Page 130 - Carrahers_Polymer_Chemistry,_Eighth_Edition

4 Polycondensation Polymers

(Step-Reaction Polymerization)

In this chapter, we will emphasize condensation polymers. Since most of these are formed from
stepwise kinetics, we will also focus on this kinetic process in this chapter. Even so, some of these
polymers can be synthesized employing ring-opening polymerizations (ROPs), which employ the
chain polymerization process for synthesis rather than the stepwise process for formation. The
bulk of discussion for chain polymerization kinetics is contained in the following several chapters
rather than here. We will begin with a comparison between the polymer types and kinetics of
polymerization.

4.1 COMPARISON BETWEEN POLYMER TYPE
AND KINETICS OF POLYMERIZATION
There is a large, but not total, overlap between the terms condensation polymers and stepwise kinet-
ics and the terms addition (or vinyl) polymers and chain kinetics. In this section we will look at each
of these four terms and illustrate the similarities and differences between them.
The terms addition and condensation polymers were first proposed by Carothers and are based

on whether the repeat unit of the polymer contains the same atoms as the monomer. An addition
polymer has the same atoms as the monomer in its repeat unit. Since many of the important addi-
tion polymers are formed from vinyl reactants, many addition polymers are also referred to as vinyl
polymers.

X X
— — (4.1)
n
H 2 C = CH → −(−CH −CH−) −
2
The atoms in the backbone of addition polymers are almost always only carbon.
Condensation polymers generally contain fewer atoms in the polymer backbone than in the reac-
tants because of the formation of byproducts during the polymerization process and the backbone
contains noncarbon atoms.

X–A–R–A–X + Y–B–R –B–Y → –(–A–R–A–B–R –B–)– + XY (4.2)

where A-X can be most Lewis bases such as -NH , -SH, -OH and B-Y can be Lewis acids
2
such as
O O O O
− − − − − − − −
−C−OH, −C−CI, −P−CI, −S−CI
− − −
R O

The corresponding polymerizations to form these polymers are, typically, chain polym-
erizations to form addition polymers and stepwise polymerizations to form condensation
polymerizations.

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