Primary amine-functional benzoxazine monomers and their use for amide-containing monomeric benzoxazines

Article abstract of DOI:10.1021/ma902556k

Amino-functional benzoxazine monomers have been successfully prepared. Several routes have been applied to incorporate amino group into benzoxazine structure. These approaches include reduction of the corresponding nitro-functional benzoxazines and deprot

Full text of DOI:10.1021/ma902556k

2748 Macromolecules 2010, 43, 2748–2758
DOI: 10.1021/ma902556k
Primary Amine-Functional Benzoxazine Monomers and Their Use for
Amide-Containing Monomeric Benzoxazines
Tarek Agag,*,† Carlos R. Arza,‡ Frans H. J. Maurer,‡ and Hatsuo Ishida*,†
†Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland,
Ohio 44106-7202, and ‡Department of Polymers and Materials Chemistry, Lund University, Box 124,
SE-221 00 Lund, Sweden
Received December 7, 2009; Revised Manuscript Received January 8, 2010
ABSTRACT: Amino-functional benzoxazine monomers have been successfully prepared. Several routes
have been applied to incorporate amino group into benzoxazine structure. These approaches include
reduction of the corresponding nitro-functional benzoxazines and deprotection of protected amino-
functional benzoxazine monomers. Various approaches that allow primary amine groups to be prepared
without damaging the existing benzoxazine groups have been evaluated. Tetrachlorophthalimide and
trifluoroacetyl are found to be suitable protecting groups. In addition, a model compound of amide-
functional benzoxazines is prepared from primary amine-functional benzoxazine. Fourier transform infrared
spectroscopy (FTIR) and 1H and 13C nuclear magnetic resonance spectroscopy (NMR) are used to
characterize the structure of the monomers. The polymerization behavior of amino-functional monomers
and model compound are studied by differential scanning calorimetry (DSC).
1. Introduction
wide variety of substrates, including such traditionally difficult
fillers to adhere as calcium carbonate20 and boron nitride.21a,b
Polymers containing benzoxazine is a new and attractive
approach in which benzoxazine moieties are incorporated as
repeating unit into the main chain of other conventional poly-
mers. The presence of reactive benzoxazines in the main chain can
partially or fully polymerize to form cross-links. By applying this
concept, we can combine the typical advantages of polybenzo-
xazine derived from monomeric precursors to the main chain
polymer backbone polymer for having a unique combination of
properties. As a result, polymers that process like thermoplastics
while final properties also exhibit advantages of thermosetting
polymers can be developed.
The functionalization of benzoxazine monomers with reactive
groups is expected to expand their applications toward further
structure modifications for new functional applications in
both monomeric benzoxazines and main-chain type polybenzo-
xazines. Property modification via synthesis of benzoxazine
monomers containing functional groups, such as acetylene,22a,b
phthalonitrile,23a-c allyl,24a-g propargyl,25a,b furan,26 nitrile and
maleminde,27a-e and carboxylic acid,28 have been actively pur-
sued. A systematic study of a series of monofunctional benzo-
xazine containing various functional groups, such as hydroxyl,
carboxyl, nitro, and aldehyde, to study the effect of the
introduction of these groups on the ring-opening polymeriza-
tion of benzoxazine monomers has also been reported by
Andreu et al.29
The current and vast growing interest in benzoxazine resin by
academia and industry has surely been due to the wide molecular
design flexibility than any other known class of resin and the
excellent mechanical and physical properties. The interesting
properties includes high glass transition temperature, low flamm-
ability, low absorption of water, stable and low dielectric con-
stant, low dissipation factor, high dimensional stability, and low
cost. In addition, its formation through thermally activated ring-
opening polymerization of benzoxazine in the absence of an
added initiator and/or catalyst does not release any volatiles, thus
eliminating the formation of voids.1a-e
Development of new benzoxazine resins, over the past decade,
has been taken in well-defined directions where, in turn, different
approaches have been carried out. Blending and alloying with
other polymers and reinforcing with inorganic particles are the
main trend within the research on monomeric benzoxazine resins.
In these approaches, benzoxazine resins have been mixed with
copolymerizable resins, such as epoxy,2a-j urethane,3a-e oxazo-
line,4a-d bismaleimide,5a,b and cyanate ester6 or with nonreac-
tive polymers, including poly(ε-caprolactone),7a-e poly(ethylene
oxide),8 polystyrene,9 and poly(methyl methacrylate).10
Benzoxazine resins are also ideally suited for composite
manufacturing, and the reinforcement with glass fibers,11a,b
cellulose fibers,12a-e and carbon fibers13a-f has been reported.
Since the molecular structure of polybenzoxazines resemble that
of lignin, one of the major components of wood, compatibility
with cellulose is good. Incorporation of nanofillers, such as
clay,14a-l carbon nanotube,15a,b polyhedral oligomeric silses-
quioxane (POSS),16a-f SiC whisker,17 barium titanate nano-
particles,18 and sol-gel nanoparticles,19 has been actively
studied. Composite application requires good adhesion at the
interface between the reinforcing material and matrix resin. The
amphoteric nature of the polybenzoxazines can accommodate a
Despite the high potential of primary amine-functional
benzoxazine monomers as a useful intermediate for further
synthesizing various benzoxazines, no study has been reported
on the synthesis due to the difficulty caused by the selectivity
problems during the monomer synthesis. The current article
describes various approaches to synthesize primary amine-
functional benzoxazine monomers. Additionally, the synthesis
and polymerization of amide-containing benzoxazine derived
from the primary amine-functional benzoxazine will be dis-
cussed.
*Corresponding authors. E-mail: hxi3@case.edu (H.I.); taa16@
case.edu (T.A.).
pubs.acs.org/Macromolecules
Published on Web 02/22/2010
r 2010 American Chemical Society

Article
Macromolecules, Vol. 43, No. 6, 2010 2749
2. Experimental Section
was filtered to remove the solid residues, followed by washing
the filtrate with 0.5 N aqueous NaOH (solution 3 ꢀ 15 mL) and
then with water. The solution was dried over sodium sulfate
anhydrous, followed by evaporation of the solvent under re-
duced pressure to afford a colorless viscous material (yield:
40%). 1H NMR (DMSO), ppm: δ = 2.18 (s, CH3), 4.41 (s, CH2
oxazine), 4.65 (s, NH2), 5.2 (s, CH2 oxazine), 6.40-6.9 (7H Ar).
