Molecular oxygen insertion polymerization into crystals of tetrakis(alkoxycarbonyl)quinodimethanes

Article abstract of DOI:10.1021/ma035997f

Solid-state alternating copolymerization took place by molecular oxygen insertion in the crystals of 7,7,8,8-tetrakis(ethoxycarbonyl)quinodimethane (1a) and 7,7-bis(ethoxycarbonyl)-8,8-bis-(methoxycarbonyl)quinodimethane (1b) to form highly crystalline ne

Full text of DOI:10.1021/ma035997f

8230
Macromolecules 2004, 37, 8230-8238
Molecular Oxygen Insertion Polymerization into Crystals of
Tetrakis(alkoxycarbonyl)quinodimethanes
Ta k a h ito Itoh ,*,† Sh in ji Nom u r a ,† Ma sa k i Oh ta k e,† Ta k efu m i Yosh id a ,†
Ta k a h ir o Un o,† Ma sa ta k a Ku bo,† Atsu sh i Ka jiw a r a ,‡ Ka zu k i Sa d a ,§ a n d
Mik iji Miya ta
Department of Chemistry for Materials, Faculty of Engineering, Mie University, 1515 Kamihama-cho,
Tsu-shi, Mie 514-8507, J apan; Department of Materials Science, Nara University of Education,
Takabatake-cho, Nara 630-8528, J apan; Department of Chemistry and Biochemistry, Graduate School
of Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, J apan; and
Department of Material and Life Science, Graduate School of Engineering, Osaka University and
Handai FRC, 2-1 Yamadaoka, Suita Osaka 565-0871, J apan
Received December 26, 2003; Revised Manuscript Received August 4, 2004
ABSTRACT: Solid-state alternating copolymerization took place by molecular oxygen insertion in the
crystals of 7,7,8,8-tetrakis(ethoxycarbonyl)quinodimethane (1a ) and 7,7-bis(ethoxycarbonyl)-8,8-bis-
(methoxycarbonyl)quinodimethane (1b) to form highly crystalline needlelike white solids for 1a and
amorphous ones for 1b. The polymer structures were confirmed by 1H NMR, 13C NMR, IR, elemental
analysis, powder XRD, and TGA measurements. However, in vacuo polymerizations of 1a and 1b in the
solid state with heating and photoirradiation did not take place. 7,7,8,8-Tetrakis(methoxycarbonyl)-
quinodimethane (1c) did not undergo solid-state alternating copolymerization with oxygen even in the
presence of oxygen, but instead it homopolymerized to form highly crystalline homopolymer. The difference
in the solid-state polymerization reactivity was discussed on the basis of molecular packing in the crystals
obtained by X-ray crystallography. In addition, it was found by ESR measurement that the solid-state
alternating copolymerizations with molecular oxygen proceed by means of a radical mechanism.
In tr od u ction
Molecular oxygen is well-known as an oxidizing agent
in the organic reactions6 and as an inhibitor and a
retarder of radical polymerizations in polymer chemis-
try, and it acts as a monomer and is incorporated in
the polymer backbone.7 Peroxide polymers can be
synthesized from solution polymerizations of vinyl
monomers8 such as styrene, methyl methacrylate, vinyl-
naphthalene, and R-methylstyrene and unsubstituted
quinodimethane9 with molecular oxygen, and their
physicochemical behavior such as autopyrozability,10,11
autocombustibility,12 speciality fuels,10 coating molding
applications,13 and initiators14 has been investigated.
Recently, it was reported that dibenzofulvene15 and
alkyl sorbate16 copolymerized with molecular oxygen in
the solid state to form a random and/or an alternating
copolymer. However, these reports did not reveal the
crystal structures of the monomers that are suitable for
copolymerization with molecular oxygen. More recently,
we found that 7,7,8,8-tetrakis(ethoxycarbonyl)quin-
odimethane (1a ) copolymerized with molecular oxygen
in the solid state to give a highly crystalline alternating
copolymer and reported it as a preliminary result.17
In this work, we investigated the polymerizations of
1a , 7,7-bis(ethoxycarbonyl)-8,8-bis(methoxycarbonyl)-
quinodimethane (1b) prepared as a novel monomer, and
7,7,8,8-tetrakis(methoxycarbonyl)quinodimethane (1c)
in the solid state under air and in the presence of
oxygen, and the relationship of the solid-state polym-
erization reactivity with their crystal structures was
discussed.
Solid-state polymerization implies that polymeriza-
tion proceeds starting from bulk monomer crystals, and
it has been divided into two classes: topotactic and
topochemical polymerizations.1 The former is the po-
lymerization that provides a polymer with a specific
crystal structure formed under control of the crystal
lattice of the monomer, and the latter is the polymeri-
zation that proceeds with no movement of the center of
gravity of the monomer molecule and only slight rota-
tion of the monomer molecule around the gravity; that
is, the crystallographic position and symmetry of the
monomer crystals are retained in the resulting polymer
crystals. Therefore, topochemical polymerization is a
promising method to obtain polymers with highly
controlled structures. A limited number of monomers
such as derivatives of diacetylene,1 2,5-distyrylpyra-
zine,2 triene and triacetylene,3 muconic acid and sorbic
acid,4 and 7,7,8,8-tetrakis(alkoxycarbonyl)quinodiem-
thane5 have been reported to undergo topochemical
polymerizations, and they are known to have strict
requirements of the monomer arrangements in the
crystals. However, it is still difficult to predict and
control the polymerization properties of compounds in
the crystals because arrangements of monomers play a
significant role. Further investigation of the crystal
structures of monomers related with solid-state poly-
merizations should enable us to control the reactivities
of the monomers and provide us models for the reaction
pathway of the polymerization reactions.
