Crystal Structures and Topochemical Polymerizations of 7,7,8,8-Tetrakis(alkoxycarbonyl)quinodimethanes

Article abstract of DOI:10.1021/ja0386086

Highly conjugated monomers, 7,7,8,8-tetrakis(alkoxycarbonyl) quinodimethanes (methoxy (1a), ethoxy (1b), isopropoxy (1c), benzyloxy (1d), chloroethoxy (1e), and bromoethoxy (1f)), were synthesized. Recrystallizations of 1a, 1c, 1e, and 1f yielded two crystal forms (prisms (1a-A) and needles (1a-B), needles (1c-A) and plates (1c-B), prisms (1e-A) and plates (1e-B), and prisms (1f-A) and needles (1f-B)), which have different molecular packing modes by X-ray crystal structure analysis, indicating that the crystals are polymorphic. In the photopolymerizations of these monomer crystals in the solid state, 1a-A, 1e-A, and 1f-A polymerized topochemically to give crystalline polymers. For their thermal polymerizations in the solid state, in addition to 1a-A, 1e-A, and 1f-A, 1e-B and 1f-B polymerized, but polymers formed from the 1e-B and 1f-B were amorphous. The packing of quinodimethane molecules in the crystals was defined by four kinds of parameters, stacking distance (d _s), the distance between the reacting exomethylene carbon atoms (d_cc), the angles formed between the stacking axis and longer axis of the monomer molecule (θ₁), and the shorter axis of the monomer molecule (θ₂), and then the polymerization reactivity of these quinodimethanes in the solid state was discussed on the basis of these parameters.

Full text of DOI:10.1021/ja0386086

Published on Web 01/29/2004
Crystal Structures and Topochemical Polymerizations of
7,7,8,8-Tetrakis(alkoxycarbonyl)quinodimethanes
Shinji Nomura,† Takahito Itoh,*,† Hirofumi Nakasho,† Takahiro Uno,†
Masataka Kubo,† Kazuki Sada,‡ Katsunari Inoue,§ and Mikiji Miyata§
Contribution from the Department of Chemistry for Materials, Faculty of Engineering, Mie
UniVersity, 1515 Kamihama-cho, Tsu-shi, Mie 514-8507, Japan, Department of Chemistry and
Biochemistry, Graduate School of Engineering, Kyushu UniVersity, 6-10-1 Hakozaki, Higashi-ku,
Fukuoka 630-8528, Japan, and Department of Material and Life Science, Graduate School of
Engineering, Osaka UniVersity and Handai FRC, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
Received September 19, 2003; E-mail: itoh@chem.mie-u.ac.jp.
Abstract: Highly conjugated monomers, 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes (methoxy (1a),
ethoxy (1b), isopropoxy (1c), benzyloxy (1d), chloroethoxy (1e), and bromoethoxy (1f)), were synthesized.
Recrystallizations of 1a, 1c, 1e, and 1f yielded two crystal forms (prisms (1a-A) and needles (1a-B),
needles (1c-A) and plates (1c-B), prisms (1e-A) and plates (1e-B), and prisms (1f-A) and needles
(1f-B)), which have different molecular packing modes by X-ray crystal structure analysis, indicating that
the crystals are polymorphic. In the photopolymerizations of these monomer crystals in the solid state,
1a-A, 1e-A, and 1f-A polymerized topochemically to give crystalline polymers. For their thermal
polymerizations in the solid state, in addition to 1a-A, 1e-A, and 1f-A, 1e-B and 1f-B polymerized, but
polymers formed from the 1e-B and 1f-B were amorphous. The packing of quinodimethane molecules
in the crystals was defined by four kinds of parameters, stacking distance (ds), the distance between the
reacting exomethylene carbon atoms (dcc), the angles formed between the stacking axis and longer axis
of the monomer molecule (θ1), and the shorter axis of the monomer molecule (θ2), and then the
polymerization reactivity of these quinodimethanes in the solid state was discussed on the basis of these
parameters.
compounds,2 diacetylene derivatives,3 triene and triacetylene
derivatives,4 and muconic acid and sorbic acid derivatives5 have
Introduction
Since primary structures of polymers such as stereoregularity,
regioselectivity, molecular weight, molecular weight distribution,
chain-end structures, and branching greatly influence physical
properties, their control has been attracting much attention in
polymer chemistry. Recent advances in “living polymerization”
and “stereospecific polymerization” enable one to control
primary structures precisely. Stereoregularity and regioselectivity
have been achieved in the presence of catalysts, which has
interaction with monomer or growing chain-end in solutions.1
Another approach to control polymer structures is utility of
regularity of monomer arrangements in the crystalline state
because positions and orientations of the monomers do not
change and motion of monomer is strongly limited. When the
polymerization progresses without moving the center of gravity
of the monomer in the crystal state, stereoregularity and
regioselectivity ought to be controlled automatically. They are
called as topochemical polymerizations. Despite high reactivi-
ties, stereoregularity, and regioselectivity, a limited number of
monomers such as 2,5-distyrylpyradine derivatives and related
(2) (a) Hasegawa, M. Chem. ReV. 1983, 83, 507-518. (b) Hasegawa, M. AdV.