13C NMR (DMSO), ppm δ = 50.35 (Ar-CH2-O) and 78,66
(O-CH2-N). FT-IR ν (cm-1) = 3357 (N-H stretching), 1513
(trisubstituted benzene ring stretching), 1226 (asymmetric
stretching of C-O-C), 1176 (C-N-C asymmetric stretching),
941(C-H out-of-plane).
2.1. Materials. Aminophenol (>98%), 4-chlorobenzene, ben-
zyl chloride (98%), isophthalic chloride, sodium borohydride,
trifluoroacetic anhydride, tetrachlorophthalic anhydride (99%),
and paraformaldehyde (99%) were used as received from Sigma-
Aldrich. 4,40-Diaminodiphenylmethane (DDM) (98%) was pur-
chased from Aldrich. Aniline was purchased from Aldrich and
prurifed by distillation. Chloroform, hexane, 2-propanol, metha-
nol, xylenes, and sodium sulfate were obtained from Fisher.
2.2. Preparation of 6,60-(Propane-2,2-diyl)bis(3-(4-nitrophenyl)-
3,4-dihydro-2H-benzo[e][1,3]oxazine) (1). Into a 100 mL round
flask were added 60 mL of chlorobenzene/xylene (1:1), bisphenol
A (4.989 g, 0.021 mol), 4-nitroaniline (6.046 g, 0.043 mol), and
paraformaldehyde (3.286 g, 0.109 mol). The mixture was stirred at
120 °C overnight. The reaction mixture was allowed to cool to
room temperature, affording yellow crystals (yield ca. 90%). 1H
NMR spectra (CDCl3, ppm, δ): 1.60 (s, C-CH3), 4.69 (s,
C-CH2-N-), 5.39 (s, N-CH2-O-), 6.75-8.18 (m, Ar). 13C
NMR spectra (DMSO, ppm, δ): 49.60 (C-CH2-N-), 76.79
(N-CH2-O). IR spectra (KBr, cm-1): 1594, 1330 (C-NO2
stretching), 1500 (stretching of trisubstituted benzene ring), 1232
(asymmetric stretching of C-O-C), 1193 (asymmetric stretching
of C-N-C), 960 (out-of-plane C-H).
2.3. Preparation of 4,5,6,7-Tetrachloro-2-(4-nitrophenyl)iso-
indoline-1,3-dione (2). In a 1 L round-bottomed flask were added
tetrachlorophthalic anhydride (41.194 g, 0.144 mol), p-nitroani-
line (20.70 g, 0.15 mol), and 300 mL of acetic acid. The mixture
was refluxed under stirring for 6 h. After cooling to room
temperature, the crystals were filtered off, followed by washing
repeatedly with 2 L of acetone. The crystals were dried under
vacuum without any further purification to give white cotton-like
crystals (yield ca. 90%). 1H NMR (DMSO), ppm: δ = 7.74-8.45
(4H, Ar). FT-IR ν (cm-1) = 1776, 1722 (imide I), 1610, 1355
(C-NO2 stretching), 1365 (imide II, C-N stretching), 746 (CdO
bending).
2.4. Preparation of 2-(4-Aminophenyl)-4,5,6,7-tetrachloroi-
soindoline-1,3-dione (3). In a 250 mL three-necked round
flask was stirred a suspension of 2 (12 g, 0.029 mol) in 150 mL
of DMF at 85 °C for 30 min under a hydrogen atmosphere. To
this suspension, Raney Ni (2.4 g) was added, and the reaction
was continued for 4 h. Then, the Raney Ni was removed by
filtration, followed by precipitation of the filtrate in water. The
precipitate was collected by suction filtration, washed several
times with water and cold methanol, and dried under vacuum at
room temperature to afford an orange powder (mp 267 °C, yield
ca. 85%). 1H NMR (DMSO), ppm: δ = 5.42 (NH2), 6.63-7.02
(4H, Ar). FT-IR ν (cm-1) = 3397 (N-H stretching), 1774, 1718
(imide I), 1367 (imide II, C-N stretching) 732 (CdO bending).
2.5. Preparation of 4,5,6,7-Tetrachloro-2-(4-(6-methyl-2H-benzo-
[e][1,3]oxazin-3(4H)-yl)phenyl)isoindoline-1,3-dione (4). Into a 25
mL round flask were added 3 (2 g, 5.319 mmol), p-cresol (0.574 g,
5.319 mmol), paraformaldehyde (0.479 g, 15.957 mmol), and
xylenes (15 mL) and stirred at 120 °C for 36 h. After cooling, the
reaction mixture was poured into 100 mL of methanol to give
an orange precipitate. The product was filtered and washed
several times with methanol, followed by drying under vacuum
to afford an orange powder (yield ca. 60%). 1H NMR (DMSO),
ppm: δ = 2.2 (s, CH3), 4.68 (s, CH2, oxazine), 5.46 (s, CH2,
oxazine), 6.60-7.30 (7H, Ar). FT-IR ν (cm-1) = 1779, 1722
(imide I), 1517 (trisubstituted benzene ring stretching), 1367
(imide II), 1205 (C-O-C asymmetric stretching), 1172 (C-
N-C asymmetric stretching), 943 (C-H out-of-plane).
2.7. Preparation of 2,20-(4,40-(6,60-(Propane-2,2-diyl)bis(2H-
benzo[e][1,3]oxazine-6,3(4H)-diyl))bis(4,1-phenylene))bis(4,5,6,7-
tetrachloroisoindoline-1,3-dione) (5). Into a 50 mL round flask, 3
(2 g, 5.31 mmol), bisphenol A (0.606 g, 2.65 mmol), and excess
of paraformaldehyde (0.4 g, 13.29 mmol) and 20 mL of xylenes
were added and stirred at 120 °C for 4 days. After cooling, the
reaction mixture was poured into methanol (100 mL), filtrated,
and washed several times with fresh methanol. Removal of
solvent by evaporation afforded a reddish-orange powder with
a purity of 75%. Typical yield: 35%. 1H NMR (DMSO), ppm:
δ = 1.55 (s, CH3), 4.69 (s, CH2 oxazine), 5.47 (s, CH2 oxazine),
6.66-7.26 (14H Ar). FT-IR ν (cm-1) =1780, 1720 (imide I),
1515 (trisubstituted benzene ring stretching), 1370 (imide II),
1215 (C-O-C asymmetric stretching), 1170 (C-N-C asym-
metric stretching), 950 (C-H out-of-plane).