† Mie University.
Exp er im en ta l Section
‡ Nara University of Education.
Ma ter ia ls. Benzene was washed with in sequence with
concentrated sulfuric acid, water, a 5% aqueous sodium
hydroxide, and again water, dried over anhydrous calcium
chloride, refluxed over metal sodium, and then distilled.
§ Kyushu University.
Osaka University and Handai FRC.
* To whom correspondence should be addressed: Ph +81-59-
231-9410; Fax +81-59-231-9410; e-mail itoh@chem.mie-u.ac.jp.
10.1021/ma035997f CCC: $27.50 © 2004 American Chemical Society
Published on Web 09/29/2004

Macromolecules, Vol. 37, No. 22, 2004
Molecular Oxygen Insertion Polymerization 8231
Tetrahydrofuran (THF) was refluxed over lithium aluminum
hydride for 12 h and distilled, and then the distillate was
distilled again over benzophenone-sodium. 2,2′-Azobis(isobu-
tyronitrile) (AIBN) was recrystallized from methanol. Pyridine
was distilled over potassium hydroxide. Titanium tetrachloride
was distilled over copper powder under reduced pressure.
Diethyl malonate was distilled under reduced pressure under
nitrogen. Carbon tetrachloride was used without further
purification. 4-[Bis(methoxycarbonyl)methylene]cyclohexanone18
and 7,7,8,8-tetrakis(methoxycarbonyl)quinodimethane (1c)5
were prepared by the methods reported previously. Yellow
prisms of 1c were obtained by the recrystallization from a
mixture solution of chloroform/hexane (1/3 v/v).
3.85 (s, 6H), 1.31 (t, J ) 10.89 Hz, 6H). 13C NMR (CDCl3): δ
165.1 (CdO), 164.6 (CdO), 139.4 ( Cd), 138.7 ( Cd), 130.2
(CH), 129.9 (CH), 126.5 ( Cd), 125.2 ( Cd), 61.8 (CH2), 52.7
(CH3), 14.1 (CH3). Anal. Calcd for C18H20O8: H, 5.53; C, 59.34;
O, 35.13. Found: H, 5.51; C, 59.14; O, 35.35.
P olym er iza tion P r oced u r e. Solid -Sta te P olym er iza -
tion . A given amount of crystals (1a , 1b, or 1c) was put in a
Pyrex ampule, which was sealed either without degassing (in
air) or with degassing under reduced pressure (in vacuo) or
purged with oxygen and with nitrogen. Thermal polymeriza-
tions were carried out by setting the ampule in an oil bath at
35, 50, and 60 °C for a given time of polymerization. An aliquot
of the reaction product in the ampule was taken out and
1
Mon om er Syn th esis. 1,4-Bis[d i(eth oxyca r bon yl)m eth -
ylen e]cycloh exa n e (2a ). Titanium tetrachloride (16 mL, 146
mmol) in carbon tetrachloride (32 mL) was added dropwisely
under nitrogen to dry stirred THF (220 mL) cooled in an ice
bath. Into this yellow mixture were added 1,4-cyclohexanedi-
one (2.30 g, 20.5 mmol) and diethyl malonate (8.02 g, 50.1
mmol). Pyridine (24 mL) in THF (26 mL) was added to the
resulting brown suspension over 1 h, and the reaction mixture
was stirred at room temperature for 3 days. Water (150 mL)
and chloroform (100 mL) were added to the reaction mixture,
the organic layer was separated, and then the aqueous layer
was extracted with chloroform (4 × 100 mL). The combined
organic fractions were successively washed with saturated
aqueous sodium chloride (100 mL) and aqueous sodium
bicarbonate (100 mL), dried over anhydrous magnesium
sulfate, and filtered, and then the solvent of the filtrate was
evaporated under reduced pressure. The crude product was
purified by column chromatography (SiO2, chloroform) followed
by recrystallization from hexane to give 2a as white needles
(3.47 g, 43%); mp 59-60 °C. IR (KBr): νCH 2940, νCdO 1688,
νCdC 1610, νC-O 1232, 1050 cm-1. UV-vis (CH3CN): 215 (ꢀ )
dissolved in chloroform-d, and H NMR spectra were measured
in order to determine the conversion. Conversions were
calculated from peak area ratios of quinoid protons of the
monomer to phenylene protons of the polymer: peaks at 7.45
ppm and at 7.54 ppm for 1a and peaks at 7.42-7.47 ppm and
at 7.50-7.57 ppm for 1b. When the polymerization took place
completely, all measurements of the reaction products were
carried out without purification by the dissolution-precipita-
tion method. When the polymerization took place incompletely,
1 mL of chloroform was added to dissolve the residual, and
the resulting solution was poured into large amount of hexane
to deposit the polymer, which was washed several times with
excess hexane and dried under reduced pressure. Photopoly-
merizations were carried out at 32-34 °C under UV irradiation
by using a high-pressure mercury lamp (Fuji Glass Work Type
HB-400, 400 W) at a distance of 12 cm. After irradiation, an
aliquot of the reaction product in the ampule was taken out
and dissolved in chloroform-d, and 1H NMR spectra were
measured to determine the conversion. The following proce-
dure was similar to that for the thermal polymerization. If the
reaction products were insoluble in chloroform, the products
were washed with chloroform and dried under reduced pres-
sure and weighed.
