Synthesis of poly(1,3-adamantane)s by cationic ring-opening polymerization of 1,3-dehydroadamantanes

Article abstract of DOI:10.1021/ma048925c

Poly(1,3-adamantane)s was synthesized by cationic ring-opening polymerization of 1,3-dehydroadamantane. The all-hydrocarbon poly(propellane), poly(5-butyl-1,3-adamantane) synthesized showed good solubility and thermal stability. This high thermal stability of aliphatic polymers was derived from the strain-free adamantane skeletons and the stable carbon-carbon bond between two bulky adamantane rings. The chemical structure of the resulting polymer was characterized by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy in conjugation with infrared measurement and elemental analysis.

Full text of DOI:10.1021/ma048925c

Macromolecules 2004, 37, 7069-7071
7069
Syn th esis of P oly(1,3-a d a m a n ta n e)s by
Ca tion ic Rin g-Op en in g P olym er iza tion of
,3-Deh yd r oa d a m a n ta n es
Sch em e 1
1
Ta k a sh i Ish izon e,* Sh in -ich i Ma tsu ok a ,
Sh ik o Sa k a i, Wa ta r u Ha r a d a , a n d Hir oyu k i Ta jim a
Department of Organic and Polymeric Materials,
Graduate School of Science and Engineering,
Tokyo Institute of Technology, 2-12-1-H-119, Ohokayama,
Meguro-ku, Tokyo 152-8552, J apan
Received May 31, 2004
Revised Manuscript Received J uly 21, 2004
1
2
Small ring propellanes such as [1.1.1]-, [2.2.2]-, and
3
[
2.2.1]propellanes have been of considerable interest
because of the high reactivity derived from inverted
4
,5
tetrahedral geometry at the bridgehead carbons. In
the field of polymer chemistry, these highly strained
propellanes can be positioned as cyclic monomers be-
cause of their ring-opening polymerizability. In fact,
several oligomers and polymers have been obtained only
via the ring-opening polymerizations of [1.1.1]propellane
At first, when 1 was reacted with CF3SO3H in CH2-
Cl2 at 0 °C for 6 h (Table 1, run 1), some white
precipitate was observed in the reaction mixture. Al-
though a polymeric product was obtained in 95% yield
17
after quenching with acetic acid, it was insoluble in
10,18
any organic solvents as previously reported.
Al-
6
-9
derivatives.
,3-Dehydroadmantane (1)
though we have thus found that the cationic polymer-
1
0,11
1
is a typical [3.3.1]-
ization of 1 also provides the poly(1) as well as the
1
2
propellane derivative and involves a tricyclic system
fused by three methylene rings. An inverted 1,3 carbon-
carbon bond of 1 readily undergoes free-radical and
electrophilic ring-opening reactions with oxygen, bro-
mine, and acetic acid to produce 1,3-disubstituted
adamantanes. Interestingly, Pincock has reported that
an insoluble polymeric product is formed by heating of
this strained hydrocarbon at 130-160 °C.1 Although
the resulting product is supposed to be a poly(1,3-
adamantane) only by IR spectroscopy and elemental
analysis, the poor solubility has precluded its detailed
characterization such as NMR spectroscopy, size exclu-
sion chromatography (SEC), and viscosity measure-
ment. To the best of our knowledge, no systematic
studies on the ring-opening polymerization of 1,3-
dehydroadamantanes and the synthesis of poly(1,3-
19
thermal polymerization, its poor solubility prohibits
further characterization.
