Aminimides derived from benzoylformic acid esters as thermally latent base catalysts

Article abstract of DOI:10.1021/ma1013836

As a novel thermal latent anionic initiator for lower temperature applications, a new class of aminimide, 1,1-dimethyl-1-(2-hydroxypropyl)amine benzoylformimide (BFI), was synthesized from benzoylformic acid methyl ester in 95% yield, and its thermal rearrangement behavior was studied in detail. Thermal rearrangement of BFI proved to take place on heating above 80 °C via the Curtius rearrangement mechanism, generating the corresponding isocyanate, hydroxyamine, and their further reaction products. BFI proved to catalyze the polymerization of epoxides and epoxide/thiol system on heating above 80 °C. They exhibit both the long pot life and the low-temperature rapid polymerization in the presence of BFI which supported the promising applications of BFI as an efficient thermal latent base catalyst for anionically polymerizable/curable systems.

Full text of DOI:10.1021/ma1013836

Macromolecules 2010, 43, 8821–8827 8821
DOI: 10.1021/ma1013836
Aminimides Derived from Benzoylformic Acid Esters as Thermally Latent
Base Catalysts
Manabu Kirino† and Ikuyoshi Tomita*,‡
†Product Development Division, Three Bond Co., Ltd., 1456 Hazama-Cho, Hachioji, Tokyo 193-8533, Japan,
and ‡Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering,
Tokyo Institute of Technology, Nagatsuta 4259-G1-9, Midori-ku, Yokohama 226-8502, Japan
Received June 22, 2010; Revised Manuscript Received September 24, 2010
ABSTRACT: As a novel thermal latent anionic initiator for lower temperature applications, a new class of
aminimide, 1,1-dimethyl-1-(2-hydroxypropyl)amine benzoylformimide (BFI), was synthesized from ben-
zoylformic acid methyl ester in 95% yield, and its thermal rearrangement behavior was studied in detail.
Thermal rearrangement of BFI proved to take place on heating above 80 °C via the Curtius rearrangement
mechanism, generating the corresponding isocyanate, hydroxyamine, and their further reaction products.
BFI proved to catalyze the polymerization of epoxides and epoxide/thiol system on heating above 80 °C. They
exhibit both the long pot life and the low-temperature rapid polymerization in the presence of BFI which
supported the promising applications of BFI as an efficient thermal latent base catalyst for anionically
polymerizable/curable systems.
Introduction
the polymerization of epoxide.13 This result may suggest that the
appropriate molecular design of the substituents on the amini-
Latent initiators that generate active species by external
stimulations such as heat and photoirradiation are important
for many industrial applications such as polymerization or curing
of adhesives, sealants, paints, coatings, molding resins, and so on.
In the case of epoxy resin, for example, both anionic and cationic
latent initiators have been extensively studied. From the practical
point of view, anionic catalysts are advantageous in that they are
less sensitive to impurities and moisture. Until now, derivatives of
dicyandiamide, dihydrazide, and imidazole have been reported to
serve as latent anionic initiators. They are solid at room tempera-
ture but melt and dissolve into the epoxy resin at elevated
temperature to initiate polymerization.1 These latent initiators of
insoluble and heterogeneous type have inevasible practical draw-
backs such as difficulty in preservation of uniform dispersion, use of
solvents, and production of optically transparent products. Thus,
miscible latent anionic initiators that dissolve in monomers and
resin under ambient conditions have been paid much attention.2
Although many cationic latent initiators such as onium salts are
reported to serve as homogeneous latent initiators for epoxides,3
only a few anionic miscible latent initiators have been reported.4
Among them, aminimides have been reported to undergo the
thermal rearrangement by means of the cleavage of the N-N bond
to produce isocyanates and tertiary amines,5,6 and the generated
amines serve as anionic initiators for epoxide. Within the authors’
knowledge, some aminimides such as lactoimide,7 propionimide,8
valerimide,8 adipimide,9 and substituted benzimide8,10,11 have been
employed as thermal latent anionic initiators for epoxides,7-10 the
epoxide/acid anhydride system,7 and the epoxide/thiol system.11,12
However, their practical activating temperature is above 150 °C,
which is not low enough for practical applications. Therefore, it is
essentially important to design a new class of catalysts that exhibit
activity at lower temperature.
mide can lower the temperature. We herein report a new class of
aminimides from benzoylformic acid ester that shows thermal
latent initiating ability at much lower temperature. Its rearrange-
ment mechanism and its application to the polymerization of
epoxide and epoxide/thiol system are also described.
