Chemistry Reference
In-Depth Information
9.9.6 Thermal Degradation of Aromatic Polysulfones
In
the weakest link was found to be the carbon-sulfur bond [
517
]. These
polymers are processed at about 300
C. At that temperature, the thermodegradative processes as well
as thermo-oxidative ones can occur. The rupture of the C-S bonds produces molecules of SO
2
and
fragments of the polymer molecules with terminal phenyl radicals [
517
]:
aromatic polysulfones,
O
Δ
SO
2
+
+
S
O
The phenyl radicals then abstract hydrogens from the methyl groups that are present when the
polysulfone is prepared from bisphenol A:
+
CH
2
+
9.9.7 Thermal Degradation of Polyethers
are subject to rupture at the ether link at around 300
C[
518
]. Products from
such ruptures are somewhat similar to those obtainable from decomposition of the polysulfones,
shown above.
The thermal degradation of
The
aromatic polyethers
was found to be initiated at the chain ends. There
appear to be three possible sites for initiation of homolytic bond cleavages [
519
]:
polyoxymethylene
9.9.8 Thermal Degradation of Cellulosic Materials
The degradation of cellulose triacetate in vacuum was analyzed with the aid of chromatography, mass
spectrometry, infra-red, and NMR spectroscopy [
517
]. The mechanism of degradation was proposed by
Scotney to consist primarily of deacetylation in the polymer chain and scission of the chain at the 1,4
glycosidic linkage between the pyranose rings [
517
]. The type of products that are formed depends upon
the degradation temperature. At temperatures above 250
C but below 350
C, unstable intermediates
form. Continued heating results in loss of carbon monoxide, carbon dioxide, and acetic acid, and
eventually end in formation of tar. Heating above 350
C causes condensation of radical intermediates,
cross-linked aromatic, and hydroaromatic ring systems. This can be illustrated as follows:
