Chemistry Reference
In-Depth Information
CH
3
C
CH
2
COO
CH=N
(g 163 I).
3.45
On the other hand, if the mesogenic unit is modified so as to have
a stronger tendency to form the liquid crystalline phase (Section 3.2),
the polymer will have more of a chance to form more stable liquid crys-
tals. This is well demonstrated by homologues of the above mentioned
two non-liquid-crystalline polymethacrylates
. Accord-
ing to Alimoglu
et al
. (1984), substitution of
−
CN groups at the ends of
biphenyl units in
3
.
43
and
3
.
45
resulted in poly[4-(p-cyanophenyl)phenyl methacry-
late] that showed a smectic phase above
Tg
, the clearing point of which is
240
◦
C. If the substitution is not by cyano but by
3
.
43
OCH
3
the resulted
poly[4-(p-methoxyphenyl)phenyl methacrylate] is also smectic (
Ti
−
=
255
◦
C;
Duran
et al
.,
1987a).
The
same
is
true
with
poly-
mer
. For example, the ethoxy substituted homologue poly[4-(p-
ethoxyphenylimino)methylphenyl methacrylate] (
3
.
45
) forms a smectic
phase with the transitions: g 198 S 284 I (Frosini
et al
., 1981). However,
even though both the polyacrylate and polymethacrylate are liquid crys-
talline, the more flexible polyacrylate has a broader temperature range for
the mesophase as shown by a comparison of the polymers
3
.
46
and
3
.
47
.
3
.
46
CH
3
CH
2
C
COO
CH=N
OC
2
H
5
(g 198 S 284 I).
3.46
H
CH
2
C
OC
2
H
5
COO
CH=N
(g 88 S 268 I).
3.47
We have discussed the influence of the flexibility of the polymer
backbone on the mesophase formation by examples of polyacrylates and
polymethacrylates. More flexible polymers should have a stronger tendency
to form more stable mesophases. Nevertheless, smectic liquid crystalline
phases are the most common mesophases formed, if they do indeed form,
by polymers in which no flexible spacers are used to connect main chain and