Experimental Section
Materials. Benzoylformic acid methyl ester, 1,1-dimethylhydra-
zine, propylene oxide, methyl benzoate, 1,1-dimethylamino-2-pro-
panol, and acetic anhydride were purchased from Tokyo Kasei
Kogyo (Japan). Benzoyl isocyanate, triethylamine, and benzyl
alcohol were purchased from Wako Pure Chemical Industries
(Japan). Pentaerythritol tetrakis(3-mercaptopropionate) was pur-
chased from Aldrich (Milwaukee, WI). EXA-850CRP (pure grade
bisphenol A diglycidyl ether) was purchased from DIC (Japan).
They were used as received.
Measurements. Nuclear magnetic resonance (NMR) spectra
were recorded with a JEOL ECP300 spectrometer in CDCl3 or
DMSO-d6 (300 and 75 MHz for 1H NMR and 13C NMR,
respectively). IR spectra were taken on a BIO-RAD FTS-40
FTIR system using SPECAC MK II heated diamond ATR
system at 25 °C. Melting points were measured on a Mettler
Toledo FP90/FP82HT thermo system and an Olympus BX50
microscope at a heating rate of 2 °C/min. Thermogravimetry/
differential thermal analyses (TG/DTA) were performed on a
Seiko Instruments TG/DTA 220 using ca. 1.0 mg of the samples.
The decomposition temperature (Td) was determined from the
onset temperature of the weight loss observed in TG at a heating
rate of 1 or 10 °C/min under a nitrogen atmosphere. Differential
scanning calorimetry analyses (DSC) were performed on a Seiko
Instruments DSC 220 at a heating rate of 10 °C/min under a
nitrogen atmosphere.
Previously, we reported that some aliphatic aminimides exhibit
initiation activity at a little lower temperature (e.g., 137.7 °C) in
Synthesis of 1,1-Dimethyl-1-(2-hydroxypropyl)amine Benzoyl-
formimide (BFI). BFI was synthesized by the method described
by Slagel5 as follows: a mixture of benzoylformic acid methyl
ester (13.6 g, 83.0 mmol), 1,1-dimethylhydrazine (5.00 g, 83.0 mmol),
*Corresponding author. E-mail: tomita@echem.titech.ac.jp.
r 2010 American Chemical Society
Published on Web 10/14/2010
pubs.acs.org/Macromolecules

8822 Macromolecules, Vol. 43, No. 21, 2010
Kirino and Tomita
and propylene oxide (4.80 g, 83.0 mmol) in 2-propanol (80 mL)
was stirred at 20 °C for 2 h and then at 40 °C for 48 h. The
reaction mixture was concentrated by evaporation, and the
residual white solid was recrystallized from methanol/ethyl
acetate to obtain BFI in 95.0% yield (19.7 g, 78.9 mmol). The
sample for elemental analysis was purified further by recrystalli-
zation twice from methanol/ethyl acetate; mp 104.0-105.0 °C
(decomposition). IR (solid, ATR): 3225 cm-1 (broad, OH), 1681
cm-1 (s, Ph-CdO), 1571 cm-1 (s, -N-CdO). 1H NMR
(CDCl3): δ 1.18 (d, 3H, CH3, J = 6.3 Hz), 3.45 (m, 2H, NCH2),
3.60 (s, 3H, NCH3), 3.63 (s, 3H, NCH3), 4.40 (m, 1H, CH), 5.39
(s, 1H, OH), 7.44 (m, 2H, C6H5), 7.56 (m, 1H, C6H5), 8.01 (m,
2H, C6H5). 13C NMR (CDCl3): δ 21.1, 52.1, 54.5, 62.6, 74.6,
128.3, 129.8, 133.4, 134.4, 168.4, 192.6. Elemental analysis Calcd
for C13H18N2O3: C, 62.38; H, 7.25; N, 11.19. Found: C, 62.30; H,
7.17; N, 11.28.
Synthesis of 1,1-Dimethylamino-2-propyl N-Benzoylcarba-
mate (3). Benzoyl isocyanate (1) (0.62 g, 4.2 mmol) was added
dropwise to a n-hexane (10 mL) solution of 1,1-dimethylamino-
2-propanol (2) (0.52 g, 5.0 mmol) at room temperature under a
nitrogen atmosphere. Within a few minutes, a white precipitate
began to form as the progress of the reaction, which was
identified as a urethane from its IR spectrum. After stirring at
room temperature for 24 h, the reaction mixture was concen-
trated by evaporation, and the residual white solid was recrys-
tallized from ethyl acetate/n-hexane to obtain 3 in 77% yield
(0.81 g, 3.2 mmol). The sample for elemental analysis was
purified further by recrystallization twice from ethyl acetate/
n-hexane; mp 79.0-80.0 °C (decomposition). IR (solid, ATR):
1765 cm-1 (s, NH-CO-O), 1697 cm-1 (s, Ph-CdO). 1H NMR
(CDCl3): δ 1.27 (d, 3H, CH3, J = 6.3 Hz), 2.16 (s, 6H, NCH3),
2.59 (dd, 1H, NCH2, J = 12.9, 8.7 Hz), 2.15-2.21 (1H, NCH2),
5.10 (m, 1H, CH), 7.41 (m, 2H, C6H5), 7.51 (m, 1H, C6H5), 7.77
(m, 2H, C6H5), 8.80 (s, 1H, OH). 13C NMR (CDCl3): δ 18.5,
45.8, 64.2, 70.0, 127.6, 128.7, 132.7, 133.3, 150.7, 165.5. Ele-
mental analysis Calcd for C13H18N2O3: C, 62.38; H, 7.25; N,
11.19. Found: C, 62.03; H, 7.17; N, 11.17.
Synthesis of 1,1-Dimethyl-1-(2-acetoxypropyl)amine Benzoyl-
formimide (4). The synthesisof 4 was performed by the acetylation
of the hydroxy group in BFI as follows: a dichloromethane
(30 mL) solution of BFI (3.00 g, 12.0 mmol), acetic anhydride
(2.45 g, 24.0 mmol), and triethylamine (1.21 g, 12.0 mmol) was
refluxed for 24 h. The reaction mixture was concentrated and
dried at 40 °C for 6 h under reduced pressure (0.23 mmHg). After
washing the residual paste with n-hexane, the white solid thus
obtained was recrystallized from ethyl acetate to obtain 4 in51.8%
yield (1.80 g, 6.22 mmol) as white crystals. The sample for
elemental analysis was purified further by recrystallization twice
from ethyl acetate; mp 100.0-101.0 °C (decomposition). IR (solid,
ATR): 1740 cm-1 (s, CH3-CdO), 1681 cm-1 (s, Ph-CdO),
1604 cm-1 (s, N--CdO). 1H NMR (CDCl3): δ 1.27 (d, 3H,
CH3, J = 6.6 Hz), 1.99 (s, 3H, C(O)-CH3), 3.35 (s, 3H, NCH3),
3.49 (s, 3H, NCH3), 3.69 (dd, 1H, NCH2, J = 13.5, 8.1 Hz), 4.14
(dd, 1H, NCH2, J = 13.5, 0.9 Hz), 5.49 (m, 1H, CH), 7.38 (m, 2H,
C6H5),7.48(m,1H,C6H5),7.98(m,2H,C6H5).13CNMR(CDCl3):
δ 19.1, 21.1, 54.1, 54.3, 65.8, 69.3, 128.2, 129.8, 133.1, 134.7, 169.0,
169.6, 192.8. Elemental analysis Calcd for C15H20N2O4: C, 61.63; H,
6.90; N, 9.58. Found: C, 61.59; H, 7.13; N, 9.55.
(CDCl3): δ 20.8, 50.8, 54.8, 62.8, 75.7, 127.1, 127.8, 129.7,
137.7, 169.9.
Thermal Decomposition Studies by Cryo-Trap GC-MS. Gas
chromatographic-mass spectrometric (GC-MS) analyses were
performed on a Thermoquest GCQ GC-MS system equipped
with Frontier laboratories UA5 (MS/HT)-30M-0.25F GC col-
umn and liquid nitrogen cryo-trap. The samples were heated at
120 °C for 3 min, and the volatile fractions were directly trapped
by liquid nitrogen and were analyzed by GC-MS. Sample
temperature: 120 °C; split flow: 40 mL/min (He gas); split ratio:
1/40; GC heating profiles: 50 °C for 5 min and then 300 °C at a
heating rate 10 °C/min; ionization voltage: 70 eV.