Phys. Org. Chem. 1995, 30, 117-171.
(3) (a) Wegner, G. Z. Naturforsch. B 1969, 24, 824-832. (b) Wenger, G. Pure
Appl. Chem. 1977, 49, 443-454. (c) Enkelmann, V. AdV. Polym. Sci. 1984,
63, 91-131. (d) Ogawa, T. Prog. Polym. Sci. 1995, 20, 943-985. (e)
Huntsman W. D. In The Chemistry of Functional Groups. Supplement C:
The Chemistry of Triple-Bonded Functional Groups; Patai, S., Rappoport,
Z., Eds.; John Wiley & Sons: New York, 1983; Chapter 22. (f) Okada, S.;
Matsuda, H.; Nakanishi, H. In Polymeric Materials Encyclopedia; Sala-
mone, J. C., Ed.; CRC Press: Boca Raton, 1996; pp 8393-8398. (g) Bloor,
D.; Chance, R. R. Polydiacetylenes; NATO ASI Series E, Applied Sciences
No. 102.; Martinus Nijhoff: Dorddrecht, 1985.
(4) (a) Kiji, J.; Kaiser, J.; Wegner, J. G.; Schulz, R. C. Polymer 1973, 14,
433-439. (b) Enkelmann, V. Chem. Mater. 1994, 6, 1337-1340. (c) Xiao,
J.; Yang, M.; Lauher, J. W.; Fowler, F. W. Angew. Chem., Int. Ed. 2000,
39, 2132-2135. (d) Hoang, T.; Lauher, J. W.; Fowler, F. W. J. Am. Chem.
Soc. 2002, 124, 10656-10657.
(5) (a) Matsumoto, A.; Matsumura, T.; Aoki, S. Macromolecules 1996, 29,
423-432. (b) Matsumoto, A.; Yokoi, K.; Aoki, S.; Tashiro, K.; Kamae,
T.; Kobayashi, M. Macromolecules 1998, 31, 2129-2136. (c) Matsumoto,
A.; Odani, T.; Chikada, M.; Sada, K.; Miyata, M. J. Am. Chem. Soc. 1999,
121, 11122-11129. (d) Matsumoto, A.; Nagahama, S.; Odani, T. J. Am.
Chem. Soc. 2000, 122, 9109-9119. (e) Odani, T.; Matsumoto, A.
Macromol. Rapid Commun. 2000, 21, 40-44. (f) Matsumoto, A.; Katayama,
K.; Odani, T.; Oka, K.; Tashiro, K.; Saragai, S.; Nakamoto, S. Macromol-
ecules 2000, 33, 7786-7792. (g) Nagahama, S.; Matsumoto, A. J. Am.
Chem. Soc. 2001, 123, 12176-12181. (h) Matsumoto, A.; Odani, T.
Macromol. Rapid Commun. 2001, 22, 1195-1215. (i) Matsumoto, A.; Sada,
K.; Tashiro, K.; Miyata, M.; Tsubouchi, T.; Tanaka, T.; Odani, T.;
Nagahama, S.; Tanaka, T.; Inoue, K.; Saragai, S.; Nakamoto, S. Angew.
Chem., Int. Ed. 2002, 41, 2502-2505. (j) Matsumoto, A.; Tanaka, T.;
Tsubouchi, T.; Tashiro, K.; Saragai, S.; Nakamoto, S. J. Am. Chem. Soc.
2002, 124, 8891-8902. (k) Tanaka, T.; Matsumoto, A. J. Am. Chem. Soc.
2002, 124, 9676-9677.
* Corresponding author. Phone: +81-59-231-9410. Fax: +81-59-231-
9410.
† Mie University.
‡ Kyushu University.
§ Osaka University and Handai FRC.
(1) Okamoto, Y.; Nakano, T. Chem. ReV. 1994, 94, 349-372.
9
10.1021/ja0386086 CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 2035-2041
2035

A R T I C L E S
Nomura et al.
