Formation of alternating copolymers via spontaneous copolymerization of 1,3-dehydroadamantane with electron-deficient vinyl monomers

Article abstract of DOI:10.1021/ja062157i

Copolymerizations of 1,3-dehydroadamantane, 1, and various vinyl monomers were carried out in THF at room temperature. On mixing 1 with electron-deficient vinyl monomers, such as acrylonitrile and methyl acrylate, in the absence of any initiator, the copolymerization spontaneously proceeded to give alternating copolymers in 28-88% yield. By contrast, no reaction of 1 occurred at all when isobutyl vinyl ether or styrene was mixed under similar conditions. These contrastive results indicate the high electron density of a central σ-bond in a strained [3.3.1]propellane derivative, 1. Alternating sequences of the resulting copolymers were characterized by NMR and MALDI-TOF-MS measurements. DSC and TGA measurements revealed the high thermal stability of the alternating copolymers containing bulky, stiff, and strain-free adamantane skeletons. Copyright

Full text of DOI:10.1021/ja062157i

Published on Web 06/15/2006
Formation of Alternating Copolymers via Spontaneous Copolymerization of
1,3-Dehydroadamantane with Electron-Deficient Vinyl Monomers
Shin-ichi Matsuoka, Naoto Ogiwara, and Takashi Ishizone*
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1-H-119, Ohokayama,
Meguro-ku, Tokyo 152-8552, Japan
Received March 30, 2006; E-mail: tishizon@polymer.titech.ac.jp
1
Highly strained small ring propellanes, such as [1.1.1]-,
Scheme 1
2
3
[
2.2.2]-, and [2.2.1]propellanes, readily afford the ring-opening
4
products with various substrates since the σ-bonds between the
bridgehead carbons with inverted tetrahedral geometry are highly
reactive. However, study of the ring-opening polymerization of
propellanes has been very limited probably due to their low
stability1 and synthetic difficulty. Only anionic and radical ring-
opening polymerizations of [1.1.1]propellane derivatives were
investigated to afford poly(propellane)s. Interestingly, the spontane-
ous copolymerization of [1.1.1]propellanes and electron-deficient
-4
5
6
7
Table 1. Copolymerization of 1 with Comonomers in THF at
Room Temperature
a
contentb
[
1]
0
time
h
yield
%
10-
3
M
c
d
run
comonomer
mol %
mol %
n
g
T °C
8
monomers proceeded to give alternating copolymers.
1
1
2
3
4
5
6
7
8
9
IBVE
St
45
49
15
51
51
51
51
80
17
48
77
24
24
24
0.5
3
0
0
,3-Dehydroadamantane,4 1, is a typical [3.3.1]propellane
,9
AN
AN
AN
AN
AN
AN
MA
MA
MA
52
28
58
62
62
30
88
58
34
35
49
49
49
49
51
28
40
49
6.0
23
17
9.4
8.8
18
8.0
9.4
9.0
161
231
226
226
222
217
86
derivative showing high reactivity toward free-radical and electro-
philic ring-opening reactions with oxygen, bromine, and acetic acid
to produce 1,3-disubstituted adamantanes. Recently, we have first
demonstrated that the cationic and free-radical ring-opening po-
lymerization of 1 or 5-butyl-1,3-dehydroadamantane (2) proceeds
via breaking of the 1,3-propellane linkage to afford the poly(1,3-
adamantane)s showing high thermal stability.10 Interestingly, the
polymerizabilities of 1 and 2 largely differ from those of [1.1.1]-
8
24
24
24
24
24
1
1
0
1
129
143
a
Initial mol % of 1 in the reaction mixture. b Ad content in the resulting
propellanes under the various reaction conditions. For example, the
1.1.1]propellanes readily undergo the anionic polymerization, but
1
6
copolymer measured by elemental analysis (runs 3-8) or H NMR (runs
[
9
-11). c Estimated by RALLS-SEC measurement. d Measured by DSC.
no reaction of 1 and 2 occurred with strong nucleophiles, such as
n-BuLi and Grignard reagent. These findings clearly show much
higher electron densities of bridgehead C-C bonds in 1 and 2
compared to those in the [1.1.1]propellanes. Herein, we newly report
the spontaneous crossover reaction between 1 and electron-deficient
vinyl monomers, such as acrylonitrile (AN) and methyl acrylate
soluble in various organic solvents, including chloroform and THF,
indicating that the structure of the copolymer is quite different from
those of both homopolymers. The composition of the copolymer
was measured by elemental analysis for 3 and by H NMR for 4,
respectively. The molecular weights of the copolymers were
determined by the RALLS-SEC measurement with RI, LS, and
n
viscosity detectors in THF, and the M values ranged from 6000 to
23 000. The SEC curves of 3 and 4 were unimodal, and the M
values were 1.6-2.9.
1
(
MA), leading to novel alternating copolymers containing bulky
and stiff adamantane (Ad) moieties, as shown in Scheme 1.
Monomer 1 was synthesized in 81% yield by the reaction of
,3-dibromoadamantane with lithium in THF.10 Although 1 was
stable in a sealed tube in C D at least for 2 years, it spontaneously
6 6
w n
/M
1
Table 1 summarizes the result of copolymerization of 1. When
we mixed 1 and AN at 1:1 molar ratio (runs 4-7), the yield of the
copolymer increased with polymerization time and reached ca. 60%
after 8 h. No apparent copolymerization further proceeded even
after 24 h. Interestingly, the Ad content in each copolymer was
constant and almost 50%. When the reaction of 1 with AN was
carried out with a molar ratio of 15:85 (run 3), the copolymer with
reacted with oxygen to give a copolymeric product having C-O-
O-C linkage. We therefore treated 1 under argon and carried out
the polymerization in an all-glass apparatus under high vacuum
conditions using break-seal technique.
9
We attempted to react 1 with 1 equiv of various vinyl monomers
showing different polymerizability, as shown in Table 1. The
reaction was performed in THF at room temperature for 24 h. In
the cases of isobutyl vinyl ether (IBVE) and styrene (St), no reaction
occurred with 1 at all to result in a quantitative recovery of the
starting comonomers. In contrast, the monomers having electron-
withdrawing groups, AN and MA, underwent the spontaneous
copolymerizations with 1 to give the corresponding copolymers, 3
and 4, in 28-88% yield under identical conditions. The copolym-
erization proceeded homogeneously and in the absence of initiator.
3
5% Ad unit was obtained in 52% yield.13 This means that most
of 1 is incorporated with AN to form the copolymer. On the other
hand, even when 4-fold 1 was reacted with AN (run 8), the resulting
copolymer was composed of only 51 mol % of the Ad moiety.
Using MA as a comonomer, similar copolymerization behavior was
observed. These results clearly indicate the lower homopolymer-
izability of 1 compared with that of AN and MA. The observed
polymerization behavior suggests that the resulting copolymers have
strongly alternating tendency. Then, we thoroughly characterized
the chemical structure of the resulting copolymers containing 50
11
After termination with acetic acid, the polymer was obtained by
precipitating the reaction mixture into methanol. In contrast to
1
0,12
homopolymers of 1
and AN, the resulting copolymers were
8708
9
J. AM. CHEM. SOC. 2006, 128, 8708-8709
10.1021/ja062157i CCC: $33.50 © 2006 American Chemical Society