Solu tion a n d Melt P olym er iza tion s. Given amounts of
crystals (1a or 1b), AIBN as an initiator, and benzene as a
solvent for 1a were placed in a Pyrex ampule, degassed by
the freeze-thaw method (repeated three times), and then
sealed. The ampule was set in a bath at 60 °C for 50 h for 1a
and at 65 °C for 24 h for 1b and then opened. The reaction
mixtures were directly for 1a and after adding 1 mL of
chloroform for 1b poured into an excess hexane to deposit the
polymers, which were purified by three cycles of redissolution
and reprecipitation. Chloroform and hexane were used as the
solvent and precipitant, respectively. The product was dried
under reduced pressure at room temperature until a constant
weight was attained.
1
1.75 × 104) nm. H NMR (CDCl3): δ 4.26 (q, J ) 7.26 Hz, 8H,
CH2), 2.76 (s, 8H, CH2), 1.29 (t, J ) 7.26 Hz, 12H, CH3). 13C
NMR (CDCl3): δ 165.2 (CdO), 157.7 ( C ), 123.5 ( C ), 61.1
(CH2), 29.4 (CH2), 14.1 (CH3). Anal. Calcd for C20H28O8: H,
7.12; C, 60.59; O, 32.29. Found: H, 7.03; C, 59.85; O, 33.12.
1-[Di(et h oxyca r b on yl)m et h ylen e]-4-[d i(m et h oxyca r -
bon yl)m eth ylen e]cycloh exa n e (2b). 2b was synthesized as
white needles in 66% yield from 4-[bis(methoxycarbonyl)-
methylene]cyclohexanone and diethyl malonate by the same
method as the procedure of synthesizing 2a ; mp 52-54 °C. IR
(KBr): νCH 2944, νCdO 1690, νCdC 1606, νC-O 1221, 1018 cm-1
.
1H NMR (CDCl3): δ 4.26 (q, J ) 7.26 Hz, 4H), 3.77 (s, 6H),
2.75 (s, 8H), 1.29 (t, J ) 6.93 Hz, 6H). 13C NMR (CDCl3): δ
165.5 (CdO), 165.1 (CdO), 158.5 ( Cd), 157.4 ( Cd), 123.6 ( Cd
), 122.8 ( Cd), 61.0 (CH2), 52.1 (CH3), 29.5 (CH2), 29.4 (CH2),
14.0 (CH3). Anal. Calcd for C18H24O8: H, 6.52; C, 58.73; O,
34.75. Found: H, 6.05; C, 59.01; O, 34.94.
Th er m a l Decom p osition . White needlelike solids (187.8
mg) obtained by thermal polymerization of 1a in the solid state
were placed in a Pyrex glass tube, which was set in a bath at
150 °C for 15 min. The solids decomposed to form transparent
viscous oil, which was purified by column chromatography
(SiO2, chloroform) to obtain 34 mg (18% yield) of 1,4-bis-
(ethoxalyl)benzene as colorless oil: IR (neat): νCH 2938, νCdO
7,7,8,8-Tetr a k is(eth oxyca r bon yl)qu in od im eth a n e (1a ).
2a (678 mg, 1.71 mmol) was dissolved in benzene (50 mL),
and this solution was added as one portion to activated
manganese dioxide (5.42 g) and molecular sieves 4 Å (2.84 g)
in benzene (350 mL) at reflux. After stirring for 15 min at
reflux, activated manganese dioxide and molecular sieves were
removed by filtration, and the solvent was evaporated under
reduced pressure. The crude yellow solids were purified by
column chromatography (SiO2, chloroform) followed by recrys-
tallization from hexane to give 1a as yellow needles (225 mg,
34%); mp 72-73 °C. IR (KBr): νCH 2938, νCdO 1690, νCdC 1639,
νC-O 1209, 1044 cm-1. UV-vis (CH3CN): 360 (ꢀ ) 5.75 × 104)
nm. 1H NMR (CDCl3): δ 7.45 (s, 4H, CH), 4.32 (q, J ) 7.26
Hz, 8H, CH2), 1.33 (t, J ) 7.26 Hz, 12H, CH3). 13C NMR
(CDCl3): δ 164.7 (CdO), 138.8 ( C ), 130.0 (CH), 126.1 ( C ),
61.7 (CH2), 14.0 (CH3). Anal. Calcd for C20H24O8: H, 6.16; C,
61.22; O, 32.62. Found: H, 6.15; C, 60.77; O, 33.08.
7,7-Bis(et h oxyca r b on yl)-8,8-b is(m et h oxyca r b on yl))-
qu in od im eth a n e (1b). 1b was synthesized as yellow needles
in 28% yield by the same method as the procedure of
synthesizing 1a ; mp 57-58 °C. IR (KBr): νCH 2950, νCdO 1689,
νCdC 1551, νC-O 1199, 1042 cm-1. UV-vis (CHCl3): 366 (ꢀ )
7.92 × 104) nm. 1H NMR (CDCl3): δ 7.45 (d, J ) 10.56 Hz,
2H), 7.45 (d, J ) 10.56 Hz, 2H), 4.32 (t, J ) 10.89 Hz, 8H),
1
1701, 1658, νCdC 1575, 1441, 1348, νC-O 1182 cm-1. H NMR
(CDCl3): δ 8.17 (s, 4H, aromatic), 4.48 (q, J ) 7.3 Hz, 4H, CH2),
1.44 (t, J ) 7.3 Hz, 6H, CH3). 13C NMR (CDCl3): δ 185.2 (Cd
O), 162.7 (CdO), 136.7 (Ar), 130.3 (Ar), 62.8 (CH2), 14.1 (CH3).
