CONCEPTUAL EXAMPLE 10.1
Repeat Units in Polymers
What is the repeat unit in polyvinylidene chloride? A segment of the polymer is represented as
H
Cl
H
Cl
H
Cl
~C
C
C
C
C
C~
Cl
H
Cl
H
Cl H
Solution
The repeat unit is
H
Cl
C
C
H
Cl
Joining three of these units forms the segment shown; joining hundreds of the units would form a molecule of
the polymer.
Exercise 10.1
What is the repeat unit in polyacrylonitrile? A segment of the polymer is represented as
~CH2CHCH2CHCH2CHCH2CHCH2CHCH2CH~
CN
CN
CN
CN
CN
CN
EXAMPLE 10.2
Structures of Polymers
Give the structure of the polymer made from vinyl fluoride (CH2
CHF). Show at least four repeat units.
Solution
The carbon atoms become bonded in a chain with only single bonds between the carbon atoms. The fluorine
atom is a substituent on the chain. (Two of the electrons in the double bond of the monomer are used to join
the units.) The polymer is
~CH2CHCH2CHCH2CHCH2CH~
F
F
F
F
Exercise 10.2A
Give the structure of the polymer made from methyl vinyl ether (CH 2
repeat units.
CHOCH3). Show at least four
Exercise 10.2B
Give the structure of the polymer made from vinyl acetate (CH2
repeat units.
CHOCOCH3). Show at least four
EXAMPLE 10.3
Condensed Structural Formulas for Polymers
Write the condensed structural formula for the polymer formed from dimethylsilanol, (CH 3)2Si2(OH)2.
Solution
Let’s start by writing out the structural formula of the monomer.
CH3
HO
Si
OH
CH3
Because there are no double bonds in this molecule, we do not expect addition polymerization. Rather, we
expect a condensation reaction in which an OH group of one molecule and an H atom of another combine to
form a molecule of water. Moreover, because there are two OH groups per molecule, each monomer can
form bonds with the neighbors on both sides. This is a key requirement for polymerization. We can represent
the reaction as follows.
CH3
HO
Si
CH3
CH3
OH + HO
Si
CH3
CH3
OH + HO
Si
CH3
CH3
OH + • • • 
Si
CH3
O
+ n H2O
n
EXAMPLE 10.03
Condensed Structural Formulas for Polymers
continued
Exercise 10.3
(a) Write the structural formula for the polymer formed from 3-hydroxypropanoic acid (HOCH2CH2COOH),
showing at least four repeat units.
(b) Write a condensed structural formula in which the repeat unit is shown in
brackets.