Chemistry Reference
In-Depth Information
7.6 Polyethers
Polyethers that form by chain-growth polymerizations of carbonyl compounds and by ring opening
polymerizations of cyclic ethers and acetals are discussed in Chap.
6
. In this section are discussed
poly(phenylene oxide)s and phenoxy resins.
7.6.1 Poly(phenylene oxide)s
These polymers are known for good thermal stability and good mechanical properties. Commercially,
these aromatic polyethers are prepared by oxidative coupling of phenols [
102
]. To obtain linear
polymers and achieve high molecular weights, 2 and 6 positions of the phenol must be protected by
substituents. This causes the aromatic rings to couple in 1,4 positions. When 2,6-dimethylphenol is
used, the reaction takes place at room temperature. Oxygen is bubbled through a solution of the
phenol in the presence of an amine-cuprous salt catalyst:
CuCl-pyridine
n
OH
O
O
2
n
Phenols with halogen substituents require higher temperatures. Large substituents can lead to
carbon to carbon coupling instead of carbon to oxygen:
O
O
The active catalyst is believed to be a basic cupric salt that forms through oxidation of cuprous
chloride followed by complexation with two molecules of the amine [
102
]:
NR
3
Cl
Cu
OH
NR
3
This is a step-growth polymerization involving phenoxy radicals. The polymer formation can be
illustrated as follows:
NR
3
NR
3
+
Cl
Cu
OH
OH
Cl
Cu
+
O
H
2
O
OH
NR
3
NR
3
