Chemoselective polycondensation of 2-amino-4,6-dichloro-1,3,5-triazine with aromatic diamines

Article abstract of DOI:10.1246/cl.2011.1132

Chemoselective polycondensation of 2-amino-4,6-dichloro-1,3,5-triazine (ADCT) was investigated with various aromatic diamines such as 4,4′-oxydianiline (ODA), 9,9-bis(4-aminophenyl)fluorene (BAFL), 4,4′-(hexafluoropropane-2,2-diyl)dianiline (BisAF), and bis(4-aminophenyl)sulfone (SODA) in the presence of potassium carbonate as a base. High-molecular weight perfectly linear polyguanamines (M_n μ 46000) were successfully obtained for the polycondensation of ADCT with BisAF, while the polycondensation of ADCT with BAFL afforded branched polyguanamines with a degree of branching of from 0.02 to 0.17.

Full text of DOI:10.1246/cl.2011.1132

doi:10.1246/cl.2011.1132
1132
Published on the web September 23, 2011
Chemoselective Polycondensation of 2-Amino-4,6-dichloro-1,3,5-triazine
with Aromatic Diamines
Yuji Shibasaki,*1 Takanori Koizumi,1 Naoya Nishimura,2 and Yoshiyuki Oishi1
1Department of Chemistry and Bioengineering, Graduate School of Engineering, Iwate University,
4-3-5 Ueda, Morioka, Iwate 020-8551
2Synthesis Research Department, Chemical Research Laboratory, Nissan Chemical Industries, Ltd.,
722-1 Tsuboi-cho, Funabashi, Chiba 274-8507
(Received July 25, 2011; CL-110627; E-mail: yshibasa@iwate-u.ac.jp)
Chemoselective polycondensation of 2-amino-4,6-dichloro-
1,3,5-triazine (ADCT) was investigated with various aromatic
diamines such as 4,4¤-oxydianiline (ODA), 9,9-bis(4-amino-
phenyl)fluorene (BAFL), 4,4¤-(hexafluoropropane-2,2-diyl)di-
aniline (BisAF), and bis(4-aminophenyl)sulfone (SODA) in
the presence of potassium carbonate as a base. High-molecular
weight perfectly linear polyguanamines (Mn µ 46000) were
successfully obtained for the polycondensation of ADCT with
BisAF, while the polycondensation of ADCT with BAFL
afforded branched polyguanamines with a degree of branching
of from 0.02 to 0.17.
NH2
N
NH2
N
K2CO3
NMP
N
N
H2N Ar NH2
H
H
N Ar N
Cl
N
Cl
N
n
ADCT
H2N
NH2
O
H2N Ar NH2
:
H2N
NH2
ODA
BAFL
O
O
F3C CF3
S
H2N
NH2 H2N
NH2
Chemoselective reactions, many of which can be observed
in living organisms, are key techniques in the construction of
complex structures from polyfunctional components. The basic
strategy for chemoselective reaction is the utilization of the
different reactivity in like functional groups such as between
aliphatic amines and aromatic amines. Various types of the
chemoselective reactions are applied to the preparation of
polymers such as polythiophenes,1,2 polyesters,3 and poly-
amides.4 Such controlled reaction affords regioregular structures,
resulting in a variety of higher-ordered polymeric architectures.
Triazine is an aromatic molecule having three nitrogen
atoms. Its derivatives are commonly prepared from cyanuric
chloride, and used for dyes,5 fluorescent brightening agents,6 and
agrochemicals.7 When a monofunctional compound is intro-
duced into cyanuric chloride, the resulting compounds can be
used as difunctional triazine-based monomers for the preparation
of polyguanamines,8,9 polyethers,10 and polythioethers.11 The
interest in polymers that incorporate the amino-s-triazine moiety
is the existence of the strong interaction between polymer main
chains via hydrogen bonding,12 numerous reactive sites along
with the polymer backbone to modify the polymer, or the
application to photopolymers. Therefore, 2-amino-4,6-dichloro-
1,3,5-triazine (ADCT), the monomer of the amino-s-triazine
functional polymer has been extensively studied.13 However,
polycondensation of ADCT with difunctional monomers could
afford branching structure, resulting in low-molecular weight
polymers, or gelation. Because aromatic diamines have less
nucleophilicity than their aliphatic counterparts, polymerization
of ADCT with aromatic diamines were expected to instantly
form a gel. To the best of our knowledge, no report has been
published about the chemoselective polycondensation of ADCT
with aromatic diamines to date, although the expected polymers
would show interesting reactivity toward electrophiles due to
the numerous regularly-aligned amino groups on the polymer
backbone. Here we report the polymerization of ADCT with
BisAF
SODA
Scheme 1. Synthesis of polyguanamines from ADCT with
various aromatic diamines.