Table 1. Photopolymerizations of 1a-f in the Solid State
Scheme 1
run monomer crystal temp. (°C) time (h)
form
conv. (%)
M
n
1
2
3
4
5
6
7
8
9
1a-A
1a-B
1b
1c-A
1c-B
1d
1e-A
1e-B
1f-A
1f-B
30
30
30
30
30
30
30
30
30
30
3
6
24
24
24
24
3
24
0.5
24
off-white prism
>99
NDa
0
0
0
0
0
>99
0
ivory prism
orange plate
NDa
NDa
>99
0
10
a Not determined (insoluble in common organic solvents).
Scheme 2
been reported to undergo topochemical polymerizations, because
they have strict requirement of the monomer arrangements in
crystalline state. Recently, we reported as a preliminary result
that a conjugated monomer, 7,7,8,8-tetrakis(methoxycarbonyl)-
quinodimethane (1a), gave two crystal forms (prisms and
needles) and exhibited drastic differences in the polymerization
ability observed between them. That is, the prisms polymerized
topochemically but the needles did not, arising from the
difference in the packing modes.6 Here, to establish general rules
in the topochemical polymerizations, it is worthwhile to clarify
the relation between crystal structures of quinodimethane
monomers and their solid-state polymerization reactivities by
using various quinodimethane monomers. In this work, we
describe the syntheses of 7,7,8,8-tetrakis(alkoxycarbonyl)-
quinodimethanes bearing various alkoxy groups and determi-
nation of their crystal structures by X-ray crystal analysis and
also discuss the relationship of the solid-state polymerization
reactivity with the packing in the crystals.
chloroform/hexane (2/3 v/v) and 1e-B from chloroform/hexane
(3/2 v/v), and 1f-A from chloroform and 1f-B from chloro-
form/ hexane (1/2 v/v). Both 1b and 1d gave only one crystal
form (yellow needles) under the all attempted recrystallization
conditions.
Solid-State Polymerization. Monomer crystals were each
subjected to polymerization by irradiation using a high-pressure
Hg lamp at 30 °C, and the results are summarized in Table 1.
1a-A, 1e-A, and 1f-A polymerized to give the corresponding
polymers as crystal-like solids, which were insoluble in common
organic solvents such as chloroform, benzene, tetrahydrofuran
(THF), dimethyl sulfoxide, N,N-dimethylformamide, methanol,
and hexane. While no polymerizations occurred for 1a-B, 1b,
1c-A, 1c-B, 1d, 1e-B, and 1f-B, and unreacted monomers
were recovered quantitatively. The resulting polymers of 1a-
A, 1e-A, and 1f-A were only characterized by IR spectroscopy
and elemental analysis because of their insolubilities in these
organic solvents. In the IR spectra of polymers from 1a-A,
1e-A, and 1f-A, characteristic absorption bands at 1533-1546
cm-1 assigned to the exocyclic conjugated carbon-carbon
double bond of the quinodimethane monomers disappeared, and
the new bands arising from carbon-carbon double bonds of
the aromatic ring were observed at ca. 1500, 1400 cm-1, and a
band arising from out-of-plane deformation of the para-
substituted benzene, characteristic of a two-adjacent-hydrogen
system, was observed at ca. 800 cm-1. These spectrum changes
observed in the solid-state polymerizations of 1a-A, 1e-A,
and 1f-A strongly support that polymerization reactions of
substituted quinodimethane molecules take place at the disub-
stituted exomethylene carbon atoms with the formation of the
corresponding stable aromatic structures.8 Moreover, elemental
analysis values of the products were in good agreement with
the calculated ones for the corresponding polymers. Therefore,
the photopolymerizations in the crystalline state proceed in the
same manner as those in the conventional polymerizations in
solution, as shown in Scheme 2.
Results and Discussion
Monomer Synthesis and Recrystallization. Monomers (1a-
f) were synthesized by a synthetic route as shown in Scheme
1. Knoevenagel condensations of 1,4-cyclohexanedione and
corresponding dialkyl malonates using titanium tetrachloride and
pyridine as a dehydrating reagent7 afforded 1,4-[bis(alkoxycar-
bonyl)methylene]cyclohexanes (2a-f) (42-68% yields). Oxida-
tion of 2a-f with activated manganese dioxide in refluxing
benzene gave 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes
(1a-f) (16-37% yields). All monomers were identified by 1H
and 13C NMR and IR spectroscopies and elemental analysis.