C O M M U N I C A T I O N S
are corresponding to the copolymers containing one more 1 unit
for series B and one more AN unit for series C. To our best
knowledge, this MALDI-TOF-MS analysis is the first experimental
evidence to prove the chain-growth process of spontaneous copo-
lymerization not the step-growth process.
The glass transition temperatures (T
by DSC increased with the content of Ad skeleton and M
the copolymers. The T values of 3 and 4 were 231 and 143 °C,
respectively. These observed values were ca. 130 °C higher than
g
) of copolymers measured
n
value of
g
1
6
those of poly(AN) (T
TGA analysis of 3 and 4 showed 10% weight loss at 451 and 467
C under nitrogen, respectively. These were much higher than those
g
) 95 °C) and poly(MA) (T
g
) 10 °C).
°
Figure 1. 13C NMR spectra of 3 (run 8) in CDCl3.
16
of homopolymers of AN (T10 ) 296 °C) and MA (T10 ) 340 °C).
In conclusion, [3.3.1]propellane 1 is newly proved to be a
versatile monomer to produce novel alternating copolymers con-
taining bulky, strain-free, and thermally stable adamantane-1,3-diyl
moieties on mixing with the polar monomers, such as AN or MA.
The preliminary experiment in the presence of a chain transfer
reagent suggests that a 1,5-diradical species (Scheme 1) is a
plausible intermediate formed at the initial stage of spontaneous
copolymerization.17 The following highly selective cross propaga-
tion between 1 and electron-deficient monomers might successively
proceed to form the corresponding alternating copolymers.
Acknowledgment. This work was supported by a Grant-in-Aid
(No. 14550833) from the Ministry of Education, Science, Sports,
and Culture, Japan. The authors thank Prof. H. K. Hall, Jr. at The
University of Arizona for his insightful suggestions.
Supporting Information Available: Experimental procedures and
characterization data (PDF). This material is available free of charge
via the Internet at http://pubs.acs.org.
Figure 2. MALDI-TOF-MS of 3 (run 8).
mol % of Ad units, by 1H and 13C NMR spectroscopies in
conjunction with MALDI-TOF-MS.
References
The H and 13C NMR spectra of 3 and 4 were completely
1
(
(
(
(
1) Wiberg, K. B.; Walker, F. H. J. Am. Chem. Soc. 1982, 104, 5239.
2) Eaton, P. E.; Temme, G. H., III. J. Am. Chem. Soc. 1973, 95, 7508.
3) Wiberg, K. B.; Bailey, W. F.; Jason, M. E. J. Org. Chem. 1976, 41, 2711.
4) (a) Wiberg, K. B. Acc. Chem. Res. 1984, 17, 379. (b) Wiberg, K. B. Chem.
ReV. 1989, 89, 975.
different from those of 1,1-biadamantane14 and poly(AN) or poly-
(
MA), indicating the highly alternating sequence and the lack of
1
3
homosequences. Figure 1 shows the C NMR spectrum of 3. In
the aliphatic region between 28 and 45 ppm, it reveals the set of
nine signal groups expected for the repeating unit of alternating
copolymer 3 along with the sharp nitrile signal at 122.2 ppm. All
(5) (a) Semmler, K.; Szeimies, G.; Belzner, J. J. Am. Chem. Soc. 1985, 107,
6410. (b) Lynch, K. M.; Dailey, W. P. J. Org. Chem. 1995, 60, 4666.
(6) (a) Schl u¨ ter, A.-D. Angew. Chem., Int. Ed. Engl. 1988, 27, 296. (b)
Schl u¨ ter, A.-D. Macromolecules 1988, 21, 1208.
1
1
1
13