2.8. Preparation of 4,40-(6,60-(Propane-2,2-diyl)bis(2H-benzo-
[e][1,3]oxazine-6,3(4H)-diyl))dianiline (BA-a-NH2). In a 25 mL
round-bottomed flask was suspended compound 5 (0.5 g, 0.861
mmol) into 5 mL of chloroform under a nitrogen atmosphere.
The suspention was stirred in an ice bath for 15 min at about
0 °C, followed by adding hydrazine monohydrate (0.258 g, 5.167
mmol). After having been stirred for 5 h under a nitrogen
atmosphere, the reaction mixture was filtered, diluted with
20 mL of chloroform, and followed by washing with 0.5 N
aqueous NaOH solution (3 ꢀ 15 mL) and then water. The
chloroform solution was dried over sodium sulfate anhydrous,
followed by evaporation of solvent under reduced pressure to
afford a pinkish-white powder (yield: 90%). 1H NMR (DMSO),
ppm: δ = 4.50 (s, CH2 oxazine), 4.59 (s, NH2), 5.29 (s, CH2
oxazine), 6.32-7.26 (8HAr). 13C NMR(DMSO), ppmδ= 48.93
(Ar-C-N, oxazine), 78.18 (O-C-N, oxazine). FT-IR (KBr),
cm-1: 3350 (N-H stretching), 1494 (stretching of trisubstituted
benzene ring), 1231 (C-O-C asymmetric stretching), 1180
(C-N-C asymmetric stretching), 955 (out-of-plane C-H).
2.9. Preparation of 4,5,6,7-Tetrachloro-2-(4-hydroxyphenyl)-
isoindoline-1,3-dione (6). Into a 1 L round flask were placed
tetrachlorophthalic anhydride (54.985 g, 0.192 mol), p-amino-
phenol (23.0840 g, 0.2114 mol), and 500 mL of acetic acid. The
mixture was stirred and refluxed for 6 h. After cooling to room
temperature, the precipitate was filtered and washed with 2 L of
methanol. Removal of solvent by evaporation afforded a yellow
1
crystal; mp 310 °C (yield ca. 87%). H NMR (DMSO), ppm:
δ = 6.88-7.22 (4H, Ar) 9.84 (OH). IR spectra (KBr, cm-1) =
3455 (O-H stretching), 1766, 1708 (imide I), 1371 (imide II,
C-N stretching), 732 (CdO bending).
2.10. Preparation of 4,5,6,7-Tetrachloro-2-(3-phenyl-3,4-dihy-
dro-2H-benzo[e][1,3]oxazin-6-yl)isoindoline-1,3-dione (7). Into a
1 L round flask were added 350 mL of xylenes, aniline (15 g,
0.161 mol), 6 (60.734 g, 0.161 mol), and excess of paraformal-
dehyde (19.351 g, 0.644 mol). The mixture was stirred at 120 °C
for 36 h. The mixture was cooled to room temperature and
filtrated off. The filtrate was concentrated to its half volume
using a rotary evaporator. Then, the solution was added drop-
wise to 2 L of hexane, filtered, and washed several times
with hexane. Removal of solvent by evaporation gave a yellow-
2.6. Preparation of 4-(6-Methyl-2H-benzo[e][1,3]oxazin-
3(4H)-yl)aniline (pC-a-NH2). Into a 25 mL round flask was
suspended 4 (0.508 g, 1 mmol) in 15 mL of diethyl ether under a
nitrogen atmosphere. The suspension was stirred for 15 min in
ice bath at about 0 °C, followed by adding hydrazine mono-
hydrate (0.15 g, 3 mmol). The suspension was stirred at -10 °C
for 5 h under a hydrogen atmosphere. The reaction mixture
1
ish-orange powder (yield ca. 60%). H NMR (DMSO), ppm:
δ = 4.74 (s, CH2, oxazine), 5.54 (s, CH2, oxazine) 6.88-7.26
(8H, Ar). 13C NMR spectra (DMSO, ppm, δ): 48.75 (Ar-C-O)

2750 Macromolecules, Vol. 43, No. 6, 2010
Agag et al.
and 78.80 (O-C-N). FT-IR (KBr), cm-1: 1781, 1722 (imide I),
1496 (stretching of trisubstituted benzene ring), 1370 (imide II),
1234 (C-O-C asymmetric stretching), 1203 (C-N-C asym-
metric stretching), 937 (out-of-plane C-H).
vacuum. The product was precipitated in 500 mL of hexanes,
filtered, and dried under vacuum overnight to give cotton-like
crystals (mp 172 °C, 88%). 1H NMR (DMSO), ppm: δ =
6.75-7.44 (4H, Ar), 9.50 (s, OH), 10.99 (s, NH). 13C NMR
spectra (DMSO, ppm, δ): 127.88 (CF3-CdO), 157.23 (q, NH-
(CdO)-CF3) and 155.38 (Ar-OH). FT-IR ν (cm-1) =
3600-3100 (N-H and O-H stretching overlap), 1702 (CdO
stretching).