We then attempted to cationically polymerize a novel
butyl-substituted monomer 2 with CF3SO3H in CH2Cl2
at 0 °C for 6 h. A white precipitate similarly formed
within several minutes, and the polymerization of 2
proceeded in the heterogeneous system. A polymer of
white powder was obtained by precipitation into metha-
0
17
nol in good yield after termination. In contrast to the
poor solubility of poly(1), the obtained polymer was
soluble in several organic solvents such as chloroform,
20
THF, and 1,2-dichlorobenzene but insoluble in hexane,
benzene, methanol, and water. The chemical structure
of the resulting polymer was thoroughly characterized
1
13
by H and C NMR spectroscopies in conjunction with
21
1
IR measurement and elemental analysis. Both H and
C NMR spectra of the polymer showed all the signals
1
3
14
adamantane) have been reported. Therefore, we have
purposefully designed a novel 5-butyl-1,3-dehydroada-
mantane, 2, by introducing a flexible butyl substituent
on the adamantane skeleton in order to increase the
13
expected to the repeating unit of poly(5-butyl-1,3-
13
adamantane), poly(2). In the C NMR spectra of 1-bu-
tyladamantane and 2, 8 and 11 signals expected on the
basis of their molecular symmetries are respectively
observed, as shown in Figure 1. The signals of adaman-
tane skeletons of 2 split and drastically shift from those
of 1-butyladamantane toward the downfield region,
except for one methylene carbon away from the propel-
lane bond. After the polymerization, 11 reasonable
signals are also detected, while one of the adamantyl
methylene carbon and quaternary carbon substituted
with a butyl group are overlapped at 34.0 ppm. Most of
the signals corresponding to the adamantane skeleton
again moved to the upfield region, where the signals of
1
5
solubility of the resulting polymer. In this communica-
tion, we report the first synthesis of soluble poly(1,3-
adamantane) via the cationic ring-opening polymeriza-
tion of 2.
The 1,3-dehydroadamantanes, 1 and 2,16 were syn-
thesized by the reaction of 1,3-dibromoadamantane or
5
-butyl-1,3-dibromoadamantane with lithium in THF at
room temperature in 71 and 83% yields (Scheme 1),
respectively. The monomers were purified by vacuum
distillation to remove ethers and were alternatively
diluted with CH2Cl2. The resulting 1,3-dehydroadaman-
tanes were very stable in a sealed tube in C6D6 at least
for several months, and no degradation and oligomer-
ization were observed. However, they spontaneously
reacted with oxygen to give the copolymeric products,
as previously reported.10 Therefore, we carefully treated
with 1 and 2 in an all-glass apparatus under high-
vacuum conditions.
1
-butyladamantane are located, suggesting the drastic
22
change of electronic environment. Most importantly,
the characteristic signal of inverted quaternary carbon
of 2 at 36.1 ppm completely disappears, and alterna-
tively a new signal corresponding to the internal
quaternary carbon of main chain linkage appears at 38.5
ppm after the polymerization. These results strongly
indicate that the ring-opening polymerization of 2
exclusively occurs to give a poly(5-butyl-1,3-adaman-
*
Corresponding author: e-mail tishizon@polymer.titech.ac.jp.
1
0.1021/ma048925c CCC: $27.50 © 2004 American Chemical Society
Published on Web 08/17/2004

7
070 Communications to the Editor
Macromolecules, Vol. 37, No. 19, 2004
Ta ble 1. Ca tion ic P olym er iza tion of 1 a n d 2 in CH2Cl2 a t 0 °Ca
M/Ib
time, h
yield, %
c
10-3Mn(SEC)d
Mw/Mnd
T10, °C
e
run
monomer type, mmol
CF3SO3H, mmol
1
2
3
4
5
1, 3.39
2, 2.85
2, 7.70
2, 8.66
2, 8.66
0.41
0.52
0.36
0.19
0.19
8.3
5.5
21
46
46
6
6
6
6
42
95f
89
78
52
72
g
g
421
445
472
485
486
1.5
3.2
4.4
6.0
1.30
1.43
1.56
1.56
a
Carried out under high-vacuum conditions (10-6 mmHg). b Initial molar ratio between monomer to initiator. c Methanol-insoluble
part. d Estimated SEC measurement calibrated by polystyrene standards in 1,2-dichlorobenzene at 135 °C. 10% weight loss temperature
e
measured by TGA under nitrogen. CHCl3-insoluble part. g No data due to the poor solubility.
f
F igu r e 1. 13C NMR spectra of 1-butyladamantane in CDCl
(A), 2 in C D (B), and poly(2) in 1,2-dichlorobenzene/C D (10/1) (C).
