GTBL042-14 GTBL042-Callister-v2 August 29, 2007 8:59
14.11 Polymerization • 605Condensation Polymerization
condensation Condensation(orstep reaction)polymerizationis the formation of polymers by step-
polymerization wise intermolecular chemical reactions that may involve more than one monomer
species. There is usually a small molecular weight byproduct such as water that is
eliminated (or condensed). No reactant species has the chemical formula of the re-
peat unit, and the intermolecular reaction occurs every time a repeat unit is formed.
For example, consider the formation of the polyester poly(ethylene terephthalate)
(PET) from the reaction between ethylene glycol and terephthalic acid; the inter-
molecular reaction is as follows:(14.5)
HO
H
H
C C
H
H
O
HO
H
H
C C
H
H
OH
Ethylene glycol Terephthalic acid
OHO C OHO
C
O
C OH H 2 O
O
C
+
This stepwise process is successively repeated, producing a linear molecule. Fur-
thermore, reaction times for condensation are generally longer than for addition
polymerization.
For the previous condensation reaction, both ethylene glycol and terephthalic
acid are bifunctional. However, condensation reactions can include trifunctional or
higher functional monomers capable of forming crosslinked and network polymers.
The thermosetting polyesters and phenol-formaldehyde, the nylons, and the poly-
carbonates are produced by condensation polymerization. Some polymers, such as
nylon, may be polymerized by either technique.Concept Check 14.8Nylon 6,6 may be formed by means of a condensation polymerization reaction in
which hexamethylene diamine [NH 2 —(CH 2 ) 6 —NH 2 ] and adipic acid react with one
another with the formation of water as a byproduct. Write out this reaction in the
manner of Equation 14.5.Note:the structure for adipic acid isH
H
C C
HH
HH
HO C C
H
H
OH
O
C
O
C
[The answer may be found at http://www.wiley.com/college/callister (Student Companion Site).]