Supramolecular Interactions in the Formation of Thermotropic Liquid Crystalline Polymers - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 139

above, the complexes of these materials form smectic-A phases and the smectic
distances suggest that the hyperbranched polymer forms a flattened structure.
Dendritic SLCPs, which use ionic interactions to bind the mesogen
and dendrimer, have also been reported by Tsiourvas et al. [103]. In
a study similar to those mentioned above, amine-terminated diaminobutane
poly(propyleneimine) dendrimers were directly complexed with the choles-
terol carboxylic acid derivative. From a supramolecular point of view this
system is more complicated than the studies with the pyridyl end-functional-
ized dendrimers in that there are potentially two different binding motifs that
can occur: namely, the carboxylic acid can either bind to a primary or a ter-
tiary amine. The studies show that in the 1 : 1 (mesogen to primary amine)
complexes about 70% of the primary amines are protonated for generations 1
and 2 while only 50% are protonated in generations 4 and 5, suggesting that
the mesogens are interacting with both sites. All of the generations form
smectic glass phases at room temperature which become smectic C ∗ phases
above T g (ca. 38 ◦ C). At higher temperatures ca. 105 ◦ C for generations 1 and
2andca.90 ◦ C for generations 4 and 5, the smectic layer thickness increases
which is assigned as an order-order transition from smectic C ∗ to smectic A.
It is interesting to note that no smectic C phase is observed for the previously
discussed structurally-similar covalent or hydrogen bonded derivatives. It is
argued that the presence of additional “internal” tertiary amine binding sites
is a possible cause of this.
Some of the earliest examples [42-45] of SLCPs belonged to the class of
side-chain materials in which the supramolecular motif itself is the mesogen
(Fig. 3g). In those materials pyridine/benzoic acid was used as the bind-
ing motif. Since 2000 there have been a number of publications which have
utilized this motif to access side-chain SLCPs. For example, supramolecu-
lar LC polyurethanes can by accessed by adding 4-dodecyloxybenzoic acid to
a polyurethane which has pyridyl units incorporated into its backbone [104].
Both side-chain and side-chain network SLCPs which are formed through
the pyridine/benzoic acid association have been recently reported by Lin
et al. [105]. They investigated the LC behavior of a series of benzoic acid
and stilbazole-containing monomers and polymers (Fig. 18). Formation of
the side-chain SLCPs generally results in an increase in the smectic tem-
perature range over the control monomeric complexes, presumably as a re-
sult of the reduced crystallinity of the polymer components. In fact, the
side chain SLCPs formed from the stilbazole polymer 37 and monomeric
benzoic acid derivative 38 do not crystallize at all, forming glassy smectic
phases (G 78 S A 127 I). Interestingly, however, side chain SLCPs with the
binding motif reversed (i.e. formed from the benzoic acid polymer 39 and
monomeric stilbazole derivative 40 ) form crystalline materials at lower tem-
perature ( < 111 ◦ C) and do exhibit higher clearing temperatures (S A 150 I).
The difference observed here is assigned primarily to the reduced pack-
ing efficiency (relative to the benzoic acid polymers) of the stilbazole poly-