Chemistry Reference
In-Depth Information
In polymers with pendant double bonds, facile cycloadditions occur upon heating [
123
-
125
]:
+
R
R
R
RRR
RR
R
Many other polymeric structures can rearrange under proper conditions. For instance, poly(4,4
0
-
diphenylpropane isophthalate) rearranges upon irradiation with UV light to a structure containing
o
-hydroxybenzophenones [
126
]:
O
O
hn
O
O
O
OH
O
O
. It may be similar to
one catalyzed by Lewis acids. Another example is a spontaneous rearrangement in the solid state of
poly(
The mechanism is believed to be that of a photo-induced
Fries rearrangement
a
-phenylethylisonitrile) [
128
]:
N
N
Based on studies of molecular models, it was concluded [
128
] that the substituents force progres-
sive, one-handed twisting of the helix shape of the molecules. This occurs to such an extent that the
vicinal imino double bonds are out of conjunction with each other. As a result, each benzylic hydrogen
atom becomes localized over the electrons of the imino groups. It proceeds in a constant screw
direction around the axis of the helix. Such steric confinement causes tautomeric rearrangements, as
shown above, which results in some relaxation of the compression. An additional driving force is a
gain in conjugation between the imino double bonds and the aromatic rings of each substituent.
Intramolecular rearrangements of polymers with ketone groups were subjects of several studies.
The
Schmidt
and
Beckmann rearrangements
were carried out on copolymers of ethylene and carbon
monoxide [
129
]:
O
H
HN
3
H
2
SO
4
N
x
x
O
NH
2
OH
OH
H
N
N
