Chemistry Reference
In-Depth Information
polymer. The other major type of polymer is condensation. In the formation
of a condensation polymer a molecule, often water or an alcohol, is elim-
inated when each polymer bond is formed. For example, a polyester made
by the reaction of a dicarboxylic acid with a dialcohol is a condensation
polymer because a water molecule is removed when each ester bond is
formed.
Polymers can be made with a single repeating unit; these are homopoly-
mers. The repeating unit can be varied to form copolymers. For example,
if ethylene is copolymerized with propylene, a copolymer can be formed.
Depending on the reaction conditions and the reactivity of the different
monomers,
copolymers
can
be
alternating,
random,
or
block.
This
is
illustrated with polymers made from monomers X and Y.
XXX
X
X
X
X
X
X
X
X
X
X
Homopolymer of X
XYX
Y
X
Y
X
Y
X
Y
X
Y
X
Alternating copolymer
XYX
Y
Y
X
X
X
Y
X
Y
X
X
Random copolymer
XXX
X
X
X
X
Y
Y
Y
Y
Y
Y
Block copolymer
Another type of copolymer is a graft copolymer with one polymer chain
built or grafted onto an existing polymer. There are many variations of these
themes and copolymers are not limited to two monomers.
Y
Y
Y
Y
Y
Y
XXX
X
X
X
X
X
X
X
X
X
X
Y
Y
Y
Y
Y
Y
Graft copolymer
Most commercial polystyrene is made by a radical process which yields
atactic polystyrene. Cationic and anionic polymerizations also yield atactic
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