R. Mahy et al. / European Polymer
Journal 42 (2006) 2389–2397
Photosensitive polymers with cinnamate units in
the side position of chains : Synthesis, monomer
reactivity ratios and photoreactivity
作者:Rachid Mahy , Boufelja Bouammali , Abdelkader Oulmidi ,
Allal Challioui , Daniel Derouet , Jean Claude Brosse
Reporter : Chih-Hao Li
Advisor : Ching-Dong Hsieh
Data : 100.05.11
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Outline
• Introduction
• Experimental
• Results and discussion
• Conclusions
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Introduction
• The synthesis of different kinds of functional polymers has
received much attention in recent years, such as temperature or
pH sensitive polymer, electric active materials, photosensitive
polymers and so on.
Contact
Alignment technique
Rubbing alignment
Photo-alignment
Contactless
Ion beam alignment
Plasma beam alignment
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Photo-alignment
• This technique has been studied by many researchers for the
practical application to the rubbing-free liquid crystal alignment
layers, which are inevitable materials in the fabrication of liquid
crystal display devices.
• In this work, we have found that the cinnamate side groups could
be also reacted by thermal energy, and this reaction is presumed
to attribute to the radical reaction of carbon double bond in the
cinnamate groups.
• We studied the effect of the chain flexibility of polymer backbone
on the reaction behavior of cinnamate side groups induced by UV
irradiation and heating.
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photochemical and thermal reaction
The photocycloaddition and thermal crosslinking reactions were supposed to
be based on two different reaction mechanisms, pericyclic reaction and
radical reaction.
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Experimental
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PEVCi
PVCi
Cinnamoyl chloride
Poly(vinyl cinnamate)
PVCi
Poly(3-ethylene-alt-1 vinyl cinnamate)
PEVCi
4,4’-(Hexafluoroisopropylidene)diphthalic anhydride–3,3’-dihydroxy-4,4’diaminobiphenyl
6FDA–HAB
7-(Methacryloyloxy)coumarin
MOC
Triethylamine
TEA
Isoquinoline
1,1’-azobis(cyclohexanecarbonitrile)
ACCN
Tetrahydrofuran
THF
N,N-dimethylformamide
DMF
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Synthesis of Photoreactive Polyimide 6FDA-HAB-Ci
The precipitate
was filtered, the
solution was
6FDA–HAB(1g，0.0013mol)
and TEA(0.26g，0.0026mol)
poured toluenewere
under
vigorous
stirring.
dissolved
in THF(10ml).
chloride(0.43g，0.0026mol)
was
The precipitateCinnamoyl
was filtered
and dried under vacuum
to
dissolved in THF(10ml).
give 87% of 6FDA-HAB-Ci.
Ice bath(0℃)
Stirring was
maintained for 24 h.
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Synthesis of Poly(7-(Methacryloyloxy)coumarin) (PMOC)
The cooled reaction solution was diluted with more
DMF(10 ml) and added dropwise with vigorous stirring
to methanol (500 ml).
MOC(1g，0.0043mol) and ACCN(0.052g，0.00022mol)
were dissolved in DMF(10ml).
The resultant precipitate was filtered off, dissolved again in
DMF(30 ml) and reprecipitated from methanol (500 ml).
This procedure was repeated until no more monomer was
present by PMOC and a white solid was obtained(0.67 g,
yield 67%).
Water bath
(60℃)
Stirring was
maintained for 24 h.
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Photochemical and thermal reactions of polymers
Thin film of a polymer was prepared by spin-coating a
polymer solution onto a quartz substrate.
heat
The thermal reaction of polymer
film was conducted by placing
the polymer film on the hot plate
at 200 ℃.
hν
The film was irradiated by a
300W high-pressure mercury
arc lamp passed through UV
filter.
The degree of reaction was monitored by UV spectroscopy.
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Model compound
Ethyl cinnamate
In order to elucidate the mechanism of photochemical and thermal
reactions of the cinnamate side groups,ethyl cinnamate was selected as
a model compound and the photochemical and thermal reactions of the
model compound were investigated.
We checked the change of UV absorbance of ethyl cinnamate with UV
irradiation or heating time.
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Results and discussion
Thermal properties of polymers
6FDA–HAB–Ci showed the highest glass transition temperature and this would
be attributed to the rigid polyimide backbone of 6FDA–HAB–Ci.
Ethylene backbone of PEVCi can increase the chain flexibility of polymer and
thus the glass transition temperature of PEVCi is found to be lowest among
the three different cinnamate polymers.
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Photochemical reaction of polymers
The degree of reaction was monitored by the decrease
in the peak intensity of –C=C– bond of the cinnamoyl
group at 284 nm by UV spectroscopy.
There was no clear relationship between the chain
flexibility of polymer and the photocycloaddition
reaction of cinnamate side groups.
Fig. 1. The change of UV absorbance of polymer films with UV irradiation,
(a)PEVCi, (b) PVCi, (c) 6FDA–HAB–Ci.
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Thermal reaction of polymers
Glass transition temperature :
6FDA–HAB–Ci > PVCi > PEVCi
The radical reaction of the cinnamate side groups can
be affected by thechain flexibility of polymers.
Fig. 2. The change of UV absorbance of polymer films with heating at 200℃,
(a) PEVCi, (b) PVCi, (c) 6FDA–HAB–Ci.
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Model reaction of cinnamate group
This result provides an additional support on the effect of the chain
flexibility on the thermal reaction of the cinnamate groups.
Fig. 3. The change of UV absorbance of ethyl cinnamate solutions (a)
with UV irradiation, (b) with heating at 200℃.
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Model reaction of cinnamate group
δ = 6、7ppm
After
*
7.7ppm
6.5ppm
δδδδ====7.4、7.5ppm
4.2ppm
Before
δ = 3.3、3.8ppm
H
O
H2
C
C
C
O
CH3
H
Fig. 4. 1H NMR spectra of ethyl cinnamate before and after UV irradiation for 20 h.
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Model reaction of cinnamate group
After
Before
There was only one group of new peaks at
3.5 and 4 ppm and these correspond to the
new protons generated by breaking the
carbon double bond of ethyl cinnamate.
Fig. 5. 1H NMR spectra of ethyl cinnamate before and after heating at 200℃ for 20 h.
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Model reaction of cinnamate group
(a)
(b)
δ = 45、47ppm
Linear carbon
δ = 35、40ppm
Fig. 6. 13C NMR spectra of ethyl cinnamate after UV (a)irradiation for 20h,
(b)heating at 200 ℃ for 20 h.
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Photo-dimerizable groups and radical reaction
The glass transition temperature of the
coumarin polymer was about 109 ℃ and
this is much lower than the heating
temperature 200 ℃.
Due to the strong electron delocalization
of coumarin groups, the radical reaction of
carbon double bond becomes more
difficult and thus the thermal crosslinking
of coumarin polymer was not observed.
Fig. 7. The change of UV absorbance of PMOC film with heating at 200 ℃.
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Conclusions
The photocycloaddition is based on the [2+2] cycloaddition reaction mechanism
and the thermal crosslinking is supposed to be based on the radical reaction
mechanism.
Due to the radical mechanism of thermal crosslinking reaction of the cinnamate
side groups, the flexibility of polymer has the considerable effect on the thermal
crosslinking of cinnamate polymers.
The difference between the photocycloaddition and thermal crosslinking of the
cinnamate side groups was confirmed by the 1H NMR and 13C NMR analysis of
the photochemical and thermal reaction of model compound.
The possibility of the radical reaction of photodimerizable molecule was also
closely related to the electron delocalization state of carbon double bond.
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Thanks for your listening!
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