Chemistry Reference
In-Depth Information
When the oxidation of a polyamide occurs through an attack by NO
2
or ozone, then the amide
groups themselves are subject to the attack [
532
]:
O
O
HNO
2
+
+
NO
2
N
N
O
H
O
O
O
3
N
+
HO
2
+
N
N
OO
OH
O
H
This appears to take place with hydrogen-bonded amide groups as well. The reaction, however, is
inhibited by benzaldehyde or by benzoic acid. When the degradation does take place, it occurs at
random [
532
].
Thermo-oxidative degradation of
polyoxyglycols
is reported to occur typically by a free-radical
mechanism with the formation of hydroperoxides. The decomposition of the peroxides leads to
formation of acids and carbonyl compounds [
533
]. A study of thermal oxidation of oligomers
(molecular weight approximately 1,900) of polyoxypropylene glycols showed that at 70-120
C the
end hydroxyl groups are not responsible for degradation and that chain ruptures occur through
decomposition of the hydroperoxides [
534
]: Two types of cleavage are possible. One can take
place through the carbon to carbon single bonds as follows:
OOH
O
O
O
O
O
O
OH
O
+
O
O
H
2
C
O
+
O
The other type of cleavage can occur through the oxygen-carbon bonds:
O
O
O
O
O
O
O
O
Both long and short molecular chains undergo degradation in an identical manner. The secondary
radicals that form as a result of the decomposition of the alkoxy radical accelerate the oxidation
process. It transforms into a chain process with an accompanying formation of various compounds.
The products are alcohols, aldehydes, and ketones. The aldehydes are easily oxidized into peracids
that degrade further into radicals.
