Chemistry Reference
In-Depth Information
which mesogenic groups are bound to dendritic or hyperbranched polymers.
Tsiourvas, Paleos et al. have reported a couple of systems for which they have
studied the properties of complexes of the cholesterol carboxylic acid deriva-
tive
34
and pyridine end-capped dendrimers [100] or hyperbranched poly-
mers [101]. Amine-terminated diaminobutane poly(propyleneimine) den-
drimers functionalized with 3-pyridyl isothiocyanate (
35
, generation 2-5)
formed smectic-A LC phases upon the addition of an equimolar quantity (rela-
tive to the number of pyridyl moieties) of
34
(Fig. 17a). All the systems formed
glassy birefringent materials at room temperature, which became birefringent
fluids above
T
g
(ca. 55
◦
C). No other transitions were observed. The smectic
periodicities only slightly increased with generation ranging from 5.4 nm in
generation 2 to 5.6 nm in generation 5, suggesting that the flexible dendrimer
forms a “flattened” conformation between the orthogonally oriented hydrogen
bonded pyridyl-cholesteryl moieties. Similar types of structures have been pro-
posed for structurally similar covalent derivatives [102]. The same group went
on to study hyperbranched polymers using the same supramolecular motif and
mesogen (Fig. 17b). This time, the polymer was a pyridine end-capped hyper-
branched polyether polyol
36
. As in the case of the dendritic SLCPs discussed
Fig. 17 a
The chemical structure of the pyridyl-functionalized PANAM
35
and the
schematic of the smectic phase which is formed upon complexation with 3-cholesteryl-
oxycarbonylpropanoic acid
34
b
The chemical structure of the pyridyl-functionalized
hyperbranched polyol
36
and schematic of the smectic phase which is formed upon
complexation with
34
Search WWH ::
Custom Search