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1H NMR (DMSO), ppm: d 5 4.72 (s, ArACH2AN, oxazine),
5.42 (s, OACH2AN, oxazine), 6.85–7.96 (12H, Ar). IR spectra
(KBr), cm21: 1774, 1719 (imide I), 1497 (stretching of tri-
substituted benzene ring), 1385 (imide II), 1231 (CAOAC
asymmetric stretching), 1179 (CANAC asymmetric stretch-
ing), 924 (out-of-plane CAH).
primary amine (aniline and DDM), formaldehyde, and imide
functional phenol (ortho- and para-isomers) as shown in
Scheme 1.
Prior to this study, we also attempted to prepare imide func-
tional diphenol using diphthalic anhydride and bis(phthalic
anhydride) with aminophenol. However, it was difficult to
obtain the purified benzoxazine monomers due to the poor
solubility of imide functional diphenol in ordinary solvents.
Preparation of 2,2’-(3,3’(4,4’-Methylenebis
(4,1-phenylene))-bis(3,4-dihydro-2H-benzo[e][1,3]
oxazin-6,3-diyl))-bis(isoindoline-1,3-dione) (pPP-ddm)
Into a 100 mL round flask were added 30 mL of xylenes,
DDM (1.49 g, 0.0075 mol), p-PP (3.59 g, 0.015 mol), and
paraformaldehyde (0.91 g, 0.03 mol). The mixture was
stirred at 120 ꢀC for 36 h. The mixture was cooled to room
temperature and filtered off. Then the solution was precipi-
tated into 100 mL of methanol. Removal of solvent by filter-
ing afforded a yellow powder. (yield ca. 50%).
To overcome the above problem, we chose phthalic anhy-
dride to prepare imide functional monophenols (p-phenol
phthalamide and o-phenol phthalamide, hereinafter abbrevi-
ated as p-PP and o-PP) as the first step, and then p-PP and
o-PP were reacted with amine and paraformaldehyde to pre-
pare the imide monofunctional and difunctional benzoxazine
monomers. At the second step, the synthesis method and the
reaction time of para-imide functional benzoxazine mono-
mers (pPP-a and pPP-ddm) exhibited great differences from
ortho-isomers (oPP-a and oPP-ddm). The synthesis of pPP-a
required excess paraformaldehyde and the reaction time was
as long as 48 h. In the case for preparing pPP-ddm, a consid-
erable amount of gel formation was observed during the
early stage of the synthesis. This insoluble gel did not disap-
pear despite applying long reaction time, leading to poor
yield. However, both the syntheses of oPP-a and oPP-ddm
completed in just 6 h, which led to a transparent solution.
One possibility is that the intramolecular hydrogen bond
between the phenolic OH group and one of the carbonyl
group decreases the polarity of o-PP, which improves the sol-
ubility of o-PP in aprotic solvent. At the same time, the intra-
molecular hydrogen bond also accelerates the ionization of
phenolic OH group during the initial stage for forming ben-
zoxazine ring. As a result, the ring-closing process of benzox-
azine for ortho-isomers becomes much easier than para-
isomers.
1H NMR (DMSO), ppm: d 5 3.71 (s, CH2), 4.65 (s,
ArACH2AN, oxazine), 5.44 (s, OACH2AN, oxazine), 6.80–7.92
(8H, Ar). IR spectra (KBr), cm21: 1773, 1720 (imide I), 1499
(stretching of trisubstituted benzene ring), 1381 (imide II),
1236 (CAOAC asymmetric stretching), 1185 (CANAC asym-
metric stretching), 944 (out-of-plane CAH).
Preparation of 2,2’-(3,3’(4,4’-Methylenebis
(4,1-phenylene))-bis(3,4-dihydro-2H-benzo[e][1,3]
oxazin-8,3-diyl))-bis(isoindoline-1,3-dione) (oPP-ddm)
Into a 100 mL round flask were added 20 mL of xylenes,
DDM (1.49 g, 0.0075 mol), o-PP (3.59 g, 0.015 mol), and
paraformaldehyde (0.91 g, 0.03 mol). The mixture was
stirred at 120 ꢀC for 6 h. The mixture was cooled to room
temperature and precipitated into 100 mL of methanol.
Removal of solvent by filtering afforded a yellow powder.
ꢀ
(yield ca. 93%, m.p. 225 C).
1H NMR (DMSO), ppm: d 5 3.71 (s, CH2), 4.63 (s,
ArACH2AN, oxazine), 5.35 (s, OACH2AN, oxazine), 6.94–7.96
(8H, Ar). IR spectra (KBr), cm21: 1780, 1723 (imide I), 1485
(stretching of trisubstituted benzene ring), 1383 (imide II),
1230 (CAOAC asymmetric stretching), 1179 (CANAC asym-
metric stretching), 925 (out-of-plane CAH).
The structures of the monomers were confirmed using 1H
NMR spectra, as depicted in Figures 1 and 2. The character-
istic resonances attributed to the benzoxazine structure,
ArACH2ANA and AOACH2ANA for pPP-a, pPP-ddm, oPP-a,
oPP-ddm are observed at 4.71, 5.50; 4.65, 5.44; 4.72, 5.42;
4.63, 5.35 ppm, respectively. Also the 1H NMR spectra con-
firm the presence of methylene group (ACH2A) at 3.71 ppm
for both pPP-ddm and oPP-ddm. Besides, the 1H NMR end-
group analysis indicates the purity of pPP-a, pPP-ddm, oPP-a
and oPP-ddm to be 97.9%, 97.0%, 99.5%, and 98.2%,
respectively.
Polymerization of Imide Functional Benzoxazines
A solution of 30% solid content of the monomers in DMF
was prepared. Then, the solution was cast over
a
dichlorodimethylsilane-pretreated glassꢀ plate. The film was
dried in an air circulating oven at 100 C for 24h to remove
the solvent completely. The film as fixed on a glass plate was
polymerized stepwise at 120, 140, 160, 200, 230 ꢀC for 1 h
each, and then slowly cooled to room temperature. They
showed dark brown color with thickness ranging from 0.1 to
0.3 mm.
There are a number of infrared absorption bands, high-
lighted in Figure 3, that are used to verify the formation of
oxazine rings in each monomer. For example, the characteris-
tic doublet at 1780 to 1773 cm21 and 1723 to 1719 cm21
are the typical bands for imide, which are attributed to the
imide CAC(@O)AC antisymmetric and symmetric stretching,
respectively.29 In addition to these bands, the presence of
imide is seen by the other characteristic bands at 1385 to
1381 cm21 which is due to the axial stretching of CAN
bonding.30,31 The bands characteristic of antisymmetric
RESULTS AND DISCUSSION
Preparation of Imide Functional Benzoxazine Monomers
A successful synthesis of imide monofunctional and difunc-
tional benzoxazine monomers has been achieved using
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