2.11. Preparation of 3-Phenyl-3,4-dihydro-2H-benzo[e][1,3]
oxazin-6-amine (A-P-NH2) by Deprotection of 7. Into a 25 mL
flask was suspended TCP-protected monofunctional benzoxa-
zine (7) (0.491 g, 1 mmol) in 10 mL of diethyl ether. The
suspension was cooled in an ice bath with stirring for 15 min,
followed by the addition of hydrazine monohydrate (3 mmol,
0.15 g) to the suspension. The mixture was stirred for 5 h in the
ice bath under a hydrogen atmosphere, followed by filtration of
the solid residues. Then, the filtrate was washed by 0.5 N
aqueous NaOH solution (3 ꢀ 50 mL) and then with water,
followed by drying over sodium sulfate anhydrous. The solvent
was removed by evaporation using a rotary evaporator under
reduced pressure to give a colorless semisolid material, which
was further purified by recrystallization from hexane (yield:
80%). 1H NMR (DMSO), ppm: δ = 4.50 (s, CH2 oxazine), 4.59
(s, NH2), 5.29 (s, CH2 oxazine), 6.32-7.26 (8H Ar). 13C NMR
(DMSO), ppm δ = 48.93 (Ar-C-N, oxazine), 78.18 (O-C-N,
oxazine). FT-IR (KBr), cm-1: 3353 (N-H stretching), 1500
(stretching of trisubstituted benzene ring), 1224 (C-O-C asym-
metric stretching), 1180 (C-N-C asymmetric stretching), 950
(out-of-plane C-H).
2.15. Preparation of 2,2,2-Trifluoro-N-(3-phenyl-3,4-dihydro-
2H-benzo[e][1,3]oxazin-6-yl)acetamide (10). Into a 50 mL round
flask were added aniline (1.3620 g, 14.6247 mmol), 9 (4 g,
14.6247 mmol), excess of paraformaldehyde (1.3176 g, 43.9
mmol), and 20 mL xylenes and stirred at 120 °C for 4 h. After
cooling, the reaction mixture was poured into 200 mL of hexane,
filtered, and washed several times with hexane. The crude
product was then dissolved in 200 mL of ethyl acetate, followed
by washing with 5 wt % of aqueous Na2CO3 solution (3 ꢀ 100)
and water (3 ꢀ 100). The solution was dried over sodium sulfate
anhydrous, followed by evaporation of solvent under vacuum to
afford white powder which was used without further purifica-
1
tion (yield 80%). H NMR (DMSO), ppm: δ = 4.67 (s, CH2,
oxazine), 5.46 (s, CH2, oxazine), 6.70-7.60 (14H, Ar), 11.09 (s,
NH). 13C NMR (DMSO), ppm: δ = 48.80 (Ar-C-N, oxazine),
78.83 (O-C-N, oxazine), 116.42 (CF3-CdO) and 154.19
(q, NH-(CdO)-CF3). FT-IR (KBr), cm-1: 3286 (N-H
stretching), 1700 (carbonyl stretching), 1496 (stretching of
trisubstituted benzene ring), 1230 (asymmetric stretching of
C-O-C), 950 (out-of-plane C-H).
2.12. Preparation of 2,20-(3,30-(4,40-Methylenebis(4,1-phenylene))-
bis(3,4-dihydro-2H-benzo[e][1,3]oxazine-6,3-diyl))bis(4,5,6,7-tet-
rachloroisoindoline-1,3-dione) (8). Into a 50 mL flask were added
20 mL of xylenes, 6 (2 g, 5.305 mmol), 4,40-methylenedianiline
(0.526 g, 2.653 mmol), and paraformaldehyde (0.3983 g, 13.2625
mmol) and stirred at 120 °C for 2 days. The reaction mixture
was cooled to room temperature and precipitated into 150 mL of
methanol. Removal of solvent afforded an orange-red powder
(yield 51%). 1H NMR (DMSO), ppm: δ = 3.73 (s, CH2), 4.67
(s, CH2 oxazine), 5.47(s, CH2 oxazine), 6.85-7.13 (14H Ar). FT-
IR (KBr), cm-1: 1785, 1730 (imide I), 1511 (stretching of
trisubstituted benzene rin), 1375 (imide II), 1228 (C-O-C
asymmetric stretching), 1210 (C-N-C asymmetric stretching),
940 (out-of-plane C-H).
2.16. Preparation of 3-Phenyl-3,4-dihydro-2H-benzo[e]-
[1,3]oxazin-6-amine (P-a-NH2) by Deportation of 10. Into a
50 mL round flask was dissolved 10 (2.034 g, 9 mmol) in a
mixture of ethyl acetate and methanol at a ratio of 100:1
(100 mL:1 mL), followed by addition of NaBH4 (1.7024 g,
45 mmol). The resulting mixture was stirred for 6 h at 20 °C
under a nitrogen atmosphere. Then the reaction mixture was
washed four times with brine and one time with water. The ethyl
acetate solution was dried over sodium sulfate anhydrous.
Removal of the solvent by a rotary evaporator under reduced
1
pressure afforded a colorless viscous material (yield 85%). H
2.13. Preparation of 3,30-(4,40-Methylenebis(4,1-phenylene))-
bis(3,4-dihydro-2H-benzo[e][1,3]oxazin-6-amine) (P-ddm-NH2)
from Deprotection of 8. Into a 50 mL flask was suspended
TCP-protected bifunctional benzoxazine (8) (1 g, 2.152 mmol)
in 15 mL of chloroform. The suspension was cooled in an ice
bath with stirring for 15 min, followed by the addition of hydra-
zine monohydrate (0.645 g, 12.915 mmol) to the suspension. The
mixture was stirred for 5 h in the ice bath under a hydrogen
atmosphere, followed by filtration of the solid residues. Then,
the filtrate was diluted with 100 mL of chloroform, washed by
0.5 N aqueous NaOH solution (3 ꢀ 50 mL) and then with water,
followed by drying over sodium sulfate anhydrous. The sol-
vent was removed under reduced pressure to give a pinkish pow-
NMR (DMSO), ppm: δ = 4.50 (s, CH2 oxazine), 4.59 (s, NH2),
5.29 (s, CH2 oxazine), 6.32-7.26 (8H Ar). 13C NMR (DMSO),
ppm δ = 48.93 (Ar-C-N, oxazine), 78.18 (O-C-N, oxazine).
FT-IR (KBr), cm-1: 3353 (N-H stretching), 1500 (stretching
of trisubstituted benzene ring), 1224 (asymmetric stretching
of C-O-C), 1180 (asymmetric stretching of C-N-C), 950
(out-of-plane C-H).