Table 1. Summary of polyguanamine synthesisa
Temp Time Yieldb
c
c
d
Run Diamine
Mn
Mw/Mn Mn(NMR)
/°C
/h
/%
1
2
3
4
5
6
7
ODA
150
150
150
180
150
180
150
3
3
24
24
3
>99
80
1500
3600
18
8.8
2.3
10.5
32
1900
4000
14000
20000
1300
37000
®
BAFL
BAFL
BAFL
BisAF
BisAF
SODA
61 14000
59 19000
88
33 46000
50
1000
12
3
2.3
®
®
aConditions: 2.5 mmol of ADCT, 2.5 mmol of diamine
monomer, 5.5 mmol of K2CO3 in 5 mL of NMP. Methanol-
insoluble part. cDetermined by GPC (NMP containing
b
¹1
d
0.01 mol L of LiBr). Determined by NMR.
various aromatic diamines involving ODA, BAFL, BisAF, and
SODA, and the evaluation of the chemoselectivity.
Polycondensation of ADCT with aromatic diamines was
performed in N-methylpyrrolidinone (NMP) in the presence of
potassium carbonate as base as shown in Scheme 1 (see the
Supporting Information about the detail of the experimental
procedures14). The results of the polymerization are summarized
in Table 1. When the polycondensation was conducted using
ODA as a diamine monomer at 150 °C for 3 h, the polymeriza-
tion solution became heterogeneous to form a low-molecular-
weight polymer (Run 1). On the other hand, the polymerization
with BAFL or BisAF afforded soluble high-molecular-weight
polymers. However, in the case of the polymerization using
Chem. Lett. 2011, 40, 1132-1134
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1133
Polymerization of ADCT with Bis-AF
8.57 ppm
BAFL at 180 °C, a larger polydispersity ratio polymer was
obtained, which indicates the formation of branching structure
(Run 4). Since the polymer with reasonable polydispersity ratio
was obtained by the polymerization of ADCT with BisAF even
at 180 °C, higher chemoselectivity seemed to be attained in
this case (Run 6). The GPC profile of the as-made polymeric
solution from ADCT with BisAF was a bimodal distribution,
indicating the formation of cyclic oligomers. Thus, the yield of
the polymer was relatively low. Polymerization hardly proceed-
ed for ADCT with SODA due to the poor solubility of the
resulting polymer (Run 7).
NH2
NH2
F3C CF3
F3C CF3
N
N
N
N
H2N
NH2
Cl
N
N
H
NH2
Cl
N
Cl
Bis-AF
ADCT
6.75 ppm
NH2
F3C CF3
N
N
Inactive
Cl
N
N
H
N
H
n
Linear polymer
Inactive
f
e
h
d
NH
NH
2
2
Polymerization of ADCT with ODA or BAFL
c
N
N
N
N
8.57 ppm
6.86 ppm
NH2
a
NH2
H N
2
N
N
N
H
g
N
N
Cl
b
H
H
n
N
N
H2N Ar NH2
N
N
i
Cl
N
N
H
Ar NH2
a
a) 150 °C, 24 h
2 n – 2 x : 2 n + x = h : g = 31.90 : 32.96
CS = 1 – x/n = 0.978
Cl
N
Cl
b
c
d
74.88
ODA, BAFL
ADCT
g
f
68.74
75.00
e
h
Inactive
35.17
32.96
35.19
i
N
N
31.90
6.5
6.50 ppm
1.00
N
NH
NH2
9.0
8.5
8.5
8.0
7.5
114.46
7.0
ppm
N
N
N
N
H
H
N
b) 180 °C, 24 h
CS = 0.831
N
Ar
Ar
117.15
N
N
127.18
N
N
H
m
n
H
66.29
62.51
58.10
9.0
Partially branched polymer
44.52
1.00
Active
8.0
7.5
7.0
6.5
ppm
Figure 1. Expanded 1H NMR spectra of polyguanamines from
ADCT with BAFL at a) 150 and b) 180 °C for 24 h.