Thermal Decomposition Studies by IR. IR spectra of the
samples after the heat treatment were taken on a real-time FTIR
system (BIO-RAD FTS-40) using heated ATR (SPECAC MK
II heated diamond ATR system) equipped with a hot stage
(115 °C) under a nitrogen atmosphere.
DSC Onset Temperature Measurement. BFI (0.10 g) and
benzyl alcohol (0.40 g) were stirred at room temperature to
obtain a homogeneous transparent mixture. A portion of this
sample (5.0 mg) was placed in an aluminum pan and completely
sealed. The thermal profiles were measured by DSC.
Thermal Decomposition Studies by 1H NMR Spectra. The
1
conversion of BFI was estimated by the H NMR spectra as
follows: a sealed NMR tube containing BFI in DMSO-d6 (0.13 M)
was heated at 80, 100, or 120 °C in an oil bath, and the NMR
spectra were measured after designated period. The conversion
of BFI was elucidated from the relative intensity of the peak for
the Nþ(CH3)2 protons with respect to that of the residual
protons of DMSO-d6. On assuming that the thermal decom-
position takes place via the first-order kinetic equation
d½BFIꢀ=dt ¼ k½BFIꢀ
the first-order kinetic coefficient (k) was calculated from the
slope of the graph for ln[BFI] vs time.
Polymerization Studies of Epoxide with BFI. EXA-850CRP
(3.44 g, 100 mmol) and BFI (0.500 g, 20.0 mmol) were stirred at
50 °C for 10 min to obtain a transparent homogeneous mixture,
and its polymerization behavior was monitored by DSC and IR
measurements as follows:
DSC Measurements: A portion of this mixture (7.5 mg) was
placed in an aluminum pan and completely sealed. The poly-
merization profile was monitored by DSC under a nitrogen
atmosphere, where the temperature of the sample was raised
rapidly from 40 to 100 °C at a heating rate of 100 °C/min, and
then the temperature was held at 100 °C for 240 min. Subsequent
heating cycles were monitored for determining the glass transi-
tion temperature (Tg) from -20 to 200 °C at a heating rate of
10 °C/min.
IR Observations: The mixture was placed on the ATR stage,
and its surface was protected with a cover glass. The real-time IR
spectra were measured at 100 °C. The conversion was estimated
from the changes of the peak intensity of the epoxide (910 cm-1
)
with respect to that of the benzene ring (1506 cm-1) in EXA-
850CRP.
Polymerization Studies of Epoxide/Thiol with BFI. BFI (2.50 ꢁ
10-2 g, 1.00 ꢁ 10-4 mol) and benzyl alcohol (1.08 ꢁ 10-1 g, 1.00 ꢁ
10-3 mol) were stirred at room temperature to obtain a homo-
geneous transparent mixture. Then, EXA-850CRP (6.88 ꢁ 10-1 g,
2.00 ꢁ 10-3 mol) and pentaerythritol tetrakis(3-mercaptopropio-
nate) (4.89 ꢁ 10-1 g, 1.00 ꢁ 10-3 mol) were addedtothe solutionto
obtain a transparent homogeneous mixture (M1). The polymeri-
zation behavior of M1 was monitored by DSC and IR measure-
ments as follows:
DSC Measurements: A portion of M1 (5.0 mg) was placed in
an aluminum pan and completely sealed. The polymerization
profile was monitored by DSC at a heating rate of 10 °C/min
under a nitrogen atmosphere. Likewise, a mixture consisting of
benzyl alcohol (1.00 ꢁ 10-3 mol), EXA-850CRP (2.00 ꢁ 10-3 mol),
Synthesis of 1,1-Dimethyl-1-(2-hydroxypropyl)amine Benzi-
mide (5). Similar to the case of BFI, 5 was prepared from methyl
benzoate (10.9 g, 80.0 mmol), 1,1-dimethylhydrazine (4.80 g,
80.0 mmol), and propylene oxide (4.60 g, 80.0 mmol) in 81.0%
yield (14.4 g, 64.8 mmol); mp 122.0-122.5 °C (lit.5 122-125 °C).
Td: 186.2 °C (TG/DTA, at a heating rate of 10 °C/min).