Decomposition of a thermal solid-state polymerization poly-
mer from 1b (200 mg) in chlorobenzene at 120 °C for 6 h
produced 1-methoxyoxalyl-4-ethoxalylbenzene as colorless
oil: 1H NMR (CDCl3): δ 8.17 (s, 4H, aromatic), 4.50 (q, J )
6.93 Hz, 2H, CH2), 4.01 (s, 3H, CH3), 1.44 (t, J ) 6.93 Hz, 3H,
CH3).
X-r a y Cr ysta llogr a p h y. The powder X-ray diffraction
(XRD) measurement of the products was carried out using
Rigaku Rotaflex RU-200B in the 2θ range from 5° to 60° at a
scan speed of 0.5°/min with sampling width of 0.02°. The
graphite-monochromated Cu KR radiation (λ ) 1.541 78 Å) was
used with the power of the X-ray generator 40 kV and 150
mA. Single crystals were obtained by recrystallization from
isopropyl ether for 1a , hexane for 1b, and a mixture of
chloroform/hexane for 1c. All single-crystal X-ray diffraction

8232 Itoh et al.
Macromolecules, Vol. 37, No. 22, 2004
Ta ble 1. Th er m a l P olym er iza tion s a n d P h otop olym er iza tion s of 1a , 1b, a n d 1c
c
run no.
1a -c/mg
state
light source
atmosphere
1a (Et)
temp/°C
time/h
conv/%
Mn
1
2
3
4
5
6
7
8a
20.4
21.0
11.1
10.5
10.1
10.9
11.4
solid state
Hg lamp
Hg lamp
dark
dark
dark
dark
dark
dark
air
vacuo
air
air
vacuo
N2
34
34
35
60
60
60
60
60
25
25
24
24
24
15
15
50
15.7
0
0
100
0
0
1500
18000
O2
vacuo
100
72
18000
2500
370
solution
1b (Me, Et)
9
100.4
112.4
100.7
100.7
101.1
100.4
109.3
solid state
Hg lamp
Hg lamp
dark
dark
dark
O2
vacuo
air
vacuo
N2
O2
32
32
50
50
50
50
65
48
48
48
48
48
48
24
22
0
100
0
0
100
58
1900
4100
10
11
12
13
14
15b
dark
dark
3900
51000
melt
vacuo
1c (Me)
16
17
18
19
53.5
54.5
46.3
37.3
solid state
Hg lamp
Hg lamp
dark
O2
vacuo
O2
32
32
60
60
6
6
6
6
100
100
100
100
NDd
NDd
NDd
NDd
dark
vacuo
AIBN, 5.1 mg; solvent, benzene 1.0 mL. AIBN, 4.9 mg. c Determined by GPC measurement using THF as an eluent and standard
a
b
d
polystyrene as a reference. Not determined (insoluble in common organic solvents).
Sch em e 1
with diethyl malonate using titanium tetrachloride and
pyridine as a dehydrating system21 gave 1,4-[bis(ethoxy-
carbonyl)methylene]cyclohexane (2a ) in 43% yield and
1-[di(ethoxycarbonyl)methylene]-4-[di(methoxycarbon-
yl)methylene]cyclohexane (2b) in 66% yield, respec-
tively, as white needles. Oxidations of 2a and 2b with
activated manganese dioxide in refluxing benzene,
followed by recrystallization from hexane, gave 1a as
yellow needles in 34% yield and 1b as yellow needles
in 25% yield, respectively.
data were collected on a Rigaku RAXIS-RAPID imaging plate
diffractometer using Cu KR radiation (λ ) 1.541 78 Å) mono-
chromated with graphite. The structures were solved by the
direct methods with the programs SIR8819 and SIR9220 and
refined by full-matrix least-squares procedures. All calcula-
tions were performed using the TEXSAN crystallographic
software package of the Molecular Structure Corp.
P olym er iza tion a n d P olym er Ch a r a cter iza tion .
Crystals of 1a , 1b, and 1c were polymerized under air
or in vacuo by irradiation with a high-pressure Hg lamp
at room temperature or by heating in the dark, and also
solution polymerization of 1a in benzene at 60 °C and
melt polymerization of 1b at 65 °C were performed for
comparison. The results are summarized in Table 1.
Mea su r em en t. All melting points were obtained with a
Yanaco MP-53 melting point apparatus. Elemental analyses
were performed on a Yanaco CHN Corder MT-5 Instruments.
The number-average molecular weights (Mn) of the polymers
were estimated by gel permeation chromatography (GPC) on
a J ASCO PU-2080 Plus equipped with TOSOH UV-8020
ultraviolet (254 nm) detector and TSK gel G2500H8 (bead size
with 10 µm, molecular weight range 1.0 × 102-2.0 × 104) and
TSK gel G3000H8 (bead size with 10 µm, molecular weight
range 1.0 × 102-6.0 × 104) using THF as an eluent at a flow
rate of 1.0 mL/min and polystyrene standards for calibration.
1H NMR and 13C NMR spectra were recorded on a J EOL J NM-
EX 270 FT NMR spectrometer in chloroform-d with tetra-
methylsilane as an internal standard. Infrared spectra were
obtained on KBr pellets with a J ASCO IR-700 spectrometer.
