polarized direction of the UV light. Due to the transparency in visible region of the
cinnamate derivatives, they are supposed to be used in displays.
The performance of LCP homopolymers to some degree depends on the structure
of polymers main chains. For example, the glass transition temperature (T g ) of one
nematic LCP of PM6ABOC2 is higher than another LCP of PA6ABOC2, as shown
in Fig. 5. Even though they show similar rate in LC isomerization phase transition,
the recovery process of PM6ABOC2 is slower than that of PA6ABOC2 due to the
difference of main chain stiffness (Kanazawa et al. 1997). For side-chain
azopolymers, the molecular reorientation depended on the length of the alkylene
spacer and the amount of the axis selectively formed cis-isomers (Uchida and
Kawatsuki 2006).
The application of azobenzene-containing LCPs as optical image storage materials was first reported in 1995 (Ikeda and Tsutsumi 1995). In a nematic glassy state,
LCPs undergo a nematic LC-to-isotropic phase transition upon photoirradiation
while they never exhibit an isotropic-to-nematic LC phase transition below their
T g s. As shown in Fig. 5b, it is obvious that the UV-irradiated area becomes isotropic
since cis-azobenzene never exhibits any LC ordering due to its bent shape. By this
way, an optical image can be stored in the LCP films by using a photomask. It was
observed that the thermal cis-trans back-isomerization of azobenzene mesogens in
polymer film occurred in 24 h at room temperature. Although the trans-form
recovered completely, the isotropic glassy domains induced at the irradiated area
still remained unchangeable at room temperature even after several years. These
results suggest that the orientation of the mesogenic trans-azobenzenes becomes
disordered below T g through thermal cis-trans back-isomerization process. However, even after the trans-form is thermally recovered, the alignment of mesogens is
Fig. 4 Photoresponsive properties of homopolymers with azobenzene (AZ) as the only mesogens
in LCPs
15 Photoresponsive Liquid Crystalline Polymers
423
cinnamate derivatives, they are supposed to be used in displays.
The performance of LCP homopolymers to some degree depends on the structure
of polymers main chains. For example, the glass transition temperature (T g ) of one
nematic LCP of PM6ABOC2 is higher than another LCP of PA6ABOC2, as shown
in Fig. 5. Even though they show similar rate in LC isomerization phase transition,
the recovery process of PM6ABOC2 is slower than that of PA6ABOC2 due to the
difference of main chain stiffness (Kanazawa et al. 1997). For side-chain
azopolymers, the molecular reorientation depended on the length of the alkylene
spacer and the amount of the axis selectively formed cis-isomers (Uchida and
Kawatsuki 2006).
The application of azobenzene-containing LCPs as optical image storage materials was first reported in 1995 (Ikeda and Tsutsumi 1995). In a nematic glassy state,
LCPs undergo a nematic LC-to-isotropic phase transition upon photoirradiation
while they never exhibit an isotropic-to-nematic LC phase transition below their
T g s. As shown in Fig. 5b, it is obvious that the UV-irradiated area becomes isotropic
since cis-azobenzene never exhibits any LC ordering due to its bent shape. By this
way, an optical image can be stored in the LCP films by using a photomask. It was
observed that the thermal cis-trans back-isomerization of azobenzene mesogens in
polymer film occurred in 24 h at room temperature. Although the trans-form
recovered completely, the isotropic glassy domains induced at the irradiated area
still remained unchangeable at room temperature even after several years. These
results suggest that the orientation of the mesogenic trans-azobenzenes becomes
disordered below T g through thermal cis-trans back-isomerization process. However, even after the trans-form is thermally recovered, the alignment of mesogens is
Fig. 4 Photoresponsive properties of homopolymers with azobenzene (AZ) as the only mesogens
in LCPs
15 Photoresponsive Liquid Crystalline Polymers
423