IR (solid, ATR): 3220 cm-1 (broad, OH), 1609 cm-1 (s,
1
-N-CdO), 1570 cm-1 (s, -N-CdO). H NMR (CDCl3): δ
1.17 (d, 3H, CH3, J = 6.3 Hz), 3.05 (dd, 1H, NCH2, J = 12.6, 1.5
Hz), 3.43 (dd, 1H, NCH2, J = 12.6, 9.9 Hz), 3.55 (s, 3H, NCH3),
3.57 (s, 3H, NCH3), 4.37 (m, 1H, CH), 6.92 (s, 1H, OH),
7.20-7.32 (3H, C6H5), 7.78 (m, 2H, C6H5). 13C NMR

Article
Macromolecules, Vol. 43, No. 21, 2010 8823
Figure 1. TG/DTA profiles of BFI at a heating rate of 10 °C/min.
Figure 2. GC profiles of the volatile fractions obtained by the pyrolysis
of BFI at 120 °C for 3 min.
Scheme 1. Synthesis of BFI
Scheme 2. Plausible Thermal Rearrangement Reaction of BFI
and pentaerythritol tetrakis(3-mercaptopropionate) (1.00 ꢁ
10-3 mol) (i.e., without BFI) and that of benzyl alcohol (1.00 ꢁ
10-3 mol), EXA-850CRP (2.00 ꢁ 10-3 mol), pentaerythritol
tetrakis(3-mercaptopropionate) (1.00 ꢁ 10-3 mol), and 2 (1.00 ꢁ
10-4 mol) in place of BFI were also subjected to the DSC
measurements to evaluate the role of BFI. The isothermal DSC
measurement of M1 was carried out by heating this mixture
(7.5 mg) from 40 to 80 °C rapidly (i.e., at a heating rate of
100 °C/min) and then the keeping the temperature at 80 °C.
IR Observations: M1 was placed on the ATR stage, and the
surface of the sample was protected with a cover glass. The real-
time IR spectra were measured at 80 °C. The conversion was
estimated from the changes of the peak intensities of both
the thiol (2571 cm-1) and the epoxide (913 cm-1) with respect
to that of the ester (1738 cm-1) in pentaerythritol tetrakis-
(3-mercaptopropionate).
to react further to give the corresponding urethanes.5 There-
fore, the reaction of BFI would also proceed in a similar
rearrangement process as shown in Scheme 2.
Identification of Products Obtained by the Thermal Rear-
rangement of BFI. To support the reaction mechanism
indicated in Scheme 2, the identification of thermal rearrange-
ment products from BFI was carried out using the GC-MS
measurement and the IR spectroscopic analyses. In the GC-
MS measurement of the volatile fractions obtained after the
pyrolysis of BFI at 120 °C for 3 min, a main peak was
observed at a retention time of 2.58 min (Figure 2), which
was identified as 2 from its MS spectrum in comparison with
that of the authentic sample. Thus, it was clearly supported
that BFI generates 2 by the N-N bond cleavage in the
rearrangement reaction.
In the time-course FT-IR spectra of the samples obtained
by heating BFI at 115 °C under nitrogen, we could monitor
the progress of the rearrangement process (Figure 3a). After
heating for 2 min, a peak at 1588 cm-1 attributable to the
carbonyl group in the aminimide (N-CdO) decreased, and
new peaks appeared at 1771 and 1735 cm-1. The peak at
1771 cm-1 is attributable to the carbonyl group in the urethane
(3), as confirmed by the IR spectrum of the authentic sample
(3). Also in the FT-IR spectrum of the sample after heating 3
at 115 °C for 20 min, the peak for the carbonyl group in the
urethane decreased and a new absorption peak at 1733 cm-1
appeared, suggesting that 3 also decomposes under the
conditions for the rearrangement of BFI. Accordingly, the
thermal cleavage of the N-N bond in BFI takes place to give
3 via 1 and 2. In this case, however, 1 could not be detected
probably because 1 reacts immediately with the hydroxy
group in 2.
Results and Discussion
Synthesis of 1,1-Dimethyl-1-(2-hydroxypropyl)amine Ben-
zoylformimide (BFI). The synthesis of BFI was performed by
using equimolar amount of benzoylformic acid methyl ester,
1,1-dimethylhydrazine, and propylene oxide by the method
for β-hydroxyaminimides described by Slagel5 (Scheme 1).
The reaction took place smoothly to give BFI in 95.0% yield
by recrystallization from methanol/ethyl acetate.