Thermogravimetric analysis (TGA) of the polymers was per-
formed on a Seiko TG/DTA 220 Instruments at a scan speed
of +5 °C/min under air. ESR measurement was performed on
a J EOL J ES RE-2X spectrometer operating in the X-band,
utilizing a 100 kHz field modulation, and a microwave power
of 1.0 mW. A TE001 mode cavity was used. Temperature was
controlled by a J EOL DVT2 variable-temperature accessory.
When the crystals of 1a were exposed to UV light at
34 °C in air or heated at 60 °C in air for 24 h, polymers
formed as white needlelike solids in 15.6% and quan-
titative yields, respectively (runs 1 and 4). In contrast,
1a did not polymerize in vacuo with irradiation or
heating and under air in the dark or without heating
(runs 2, 3, and 5). Therefore, polymer formation upon
UV irradiation is due to photoinitiation, but not thermal
initiation. These results strongly suggest the participa-
tion of oxygen in the polymerizations. To clarify role of
oxygen in the polymerization, thermal polymerizations
of 1a in the solid state at 60 °C were performed in the
presence of oxygen and nitrogen (runs 6 and 7). The
monomer 1a polymerized only in the presence of oxygen
to give a polymer in a quantitative yield as white
needlelike solids, but not in the absence of oxygen. This
indicates that molecular oxygen truly participates in
both thermal polymerizations and photopolymerizations
in the solid state.
When crystals of 1b were exposed to UV light at 32
°C in the presence of oxygen or heated at 50 °C in air
for 48 h, polymers formed as white needlelike solids in
22.1% and a quantitative yields, respectively (runs 9 and
11). In contrast, 1b did not polymerize in vacuo with
irradiation and heating (runs 10 and 12). And also, the
Resu lts a n d Discu ssion
Mon om er Syn th esis. Monomers 1a and 1b were
prepared by a synthetic route as shown in Scheme 1.
Knoevenagel condensations of 1,4-cyclohexanedione
and 4-[bis(methoxycarbonyl)methylene]cyclohexanone

Macromolecules, Vol. 37, No. 22, 2004
Molecular Oxygen Insertion Polymerization 8233
F igu r e 2. 13C NMR spectra in chloroform-d of (a) an alternat-
ing copolymer of 1a with oxygen (run 4) and (b) a homopolymer
of 1a (run 8).
F igu r e 1. 1H NMR spectra in chloroform-d of (a) an alternat-
ing copolymer of 1a with oxygen (run 4) and (b) a homopolymer
of 1a (run 8).
participation of molecular oxygen in the polymerizations
of 1b in the solid state was confirmed by the polymer-
izations in the solid state in the presence of oxygen and
nitrogen (runs 13 and 14). The polymerization behavior
of 1b was almost similar to that of 1a . On the other
hand, when crystals of 1c were exposed to UV light at
32 °C or heated at 60 °C in the presence of oxygen and
in vacuo for 6 h, all cases formed polymers as white
crystalline solids, insoluble in common organic solvents,
in almost quantitative yields (runs 16-19). The polym-
erization behavior of 1c was significantly different from
those of 1a and 1b.
White needlelike solids obtained by the thermal
polymerizations of 1a in the solid state at 60 °C (run 4)
and of 1b at 50 °C (run 11) were characterized by H
F igu r e 3. 1H NMR spectra in chloroform-d of (a) an alternat-
ing copolymer of 1b with oxygen (run 11) and (b) a homopoly-
mer of 1b (run 15).
1
NMR and 13C NMR and IR spectroscopies, GPC, el-
emental analysis, and powder X-ray measurement. The
data were also compared with those of the polymers
obtained from the solution polymerization of 1a (run 8)
and from the melt polymerization of 1b (run 15). On
the other hand, the resulting polymer from 1c was
characterized only by IR spectroscopy and elemental
analysis because of their insolubility in common organic
solvents. Number-average molecular weights (Mn) were
determined to be 18 000 for the polymer from the
polymerization in the solid state and 2500 by the
solution polymerization for 1a and 4100 for the polymer
from the polymerization in the solid state and 51 000
by the solution polymerization for 1b. The 1H NMR and
13C NMR spectra are shown in Figures 1 and 2 for the
products obtained by the thermal solid-state polymer-
ization in the presence of oxygen and the solution
polymerization in the dark of 1a and in Figures 3 and
4 for those obtained by the thermal solid-state polym-
erization in the presence of oxygen and the melt
polymerization in the dark of 1b, respectively, where
each peak was assigned to the respective protons and
carbons of chemical structures illustrated therein.