3 6 6 6 6
tane) through breaking of the 1,3-propellane σ-bond.
Furthermore, this also supports the similar chemical
structure of poly(1) containing an adamantane-1.3-diyl
linkage via the ring-opening polymerization of 1.
Table 1 shows the polymerization result of 2. When
the polymerizations were performed at the low monomer-
to-initiator ratios (M/I) (runs 2 and 3), the polymer
yields reached 80-90% within 6 h at 0 °C. At higher
feed ratio of M/I ) 46, the polymerization of 2 slowly
proceeded and gave poly(2) in 52% yield after 6 h. Under
similar conditions, the polymer yield increased to 72%
after 42 h polymerization (run 5). The SEC curves of
poly(2) measured in 1,2-dichlorobenzene were always
unimodal, and the polydispersity indices, Mw/Mn, were
1
.3-1.6. The SEC curves shift toward higher molecular
weight side as the M/I ratios increase from 6 to 21, and
4
6, as shown in Figure 2. The Mn value estimated by
2
3
using polystyrene standards reached 6000 at 72% yield
when the polymerization was carried out at 0 °C for 42
h. The number-average degree of polymerization of this
poly(2) sample could be estimated at greater than 30.
The molecular weights of poly(2) can be controlled to
some extent by changing the feed molar ratio of mono-
mer to initiator, indicating the infrequent chain transfer
and termination reactions. This means that a propagat-
ing 1-adamantyl triflate24 at the bridgehead position is
fairly stable during the course of cationic ring-opening
polymerization of 2. This is supported by the unusual
stability of the nonplanar 1-adamantyl carbocation due
to the hyperconjugation effect through the rigid ada-
F igu r e 2. SEC curves of poly(2)s measured in 1,2-dichlo-
robenzene at 135 °C. Peak A: run 2, M/I ) 5.5, M
/M ) 1.30. Peak B: run 3, M/I ) 21, M
.43. Peak C: run 5, M/I ) 46, M ) 6000, M
n
) 1500,
M
1
w
n
n
) 3200, M
w
/M
n
)
n
w
/M
n
) 1.56.
mantane skeleton, as previously pointed out.2
5-27
In
addition, 1,2-elimination of the 1-adamantyl cation is
strongly prevented because the resulting alkene, ada-
2
8-30
mantene, is highly distorted,
if produced.
The TGA analysis of poly(1) and poly(2) showed 10%
weight loss at 421 and 486 °C under nitrogen, respec-

Macromolecules, Vol. 37, No. 19, 2004
Communications to the Editor 7071
(16) Selected data for 2: 1H NMR (C6D6, 300 MHz): 0.89 (t, J )
tively. It is certain that this high thermal stability of
both aliphatic polymers derives from the strain-free
adamantane skeletons and the stable carbon-carbon
bond between two bulky adamantane rings.
In conclusion, we have successfully synthesized a new
all-hydrocarbon poly(propellane), poly(5-butyl-1,3-ada-
mantane), showing good solubility and thermal stability
via the cationic ring-opening polymerization of 5-butyl-
7
.1 Hz, 3H, CaH3), 1.09-1.29 (m, 10H, CH2CH2CH2CH3, one
of C4H2, one of C8H2, one of C9H2, one of C10H2), 1.63 (s,
H, C6H2), 1.73 (d, J ) 10.4 Hz, one of C4H2 and one of
C9H2), 1.86 (d, J ) 10.4 Hz, 2H, one of C8H2 and one of
2
1
3
C10H2), 1.97-2.05 (2d, 2H, C2H2), 2.81 (s, 1H, C7H).
C
NMR (C6D6, 75 MHz): 14.4 (Ca), 24.2 (Cb), 27.8 (Cc), 36.1
(
(
C1, C3), 37.8 (Cd), 42.6 (C6), 45.3 (C8, C10), 48.1 (C-2), 49.8
C4, C9), 53.5 (C7), 64.4 (C5).
