An efficient catalyst for low temperature solid-phase cyclization of poly(o-hydroxyamide)

Article abstract of DOI:10.1246/cl.2004.1342

An efficient acid catalyst for the low-temperature solid-phase cyclization of poly(o-hydroxyamide) (PHA) has been found. Thermal cyclization of PHA into poly(benzoxazole) (PBO) proceeded quantitatively at 250°C in 10min in the presence of 10 wt % of a photoacitve compound, (5-propylsulfonyloxyimino-5H- thiophen-2-ylidene)-2-(methylphenyl)-acetonitrile (PTMA).

Full text of DOI:10.1246/cl.2004.1342

1342
Chemistry Letters Vol.33, No.10 (2004)
An Efficient Catalyst for Low Temperature Solid-phase Cyclization of Poly(o-hydroxyamide)
Fumihiro Toyokawa, Ken-ichi Fukukawa, Yuji Shibasaki, and Mitsuru Uedaꢀ
Department of Organic and Polymeric Materials, Graduate School of Science and Engineering,
Tokyo Institute of Technology, 2-12-1-H120, O-okayama, Meguro-ku, Tokyo 152-8552
(Received July 21, 2004; CL-040858)
An efficient acid catalyst for the low-temperature solid-
phase cyclization of poly(o-hydroxyamide) (PHA) has been
F3C CF3
H2N
HO
NH2
OH
ClCO
O
COCl
found. Thermal cyclization of PHA into poly(benzoxazole)
(PBO) proceeded quantitatively at 250 ꢁC in 10 min in the
presence of 10 wt % of a photoacitve compound, (5-propyl-
sulfonyloxyimino-5H-thiophen-2-ylidene)-2-(methylphenyl)-
acetonitrile (PTMA).
+
6FAP
OBBC
H
N
F3C CF3
H
N
O
LiCl
O
OH
O
NMP
HO
n
PBOs have been used as protection and insulation layers for
very large scale integration circuits (VLSI) and multichip mod-
ules for computers owing to their high thermal stability and excel-
lent mechanical property.1–4 Photosensitive PBOs (PSPBOs)5–17
have been developed to simplify the processing steps because
phenolic hydroxyl groups in precursors of PBOs provide
adequate solubility toward an aqueous alkaline developer. Up
to now the PSPBO based on the PHA derived from 4,40-
(hexafluoroisopropylidene)bis(o-aminophenol) (6FAP) and 4,40-
oxybis(benzoic acid) derivatives18,19 with a photosensitive com-
pound is widely used, in which the image of the PSPBO is finally
converted into that of PBO by thermal treatment at 350 ꢁC. This
high-temperature process is hardly applicable to the conventional
electronic applications containing at least one more thermally un-
stable organic component. Therefore, development of novel cat-
alysts enabling low temperature solid-phase cyclization of PHAs
is required.
Recently, p-toluene sulfonic acid (p-TSA) and p-nitroben-
zyl 9,10-dimethoxyanthracene-2-sulfonate (NBAS) were found
to be effective catalysts to lower the cyclization temperature of
O-tert-butoxycarbonylated PHA (t-BOCPHA) derived from
6FAP with 4,40-oxybisbenzoyl chloride (OBBC). The thermal
cyclization temperature was 290 ꢁC in the presence of NBAS,
significantly lower than non-catalytic cyclization at 346 ꢁC.20
Process temperature below 250 ꢁC, however, is preferable in
the semiconductor manufacturing. PTMA is known to be an ex-
cellent photoacid generator with high quantum yield at 436-nm
wavelength.21 Here, we present PTMA an excellent low-temper-
ature cyclization catalyst of PHA, where 10 wt % of PTMA is
enough to complete the cyclization at 250 ꢁC in a short time.
PHA was prepared by polycondensation of 6FAP with
OBBC in 1-methyl-2-pyrrolidinone (NMP) in the presence
of LiCl at 0 ꢁC for 30 min, and room temperature for 24 h
(Scheme 1).22 The number average molecular weight (Mn) and
polydispersity (Mw=Mn) of PHA were determined by GPC (in
DMF at 40 ꢁC, PSt calibration) to be 25000 and 1.6, respectively.