Those monomers were recrystallized from various conditions
to obtain fine crystals for polymerization and single crystals
suitable for X-ray crystallography. Recrystallizations of 1a, 1c,
1e, and 1f from hexane gave a mixture of two crystal forms,
yellow prisms (1a-A) and yellow needles (1a-B) for 1a,
yellow needles (1c-A) and pale yellow plates (1c-B) for 1c,
yellow prisms (1e-A) and pale yellow plates (1e-B) for 1e,
and yellow prisms (1f-A) and yellow needles (1f-B) for 1f,
indicating that they have polymorphism. After many trials of
screening of recrystallization conditions such as solvents, con-
centrations, and temperature, we found the conditions that gave
one of two polymorphs exclusively for 1a, 1c, 1e, and 1f; 1a-A
from chloroform/hexane (1/3 v/v) and 1a-B from methanol,
1c-A from hexane at high concentration (250 mg/40 mL) and
1c-B at low concentration (160 mg/40 mL), 1e-A from
On the other hand, we tried thermal polymerizations of these
monomer crystals by heating in the dark at a temperature 10
°C lower than each melting point, and the results are summarized
(8) (a) Iwatsuki, S.; Itoh, T. Macromolecules 1980, 13, 983-989. (b) Iwatsuki,
S.; Itoh, T.; Yokotani, I. Macromolecules 1983, 16, 1817-1823. (c)
Iwatsuki, S.; Itoh, T.; Iwai, T.; Sawada, H. Macromolecules 1985, 18,
2726-2732. (d) Itoh, T.; Okano, H.; Hishida, T.; Inokuchi, A.; Kamei, N.;
Sato, T.; Kubo, M.; Iwatsuki, S. Tetrahedron 1997, 53, 15247-15261. (e)
Itoh, T.; Iwatsuki S. Macromol. Chem. Phys. 1997, 198, 1997-2016. (f)
Itoh, T. Prog. Polym. Sci. 2001, 26, 1019-1059.
(6) Itoh, T.; Nomura, S.; Uno, T.; Kubo, M.; Sada, K.; Miyata, M. Angew.
Chem., Int. Ed. 2002, 41, 4306-4309.
(7) Lehnert, W. Tetrahedron 1973, 29, 635-638.
9
2036 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004

7,7,8,8-Tetrakis(alkoxycarbonyl)quinodimethanes
A R T I C L E S
Figure 1. 13C NMR spectrum in chloroform-d of the polymer of 1e-B obtained by solid-state thermal polymerization.
Table 2. Thermal Polymerizations of 1a-f in the Solid State
run monomer crystal temp. (°C) time (h)
form
conv. (%)
M
n
11
12
13
14
15
16
17
18
19
20
21
22
1a-A
1a-B
1b
1c-A
1c-B
1d
60
60
60
100
90
60
90
105
60
120
60
60
3
6
off-white prism
47
0
0
0
0
NDa
24
24
24
24
24
24
24
15
87
0
1e-A
1e-B
1f-A
1f-B
1eb
ivory prism
yellow solid
orange plate
white solid
72
94
46
>99
21
2
NDa
15000
NDa
NDa
white powder
4100
3400
1fc
4 days white powder
a Not determined (insoluble in common organic solvents). b Solution
polymerization in toluene, 2.5 mL; 1e, 372 mg; AIBN, 6.0 mg. c Solution
polymerization in chloroform, 10 mL; 1f, 400 mg; AIBN, 10 mg.
in Table 2. In addition to photopolymerizable 1a-A, 1e-A,
and 1f-A, 1e-B and 1f-B were found to be polymerized by
heating. The polymer yields at the thermal polymerizations for
1a-A, 1e-A, and 1f-A were lower than those at the photo-
polymerizations. Thermal polymerizations of 1e-B at 105 °C
and of 1f-B at 120 °C gave the corresponding polymers as
yellow solids and a white one, respectively. The polymers of
1a-A, 1e-A, and 1f-A had the same solubilities as the
polymers obtained by the photopolymerizations. On the other
hand, the polymer of 1e-B was soluble in chloroform, THF,
and benzene but insoluble in methanol and hexane, and the
polymer of 1f-B was insoluble in common organic solvents
such as chloroform, THF, benzene, methanol, and hexane. For
all cases, solid-state thermal polymerization occurred; the IR
spectra of the polymers had similar changes to those produced
by photopolymerization. Here, the polymer of 1e-B was further
characterized by GPC and 13C NMR spectroscopy because of
its high solubility toward common organic solvents. The
number-average molecular weight (Mn) was determined to be
15 000, and the 13C NMR spectrum of the polymer of 1e-B is
shown in Figure 1, which was the same as that of the polymer
obtained by solution polymerization described below, supporting
the formation of the corresponding stable para-substituted
benzene structure by radical coupling reactions between the
exomethylene carbon atoms of the quinodimethane structure.