The polymers obtained by the solid-state polymeriza-
tions exhibited much sharper peaks than those obtained
F igu r e 4. 13C NMR spectra in chloroform-d of (a) an alternat-
ing copolymer of 1b with oxygen (run 11) and (b) a homopoly-
mer of 1b (run 15).
in the 13C NMR spectrum, the peak at 89.4 ppm (d in
Figure 2a) assigned to the quarternary carbon atom in
the solid-state polymerization polymer was observed 19
ppm further downfield than the corresponding one (70.0
ppm (d) in Figure 2b) in the solution polymerization
polymer. For the polymer from 1b, the chemical shifts
assigned to the aromatic protons (7.52 ppm (a) in Figure
3a) in the 1H NMR spectrum and the quarternary
carbon (89.3 ppm (d, d′) in Figure 4a) in the 13C NMR
spectrum were observed in a lower field than the
corresponding ones (6.3-7.0 ppm in Figure 3b and 70.0
ppm in Figure 4b) of the polymer obtained by the melt
polymerization like as 1a . These deshieldings observed
1
by the solution or melt polymerization. In the H NMR
spectrum of the polymer from 1a , a peak at 7.53 ppm
(a in Figure 1a) assigned to the phenylene protons of
the polymer obtained by thermal solid-state polymeri-
zation was observed in a lower field compared to the
corresponding one (6.6-6.9 ppm (a) in Figure 1b) of the
polymer obtained by the solution polymerization. Also,

8234 Itoh et al.
Macromolecules, Vol. 37, No. 22, 2004
F igu r e 6. IR spectra (KBr) of (a) monomer 1b, (b) an
alternating copolymer of 1b with oxygen (run 11), and (c) a
homopolymer of 1b (run 15).
F igu r e 5. IR spectra (KBr) of (a) monomer 1a , (b) an
alternating copolymer of 1a with oxygen (run 4), and (c) a
homopolymer of 1a (run 8).
adjacent-hydrogen system. These changes observed in
the IR spectra support that this reaction follows the
conventional mode observed for substituted quin-
odimethane molecules: the polymerization takes place
at disubstituted exomethylene carbon atoms with for-
mation of the corresponding stable aromatic structure.22
Unfortunately, a peak assigned to the peroxide group
in the polymers obtained by the solid-state polymeri-
zation was not observed because of peak overlap with
the C-O absorption assigned to the ester group. It is,
therefore, concluded that the polymers obtained by the
solid-state polymerization are the alternating copoly-
mers of 1a and 1b with molecular oxygen. On the other
hand, the IR spectrum of the polymer from 1c obtained
by the solid-state polymerization in the presence of
oxygen was completely the same as the one obtained in
vacuo and also identical to that of the homopolymer
obtained from the solution polymerization of 1c in
benzene initiated by AIBN.5 These findings for 1c
indicate that the products from 1c by the solid-state
polymerizations in the presence of oxygen and in vacuo
are the homopolymer of 1c, and 1c does not copolymer-
ize with molecular oxygen.
The powder X-ray diffraction (XRD) patterns of
monomers, polymers by solid-state polymerization, and
the polymers reprecipitated from chloroform-hexane
are shown in Figure 7. For the solid-state polymeriza-
tion of 1a , the relatively sharp diffraction patterns were
observed at the reaction mixtures at conversions of 46%
and 86% and even at 100% conversion. This indicates
that the monomer 1a maintains the crystallinity during
and after completion of the polymerization. However,
the powder XRD patterns illustrated that the polymer
reprecipitated from chloroform-hexane has no signifi-
cant peaks, which implies changes to the amorphous
state (Figure 7f). On the other hand, for the polymeri-
in the NMR spectra indicate the presence of electron-
withdrawing groups such as oxygen next to the units
of 1a and 1b in the polymers.
The elemental analysis values (H, 5.62; C, 56.42; O,
37.96) of the polymer obtained from the solid-state
polymerization of 1a were in good agreement with the
values (H, 5.70; C, 56.60; O, 37.70) calculated for an
alternating copolymer of 1a with molecular oxygen, but
not with the found values (H, 6.10; C, 60.89; O, 33.01)
for the homopolymer of 1a obtained by the solution
polymerization. The elemental analysis values (H, 5.08;
C, 54.48; O, 40.44) of the polymer obtained from the
solid-state polymerization of 1b were in good agreement
with calculated values (H, 5.09; C, 54.55; O, 40.36) as
the 1:1 alternating copolymer of 1b with molecular
oxygen. In contrast, the elemental analysis values (H,
4.78; C, 56.93; O, 38.29) of the polymers obtained from
the solid-state polymerization of 1c in the presence of
oxygen were in good agreement with the ones (H, 4.80;
C, 57.14; O, 38.06) calculated for the homopolymer of
1c.
IR spectra are shown in Figure 5 for the monomer
and the polymer from the solid-state and solution
polymerizations of 1a and in Figure 6 for the monomer
and the polymer from the solid-state and melt polymer-
izations of 1b. A characteristic absorption band at 1550
cm-1 assigned to the exocyclic conjugated carbon-
carbon double bond of 1a and 1b was absent in the IR
spectra of the resulting products. The arising absorption
bands at 1492 and 1411 cm-1 are assigned to carbon-
carbon double bonds of the aromatic ring and that at
811 cm-1 is to out-of-plane deformation of the para-
disubstituted benzene, which is characteristic for a two-

Macromolecules, Vol. 37, No. 22, 2004
Molecular Oxygen Insertion Polymerization 8235
F igu r e 8. TGA curves of (a) (s) an alternating copolymer of
1a with oxygen (run 4) and (- - -) and a homopolymer of 1a
(run 8) and of (b) (s) an alternating copolymer of 1b with
oxygen (run 11) and (- - -) a homopolymer of 1b (run 15).
shown in Figure 8. The TGA measurements showed that
the solution polymerization polymer of 1a and melt
polymerization polymer of 1b begin to decompose at
about 210 °C, but the solid-state polymerization poly-
mers show a two-stage decomposition and begin to
decompose at about 110 °C for 1a and at about 70 °C
for 1b. The weight losses from 110 to 150 °C for 1a and
from 70 to 150 °C for 1b amount to 17% and 19%,
respectively, which correspond approximately to the
weight percent of an ethoxycarbonyl group from each
unit of 1a and 1b. When the polymers from 1a and 1b
obtained by the solid-state polymerization were heated
at 150 °C for 15 min, 1,4-bis(ethoxalyl)benzene (3a ) and
1-ethoxazyl-4-methoxzaylbenzene (3b) were isolated in
18% and 15% yields, respectively, according to the
mechanism as shown in Scheme 2. This indicates that
both polymers have thermally degradable groups such
as peroxide bonds.
