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Synthesis of photo-sensitive polymers containing
carbon-carbon double bond side groups for
application on photo-alignment of liquid crystals
Reporter : Chih-Hao Li
Advisor : Ching-Dong Hsieh
Date: 100.09.28
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Report of last semester
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Outline
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Introduction
Paper review
Motivation
Experimental
Results and discussion
Conclusions
Future work
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Introduction
Rubbing alignment
• Nowadays, the mechanical rubbing of polyimide (PI) and
polystyrene (PS) substrates has been widely studied as a
method of fabricating LC alignment layers. However, the
rubbing process has disadvantages such as electrostatic charge,
dust generation, and physical damage to the alignment layer
surfaces.
Rubbing roll
Alignment layer
Move direction
Glass plate
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Photo-alignment
• Photoalignment has been taken a notice of promising noncontact
alignment techniques to be used for the next generation LC
display applications, due to its various advantages such as its
cleaness, suitability for large glass substrates, and unrestrictedness
to surface morphology.
Alignment layer
θ
UV Source
Glass plate
Polarizer
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Photo-reaction
hυ
(a)
(b)
or
Fig. 1. Photochemical reaction mechanisms of PCEMA, (a)E–Z isomerization
reaction,(b) [2+2] photoaddition reaction.
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Paper review
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Paper review
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Motivation
In order to utilize the anisotropic distribution of photodimers of
photocrosslinkable polymers for the molecular orientation film, the stable
orientation of photodimers is required. However, the practical applications
of photocrosslinkable polymers are quite restricted due to significant
thermal relaxation of the photocrosslinkable polymers at high temperature,
which causes the randomization of photodimers.
The synthesis, photo-reaction and photo-induced liquid crystals(LC)
alignment of methacrylate homopolymer(PCEMA) containing cinnamate
side group are reported in this work. The polymers were blended with
crosslinking agent (DOD-Ci) to enhance thermo-stability. In this research,
we use the photo-alignment method to improve the disadvantages of the
rubbing method, and investigated the photo-reaction and alignment
Properties of alignment films.
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Experimental
O
H
C
C
Materials
Cinnamoyl chloride
4,4’-Biphenol
2-Hydroxyethyl methacrylate
2,2'-Azobis(2-methylpropionitrile)
Triethylamine
Ethyl acetate
Hexane
Propan-2-ol
Tetrahydrofuran
C
H
Cl
Cinnamoyl chloride
DOD
HEMA
AIBN
TEA
EAc
IPA
THF
OH
HO
DOD
H
CH3
C
C
H
C
O
O
H
H
C
C
H
H
OH
HEMA
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Synthesis of PHEMA
The cooled reaction solution and added dropwise with
vigorous
stirring77mmol)
to mixed
of2.3mmol)
Hexanewere
and EAc.
HEMA(10g,
and solution
AIBN(0.38g,
dissolved in IPA(80mL).
Dissolved again in IPA and reprecipitated from
mixed solution.
H CH
3
AIBN
nC C
H C O
Water
Thisbath
procedure
(60℃)
H CH3
C C
H H
IPA
n
H C O H H
monomer
O was
C C OH
was repeated until no more
O
C C OH
present by PHEMA and a white solid was obtained(7.25
H
H g,
H H
yield 72.5%).
Stirring was
maintained for 24 h.
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Synthesis of photosensitive polymer PCEMA
H CH3
H CH3
C C
O
n
H C O H H
O C C OH
+
C
Cl
TEA
H
C
C
H
THF
C C
O
n
H C O H H
O C C O
H
C C
H
H H
H H
Cinnamoyl chloride(1.27g, 7.6mmol) was
dissolved in THF(10mL).
The precipitate was filtered, washed with
Na2CO3 solution, and water.
PHEMA(0.5g, 3.8mmol) and TEA(0.77g, 7.6mmol) were
dissolved in THF(15mL).
The precipitate was filtered and dried under vacuum to
give 71% of PCEMA.
Ice bath(0℃)
Stirring was
maintained for 24 h.
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Synthesis of cross-linking agent DOD-Ci
HO
OH
H
H
O
C
C
C
Cl
TEA
H
H
O
C
C
C
O
O
O
H
H
C
C
C
+
EAc
The
Cinnamoyl chloride(3g, 18mmol) was
precipitate was
filtered,
washed with
dissolved
in EAc(15mL).
Na2CO3 solution, and water.
DOD(1.12g, 6mmol) and TEA(1.82g, 18mmol) were
solvent of thedissolved
dried filtrate
was evaporated
in EAc(20mL).
Finally, the
under reduce pressure and dried under vacuum to give
82% of DOD-Ci.
Ice bath(0℃)
Stirring was
maintained for 24 h.
