Chemistry Reference
In-Depth Information
9.2.5.6 Diels-Alder Condensations
Crotonic acid esters of cellulose undergo addition reaction with cycloaliphatic amines, like
morpholine or piperidine and with aliphatic primary amines [
79
]. Unsaturated polymers can also
undergo Diels-Alder reactions. One example is a reaction of hexachlorocyclopentadiene with
polycyclopentadiene [
80
]:
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
+
Cl
Cl
Cl
The addition takes place in an inert atmosphere at 140-150
C. Over 90 mol.% conversion is
achieved in 6 h.
Diels-Alder condensations of fumaric and maleic acids polyesters with various dienes [
81
] can
serve as another example. These reactions require 20 h at room temperature. Diels-Alder
condensations can also be carried out on polymers of 1,3,5 hexatriene, 1,3,5-heptatriene, and
2,4,6-octatriene [
82
]. Sulfonate-substituted maleic anhydride adds to low functionality hydrocarbon
elastomers, like EPDM, presumably via an Alder-ene type reaction [
83
]:
polymer
SO
3
H
SO
3
H
polymer
SO
3
O
O
O
O
O
O
O
O
O
Thiols add to diene rubbers by a free-radical mechanism [
84
]. Thus, antioxidants,
like
4-(mercaptoacetamido)-diphenylamine, add -SH groups to the double bonds of
cis
-polyisoprene
and polybutadiene in the presence of free-radical initiators [
84
].
Thiol compounds also add photochemically to polymers containing double bonds. For instance,
unsaturation can be introduced into polyepichlorohydrin by a partial elimination reaction.
The product then reacts with mercaptans, aided by a photosensitizer (like benzophenone) and
ultraviolet light [
85
]:
O
O
O
CH
2
Cl
CH
2
Cl
O
hn/BP
HSR
O
O
CH
2
SR
CH
2
Cl