Thermal Decomposition Behavior of BFI. In the TG/DTA
measurement of BFI at a heating rate of 10 °C/min (Figure 1),
the decomposition temperature (Td) was observed at
119.0 °C, which is significantly lower than those reported
for aliphatic aminimides (156.2-212.1 °C).13 From the
melting point measurement of BFI, the irreversible melting
behavior was observable at 104.0-105.0 °C. Thus, the
endothermic peak starting from 107.0 °C in the DTA experi-
ment is most probably not due to the simple melting, but
ascribable to the irreversible chemical reaction.
It has been reported that some aminimides undergo
thermal cleavage of the N-N bond to produce the corre-
sponding isocyanates and tertiary amines via the Curtius-
type rearrangement.6 In the case of β-hydroxyaminimides,
the generated β-hydroxyamines and isocyanates are reported

8824 Macromolecules, Vol. 43, No. 21, 2010
Kirino and Tomita
Figure 5. TG/DTA measurement of 3 under nitrogen at a heating rate
of 1 °C/min.
Figure 3. FT-IR spectra of samples obtained by heating BFI (a) and a
urethane (3) (b) at 115 °C under nitrogen.
Figure 6. GC profile of volatile fractions obtained by heating the
urethane (3) at 120 °C for 3 min.
Scheme 3. Thermal Decomposition Mechanism of BFI
Figure 4. FT-IR spectra of the sample obtained after heating the
acetylated BFI (4) at 115 °C for 0, 1.2, 2.5, and 10 min under nitrogen.
To detect 1, the acetylated BFI (4) was synthesized from
BFI and its thermal rearrangement behavior was monitored
by the FT-IR spectra (Figure 4). After 1.2 min at 115 °C, a
strong absorption peak appeared at 2241 cm-1 attributable
to 1. This result supported that BFI generates 1 by the
thermal rearrangement process. After the prolonged reac-
tion period, the peak at 2224 cm-1 gradually decreased and
disappeared completely after 10 min, indicating that the acyl
isocyanate (1) is highly reactive and decomposes also in the
absence of 2.
Thermal Decomposition of Urethane (3). As mentioned
above, 3 produced by the reaction of 1 and 2 also decomposes
under the conditions for the rearrangement of BFI. When
the crystals of 3 was heated above its melting point at 79.0-
80.0 °C, the irreversible chemical reaction takes place. As is
also clear from its TG/DTA measurements at a heating rate
of 1 °C/min, 3 exhibited an endothermic peak with an onset
temperature at 80 °C and Td at 86.8 °C (Figure 5).
residual weight in the TG analysis may suggest that the
generated 2 volatilized under the measurement conditions.
To clarify this, GC-MS measurement of 3 was carried out in
the same manner to BFI. Figure 6 shows GC profile of the
volatile fractions obtained by the treatment of 3 at 120 °C for
3 min. The MS spectrum of the main peak at 2.56 min was
identical to that of the authentic 2. Thus, it was confirmed
that 3 also generates 2 by the thermal decomposition process.
In general, the bond dissociation of urethanes is often
applied to industrial processes, and the urethanes are classi-
fied as “blocked isocyanates”. The dissociation temperature
of “blocked isocyanates” ranges from 120 to 250 °C, which is
affected largely by the substituents. Especially, the electron-
withdrawing substituents on the nitrogen atom tend to lower
the dissociation temperature.14 Accordingly, the lower dis-
sociation temperature of 3 (86.6 °C) is most probably due to
its electron-withdrawing carbonyl substituent on the nitro-
gen atom.
As mentioned above, urethanes are known to be cleaved
on heating to produce the corresponding isocyanates and
alcohols.14 This bond cleavage mechanism would also work
in the case of 3 which can be attributed to the weight loss
observed in the TG analysis above its Td. The decrease of the
On the basis of these results, we believe that the decomposi-
tion of BFI proceeds in the mechanism as shown in Scheme 3.
The isocyanate (1) and the amine (2) are generated by the
Curtius-type rearrangement of BFI. Then, the generated 1and 2

Article
Macromolecules, Vol. 43, No. 21, 2010 8825
Figure 7. DSC profiles of (a) BFI and (b) aminimide (5) in benzyl alcohol
(20 wt % solution) at a heating rate of 10 °C/min.
Figure 8. 1H NMR spectra of BFI in DMSO-d6 after heating at 100 °C
produce 3, and 3 is in equilibrium with its dissociated form, 1
and 2. Because 1is susceptible to degrade into complex products
due to its high reactivity, we could detect 2as the sole identifiable
product.
for 0, 20, and 60 min.