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LC cell assembly
PCEMA+ Chloroform
spin coating
UV light:
7.94J/cm2
45°
13cm
Liquid crystal
Glass substrate
Spacer(30μm)
LC cell
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Results and discussion
Structure identification of polymer and compound
C=C(1625 cm-1)
(b)
H CH3
nC C
H C O
H H
O
C C OH
H H
AIBN IPA
(a)
H CH3
C C
n
H C O H H
O C C OH
H H
Fig. 2. FT-IR spectrum of (a) HEMA, (b) PHEMA.
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-1、1705cm
-OH(3200-3600 cm-1) O-C=O(1765
C=Ccm
(1650
cm-1) -1cm
) -1)
C-O-C(1040
H
H
O
C
C
C
O
O
O
H
H
C
C
C
(b)
DOD-Ci
(a)
H
CH3
C
C
H
C
n
O
O H
H
C
C
H
H
O
O
C
PCEMA
Fig. 3. FT-IR spectrum of (a) PCEMA, (b) DOD-Ci.
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c
b
c
c
c
a
b
c
a
c
a b c
Theoretical values =1:1:9
Actual values =0.99:1:9.01
c
b
a
Fig. 4. 1H NMR spectra of the DOD-Ci.
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H
CH3
C
C
n
H
O H
C
O
a b c d
Theoretical values =1:1:5:4
Actual values =0.99:1:5.16:3.71
d
H
O
a
C
C
H
H
O
C
b
c
c
a
d
c
b
Fig. 5. 1H NMR spectra of the PCEMA.
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Photochemical reaction
The UV-Vis spectra of cinnamate-containing monomer (DOD-Ci) and polymer
PCEMA shows that C=C double bond disappears after UV irradiation for 30 min.
(a)
(b)
290nm
Fig. 6. The change of UV absorbance of polymer and compound solution with UV
irradiation, (a)PCEMA, (b) DOD-Ci.
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Before irradiation
c
b
c
a
c
b
cc
b
c
a
c
a
After irradiation
b’ a’
a’
b’
d
d
b’ a’
d
Fig. 7. 1H NMR spectra of DOD-Ci before and after UV irradiation for 30min.
(a)
(b)
290nm
(c)
(d)
290nm
290nm
Fig. 8. The change of UV absorbance of polymer solution with UV irradiation, (a)PCEMA,
(b)PCEMA/DOD-Ci = 9/1, (b)PCEMA/DOD-Ci = 8/2, (b)PCEMA/DOD-Ci = 7/3.
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Alignment Property
Groove
Polarizer Direction:
Rubbing alignment
a
b
photo-alignment
a
b
Fig. 9. Photographs of (a) 0° dark and (b) 45° bright states of LC cells under polarised
microscopy. Cells were prepared using PCEMA as Rubbing alignment and
Photo-alignment coating.
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a
Dark state
Polarizer Direction:
b
Bright state
c
Fig. 10. Photographs of 0° dark and 45° bright states of LC cells under polarised
microscopy. Cells were prepared using (a)PCEMA/DOD-Ci = 9/1,
(b)PCEMA/DOD-Ci = 8/2, and (c)PCEMA/DOD-Ci = 7/3 as photo-alignment coating.
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Thermal stability
a
Polarizer Direction:
b
c
d
Fig. 11. Photographs of 0° dark and 45° bright states of LC cells under polarised
microscopy. Cells were prepared using (a)PCEMA , (b)PCEMA/DOD-Ci = 9/1,
(c)PCEMA/DOD-Ci = 8/2, and (d)PCEMA/DOD-Ci = 7/3 as photo-alignment
coating and then annealed at 100 ℃ for 1h.
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Conclusions
1H
NMR showed that DOD-Ci and PCEMA was synthesized sucessfully and
actual values of peak area was consistent of theoretical values.
The UV-vis spectra of cinnamate-containing DOD-Ci and polymer PCEMA
shows that C=C double bond disappears after UV irradiation for 30min, and as
the weight percent of the DOD-Ci increased from 0 to 30%, the photostability
times of the polymer decreased from 30min to 4min.
DOD-Ci containing cinnamate groups can produce E–Z isomerization and [2+2]
photoaddition reaction upon their exposure to nonlinearly polarized ultraviolet
(NP-UV) light.
The POM images of the LC cell placed between two crossed polarizers show
dark and bright states when the cell was rotated from 0 to 45° with respect to the
polarization direction.
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Future work
Synthesis of PHEMA derivatives containing photo-reactive side groups.
O
O
OH
Cl
+
DCC
HO
O
Cl
+
H
CH3
C
C
O
n
H
C
O
O H
H
C
C
H
H
K2CO3
H
CH3
C
C
n
H
O
O
C
O
O H
H
C
C
H
H
OH
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References
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Thanks for your listening!
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