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pendicular orientation by heating the sample above the
T
g
of both blocks but
below the ODT under the AC field. Control experiments showed that such
alignment switching does not occur with the block copolymer by itself or with
a side chain polymeric aggregates in which the side chains are non-mesogenic
side chains, demonstrating the importance of liquid crystallinity to the ori-
entational switching. Furthermore, structurally similar covalent side-chain
LCPs and a SLCP with a lower fraction (0.5 molar ratio) of the mesogen also
showed no orientational switching. The proposed mechanism for this process
involved the presence of some “free” mesogen, which from FT-IR is present in
the SLCP with a 0.8 molar ratio of the mesogen that helps to plasticize both
blocks, resulting in “higher mobility” of the material and thus allowing the
electric field induced orientational switching below the ODT (Fig. 15b).
Other non-covalent interactions, for example, ionic interactions, can be
used to bind a mesogen to a polymer backbone. Thünemann et al. showed
that poly(ethylene oxide)-block-poly(l-lysine) (
32
), in which the lysine units
are positively charged, can form side-chain SLCPs with negatively charged
mesogenic units, such as the discotic-columnar phase forming hexabenzo-
coronene (
33
) [99]. This side-chain SLCP forms two thermotropic liquid crys-
tal columnar phases, exhibiting an order-order transition at 54
◦
Conheat-
ing. The proposed structure involves poly(l-lysine), which forms a
-helical
structure surrounded symmetrically by six columns of hexabenzocoronene
cores (Fig. 16).
Most of the work to date has focused on side-chain SLCPs in which the poly-
meric component is linear. However, there have been a few reports recently in
α
Fig. 16
The molecular structure of two components, poly(ethylene oxide)-
block
-poly(l-
lysine) (
32
) and hexa-peri-hexabenzocoronene (
33
), used to form an ionic complex SLCP
andamodelofits
α
-helical-
within
-discotic columnar structure. Each
α
-helical poly(l-
lysine) chain is surrounded symmetrically by six columns of
33
(disks) [99]
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