The structure of active spices from 1a was directly
investigated by ESR spectroscopy during thermal po-
lymerization in the solid state under air. The ESR
spectrum from crystals of 1a under air at 62 °C in 30
min is shown in Figure 9a, where the ESR spectrum
shows a broad triplet at a g value of 2.0030 with a
coupling constant of 5.0 G. Coupling constants of the
hydrogen at 2- and 6-positions of benzyl type radicals
are reported to be about 5 G,23 and also the observed
ESR spectrum is in good agreement with the corre-
sponding one simulated with the coupling constant of
5.0 G as shown in Figure 9b. Therefore, the observed
ESR spectrum could be assigned to a propagating di-
(ethoxycarbonyl)benzyl radical with the two equivalent
hydrogens (Ha) at 2- and 6-positions of the phenylene
group.
F igu r e 7. XRD patterns of (A) (a) monomer 1a , (b) 16%
conversion, (c) 46% conversion, (d) 86% conversion, (e) 100%
conversion, and (f) reprecipitated polymer and (B) (a) monomer
1b, (b) 31% conversion, (c) 88% conversion, (d) 100% conver-
sion, and (e) reprecipitated polymer.
zation of 1b in the solid state, the relatively sharp
powder XRD patterns were observed until 88% but
became broad at 100% conversion, indicating that the
monomer 1b has loss of the crystallinity during and
after completion of the polymerization. Moreover, the
powder XRD patterns illustrated that the polymer
reprecipitated from chloroform-hexane has no signifi-
cant peaks as well as the corresponding polymer from
1a , and it is amorphous (Figure 7f). The changes
observed in powder XRD patterns indicate that the
thermal solid-state polymerizations of 1a and 1b pro-
ceed under the influence of the crystal lattice to form
the alternating copolymer with a highly ordered crystal
structure. The powder XRD patterns of the polymer
from 1c obtained by the solid-state polymerization in
the presence of oxygen showed very sharp peaks even
at complete conversion, and no loss of crystallinity was
observed before and after the polymerization. This
indicates that 1c undergoes polymerization in topochem-
ical mode even in the presence of oxygen to form highly
crystalline homopolymer.
This result indicates that polymerization reaction of
1a in the solid state takes place at the disubstituted
exomethylene carbon atoms and proceeds through a
The thermal behavior of the polymers of 1a and 1b
was investigated by TGA, and their TGA curves are

8236 Itoh et al.
Macromolecules, Vol. 37, No. 22, 2004
Sch em e 2
Ta ble 2. Cr ysta llogr a p h ic Da ta for th e Cr ysta ls of 1a , 1b,
a n d 1c
radical mechanism and that the propagating species is
di(ethoxycarbonyl)benzyl radical. The radical concentra-
tion change during the polymerization reaction was
investigated by ESR spectrometry using 2,2,6,6-tetra-
methyl-4-hydroxy-1-piperidinyloxy as a standard. Radi-
cal concentration increased rapidly with time and
reached to a maximum value of 6.9 × 10-5 mol/kg in 1
h and then gradually decreased to 6.1 × 10-5 mol/kg in
2 h, 4.9 × 10-5 mol/kg in 3 h, 2.6 × 10-5 mol/kg in 21 h,
and 2.3 × 10-5 mol/kg in 24 h. The decrease in the
radical concentration after reaching to a maximum
value is relatively small, and even after 100% conversion
at 24 h, large amounts of radical are still alive. This
indicates that a long-lived propagating radical is formed
in this solid-state polymerization because of immobility
of the polymer chain produced.
parameter
1a
1b
1c
substituent
formula
formula wt
crystal system
space group
a, Å
ethyl
20H24O8
392.40
orthorhombic monoclinic
Iba2
13.483(2)
21.393(3)
6.8956(9)
90
90
90
ethyl; methyl methyl
C
C18H20O8
364.35
C16H16O8
336.29
monoclinic
P21/n
P21/n
12.443(5)
5.108(1)
14.466(5)
90
8.6787(7)
7.5719(7)
12.761(1)
90
b, Å
c, Å
R, deg
â, deg
101.76(1)
90
105.193(2)
90
γ, deg
V, Å3
1988.9(5)
4
1.310
860
900.2(5)
2
809.2(1)
2
Z
F
calc, g/cm3
1.344
1638
1.380
1828
unique reflecns
no. obsd reflens 832
1084
1477
Cr ysta l Str u ctu r e a n d P a ck in g of Molecu les. To
clarify the relationship of the molecular packing in the
crystals with the polymerization reactivity, we investi-
gated the crystal structures of 1a , 1b, and 1c by X-ray
crystallography. The crystallographic data of 1a , 1b, and
1c are summarized in Table 2, and their crystal
structures are shown in Figure 10. Unfortunately, in
the crystal structure of 1b, the terminal methyl groups
of the ethoxycarbonyl groups are highly disordered, and
the position of these methyl groups cannot be deter-
mined.