Thermal Decomposition Behavior of BFI in Alcohol Solu-
tion. To estimate the thermal decomposition behavior of BFI
in solution, benzyl alcohol was used as a solvent because of
the good solubility of BFI and its high boiling point. Figure 7
shows DSC profiles of 20 wt % solution of BFI in benzyl
alcohol and that of aminimide without acyl moieties (5).10
In the DSC measurement of the BFI solution, an exother-
mic peak with an onset temperature of 116.9 °C was ob-
served, which was close to the Td of BFI determined by TG/
DTA (119.0 °C). Therefore, the exothermic peaks observed
in this experiment are most probably ascribable to the
thermal rearrangement reaction to give 1 and 2 and the
subsequent addition reaction of 1 and alcohol moieties in 2
and/or the solvent. In comparison, the aminimide (5) ex-
hibits the onset of the exothermic peak at 190.0 °C, which is
significantly higher than that of BFI. This result clearly
indicates that the R-acyl substituent in BFI does lower the
temperature required for the rearrangement of aminimides.
Kinetic Studies of Thermal Decomposition of BFI. As
mentioned above, the DSC profile indicates that the decom-
position of BFI occurs above 80 °C. So as to perform the
quantitative analyses of this thermal decomposition, the
kinetic studies were performed using NMR measurements
at 80-120 °C. Figure 8 shows representative time-course 1H
NMR spectra of BFI heated at 100 °C. As the progress of the
reaction, the intensity of the peaks for Nþ(CH3)2 (3.39 and
3.51 ppm) and NþCH2 (3.41-3.82 ppm) of the aminimide
decreased, while peaks at 2.02 and 2.50 ppm attributable to
N(CH3)2CH2 moieties in 2 and 3, respectively, newly ap-
peared. This result is in good accordance with the idea that
the decomposition of BFI generates 2 and 3, as shown in
Scheme 3. Similar experiments were carried out at 80 and
120 °C. From the peak intensity of the protons in the
NþCH3, the conversion of BFI was determined, and the
time-conversion curves at 80, 100, and 120 °C were plotted
as shown in Figure 9a. From the kinetic plots of these
conversion curves (Figure 9b), the thermal decomposition
of BFI can be fitted well by the first-order kinetic equation
(i.e., d[BFI]/dt = k[BFI]). This result is in accordance with
the preceding reports in which the thermal decomposition of
Figure 9. (a) Time-conversion curves of a DMSO-d6 solution of BFI
(0.13 M) at 80, 100, and 120 °C and (b) their kinetic plots.
the aminimides follows the first-order kinetic equation.8,9,15 The
kinetic coefficients (k) of the rearrangement of BFI at 80, 100,
and 120 °C were estimated as 1.8 ꢁ 10-5, 4.4 ꢁ 10-4, and 3.0 ꢁ
10-3 s-1, respectively. These values are significantly larger than
that of aminimides without R-acyl moieties (i.e., the kinetic
coefficient of 1,1-dimethyl-1-(2-hydroxypropyl)amine propio-
nimide was reported as 6.4 ꢁ 10-5 s-1 at 150 °C).8
Mechanistic Consideration for High Activity of BFI. On the
basis of the results obtained from the analyses of the thermal
rearrangement products and the preceding reports on the
rearrangement of some aminimides, the benzoyl cation is the
most plausible intermediate in the Curtius-type rearrange-
ment of BFI (Scheme 4). To explain the high activity of BFI

8826 Macromolecules, Vol. 43, No. 21, 2010
Kirino and Tomita
Scheme 4. Plausible Rearrangement Mechanism of BFI
Figure 10. Relationship between D(Rþ-H-) and Td of aminimides
possessing the corresponding substituents (R-CON--Nþ(CH3)2-
CH2CH(CH3)OH).
