Chemistry Reference
In-Depth Information
Figure 6.23. The circular dichroism (in relative unit) spectra of PMLG films dried from
solutions of the polymer in (1) dichloroethane; (2) dichloroethane/dimethyl formamide,
and (3) chloroform/dimethyl formamide. (From Uematsu and Uematsu, 1984.)
CH
2
OH
NHAc
CH
2
OH
NHAc
O
O
O
O
OH
OH
OH
OH
OH
O
H
O
O
n
NHAc
CH
2
OH
NHAc
CH
2
OH
Figure 6.24.
The chemical formula of the cellulose.
methacrylic acid, or other solvents, and then the solvent was polymerized.
The cholesteric structure remains in the new polymer/polymer solution.
The thin film of the sample was transparent, displaying a color.
Other important lyotropic cholesteric liquid crystalline polymer are the
cellulose esters. Cellulose is a natural polymer. Their chemical formula is
shown in Figure 6.24.
The derivatives of cellulose esters exhibit the lyotropic cholesteric phase
in many solvents. Cellulose is less rigid than PBG. The persistence length of
PBG is about 2000 A while the latter is between 130 and 330 A, depending
on the chemical formula of the substitute and the solvent. The cellulose
derivatives are cheap in cost and easy to process, and hence were studied
extensively. Among the derivatives, hydroxypropyl cellulose (HPC) is one
of most well studied.