In this way, 1e-B and 1f-B showed different polymerization
behavior, depending upon the polymerization conditions; they
polymerized in the solid-state thermal polymerization conditions
but not in the photopolymerization conditions. Probably, in
Figure 2. Powder XRD patterns of (a) 1e-B, (b) 1e-A, (c) polymer of
1e-A obtained by photopolymerization, and (d) polymer of 1e obtained
by solution polymerization.
photopolymerization at temperatures as low as 30 °C, the motion
of the molecules in the crystals is significantly limited, but at
temperatures near each melting point, the molecules in the
crystals would be allowed to move into reaction because of
enhanced molecular motion. To compare the solid-state poly-
merization reactivity of 1e and 1f, their solution polymerizations
with AIBN as an initiator were carried out, and the results (run
21 and 22) are shown in Table 2. The molecular weights and
the polymer yields were lower in comparison with those in the
solid-state polymerization.
Crystallinity of Obtained Polymers. Polymers of 1a-A,
1e-A, and 1f-A obtained by photopolymerizations and solid-
state thermal polymerizations and also the polymer of 1f-B
by solid-state thermal polymerization were insoluble in common
organic solvents, and their shapes were similar to those of the
corresponding monomers. Thus, the crystallinity of the obtained
polymers was investigated by powder XRD. The powder XRD
patterns of monomers 1e-A, 1f-A, and 1f-B and the corre-
sponding polymers are shown in Figures 2 and 3, respectively
Very sharp diffraction patterns of the polymers obtained by
the photopolymerizations of 1e-A and 1f-A indicate that
9
J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004 2037

A R T I C L E S
Nomura et al.
Table 3. Crystallographic Data for Crystals of 7,7,8,8-Tetrakis(alkoxycarbonyl)quinodimethanes
monomer
1a−A
1a−B
1b
1c−A
1c−B
1d
1e−A
1e−B
1f−A
1f−B
formula
fw
crystal system
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C16H16O8
336.29
monoclinic triclinic
C16H16O8
336.29
C20H24O8
392.40
C24H32O8
448.51
C24H32O8
448.51
C40H32O8
640.68
C20H20Cl4O8 C20H20Cl4O8 C20H20Br4O8 C20H20Br4O8
530.19
530.19
monoclinic
707.99
triclinic
707.99
monoclinic
P21/c (#14)
4.9861(5)
30.653(2)
8.0969(5)
90
98.386(4)
90
1224.3(2)
2
orthorhombic monoclinic monoclinic monoclinic monoclinic
P21/n (#14) P1h (#2)
Iba2 (#45)
13.483(2)
21.392(3)
6.8956(9)
90
90
90
1988.9(5)
4
1.310
860
C2/c (#15)
24.60(1)
9.724(1)
10.864(2)
90
109.32(2)
90
2452(1)
4
C2/c (#15)
15.760(6)
8.4013(8)
19.395(2)
90
99.29(2)
90
2534.27
4
P21/c (#14) P21/c (#14) P21/c (#14) P1h (#2)
8.6787(7)
7.5719(7)
12.761(1)
90
105.193(2)
90
809.2(1)
2
1.380
8.6023(4)
8.889(2)
5.2870(6)
96.305(4)
105.636(5)
87.323(8)
386.87(9)
1
10.8775(8)
7.9949(3)
18.0881(9)
90
92.459(5)
90
1571.6(2
2
1.354
7.6460(5)
15.981(2)
10.006(1)
90
105.371(4)
90
11.934(3)
7.640(1)
12.737(2)
90
97.145(9)
90
6.9884(8)
7.7551(6)
12.177(1)
102.295(3)
97.575(3)
106.277(6)
605.92(10)
1
1178.9(2)
2
1152.3(4)
2
Z
F
calc, g/cm3
1.443
1711
1360
1.215
1774
1679
1.175
1922
1514
1.493
1.528
1.940
1.920
unique reflecns 1828
no. obsd reflens 1477
2652
2276
2099
2034
2063
2167
832
1713
1749
1871
1490
R1
0.046
0.062
0.072
0.053
0.053
0.056
0.051
0.109
0.103
0.070
R, Rw
0.106, 0.133 0.131, 0.183 0.291, 0.156 0.083, 0.117 0.076, 0.091 0.116, 0.151 0.090, 0.133 0.253, 0.267 0.151, 0.357 0.109, 0.196
GOF
2θmax, deg
temp, °C
1.27
55.0
25
1.82
54.9
25
1.56
136.3
23
1.67
51.2
-76
1.51
51.2
-76
1.86
136.3
-69
1.37
136.4
23
2.00
136.4
23
1.75
66.8
-80
1.49
136.4
23
were ca. 20 000. It is, therefore, considered that the insolubility
in common organic solvents for both polymers of 1e-A and
1f-A obtained by solid-state polymerization is due to their high
crystallinities and/or high molecular weights.
