Chemistry Reference
In-Depth Information
O
K
2
CO
3
O
O
n
O
150
o
C
n
O
O
Another example is a ring opening polymerization of an oxalate [
39
]. Again, only low molecular
weight polymers result:
O
O
O
n
O
O
n
O
O
Lactides, on the other hand, when subjected to ring opening polymerization with Lewis acids yield
high molecular weight polymers [
41
]:
O
O
O
n
O
n
O
O
-hydroxycarboxylic acids can polymerize to high molecular weight polymers through
formation of anhydrosulfides [
42
]:
Also,
a
O
SOCl
2
O
O
n
O
HO
n
OH
S
n
O
O
O
In addition, it was reported [
49
] that polyesterification reactions are possible at room temperature.
High molecular weight polyesters form directly from carboxylic acids and phenols. These solution
polymerization reactions proceed under mild conditions, near neutral pH. Equimolar mixtures of
acids and alcohols condense as the reactions are being driven by additions of water across
carbodiimide groups. Substituted ureas form as by-products:
O
+
RN
NR
RCOOH
+
R'OH
R
R'
RCOOR'
+
NN
H
H
The reaction is useful in preparations of isoregic ordered chains with translational polar symmetry.
It can also be applied in polymerizations of functional or chiral monomers.
7.2.1.2 Commercial Linear Saturated Polyesters
Many linear aliphatic polyesters are produced commercially. They are relatively low in molecular
weight, less than 10,000. The main use of these materials is as plasticizers for poly(vinyl chloride)
polymers and copolymers. Such polyesters are usually formed from dicarboxylic acids and glycols.
Often, monocarboxylic acids or monohydroxy compounds are added towards the end of the reaction, in
