Chemistry Reference
In-Depth Information
The reactions result in formations of six-membered monocyclic and fused polycyclic units. These
reactions of carbon cations should also lead to molecular rearrangements, like 1,2 shifts of protons,
resulting in formations of five-membered rings and spiro cyclopentane repeat units [
111
].
Cyclization reactions of polyisoprene can be catalyzed by TiCl
4
[
112
] and by sulfuric acid
[
113
-
115
,
117
]. The products appear similar in the infra-red spectra [
110
] with only a few minor
differences. Also, there are only a small number of fused rings in the product.
Polyacrylonitrile converts to a red solid when heated above 200
C[
116
]. Only a small amount of
volatile material is given off. Further heating of the red residue to about 350
C or higher converts it to
a black brittle material. This black material has a ladder structure:
D
NNN
NNN
Heating of polyacrylonitrile in the presence of oxygen yields some quinone-type structures:
OO
NN
HHH
N
Further heating of the polymer, at very high temperatures, in excess of 2,000
C, results in formation
of graphite-like structures [
116
]. All, or almost all nitrogen is lost, probably as HCN and N
2
.
Migration of double bonds is a well-established phenomenon in polymers from conjugated dienes.
It occurs, for instance, during vulcanization of rubber (discussed in a later section). It also occurs upon
simply heating some polymers [
117
-
119
]. Thus, the double bonds shift in natural rubber when it is
heated to temperatures of 150
C or above [
120
]:
D
O
2
OO
Hydro chlorination of rubber in solution causes a different kind of double bond shirt [
121
]:
HCl
HCl
Cl
