivatives. Many chemists say that,
since 1909 when the first synthetic polymer plastics were produced, we have been living in the “polymer
era”. Polymer chemistry is a huge (and lucrative) field in which chemists produce polymers that are tailored
specifically for certain applications: fabrics, plastics, packaging, car parts and almost every aspect of modern
life.
The two major types of polymers, named for the way in which they form, are addition polymers and
condensation polymers.
ADDITION POLYMERS
Addition polymers are formed when monomer units add to one another. No by-products are formed along
with the polymer. Most addition polymers form when double bonds in the monomers “open up” and form
bonds with other monomer molecules.
The mickey mouse model shows how the double bond in two ethene (CH2=CH2) monomers “open” to form
a polymer called polyethene (which is also known as polyethylene).
+
One example of an addition polymer is polypropene. It is formed by the addition of thousands, perhaps
millions, of propene molecules. Teflon, polystyrene, Orlon and Plexiglas are other examples of addition
polymers. (see page 83 of McGraw-Hill)
CH3
H
C C
H
H
+
H
C C
H
H
CH3
many propene molecules
H
H3C
H3C
H
H
H3C
C
C
C
C
C
C
H
H
H
H
n H
H
polypropene
The general equation for the addition polymerization reaction that makes polyethene (polyethylene) is :
CONDENSATION POLYMERS
Condensation polymers are formed as a result of condensation reactions to form either ester or amide
linkages. A smaller molecule, usually water, is also produced as the polymer is formed. In order for a
polymer to form, the monomer must have two functional groups that are capable of undergoing
condensation reactions- often one at each end of the molecule. “Polyester” gets its name from the fact that it
is made when many ester bonds (carboxylic acid + alcohol) are formed. Protein, starch and nylon are also
condensation polymers.
O
O
H
HO
C
R
O
O
H
/
H
H
/
C
OH
+ HO C R C OH
H
a dicarboxylic acid
O
C R
C O C R C
H
H
a dialcohol
H
+ H2O
n
a polyester
Proteins are made when amino acids (which have both an amine and a carboxylic acid group) are held
together in long chains by peptide bonds. For example:
H2O
H2O
amide
amide
H2O
amide
+ 3 H2O
a “poly peptide” or small protein molecule
Proteins are made of hundreds or thousands of amino acids joined into giant polymers. Changing the type
and order of the amino acids changes the structure of the protein. Different proteins make up our skin, bone,
teeth, hair, fingernails, haemoglobin in our blood, antibodies, enzymes, muscle and almost every other
structure in our body.