Figure 2. Plausible mechanism in polyguanamine synthesis.
1
the integration values of protons (i) and ( f ) in H NMR spectra
Figure 1 depicts the expanded 1H NMR spectra of the
polymers obtained from ADCT with BAFL at a) 150 and b)
180 °C for 24 h. In addition to the signals assignable to protons
of the polymer main chain segment, a signal assignable to
terminal amino proton (i) is observed at 6.4 ppm. These were
assigned from the 1H NMR signals of the monomers and
2-amino-6-chloro-4-(4-methoxyanilino)-1,3,5-triazine (ADCT-
AN) model compound. The molecular weights estimated from
show good agreement with those from GPC measurements. The
chemoselectivity (CS) of the polymerization was estimated from
the following equation, in which n is the degree of polymer-
ization and x is the number of branching.
CS ¼ 1 ꢀ x=n
ð1Þ
These two parameters n and x can be correlated with the
1
integrations in the H NMR spectrum as follows;
ðNumber of hydrogens in NH2Þ:ðNumber of hydrogens in guanamineÞ ¼ ð2n ꢀ 2xÞ:ð2n þ xÞ ¼ h:g
ð2Þ
Thus, the CS can be calculated to be 0.978 and 0.831 for
a) and b), respectively. From these results, higher polymeriza-
tion temperature of ADCT with BAFL resulted in branched
structure in the polymer architecture.
in Figure 2, the chemical shifts of the amino groups in ADCT
and ADCT-AN were at 8.57 and 6.86 ppm, respectively. After
the polymerization with BisAF, the amino protons appeared at
6.75 ppm. In the case of the polymerization with BAFL, these
protons shifted further upfield to 6.50 ppm. At 150 °C, the amino
function of ADCT segment in the polymer backbone was almost
inactive for the condensation with chlorotriazine moiety, but it
can react at 180 °C to afford branching structures. Because the
amino group in the ADCT-BisAF polymer has lower electron
density due to the strong inductive effect of six fluorine atoms,
there is almost no branching in ADCT-BisAF polymerization
even at 180 °C.
The CS for the polymer from ADCT with BisAF was nearly
1 even at 180 °C polymerization (Run 6). We initially expected
that the branching could be formed as a result of the competitive
condensation between dichloride in ADCT with diamines and
amine groups in ADCT, but the experimental results were in
complete disagreement; higher CS was achieved in the case of
diamine monomer with lower nucleophilicity, BisAF. Thus, in
order to know the reactivity of the amino function in the ADCT
segment before and after the polymerization, 1H NMR spectrum
of the intermediate model compound ADCT-AN, which was
obtained from ADCT with p-anisidine, was measured. As shown
As the thermal properties of the resulting polymers, we
measured the glass transitions (Tg) by differential scanning
calorimetry (DSC) and 5%-weight-loss temperatures (Td5) by
Chem. Lett. 2011, 40, 1132-1134
© 2011 The Chemical Society of Japan
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1134
thermogravimetry under nitrogen. The Tg and the Td5 were 266
and 477 for ADCT-BAFL (Run 3), and 121 and 488 °C for
ADCT-BisAF polymer samples (Run 6), respectively. The
bulky pendant fluorene group as well as the stiffness of the
aromatic polyguanamine backbone gave rise to the high
thermostability of the ADCT-BAFL polymer sample. Thus,
the reason for the lower Tg of the ADCT-BisAF polymer sample
could be attributed to the flexible hexafluoropropane-2,2-diyl
group.
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6
In conclusion, polycondensation of ADCT with various
aromatic amines was investigated in an aprotic polar solvent,
and it is revealed that the chemoselectivity of the polymerization
was affected by the nucleophilicity of the amino group in the
ADCT segment after the polymerization. These changes of the
reactivity of the amino group along the polymer chains would be
useful for the design of linear to hyperbranched architecture in
polyguanamine synthesis.
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This study was supported by the Foundation for Japanese
Chemical Research.
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Chem. Lett. 2011, 40, 1132-1134
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/