2.17. Preparation of N,N0-(3,30-(4,40-Methylenebis(4,1-phenylene))-
bis(3,4-dihydro-2H-benzo[e][1,3]oxazine-6,3-diyl))bis(2,2,2-tri-
fluoroacetamide) (11). Into a 50 mL round flask were added
15 mL of chlorobenzene/xylenes (1:1) and 4,40-diaminodiphenyl-
methane (1.9331 g, 9.7500 mmol), 9 (4.00 g, 19.50 mmol), and
excess of paraformaldehyde (1.464 g, 48.75 mmol), and the
mixture was stirred at 120 °C for 3 h. The reaction mixture was
poured into 200 mL of hexane, filtered, and washed twice with
hexane. Then, the crude product was dissolved in 200 mL of ethyl
acetate, followed by washing with 5 wt % of aqueous Na2CO3
solution (3 ꢀ 100) and water (3 ꢀ 100). The solution was dried
over sodium sulfate anhydrous, followed by evaporation of
solvent under vacuum to afford a white powder which was used
without further (yield 87%). 1H NMR (DMSO), ppm: δ = 3.70
(s, CH2), 4.60 (s, CH2, oxazine), 5.39 (s, CH2, oxazine), 6.72-7.45
(14H, Ar), 11,06 (s, NH). 13C NMR (DMSO), ppm: δ = 48.99
(Ar-C-N, oxazine), 79.09 (O-C-N, oxazine), 116.40 (CF3-
CdO), 154.19 (q, NH-CdO-CF3). FT-IR (KBr), cm-1: 3288
(N-H stretching), 1706 (carbonyl stretching), 1500 (stretching of
trisubstituted benzene ring), 1226 (asymmetric stretching of
C-O-C), 956 (out-of-plane C-H).
1
der. H NMR (DMSO), ppm: δ=3.71 (s, CH2), 4.44 (s, CH2
oxazine), 4.57 (s, NH2), 5.22 (s, CH2 oxazine), 6.28-7.05 (14H
Ar). 13C NMR (DMSO), ppm δ = 49.07 (Ar-C-N, oxazine),
78.45 (O-C-N, oxazine). FT-IR ν (cm-1) = 3351 (N-H
stretching), 1502 (stretching of trisubstituted benzene ring),
1222 (asymmetric stretching of C-O-C), 1182 (asymmetric
stretching of C-N-C), 950 (out-of-plane C-H).
2.14. Preparation of 2,2,2-Trifluoro-N-(4-hydroxyphenyl)ace-
tamide (9). Into a 250 mL round flask were charged p-amino-
phenol (7.709 g, 0.070 mol) and THF (100 mL) and cooled in an
ice bath for 15 min. Trifluoroacetic anhydride (19.6 mL, 0.141
mol) was added dropwise with stirring in 30 min. Then, the
reaction mixture was stirred in the ice bath for an additional
1.5 h. The solvent was removed by a rotary evaporator, followed
by dissolving the residue in ethyl acetate (200 mL). The solution
was washed with saturated aqueous sodium bicarbonate solu-
tion (3 ꢀ 200 mL) and water (3 ꢀ 100 mL). The solution was
dried with sodium sulfate, filtered, and concentrated under
2.18. Preparation of 3,30-(4,40-Methylenebis(4,1-phenylene))-
bis(3,4-dihydro-2H-benzo[e][1,3]oxazin-6-amine) (P-ddm-NH2)
from Deprotection of 11. Into a 50 mL flask was dissolved 11

Article
Macromolecules, Vol. 43, No. 6, 2010 2751
(4.1810 g, 9 mmol) in a mixture of ethyl acetate/methanol at a
ratio of 100:1 (200 mL:2 mL), followed by addition of NaBH4
(1.7024 g, 45 mmol). The resulting mixture was stirred for 7 h at
20 °C under a nitrogen atmosphere. Then, the reaction mixture
was washed with brine (3 ꢀ 100) and with water. The solution
was dried over sodium sulfate anhydrous, followed by precipi-
tation in hexane. The precipitate was filtered and dried at room
temperature to give white powder, which was stored under an
inert atmosphere until use (yield 75%). 1H NMR (DMSO),
ppm: δ = 3.71 (s, CH2), 4.44 (s, CH2 oxazine), 4.57 (s, NH2),
5.22 (s, CH2 oxazine), 6.28-7.05 (14H Ar). 13C NMR (DMSO),
ppm δ = 49.07 (Ar-C-N, oxazine), 78.45 (O-C-N, oxazine).
FT-IR ν (cm-1) = 3351 (N-H stretching), 1502 (stretching of
trisubstituted benzene ring), 1222 (asymmetric stretching of
C-O-C), 1182 (asymmetric stretching of C-N-C), 950 (out-
of-plane C-H).
Scheme 1. Preparation of Dinitro-Functional Benzoxazine Monomer
2.19. Preparation of N1,N3-Bis(3-phenyl-3,4-dihydro-2H-benzo-
[e][1,3]oxazin-6-yl)isophthalamide (12). Into a 25 mL flask were
dissolved P-a-NH2 (1.157 g, 5.113 mmol) and triethylamine
(4.8 mL) in 50 mL of chloroform and cooled in an ice bath.
The solution was stirred for 15 min, followed by dropwise
addition of the 50 mL of chloroform solution of isophthaloyl
chloride (0.399 g, 1.967 mmol). The mixture was stirred for 1 h in
the ice bath. The solution was washed with 0.5 N aqueous
solution (3 ꢀ 100) and with water. The solution was dried over
sodium sulfate anhydrous, followed by concentration and pre-
cipitation in 200 mL of hexane. The precipitate was removed by
filtration and dried to give a white powder (yield 95%). 1H NMR
(DMSO), ppm: δ = 4.67 (s, CH2, oxazine), 5.44 (s, CH2,
oxazine), 6.72-8.47 (20H, Ar), and 10, 25 (s, NH). 13C NMR
(DMSO), ppm: δ = 48.98 (Ar-C-N, oxazine), 78.71 (O-C-N,
oxazine), and 130.31 (C-NH) and 164.58 (Ar-CdO-NH). FT-
IR (KBr), cm-1: 3288 (N-H stretching), 1646 (crbonyl
stretching), 1496 (stretching of trisubstituted benzene ring),
1226 (asymmetric stretching of C-O-C), 1186 (asymmetric
stretching of C-N-C), 954 (out-of-plane C-H).
amine-functional benzoxazines. In the first approach, novel
dinitro-functional benzoxazine (1) was prepared from
p-nitroaniline, bisphenol A, and paraformaldehyde as
shown in Scheme 1. Our recently reported method, in which
xylenes as a nonpolar, high-boiling-point solvent, was used
at 140 °C.31 The structure of the novel monomer was
2.20. Measurements. 1H and 13C NMR spectra were acquired
on a Varian Oxford AS600 at a proton frequency of 600 MHz
and its corresponding carbon frequency of 150.9 MHz. The
1
determined from H NMR, 13C NMR, and IR spectra. In
1
the H NMR spectra, the typical resonances attributed to
1
average number of transients for H and 13C MNR measure-
benzoxazine structure are observed at 4.69 and 5.39 ppm.
