Chemistry Reference
In-Depth Information
(
3
.
17
):
O
C
CH
(
O
CH
2
)
11
3
.
17
CH
3
Some of the results for the polymer
3
.
17
are shown in Table 3.5.
As shown in Table 3.5, the low molecular weight polymer of
Mn
1100
is non-liquid-crystalline. The sample of
Mn
3500 is monotropic while those
with
Mn
of 10200 and higher are enantiotropic. The thermal stability of
the mesophase increases with increasing molecular weight as shown by the
higher clearing temperature
Ti
of the sample with higher molecular weight.
Percec
et al
. (1989) also studied the effect of molecular weight in side-group
type liquid crystal polymers. The similar monotropic to enantiotropic trans-
formation was found in these systems. The crystallization of side groups was
considered to be responsible for the transformation in these cases. The poly-
mer with a higher molecular weight has a lower crystallizability of the side
groups. In contrast, the crystallization of the main-chain type polymers
seems not to be affected in such a way by the molecular weight. In the
latter case, samples with higher molecular weights have a higher melting
point in the region of low molecular weights.
The principle of the monotropic to enantiotropic transformation by
increasing molecular weight has been demonstrated by the above exam-
ples. However, for a full understanding of this phenomenon, further studies
are required. For the main-chain type liquid crystal polymers with alternat-
ing sequences of the rod-like and the flexible segments, Kohlhammer
et al
.
(1989) have found that the orientational order of the flexible segments is
higher in the samples of higher molecular weights. In other words, the con-
tribution by the flexible segments to liquid crystalline ordering is higher in
Table 3.5.
Phase property and molecular weight of the
∗
.
polymer
3
.
17
Mn
Mw
Tm
Ti
Tlc
Tc
Remark
1100
2300
101.5
-
-
89.8
non l.c.
3500
6700
117.9
-
111.5
97.5
monotropic
6700
10200
121.6
134.0
129.7
104.8
enantiotropic
10900
15200
124.0
147.9
143.6
107.5
enantiotropic
29400
92300
126.2
152.0
139.0
93.3
enantiotropic
∗
Source: Percec and Nave (1987).