R, Rw
R
GOF
2θmax, deg
temp, °C
0.291; 0.156
0.108; 0.200
0.079
1.39
136.5
23
0.106; 0.133
0.046
1.27
55.0
25
0.072
1.56
136.3
23
In the crystal structure of 1a , the molecules form a
one-dimensional column by the stacking of the quino-
dimethane rings along the crystallographic c axis. The
stacking axes are nearly perpendicular to the molecular
plane of the quinodimethane ring, and the stacked
molecules are rotated successively by 60°. The face-to-
face distance between units of 1a in the stacked column
is 3.4 Å, which corresponds to the π-π stacking distance
of the aromatic rings.24 The distance between the
exomethylene carbon atoms in the column is 4.3 Å. This
packing mode of the molecules of 1a in the crystals is
quite different from those found for 1c as shown in
Figure 10, which undergoes the homopolymerization. In
the crystal structure of 1b, the molecules construct
another one-dimensional columnar structure by the
stacking of the quinodimethane rings along the crystal-
lographic b axis, and also the stacking axis is not
perpendicular to the molecular plane of the quin-
odimethane rings like as 1c. However, 1b has a stacking
distance (ds ) 5.1 Å) between the quinodimethane
moieties and a distance (dcc ) 5.1 Å) between the
exomethylene carbon atoms, which are greatly different
from those (ds ) 7.6 Å and dcc ) 3.9 Å)5 of the
topochemically polymerizable 1c. Therefore, 1a and 1b
do not undergo homopolymerization in the solid state,
due to the inadequate molecular packing in the crystals.
Instead, both 1a and 1b copolymerized with molecular
oxygen to form the alternating copolymers, and also they
have maintained relatively high crystallinity until a
conversion as high as about 80%. Molecular oxygen
normally exists as a triplet (i.e., a diradical) in its
ground state with a bond length of 1.2 Å, which is much
shorter than the distance between the exomethylene
carbon atoms for 1a (4.29 Å) and for 1b (5.1 Å). A
F igu r e 9. ESR spectrum of the propagating radical from 1a
crystals in 30 min under air at 62 °C: (a) observed and (b)
simulated; Ηa ) 5.0 G.

Macromolecules, Vol. 37, No. 22, 2004
Molecular Oxygen Insertion Polymerization 8237
F igu r e 10. Crystal structures of (a) 1a , (b) 1b, and (c) 1c. Open and solid circles represent carbon and oxygen atoms, respectively.
Hydrogen atoms are omitted for clarity.
dioxygen unit may act as a hinge to bind neighboring
quinodimethane molecules at their exomethylene carbon
atoms. These distances are just suitable for the oxygen
insertion into the polymer chains to yield the alternating
copolymers. To clarify the polymerization mechanism,
the molecular weights of the alternating copolymers
produced at 60 °C in air were measured at different
reaction times (3, 6, 9, 12, 18, and 24 h). They were in
the range of 18 900 at the initial stage to 15 200 at the
final stage with low molecular weight byproducts due
to the slow decomposition of peroxide bond formed in
the polymer, indicating that no significant changes in
the molecular weight of the polymers was observed
during the polymerization in the solid state. This
suggests that the alternating copolymerization in the
solid state proceeds by means of chain reaction mech-
anism. Tokitoh et al. reported that the reaction of
overcrowded distibene with molecular oxygen in the
solid state takes place through a single crystal to a
single crystal process, and also a “domino” type reaction
is caused by the oxidation of the molecules of distibene
lying on the exterior surface of the single crystals.25
Powder XRD measurements of 1a and 1b indicate that
they retain relatively high crystallinity up to high
conversion, and also 1a maintains further the crystal-
linity up to much higher conversion than 1b. It is,
therefore, considered that the reactions of 1a and 1b
with molecular oxygen start on the surface of their
crystals and then proceed along a one-dimensional
columnar of the crystals with the diffusion of molecular
oxygen inside the crystals, though there are no decisive
proofs to support fast diffusion of the molecular oxygen
into the crystal lattice. The difference observed between
1a and 1b is considered to be attributed to (1) the
shorter distance between the exomethylene carbon
atoms in the 1a crystals (4.3 Å) than in 1b ones (5.1 Å),
resulting in much slower collapse by smaller movement
of the molecules of 1a in the crystals, and (2) a smaller
displacement between each column generated by the
polymerization of 1a in comparison with 1b because the
crystals of 1a have the hexagonal close packing struc-
ture and those of 1b do not.
In summary, both 1a and 1b copolymerized sponta-
neously and alternatingly with molecular oxygen in the
solid state to form highly crystalline needlelike white
solids for 1a and amorphous ones for 1b by means of a
radical mechanism, respectively. Alternating copolymer
structures obtained by the thermal polymerization and
photopolymerization in the solid state were confirmed
1
by H and 13C NMR, IR, elemental analysis, and TGA
measurements On the other hand, 1c does not undergo
solid-state alternating copolymerization with oxygen
even under oxygen atmosphere, but instead it does the
homopolymerization. No thermal and photopolymeriza-
tions of 1a and 1b in the solid state were observed in
vacuo, which was explained by the lack of structural
prerequisite for topochemical polymerization.
Ack n ow led gm en t. A part of this work was sup-
ported by “Nanotechnology Support Project” of the
Ministry of Education, Culture, Sports, Science and
Technology (MEXT), J apan.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic files (CIF). This material is available free of charge
via the Internet at http://pubs.acs.org.
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