Photocrosslinking System Based on
Poly(vinyl phenol) and Fluorene Derivatives with
Epoxy Unit Using Photoacid and
Photobase Generators
Haruyuki Okamura, Chika Harada, Satoshi Morishita, Masamitsu Shirai,
Masahiro Tsunooka, Tsuyoshi Fujiki*, Shin-ichi Kawasaki* and Mitsuaki Yamada*
Department of Applied Chemistry, Graduate School of Engineering,
Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan
* Research & Development Department, Osaka Gas Co., Ltd.,
6-19-9 Akanejima, Konohanaku, Osaka 544-0051, Japan
Keywords: photocrosslinking, fluorene, epoxide, poly(vinyl phenol), photoacid generator, photobase generator
1. Introduction
Photo-induced
acid-catalyzed
crosslinking
systems have been widely studied by many
workers
[1].
The
highly
sensitive
photocrosslinking materials can be used as
negative-type photoresists, coating materials and
printing materials.
Epoxides and polymers
containing cyclic ether units are cationically or
anionically crosslinkable. Photocrosslinking of
these compounds can be accomplished by the
photolysis of initiator molecules, followed by
reactions of the resulting photoproducts with cyclic
ethers.
Photoacid generators and photobase
generators can be used as an initiator for the
photoinduced crosslinking [2, 3].
In this paper we report the photoinduced
insolubilization of polymeric materials based on
poly(vinyl phenol) and fluorene derivatives having
epoxy moieties as a crosslinker. Photoacid and
photobase generators were used as an initiator of
insolubilization.
The crosslinked materials
containing fluorene units are expected to be
thermally stable and to show high refractive index.
2. Experimental
Poly(vinyl phenol) (PVP) (Mn = 8000) (Aldrich)
and
triphenylsulfonium
triflate
(TPST)
(Midorikagaku) were used as received. Fluorene
derivatives
4,4’-(9-fluorenylidene)bis(phenoxyethyl glycidyl ether) (FBPEG) (softening
temperature: ca. 50 oC) and 4,4’-(9-fluorenylidene)
bis(phenyl glycidyl ether) (FBPG) (mp: 150 oC)
were supplied from Osaka Gas Co., Ltd.
O-Phenylacetyl acetonaphtone oxime (PaAnO)
was prepared as reported previously. [4]
CH2
CH
n
OH
PVP
S CF3SO3
TPST
O
Ch3
CH2 C O N C
PaAnO
CH2
CH CH2 O
CH2 CH
O
O
CH2
FBPG
CH CH2 O
O
CH2
O
CH2
O
CH2 CH
CH2
CH2
CH2
O
O
FBPEG
Scheme 1
O
CH2
Sample films (~ 0.2 m) were prepared by
casting polymer solutions containing fluorene
derivatives and TPST or PaAnO onto quartz plate
or silicon wafer. Cyclohexanone and diglyme
were used as solvents.
Sample films were
irradiated at 254 nm using a low-pressure Hg lamp
(4 W). Baking of the films was carried out with a
conventional hot plate. Irradiated polymer films
were developed in tetrahydrofuran and insoluble
fraction was determined by comparing the film
thickness before and after developments.
Thermal decomposition behavior was investigated
with Rigaku TAS 100 thermogravimetric analyzer
(TGA) under nitrogen flow.
3. Results and discussion
When PVP/FBPG (2/1 or 4/1, mol/mol) film
containing 2 wt% of TPST was irradiated at 254
nm with a dose of 750 mJ/cm2, no insolubilization
was observed. However, the insolubilization was
observed when the irradiated films were baked at a
given temperature. Fig. 1 shows the relationship
between insoluble fraction and post-exposure-bake
(PEB) temperature for PVP/FBPG based film
irradiated with a dose of 36 mJ/cm2. The sample
became insoluble with the increase of PEB
temperature.
The onset temperature for the
insolubilization was dependent on the PVP/FBPG
ratio.