Crystal Structures and Polymerization Reactivity in the
Crystalline State. To clarify the packing modes of the mole-
cules in the crystals, we investigated the crystal structures by
X-ray crystallography systematically. Measurements were car-
ried out using the imaging plate diffractometer system, and dur-
ing measurements polymerizations of monomer crystals did not
take place. The crystallographic data of 1a-f are summarized
in Table 3, and their crystal structures are shown in Figure 4.
X-ray studies revealed differences of the crystal structures
of two polymorphs of 1a, 1c, 1e, and 1f. In the latter three
quinodimethanes, the polymorphisms are attributed to both the
conformational difference of the ester groups and the crystal
packings. Flexibilities of the alkyl chains and free rotation
between exomethylene and carbonyl groups give variations of
conformational isomerism. From the lattice parameters and the
crystal structures, there are no apparent robust structural motifs
in these compounds. However, the planar quinodimethane
moieties tend to stack along one axis to form columnar structures
as shown Figure 5.
Figure 3. Powder XRD patterns of (a) 1f-A, (b) polymer of 1f-A obtained
by photopolymerization, (c) 1f-B, and (d) polymer of 1f-B obtained by
solid-state thermal polymerization.
1e-A and 1f-A show no less crystallinity after completion of
the polymerizations. Further, 2θ of diffraction peaks arising from
crystalline polymers are in fairly good agreement with those of
the respective monomers. In particular, the powder XRD pattern
of polymer from the solid-state polymerization of 1e-A is
significantly different from that of polymer obtained from the
solution polymerization (run 21 in Table 2) of 1e in toluene
initiated by AIBN (Figure 2). Therefore, these points indicate
that the polymerizations of those crystals as well as 1a-A6
proceed topochemically. On the other hand, the broad diffraction
pattern of polymer from the solid-state thermal polymerization
of 1f-B indicates that 1f-B shows loss of crystallinity during
the polymerization (Figure 3). The crystalline polymers of 1e-A
and 1f-A obtained by photopolymerization and thermal
polymerization in the solid-state melted at 149-156 and 155-
164 °C, respectively. After melting, the solubility of both
polymers changed dramatically, and they became soluble in
The stacking manner in the columnar structure is affected
by the alkyl groups of the esters. Moreover, association modes
of the columns to 3D crystalline lattice are also changed by the
ester groups. Therefore, the alkyl groups induce the change of
monomer packing as well as polymerization reactivity in the
crystalline state.
To discuss molecular arrangements of quinodimethanes in
the crystal structures in relation to the solid-state polymerization
reactivities, we investigated the stacking manners in the colum-
nar structures by using structural parameters (ds, dcc, θ1, and
θ2). They are used by estimation of the stacking manner for
diene monomers, because the quinodimethane monomers have
planar structures similar to diene monomers.5i We examined
these parameters defined as the angles formed between the stack-
ing axis and longer axis of the monomer molecule (θ1) and the
shorter axis of the monomer molecule (θ2), the distance between
equivalent atoms in the stacked monomers (stacking distance,
ds), and the distance between the reacting exomethylene carbons
1
chloroform, THF, and benzene. Also, their H NMR and 13C
NMR spectra were the same as those of the polymers obtained
by their solution polymerizations, and their molecular weights
9
2038 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004

7,7,8,8-Tetrakis(alkoxycarbonyl)quinodimethanes
A R T I C L E S
Figure 4. Crystal structures of the quinodimethane monomers: (a) 1a-A, (b) 1a-B, (c) 1b, (d) 1c-A, (e) 1c-B, (f) 1d, (g) 1e-A, (h) 1e-B, (i) 1f-A,
and (j) 1f-B. Hydrogen atoms are omitted for clarity. Open and filled circles represent carbon and oxygen atoms, respectively.
