Chemistry Reference
In-Depth Information
Polystyrenes that are substituted on the benzene ring, like poly(vinyl toluene), behave similarly to
polystyrene when pyrolyzed [
457
]. Also, poly(
-methylstyrene) at 350
C yields 44.4% monomer as
compared to polystyrene that yields 40.6% monomer at these conditions. The rate, however, for
polystyrene at this temperature is 0.24 mol.%/min, while for poly(
m
m
-methylstyrene) it is 0.9 [
457
].
9.8.4 Thermal Degradation of Methacrylic and Acrylic Polymers
The thermal degradation of
is a process of depo-
lymerization to monomers at temperatures up to 250
C, provided that the alkyl group is small, less
than butyl [
468
]. Poly(
polymers of acrylic
and
methacrylic alkyl esters
-butyl methacrylate) yields quantitatively isobutene instead. It was shown that
thermal depolymerization to monomers is probably common to all poly(methacrylate ester)s. As the
size of the alkyl group increases, however, particularly within secondary or tertiary structures, there is
increased tendency for the alkyl group to also decompose. This decomposition interferes with the
depolymerization process
Thermal stability of poly(methyl methacrylate) appears to vary with the molecular weight. For
instance, a sample of the polymer of molecular weight of 150,000 when heated in vacuum for 30 min
at 318
C yields 74.3% volatiles. By comparison, a sample of this polymer of molecular weight of
5,100,000 when heated for 30 min at 319
C yielded only 35.2% volatiles [
456
].
The thermal stability of copolymers of long-chained diol dimethacrylates was investigated [
583
].
These copolymers included 1,4-butane-, 1,5-pentane-, 1,6-hexane-, 1,8-octane-, 1,10-decane-, or
1,12-dodecanediol dimethacrylates, respectively, as well as 2,2-bis[4-(2-hydroxy-3-methacryloyl-
oxypropoxy)-phenyl]propane and triethylene glycol dimethacrylate. The polymers were found to be
thermally stable up to
t
250
C, as shown by the initial decomposition temperature and their
degradation profiles.
A quantitative investigation of the thermal degradation of poly(ethyl acrylate), poly(
n
-propyl
acrylate), poly(isopropyl acrylate), poly(
-butyl acrylate), and poly(2-ethylhexyl acrylate)
demonstrated that the principle volatile products are carbon dioxide, olefin, and alcohol
corresponding to the alkyl group [
469
,
470
]. The following mechanism of degradation was proposed
[
469
,
470
]:
n
O
O
O
O
O
R
O
O
O
O
+
CO
2
+
O
R'
R
R'
R
R'
R
R
R'
R'
R
R'
More recently, another study was carried out on the thermal decomposition of homopolymers of
ethyl methacrylate,
-butyl methacrylate, and 2-hydroxyethyl methacrylate as well as their
copolymers [
471
]. The copolymers of hydroxyethyl methacrylate with ethyl methacrylate and butyl
methacrylate were found to degrade by unzipping to yield the monomers similarly to poly(methyl
methacrylate). In addition, there is competition between unzipping and cross-linking in binary
copolymers of hydroxyethyl methacrylate with ethyl methacrylate and in
n
n
-butyl methacrylate.
, particularly acrylonitrile, was studied in detail
[
472
-
478
]. It was shown that there can be two paths of degradation, depending upon the temperature
Thermal degradation of
nitrile polymers