In the synthesis of thermally stable photosensitive polymers,
diazonaphthoquinone (DNQ) and PTMA23 are used as a photo-
dissolution inhibitor and a photoacid generator, respectively,
and these photoactive compounds produce strong sulfonic acids
by photoirradiation or thermal treatment24,25 (Scheme 2). Thus,
these compounds would be expected to work as catalysts for
PHA
Scheme 1. Synthesis of PHA.
low-temperature cyclization of PHA after image formations.
As DNQ, we chose 1-{1,1-bis[4-(2-diazo-1-(2H)naphthalenone-
4-sulfonyloxy) phenyl]ethyl}-4-{1-[4-(2-diazo-1(2H)naphthale-
none-4-sulfonyloxy)phenyl]-methylethyl}benzene (S-DNQ).
OR
O
CO
N2
H2O
OR
R =
∆
SO3H
SO2
OR
S-DNQ
O
O
N
S
HO
O
O
O
S
H2O
S
∆
C
N
PTMA
Scheme 2. Acid generation from S-DNQ and PTMA.
F3C CF3
N
O
N
O
O
PHA
Cure
n
PBO
Scheme 3. Transformation of PHA into PBO.
These compounds were added to a solution of PHA in ꢀ-
butyrolactone and the mixture was stirred at room temperature
for 1 h. The solution was spin-cast on a silicon wafer, and baked
at 120 ꢁC for 5 min, resulting in 2–3-mm thick films. The refer-
ence PBO film was prepared by heating a PHA film at 250,
300, and 350 ꢁC, respectively for 1 h under nitrogen (Scheme 3).
The degree of cyclization was determined assuming the ab-
sorptions at 1051 (C–O stretch of benzoxazole) and 1250 cmꢂ1
(C–O stretch of phenyl ether) had no influence by the catalyst
and solvent.
Figure 1 shows the change in the IR spectra of the PHA film
Copyright ꢀ 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.10 (2004)
1343
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2000 1800 1600 1400 1200 1000 800 600
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]
Figure 1. IR spectra of 1) PHA film after spin-cast. 2) PHA film
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film containing 10 wt % PTMA baked at 250 ꢁC. 4) reference
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containing 10 wt % PTMA upon heating at various temperatures
for 10 min and the reference PBO film. The degree of cyclization
in the presence of PTMA is 40% at 200 ꢁC, and accelerated at
250 ꢁC, reaching 100% in 10 min.
The progress of cyclization at 250 ꢁC in various catalysts
including p-TSA, S-DNQ, and PTMA is shown in Figure 2.
The cyclization is completed in a few minutes in the presence
of p-TSA and PTMA. On the other hand, S-DNQ accelerates
the cyclization comparing the absence of catalyst, but the degree
of cyclization is around 60% even after 2 h. This phenomenon
may be explained by thermal cross-linking of decomposed
products derived from S-DNQ, which inhibits the diffusion of
sulfonic acid moieties (Figure 2).
The cyclization process involves several interrelated ele-
mental reactions, and dynamic changing physical properties
such as diffusion rate, chain mobility, solvation, and acidity.
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lization mechanism. In this work, sulfonic acids would acceler-
ate the attack of a phenolic hydroxyl group on an amide carbonyl
unit through protonation on the oxygen of the amide group.
In summary, we have found that the photoacid generator
PTMA accelerates the thermal cyclization of PHA films at
low temperature. This method not only will provide a potentially
efficient route for the low-temperature solid-phase cyclization of
PHA, but also will be very useful for the PSPBO process.
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References and Notes
1
1
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Published on the web (Advance View) September 18, 2004; DOI 10.1246/cl.2004.1342