The FT-IR spectra showed the characteristic absorption
bands of benzoxazine structure at 1230 cm-1 due to the
stretching of C-O-C and the band at 960 cm-1 due to the
out-of-plane bending vibration of the benzene ring that is
attached to the oxazine ring.32 Also, the bands at 1594 and
1330 cm-1 are attributed to the C-NO2 group.
Several methods have been applied for the reduction of 1
to diamino-functional benzoxazine (BA-a-NH2), including
hydrozinium monoformate/metal, MH4Cl/metal Pd/C/
ment was 64 and 1024, respectively. A relaxation time of 10 s was
used for the integrated intensity determination of 1H NMR
spectra. Fourier transform infrared (FTIR) spectra were ob-
tained using a Bomem Michelson MB100 FTIR spectrometer,
which was equipped with a deuterated triglycine sulfate (DTGS)
detector and a dry air purge unit. Coaddition of 32 scans was
recorded at a resolution of 4 cm-1. Transmission spectra were
obtained by casting a thin film on a KBr plate for partially cured
samples. Elemental analysis was performed by MHW Labora-
tories. A TA Instruments DSC model 2920 was used with a
heating rate of 10 °C/min and a nitrogen flow rate of 60 mL/min
for all tests of differential scanning calorimetric (DSC) study.
All samples were crimped in hermetic aluminum pans with lids.
Dynamic mechanical analyses were done on a TA Instruments
Q800 DMA applying controlled strain tension mode with
amplitude of 10 μm and a ramp rate of 3 °C/min. Thermogravi-
metric analyses (TGA) were performed on a TA Instruments
Q500 TGA with a heating rate of 10 °C/min in a nitrogen
atmosphere at a flow rate of 40 mL/min.
NH2NH2 H2O, Pd/C/H2, Raney Ni/NH2NH2.H2O, FeCl3/
3
charcoal/NH2NH2.H2O, NaBH4/Raney Ni, and others.
However, all the methods applied for reduction were un-
successful to afford the BA-a-NH2 monomer that can be
easily purified. This is attributable to many side reactions
due to the instability of benzoxazine structure under the
reduction conditions.
The second pathway applied for obtaining amino-func-
tional benzoxazine was by using amine-protected phenols
or amines for synthesis of benzoxazine monomers, followed
by deprotection to liberate amine. The first approach in
this pathway is based on the synthesis of both mono-
and bifunctional benzoxazines using monoamine-protected
p-phenylenediamine (3), following Scheme 2. At the first
stage, tetrachlorophthalimide (NTCP)-protected p-nitro-
aniline (2) was prepared followed by reduction to afford 3.
The synthesis of amine protected-benzoxazines was achie-
ved using xylenes as a nonpolar, high-boiling-point solvent
at 140 °C, followed by deprotection using hydrazine hydrate
at 20 °C.
3. Results and Discussion
3.1. Preparation of Primary Amine-Functional Benzo-
xazines. Bicyclic benzoxazine monomers are typically
synthesized via condensation reaction of primary amine,
formaldehyde, and phenol. The one-step synthesis of pri-
mary amine-functional benzoxazines is quite difficult due to
the reaction of primary amine with formaldehyde to form a
triaza structure as intermediate structure of benzoxazine.30
We have applied two approaches to synthesize primary

2752 Macromolecules, Vol. 43, No. 6, 2010
Scheme 2. Preparation of Amino-Functional Benzoxazine Monomers Using TCP-Protected p-Nitroaniline
Agag et al.
The TCP-protected monofunctional benzoxazine (4)
was synthesized from 3, p-cresol, and paraformaldehyde
without any difficulties, followed by deprotection to afford
amino-monofunctional benzoxazine monomer (pC-a-NH2).
1
The structure of pC-a-NH2 was verified by H NMR, as
shown in Figure 1. The preparation of TCP-protected bifunc-
tional benzoxazines (A-P-NH2) was slightly more difficult
due to the poor solubility and heterogeneous nature of the
reaction facilitates side reactions, which lead to poor yield.
TCP-protected aminophenol (6) was also prepared and
used for preparation of primary amine-monofunctional
(P-a-NH2) and bifunctional (P-ddm-NH2) benzoxazines, as
shown in Scheme 3. Applying this pathway will save reduc-
tion step in the previous TCP-protected p-phenylenediamine
(3)-based benzoxazines. TCP-protected monofunctional
benzoxazine (7) was prepared from the reaction of 6, aniline,
and paraformaldehyde, followed by deprotection to give
primary amine-monofunctional benzoxazine monomer
1
(P-a-NH2). The structure of P-a-NH2 was verified by H
NMR, as shown in Figure 2.
The structure P-a-NH2 was further confirmed by IR, and
the results are shown in Figure 3. IR spectra show the
disappearance of the typical characteristic peaks of the
protecting TCP group at 1781 and 1722 cm-1 (imide I) and
1370 cm-1 (imide II) and the presence of the typical char-
acteristic peak at 937 cm-1 due to the benzoxazine structure.
TCP-protected bifunctional benzoxazines (8) was pre-
pared from 7 and 4,40-methylenedianiline (DDM) and par-
aformaldehyde as previously mentioned. In this case of
bifunctional monomer, a considerable amount of gel forma-
tion was present as a consequence of the reaction during the
course of the reaction. This insoluble gel did not disappear
despite applying long reaction time, leading to poor yield.