Table 1. D(Rþ-H-) and Td of Aminimides Having the Corresponding
Substituents
Figure 11. Isothermal DSC profile of bisphenol A diglycidyl ether
containing BFI (20 mol %) at 100 °C.
a See ref 19. b Estimated by TG/DTA (heating rate: 10 °C/min). c See
ref 13.
at low temperature, we focused the thermodynamic stability
of the carbocation in form of the migrating group.16
In the Curtius-type 1,2-rearrangement reactions, it is
reported that the rate of the rearrangement increases as a
function of the thermodynamic stability of the carbocationic
form of the migrating groups.17 In the case of BFI, it is
assumed that migrating group is the benzoyl cation that has
been reported to be significantly more stable than alkyl or
aryl cations.18 Because heterolytic bond dissociation energies
[D(Rþ-H-)]18,19 would be informative to compare the
thermodynamic stability of carbocations, they were com-
pared with Td of aminimides bearing the corresponding
substituents (Table 1 and Figure 10). Although more detailed
studies should be performed for the precise discussion on the
relationship of Td and D(Rþ-H-) by also taking the steric
factors into consideration,12,13,20 it is apparent that the lower
D(Rþ-H-) value results in the lower Td of the correspond-
ing aminimides.
Figure 12. Time-conversion curve of bisphenol A diglycidyl ether
containing BFI (20 mol %) measured by the real-time IR measurements
at 100 °C.
mixture was observed during that period. These results
strongly support that BFI is quite suitable for the thermal
latent catalyst of epoxides that can be used under mild
polymerization conditions.
Thermal Polymerization of Epoxide Catalyzed by BFI.
The polymerization behavior of epoxides in the presence
of BFI was evaluated by the isothermal DSC and the IR
measurements using pure bisphenol A diglycidyl ether
(EXA-850CRP) as an epoxide monomer. A mixture of BFI
(20 mol %) and the epoxide was heated using DSC at 100 °C
(Figure 11), in which an exothermic peak attributable to the
polymerization of the epoxide is observable at the early stage
of the polymerization. The conversion of epoxide reached
90% at 65 min (Figure 12), indicating that the polymeriza-
tion proceeds smoothly at 100 °C. The Tg of the product after
the DSC experiment was 84.4 °C, which supported that the
current system formed the cross-linked product. The pot life
of the mixture of BFI and the epoxide is more than 3 weeks at
25 °C. That is, no significant increase of the viscosity of this
Thermal Polymerization of the Epoxide/Thiol System by BFI.
The BFI-catalyzed polymerization behavior of the epoxide/thiol
system was likewise evaluated from the DSC measurements
using pure bisphenol A diglycidyl ether (EXA-850CRP) and
pentaerythritol tetrakis(3-mercaptopropionate) as monomers,
using benzyl alchol as a solvent. A homogeneous mixture of the
epoxide (2.00 ꢁ 10-3 mol), thiol (1.00 ꢁ 10-3 mol), BFI (1.00 ꢁ
10-4 mol), and benzyl alcohol (1.00 ꢁ 10-3 mol) was subjected
to the measurement of DSC at a heating rate of 10 °C/min. As
references, a mixture of epoxide, thiol, benzyl alcohol, and 2
instead of BFI and that of epoxide, thiol, and benzyl alcohol

Article
Macromolecules, Vol. 43, No. 21, 2010 8827
catalyze the thermal polymerization of epoxide and the epoxide/
thiol system above 80 °C, while the homogeneous mixture of BFI
and epoxy resin could be stored at ambient temperature for at
least 2 weeks without significant increase of the viscosity. The
characteristics of BFI in both the long pot life and the low-
temperature rapid polymerization indicate its promising applica-
tion to the efficient thermal latent base catalyst for the polymer-
ization and curing of epoxide and epoxide/thiol resin.
Acknowledgment. We gratefully acknowledge Professor
Takeshi Endo of Molecular Engineering Institute, Kinki University,
who kindly directed the authors to the research works of amini-
mides. We are also grateful to Mr. Takao Goto of Threebond Co.
for his kind assistance in GC-MS measurements.
References and Notes
Figure 13. DSC profiles of epoxide/thiol system with 2 (a), with BFI
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Figure 14. Time-conversion curves of the epoxide/thiol system with
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A novel aminimide, 1,1-dimethyl-1-(2-hydroxypropyl)amine
benzoylformimide (BFI), was synthesized from benzoylformic
acid methyl ester, 1,1-dimethylhydrazine, and propylene oxide in
95% yield, and its thermal rearrangement behaviorwas studied in
detail by TG/DTA, IR, GC-MS, 1H NMR, and DSC analyses.
BFI was found to decompose above 80 °C via the Curtius-type
rearrangement to generate benzoyl isocyanate, 1,1-dimethylami-
no-2-propanol, and their further reaction products. BFI prove to