Table 4. Stacking Parameters for Crystals of 1a-fa
monomer
θ1 (deg)
θ2 (deg)
d (Å)
s
dcc (Å)
1a-A
1a-B
1b
1c-A
1c-B
1d
30
55
90
46
49
60
43
32
40
50
33
56
89
62
90
74
41
72
47
83
70
52
89
65
7.6
5.3
3.4
5.4
8.9
9.9
3.9
5.0
4.3
4.4
6.8
7.7
Figure 5. Stacking model for the quinodimethane monomers in the crystals,
and the definition of stacking parameters for the prediction of the
topochemicalpolymerization reactivity. ds is the stacking distance between
the adjacent monomers in a column; dcc is the distance between the reacting
exomethylene carbons; θ1 and θ2 are the angles between the stacking axis
and longer axis of the monomer molecule and the shorter axis of the
molecule.
1e-A
1e-B
7.6
7.4
4.2
5.2
1f-A
1f-B
7.0
5.0
3.8
5.0
a θ1, θ2, tilt angles of the molecular palne; dcc, distance between the
reacting exomethylene carbons; ds, stacking distance.
(dcc). The parameters of 1a-f are summarized in Table 4, and
the columns in the crystal structures are shown in Figure 6.
On the basis of stacking manners of the columnar structures,
the crystal structures are divided into several groups: (i) the
stacking axis is perpendicular to the molecular plane of the
quinodimethane, that is, both the tilt angles (θ1 and θ2) are 90°
for 1b, (ii) the stacking axis is tilted to the direction of the longer
molecular axis (θ1 * 90°) and not to that of the shorter
9
J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004 2039

A R T I C L E S
Nomura et al.
Figure 6. Columnar stackings of the quinodimethane monomers: (a) 1a-A, (b) 1a-B, (c) 1b, (d) 1c-A, (e) 1c-B, (f) 1d, (g) 1e-A, (h) 1e-B, (i) 1f-A,
and (j) 1f-B. Hydrogen atoms are omitted for clarity. Open and filled circles represent carbon and oxygen atoms, respectively.
molecular axis (θ2 ) 90°) for 1a-A, 1e-A, and 1f-A, and
(iii) the stacking axis is tilted to an arbitrary direction (θ1 *
90°, θ2 * 90°) for 1a-B, 1c-A, 1c-B, 1d, 1e-B, and 1f-B.
In the first type, the quinodimethane stacks exactly on the plane
of the neighboring quinodimethane. The length between two
quinodimethane planes, ds, is 3.4 Å, which corresponds to the
width of the quinodimethane and the length of π-π stacking.
Steric repulsions between the ester moieties induce rotation of
the quinodimethane plane along the stacking axis (60°). As a
result, the distance between the reacting exomethylene carbon
atoms, dcc, is 4.3 Å and a little longer for polymerizations. In
the second type, the stacking axis is inclined to the long
molecular axis of the quinodimethane plane, and this produces
offset stacking of the quinodimethanes. Then, the stacking
distances are longer than the first type and the distances between
the exomethylene carbons are shorter. No offsets to the shorter
molecular axis get the reacting carbons close to each other.
Therefore, the stacking distances are in the small range of 7.0-
7.6 Å, and dccs are 3.8-4.2 Å. In the last group, the stacking
axes are tilted to arbitrary directions, which provides a wide
range of stacking manners in the columns. The crystal structures
of 1a-B, 1c-B, and 1f-B have parallel stacking, similar to
those of the first two types, and 1c-A provides the similar
parallel stacking but the quinodimethanes are arranged in a
zigzag fashion. In the cases of 1d and 1e-B, the quinodimethane
molecules are no longer parallel to the nearest neighbors.
Therefore, the stacking distances are in the range of 7.4-9.9 Å
and dccs are 5.2-7.7 Å.
On the other hand, monomers examined in this work could
be classified into three groups by the difference in solid-state
polymerization reactivities: (i) topochemical polymerizations
by the photopolymerizations and the thermal polymerizations
occurred to afford highly crystalline polymers for 1a-A, 1e-
A, and 1f-A, (ii) the thermal polymerizations occurred to give
9
2040 J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004

7,7,8,8-Tetrakis(alkoxycarbonyl)quinodimethanes
A R T I C L E S
amorphous polymers for 1e-B and 1f-B, and (iii) no poly-
merizations took place for 1a-B, 1b, 1c-A, 1c-B, and 1d.