The 1H NMR spectra of the soluble portion of the reaction
mixture showed the presence of benzoxazine structure as well
Figure 1. 1H NMR spectra of primary amine-monofunctional benzo-
xazine monomer (pC-a-NH2) along with the starting materials.
as a considerable amount of side-reaction products which
were, despite numerous attempts for purification, very diffi-
cult to remove. Moreover, different solvents, among the
normally used for synthesis of benzoxazine monomers, were
also employed, such as chloroform, dioxane, and toluene,
giving equal or even worse results.
N-Trifluoroacetyl (TFA) was used as another amine pro-
tecting and easily leaving group. TFA-protected p-amino-
phenol (9) was prepared and used for the synthesis of
primary amine-monofunctional and -bifunctional benzo-
xazines, as shown in Scheme 4.

Article
Macromolecules, Vol. 43, No. 6, 2010 2753
Scheme 3. Preparation of Amino-Functional Benzoxazine Monomers Using TCP-Protected p-Aminophenol
Figure 3. IR spectra of TCP-protected (7) and deprotected primary
amine-monofunctional benzoxazine monomer (P-a-NH2).
to amine was easily achieved by using an ethyl acetate/
methanol solution of sodium hydroxide in a reasonable high
yield.
Figure 2. 1H NMR spectra of the primary amine-monofunctional
benzoxazine monomer (P-a-NH2) along with its starting materials.
The structures of the TFA-protected benzoxazines were
confirmed by 1H and 13C NMR and FT-IR analyses. Figure 4
1
shows the H NMR spectra of primary amine-functional
By using TFA-protected p-aminophenol, both protected
monofunctional (10) and bifunctional (11) benzoxazines
were prepared in good yields and short reaction times by
using a new solvent system of a mixture of chlorobenzene/
xylene (1:1 v/v) at 130 °C. These reactions were also carried
out using different solvents such as xylene, dioxane, xylene/
dioxane, DMSO, xylene/DMSO, and chlorobenzene but
without having the same satisfactory results as in the case
of the mixture of chlorobenzene/xylene. The deprotection
bisbenzoxazines along with their starting materials. The 1H
NMR spectra of the TFA-protected, diamino-functional
benzoxazine (11) show the singlet NH- proton resonance at
11.06 ppm and the typical benzoxazine resonances at 4.60
and 5.39 ppm. The formation of amine-containing benzo-
xazines has been indicated by the frequency shift of the
benzoxazine resonances from 4.67 and 5.46 ppm to 4.51 and
5.29 ppm for monofunctional monomer and from 4.60 and
5.39 ppm to 4.44 and 5.22 ppm for bifunctional monomer.

2754 Macromolecules, Vol. 43, No. 6, 2010
Agag et al.
Scheme 4. Preparation of Amino-Functional Benzoxazine Monomers Using TFA-Protected p-Aminophenol
Figure 5. IR spectra of TCP-protected (11) and deprotected (P-ddm-
NH2)-amino-bifunctional benzoxazine monomer.
mode of the benzoxazine group at 950 cm-1 in the case of
monofunctional and 956 cm-1 in the case of bifunctional, the
bands corresponding to the NH stretching mode at 3286 and
3288 cm-1 for monofunctional and bifunctional, respec-
tively, and the carbonyl stretching mode at 1700 cm-1 in
the case of monofunctional and 1706 cm-1 in the case of
bifunctional were observed. The new characteristics bands
due to the primary amine group stretching appeared at 3430,
3353, and 3224 cm-1 for the monofunctional benzoxazine
and at 3419, 3351, and 3210 cm-1 for the bifunctional
benzoxazine.
Figure 4. 1H NMR spectra of TFA-protected (7) and deprotected
diamino-functional benzoxazine (P-ddm-NH2) along with its starting
materials.
Also, new resonance appeared due to -NH2 proton, at
4.52 ppm for monofunctional and 4.57 for bifunctional
amino-containing benzoxazines.
The structures of two monomers were also confirmed by
FT-IR. Figure 5 shows the FT-IR spectra for P-ddm-NH2 as
an example. In addition to the bands from the C-O-C
antisymmetric stretching mode at 1230 cm-1 for monofunc-
tional and 1226 cm-1 for bifunctional, and the benzene ring
A model compound of amide-containing benzoxazine
was prepared to study the reactivity of primary amine-func-
tional benzoxazine and the properties of amide-functional

Article
Macromolecules, Vol. 43, No. 6, 2010 2755
Figure 7. IR spectra of P-a-NH2 and model 12.
Figure 6. 1H NMR spectra of P-a-NH2 and model 12.
Scheme 5. Preparation of Amide-Containing Benzoxazine Using
Amino-Functional Benzoxazine Monomer (P-a-NH2)
Figure 8. DSC thermograms of TCP-protected monofunctional amine
(10), P-a-NH2, and model 12.
TCP-protected monofunctional benzoxazine (10), P-a-
NH2, and model 12 for comparison. Monomer 10 shows
an endotherm at 168 °C due to melting and a typical DSC
benzoxazine exothermic peak with onset at 184 °C and a
maximum at 210 °C. However, the primary amine-functional
benzoxazine shows, in addition to the sharp endotherm due
to melting at 57°, multiple thermal events in the form of
several exotherms. Three exothermic peaks were observed
with the maxima at 96, 135, and 218 °C, attributing to the
reaction between benzoxazine structure and the primary
amine group along with the typical ring-opening of benzo-
xazine structure at higher temperature. Because of the sudden
endotherms ovserved at 225 °C, which could be attributed to
partial degradation, the peak position of the 218 °C was
probably underestimated. The DSC profile of model 12,
which contains an amide linkage, was also studied. Unlike
P-a-NH2, a typical DSC benzoxazine exothermic peak was
observed with onset at 194 °C and a maximum at 223 °C,
attributed to benzoxazine polymerization. This cure beha-
vior of the amide-containing benzoxazine also suggests that
the presence of amide (-NH-CO-) linkage enhanced the
polymerization at a relatively lower temperature in compar-
ison with typical amine/phenol benzoxazines.
benzoxazine as well. A model compound was successfully
synthesized from the reaction of primary amine-containing
monofunctional benzoxazine (P-a-NH2) and acid chloride,
as shown in Scheme 4. The structure of the model 12
1
was confirmed by H and 13C NMR and FT-IR analyses.