Insolubilization was not observed for
unirradiated samples with heating at 160 oC for 2
min. In Fig. 2 photocrosslinking properties of
PVP films and FBPG films with 2 wt% of TPST
are shown. Insolubilization did not occur for both
films irradiated with a dose of 36 mJ/cm2 and PEB
treatment at 160 oC for 2 min. These results
indicate that the insolubilization was caused by the
reaction of epoxy moieties in FBPG and PVP.
Insolubilization of PVP/FBPG films was
enhanced by increase of PEB time as well as PEB
temperature.
Fig. 3 shows the relationship
between insoluble fraction and PEB time.
Insoluble fraction was observed to be ca. 90% for
the sample of the PVP/FBPG (4/1) film with 2
wt % of TPST irradiated with a dose of 36 mJ/cm2
and PEB treatment at 140 oC for 2 min. The
dependence of insolubilization of PVP/FBPG films
on the irradiated dose is shown in Fig. 4. When
the sample film was irradiated with a dose of 10
mJ/cm2 and PEB treatment at 140 oC for 2 min, the
insoluble fraction was found to be 90%. Little
changes of insoluble fraction were observed at
exposure dose above 10 mJ/cm2. On the other
hand, insoluble fraction of sample films decreased
to 78 % on irradiation with a dose of 140 mJ/cm2
when the PEB treatment was done at 140 o C for
100
80
60
40
20
0
80
100
120
140
PEB temperature ( ℃ )
160
Fig. 1. Effect of PEB temperature on insolubilization
of PVP/FBPG films containing 2 wt% TPST.
(○, ●) PVP/FBPG = 4/1, (□, ■) PVP/FBPG = 2/1.
Open symbol: Exposed at 254 nm with 36 mJ/cm2.
Closed symbol: Unexposed. PEB time: 2 min.
Development: THF for 10 min.
100
80
60
40
20
0
80
100
120
140
PEB temperature ( ℃ )
160
Fig. 2. Effect of PEB temperature on insolubilization
of irradiated films containing 2 wt% TPST.
(○) PVP/FBPG = 4/1, (□) PVP, (△) FBPG.
Exposed dose: 36 mJ/cm2 at 254 nm. PEB time: 2 min.
Development: THF for 10 min.
0.5 min.
These results indicate that PEB
conditions are one of the most important factors for
the
photoinduced
insolubilization
of
PVP/FBPG/TPST system.
The effect of structure of the crosslinkers on the
insolubilization efficiency was studied. Fig. 5
shows the relationship between insoluble fraction
and PEB temperature for PVP/FBPEG (4/1) and
PVP/FBPG (4/1) films containing 2 wt% of TPST
o n i r r a d i a t i o n w i t h a d o s e o f 3 6 mJ / c m 2 .
100
80
60
40
20
0
0
1
2
3
4
PEB time (min)
5
Fig. 3. Effect of PEB time on insolubilization of films
containing 2 wt% TPST.
(○, ●) PVP/FBPG = 4/1, (□) PVP, (△) FBPG.
Open symbol: Exposed at 254 nm with 36 mJ/cm2.
Closed symbol: Unexposed. PEB temperature: 140 oC.
Development: THF for 10 min.
100
80
60
point of FBPEG. FBPEG films containing 2 wt%
of TPST irradiated with a dose of 36 mJ/cm2 and
PEB treatment above 140 oC became insoluble
(Fig. 6), while insolubilization of FBPG films was
not observed in the same treatment.
It is
considered that the reaction for insolubilization of
PVP/FBPEG films was the crosslinking of epoxy
moieties of FBPEG with PVP and the
photoinduced acid-catalyzed polymerization of
epoxy
moieties
in
FBPEG
occurred
simultaneously.
The thermal degradation of the crosslinked
PVP/FBPG films was observed at about 300 oC by
TGA analysis, which suggests that crosslinked
PVP/FBPG films have good thermal stability.
Crosslinked PVP/FBPG films showed slightly
higher refractive indices (nD : 1.61 ~ 1.62)
compared to that of PVP (nD : 1.60).
It is known that epoxy derivatives act as a
crosslinker of phenol-novolac resin in the presence
of tertiary amines or KOH [5]. However, no
attempt has been made for photoinduced
base-catalyzed crosslinking system of epoxy
derivatives and PVP.