All the topochemically polymerizable monomers (1a-A, 1e-
A, and 1f-A) are in the second type of crystal structures with
parameters of θ1 ) 30-33°, θ2 ) 83-89°, ds ) 7.0-7.6 Å,
and dcc ) 3.8-4.2 Å. Nearly face-to-face stacking with some
offset along the longer molecular axis is requisite for crystalline
state polymerizations of quinodimenthane monomers. When
monomer molecules were stacked in this specific distance in
the crystals, reacting exomethylene carbons can be brought close
enough (dcc ) 3.8-4.2 Å) only by rotation of the monomer
without movement of a translational direction. In particular, the
ds is quite similar to that of the repeating distance (about 7.3
Å, calculated by molecular modeling) of the resulting polymer.
This similarity of the unit lengths before and after polymeri-
zation affords high reactivities in the crystalline state and
polymers with high crystallinity and molecular weight.
Figure 7. Packing mode of molecules in the crystals for 1e-B and possible
direction of polymerization.
if quinodimethane monomers have a ds value of about 7.3 Å in
crystals, polymerization reactions would take place topochemi-
cally along the column axis. As the monomers in group i have
ds values of 7.0-7.6 Å, close to the fiber period of about 7.3
Å, topochemical polymerization could surely take place. For
the monomers in group ii, as 1f-B has a ds value of 5.0 Å
smaller than ca. 7.3 Å, expansion to the direction along the
column axis might take place on polymerization in the crystals,
resulting in amorphous polymer. On the other hand, 1e-B has
a ds value of 7.4 Å and is expected to polymerize topochemically
to give a crystalline polymer. However, larger dcc and/or two
possible directions of polymerization led to amorphous poly-
mers. These observations in quinodimethanes are quite similar
to those of topochemical polymerizations in dienes for ds )
4.9-5.2 Å5 and trienes and triynes for ds ) 7.3 Å.4
On the other hand, the ds of the monomers in the groups ii
and iii, except for 1e-B, is much shorter or longer than 7.3 Å.
Longer ds in 1c-B, 1d, and 1c-A have dcc values more than
4.2 Å, and 1c-B and 1d have ds values more than 8.5 Å;
monomer molecules in crystals cannot move such a long
distance and fail to polymerize. Most of them cannot polymerize
in the crystalline state efficiently. From the above points, it is
concluded that topochemical polymerization of quinodimethanes
needs to have a dcc value of about 4.0 Å and translational
arrangement of the monomers along the direction of polymer-
ization, in addition to a ds value of about 7.3 Å, which is the
fiber period of quinodimethane polymers. In the case of 1e-B,
polymerization occurred at high temperature, and the poly-
merization led to an amorphous polymer. This can be explained
as follows. First, 1e-B has a ds value of 7.4 Å and a dcc value
of 5.2 Å, and the latter value is larger than the dcc value of ca.
4.0 Å suitable for topochemical polymerization. This means that
monomer molecules have to move a long distance to polymerize.
As a result, collapse of the crystals occurs and an amorphous
polymer is produced. Second, there are two nearest-neighboring
molecules because of the screw axis in the space group (P21/
c), and therefore, there are two possible directions (path A and
path B) for the polymerization reaction as shown in Figure 7,
and the carbon-carbon bond formation between the reacting
exomethylene carbons might occur at random, resulting in an
amorphous polymer.
Conclusion
Novel highly conjugated monomers, 7,7,8,8-tetrakis(alkoxy-
carbonyl)quinodimethanes with methoxy (1a), ethoxy (1b),
isopropoxy (1c), benzyloxy (1d), chloroethoxy (1e), and bro-
moethoxy (1f) as alkoxy groups, were synthesized, and their
polymerizations in the crystalline state were investigated. Some
of 1a-f afforded two crystal forms depending upon recrystal-
lization conditions, and their crystal structures were determined
by X-ray crystallography. It was found that topochemical
polymerizations of the quinodimethane monomers might take
place when they are packed in the crystals with parameters of
θ1 ) 30-33°, θ2 ) 83-89°, ds ) 7.0-7.6 Å, and dcc ) 3.8-
4.2 Å.
Supporting Information Available: Experimental procedures,
spectroscopic and analytical data, and X-ray crystallographic
data in CIF format for 7,7,8,8-tetrakis(alkoxycarbonyl)quin-
odimethanes (1a-f). This material is available free of charge
via the Internet at http://pubs.acs.org.
As another possibility, phase transition of the crystals, is
plausible because a weak endothermic peak was observed at
102 °C for 1e-B by DSC measurement, and details are now in
progress.
The fiber period of quinodimethane polymers could be
estimated to be about 7.3 Å by molecular modeling. Therefore,
JA0386086
9
J. AM. CHEM. SOC. VOL. 126, NO. 7, 2004 2041