(
17) 1-Acetoxyadamantanes, 1,3-adducts of acetic acid, and un-
reacted 1 or 2 were observed in the reaction mixture after
quenching the polymerization with acetic acid.
1
,3-dehydroadamantane. A detailed investigation on the
polymerizability and the polymerization behavior of 1,3-
dehydroadamantanes is now in progress.
(18) Even tetramer of adamantane is hardly soluble in any
organic solvent. See ref 15.
(
19) Selected data for poly(1) obtained by cationic polymeriza-
tion: IR (KBr): 2926, 2903, and 2852 (C-H), 1449 and 1348
Ack n ow led gm en t. This work was supported by
Tokuyama Foundation and by a Grant-in-Aid (No.
4550833) from the Ministry of Education, Science,
-1
cm (C-H). Anal. calcd for (C10H14)n: C, 89.49; H; 10.51;
1
found: C, 84.08; H, 9.98.
Sports, and Culture, J apan. We thank Professor Takeshi
Shiono and his research group for the high temperature
SEC measurement.
(20) Although the poly(2)s with Mns lower than 2000 were readily
soluble in THF, the poly(2)s having higher Mn values
became partially insoluble in THF but completely soluble
in 1,2-dichlorobenzene at 80 °C.
(
21) Selected data for poly(2): 1H NMR (1,2-dichlorobenzene/
C D , ) 10/1, 300 MHz): 0.93 (bs, 3H, CH ), 1.2-1.6 (m,
Refer en ces a n d Notes
6
6
3
1
8H, CH2CH2CH2CH3, C2H2, C4H2, C6H2, C8H2, C9H2,
(
(
(
1) Wiberg, K. B.; Walker, F. H. J . Am. Chem. Soc. 1982, 104,
239.
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976, 41, 2711.
13
C10H2), 2.16 (bs, 1H, C7H); C NMR (1,2-dichlorobenzene/
5
C6D6, ) 10/1, 75 MHz): 14.2 (Ca), 24.1 (Cb), 25.3 (Cc), 30.6
(
C7), 34.0 (overlapped, C2 and C5), 35.7 (C8, C10) 38.5 (C1,
7
C3), 41.4 (C4, C9), 42.4 (C6), 45.3 (Cd). IR (KBr): 2926 and
2
(
-1
854 (C-H), 1453, and 1348 cm (C-H). Anal. calcd for
1
C14H22)n: C, 88.35; H; 11.65; found: C, 87.17; H, 11.47.
(
(
(
(
4) Wiberg, K. B. Acc. Chem. Res. 1984, 17, 379.
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(
(
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23) Unpublished result. The molecular weight of poly(2) was
independently estimated by the comparison with a series
of oligo(5-butyl-1,3-adamantane)s synthesized by the Wurtz-
type coupling reaction of 3-butyl-1-bromoadamantane or
(
(
8) Schl u¨ ter, A.-D. Angew. Chem., Int. Ed. Engl. 1988, 27, 296.
9) Schl u¨ ter, A.-D. Macromolecules 1988, 21, 1208.
5
,5′-dibutyl-3-dibromo-1,1′-biadamantane.
(
(
(
24) Takeuchi, K.; Moriyama, T.; Kinoshita, T.; Tachino, H.;
(
(
(
(
(
10) Pincock, R. E.; Schmidt, J .; Scott, W. B.; Torupka, E. J . Can.
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2
040.
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1
13) The framework of poly(1,3-adamantane)s can be involved
in the diamond lattice, as previously shown in ref 14.
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synthetic route, insoluble poly(1,3-adamantane) was simi-
larly obtained by the Wurtz-type coupling reaction of 3,3′-
dibromo-1,1′-biadamantane with sodium in xylene.
(27) Takeuchi, K.; Okazaki, T.; Kitagawa, T.; Ushino, T.; Ueda,
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(
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(
30) Conlin, R. T.; Miller, R. D.; Michl, J . J . Am. Chem. Soc. 1979,
1
01, 7637.
MA048925C