Figure 6 shows the 1H NMR spectra of 12. The spectra of the
model compound 12 exhibit a slight increase in the chemical
shifts that belong to the benzoxazine structure from 4.51
and 5.29 ppm to 4.67 and 5.44 ppm, and the appearance of
the NH proton resonance of amide at 10.25 ppm, confirming
the formation of an amide bond.
The structure of model compound 12 was further char-
acterized by FT-IR, and its spectrum is shown in Figure 7.
New bands appeared at 3288 and 1646 cm-1 due to the N-H
stretching and CdO stretching of amide configuration. Also,
symmetric stretchings of C-O-C and C-N-C are ob-
served at 1226 and 1186 cm-1, respectively. The character-
istic absorption benzene ring mode of benzoxazine is shown
Polymerization behavior of the TCP-protected bifunc-
tional benzoxazine (11) and amino-bifunctional benzoxazine
(P-ddm-NH2) is studied, and the DSC thermograms are
shown in Figure 9. Monomer 11 shows a sharp endotherm
at 216 °C, and the ring-opening reactions took place right
after the melting, which is indicated with the exothermic peak
at 236 °C. However, for the primary amine-functional
at 950 cm-1
.
3.2. Thermal Properties of Monomers. It is known that 1,3-
benzoxazine exhibits an exothermic ring-opening polymeri-
zation reaction around 200-250 °C, which can be monitored
by DSC. Figure 8 shows the DSC thermogram for the

2756 Macromolecules, Vol. 43, No. 6, 2010
Agag et al.
Figure 9. DSC thermograms of TCP-protected bifunctional amine (11)
and P-ddm-NH2.
Figure 11. Vicolestic properties of of poly(BA-a) and poly(12).
Figure 10. Storage and modulus moduli-temeprature relationship of
of poly(BA-a) and poly(12).
Figure 12. TGA thermograms of poly(BA-a) and poly(12).
bisbenzoxazine, P-ddm-NH2, similar multithermal events
were observed as P-a-NH2. Three exotherms were observed
with the maxima at 105, 164, and 243 °C, attributing to the
interaction between benzoxazine and amino group along
with the typical ring-opening of benzoxazine structure at
higher temperature. The molecular mechanism of this multi-
thermal event for the primary amine-catalyzed polymeriza-
tion has not yet been studied. One possibility is that the
reaction is locally heterogeneous. The other possibility is that
the amine might be acting as reactant and multistage con-
sumption of the amine may have caused the multiple thermal
events. Further detailed study is needed to explain this
complex phenomenon.
3.3. Thermal Properties of Amide-Containing Benzoxazine.
Thermal properties of model compound 12 after polymeri-
zation at 240 °C for 1 h have been investigated in comparison
with the typical polybenzoxazine, poly(BA-a) derived from
bisphenol A/aniline bifunctional benzoxazine (BA-a). The
viscoelastic properties of thermoset of poly(model 12) and
poly(BA-a) have been studied. Figure 10 shows the tempera-
ture dependence of the storage modulus and loss modulus,
whereas Figure 11 shows the tan δ for the polybenzoxazine
thermosets.
The storage modulus (E0) of poly(BA-a) decreased sharply
at ca. 130 °C with glass transition temeprtature (Tg) observed
at 154 and 168 °C from the maximum of the loss modulus and
tan δ, respectively. For poly(model 12), the storage modulus
maintained nearly a constant value of more than 1 GPa up to
200 °C in comparison to the typical poly(BA-a) of around
140 °C. The Tg shifted to as high as 198 and 227 °C from the
maximum of loss modulus and tan δ, respectively. The
interesting properties of polybenzoxazines are generally
attributed to the inter- and intramolecular hydrogen bond-
ing between hydroxyl groups of phenolic structure and/or
intramolecular 6-membered ring formation between the
phenolic structure and Mannich base bridge. However, in
this case of amide-containing polybenzoxazine, in addition
to the typical hydrogen bonding, amide groups are expected
to participate in further hydrogen bonding among polymer
chains and hence induce lateral reinforcement across the
polymer network structure.
Thermal stability of model compound 12 after polymeri-
zation at 240 °C for 1 h in comparison with the typical
bisphenol A/aniline bifunctional benzoxazine (B-a) was in-
vestigated by TGA. TGA profiles of the polymers, poly-
(Ba-a) and poly(12), are shown in Figure 12. The 5 and 10%

Article
Macromolecules, Vol. 43, No. 6, 2010 2757
weight loss temperatures (Td5 and Td10) for poly(BA-a) are
310 and 327 °C, respectively, whereas T5 and T10 for poly(12)
are 341 and 380 °C, respectively. The char yield at 800 °C are
32 and 57%, for of poly(BA-a) and poly(12), respectively.
This enhanced thermal stability of poly(12) as a monofunc-
tional benzoxazine without any additional cross-linking site
suggests that the presence of amide linkage play a significant
role in enhancing the thermal properties.
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4. Conclusion
Several routes have been applied to prepare amino-functional
benzoxazine structure. The reduction of nitro-functional benzo-
xazine to the corresponding primary amine-functional benzo-
xazine monomers was unsuccessful due to many side reactions,
owing to the instability of benzoxazine structure under reduction
conditions. The most convenient approach was found to be the
protection of primary amine-functional benzoxazines, followed
by deprotection at mild conditions that is not harmful for
benzoxazine structure. It was found that trifluoroacetyl group
as the protecting group is a convenient pathway that allows easy
synthesisfor protected benzoxazines andcan be removed easily as
well. Furthermore, the reactivity of primary amine-functional
bezoxazine toward further modifications has been studied by
preparation of amide-functional benzoxazine as model com-
pound, indicating the high reactivity of the benzoxazines toward
further modification. The polymerization behavior of amino-
functional monomers studied by DSC showed thermograms with
multithermal event in the form of several exotherms at different
temperature ranges.
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