PaAnO is known to
generate benzyl amine on irradiation at 254 nm
(Scheme 2).
The insolubilization was observed for
PVP/FBPEG (4/1) film containing 10 wt% PaAnO,
when irradiated at 254 nm with a dose of 200
mJ/cm2 and PEB treatment above 140 oC for 5 min.
Fig. 7 shows the relationship between insoluble
40
20
100
0
0
20 40 60 80 100 120 140
Exposure dose (mJ/cm2)
Fig. 4. Effect of irradiation dose on insolubilization of
irradiated films containing 2 wt% TPST.
(○, ●) PVP/FBPG = 4/1, (□) PVP, (△) FBPG.
Open symbol: PEB treatment at 140 oC for 2 min.
Closed symbol: PEB treatment at 140 oC for 0.5 min.
Development: THF for 10 min.
Insolubilization of PVP/FBPEG film occurred with
the PEB treatment at lower temperature compared
to PVP/FBPG film.
Insolubilization of
unirradiated PVP/FBPEG films with heating at 160
o
C for 2 min did not occur. The lower PEB
treatment temperature for the PVP/FBPEG system
is due to the high reactivity of the epoxy moiety in
FBPEG due to its flexibility and lower melting
80
60
40
20
0
70
100
130
PEB temperature ( ℃ )
160
Fig. 5. Effect of fluorene derivative structure on
insolubilization of films containing 2 wt% TPST.
(○, ●) PVP/FBPG = 4/1, (□, ■) PVP/FBPEG = 4/1.
Open symbol: Exposed at 254 nm with 36 mJ/cm2.
Closed symbol: Unexposed. PEB time: 2 min.
Development: THF for 10 min.
100
CH2
80
C O
O
N
60
h
CH2
CO2
N
C
CH2
CH2
- CO2
Ch3
H2O
NH2
+
O
Ch3
C
Ch3
N
C
C
Ch3
40
20
Scheme 2
0
70
100
130
PEB temperature ( ℃ )
160
Fig. 6. Insolubilization PVP/FBPEG and FBPEG
films containing 2 wt% TPST.
(○, ●) FBPEG, (□, ■) PVP/FBPEG = 4/1.
Open symbol: Exposed at 254 nm with 36 mJ/cm2.
Closed symbol: Unexposed. PEB time: 2 min.
Development: THF for 10 min.
100
80
60
40
20
0
130
140 150 160 170
PEB temperature (℃ )
180
Fig. 7. Insolubilization of PVP/FBPEG (4/1) films
containing PaAnO.
PaAnO: (○, ●) 5 wt%, (□, ■) 10 wt%.
Open symbol: Exposed at 254 nm with 200 mJ/cm2.
Closed symbol: Unexposed. PEB time: 5 min.
Development: THF for 10 min.
fraction and PEB temperature for PVP/FBPG
based film irradiated with a dose of 200 mJ/cm2.
The insoluble fraction increased with PEB
temperature.
The onset temperature for the
insolubilization was dependent on the amount of
PaAnO added.
PVP/FBPEG (4/1) film
containing 10 wt% PaAnO became insoluble on
heating above 170 oC. Decomposition of PaAnO
was observed at 192 oC by TGA measurement.
This insolubilization may be due to the
decomposed compound of PaAnO at 170 oC.
When the amount of PaAnO was reduced to be 5
wt% in films, the insolubilization was observed for
the irradiated film with PEB treatment above 140
o
C. Insolubilization did not occur for the samples
without irradiation on PEB treatment at 180 oC for
5 min. These results indicate that photoinduced
base-catalyzed crosslinking system of PVP/BPEFG
requires the proper content of PaAnO.
PEB condition is also important to enhance the
insoluble fraction of PVP/FBPEG/PaAnO system.
In the case of PVP/FBPEG film containing 5 wt%
of PaAnO, insoluble fraction reached to 90% after
irradiation (200 mJ/cm2) and PEB treatment at 150
o
C for 8 min.
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