(7) Kaszynski, P.; Michl, J. J. Am. Chem. Soc. 1988, 110, 5225.
the signals can be assigned by the H- H, H- C, and DEPT pulse
sequences and by comparison with several authentic compounds,
such as 1,3-dimethyladamantane and 1,3-dibutyladamantane.12 Since
two sharp signals assigned to the quaternary carbons of the Ad
ring in the main chain are observed at 33.5 and 36.0 ppm, only the
central 1,3-linkage of 1 should be exclusively opened to participate
in the polymerization. The simplicity of the spectrum indicates not
only the alternating sequence but also the highly regulated head-
to-tail linkage of 3. Nevertheless, several methylene carbons on
the Ad skeleton are split probably due to the two diads, syn and
anti, derived from newly formed centers of asymmetry along with
the main chain.
(
8) (a) Bothe, H.; Schl u¨ ter, A.-D. Makromol. Chem., Rapid Commun. 1988,
9, 529. (b) Sreenivasulu Reddy, V.; Ramireddy, C.; Qun, A.; Munk, P.
Macromolecules 1991, 24, 3973.
(9) (a) Pincock, R. E.; Schmidt, J.; Scott, W. B.; Torupka, E. J. Can. J. Chem.
1972, 50, 3958. (b) Scott, W. B.; Pincock, R. E. J. Am. Chem. Soc. 1973,
9
5, 2040. (c) No, B. I.; Butov, G. M.; Mokhov, V. M.; Solomon, O. G.
Russ. J. Gen. Chem. 1998, 68, 1224.
(10) Ishizone, T.; Matsuoka, S.; Sakai, S.; Harada, W.; Tajima, H. Macro-
molecules 2004, 37, 7069.
(
(
(
(
11) 1-Acetoxyadamantane, 1,3-adduct of acetic acid and unreacted 1, was
recovered from the reaction mixture after quenching the polymerization.
12) Ishizone, T.; Tajima, H.; Matsuoka, S.; Nakahama, S. Tetrahedron Lett.
2001, 42, 8645.
13
13) C NMR spectrum revealed that the copolymer (run 3) was not perfectly
alternating and unequivocally contained an oligo(AN) sequence.
14) Ishizone, T.; Tajima, H.; Torimae, H.; Nakahama, S. Macromol. Chem.
Phys. 2002, 203, 2375.
The MALDI-TOF-MS of 3 also supports the chemical structure
of an alternating copolymer derived from 1 and AN, as shown in
Figure 2. Three series of signals (A, B, and C) with the intervals
of 187.28 Da are clearly observed between 1000 and 5000 mass/
charge region.15 This strongly shows that there are three series of
copolymers having the same repeating units, and the observed
intervals are corresponding to a total mass (187.28 Da) of 1 and
AN. If the strongest series of signals (series A) contain the same
number of comonomer units, the other two minor series of signals
(15) It was very difficult to analyze the MALDI-TOF-MS of 3 and 4
presumably due to their low ionization tendency. In fact, Figure 2 only
shows the low molecular weight fractions of copolymer 3 (run 8). We
consider that three series of copolymers possess the same terminal
structures with ca. 95 Da, which is almost consistent with a total mass of
sodium and THF, although the terminal structures of copolymers have
not been identified yet.
(
16) No glass transition behavior was observed for poly(1) before thermal
degradation around 300 °C (T10 ) 480 °C).
(17) For reviews, see: (a) Hall, H. K., Jr.; Padias, A. B. Acc. Chem. Res. 1990,
23, 3. (b) Hall, H. K., Jr.; Padias, A. B. Acc. Chem. Res. 1997, 30, 322.
JA062157I
J. AM. CHEM. SOC.
9
VOL. 128, NO. 27, 2006 8709