Two-step and reversible phase transitions of organic polymer crystals produced by topochemical polymerization

Article abstract of DOI:10.1021/ma048905a

We describe here the novel phase transition of organic polymer crystals that are directly fabricated by the topochemical polymerization of the 4-bromo- and 4-chlorobenzyl esters of (Z,Z)-muconic acid as the 1,3-diene monomers in the crystalline state. The

Full text of DOI:10.1021/ma048905a

8538
Macromolecules 2004, 37, 8538-8547
Two-Step and Reversible Phase Transitions of Organic Polymer
Crystals Produced by Topochemical Polymerization
Akikazu Matsumoto*,†,‡ and Hideyuki Nakazawa‡
Department of Applied Chemistry, Graduate School of Engineering, Osaka City University, and
PRESTO, Japan Science and Technology Corporation Agency (JST),
Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
Received June 3, 2004; Revised Manuscript Received August 18, 2004
ABSTRACT: We describe here the novel phase transition of organic polymer crystals that are directly
fabricated by the topochemical polymerization of the 4-bromo- and 4-chlorobenzyl esters of (Z,Z)-muconic
acid as the 1,3-diene monomers in the crystalline state. The obtained polymers are thermally stable, and
their crystal structures reversibly change in two steps according to the temperature. The phase transition
of the organic polymer crystals has been revealed on the basis of the results of thermal analyses including
thermogravimetric analysis (TG), differential thermal analysis (DTA), and differential scanning calo-
rimetry (DSC), as well as powder X-ray diffraction (XRD), single-crystal structure analysis, and IR
spectroscopy under temperature control. We have evaluated a change in cell lengths from d-spacing values
observed by XRD at various temperatures and concluded that the conformational change in the ester
moiety of the polymer side chain induces a noncontinuous change in the crystal structures as the phase
transition, which can be detected by X-ray diffraction measurement and thermal analyses.
Introduction
tions.12,13 It is applied to the architecture of polymeric
crystalline material consisting of well-controlled chain
and crystal structures. Topochemical polymerization
proceeds via a specific crystal-to-crystal reaction mech-
anism, leading to the formation of polymer crystals that
cannot be manufactured by the crystallization of a
preformed polymer.14-24 For polymers containing a
partly crystalline structure, the detail of the change in
crystal structure is sometimes illegible due to the
presence of amorphous regions. In contrast, polymer
crystals produced by topochemical polymerization have
a high quality in their crystallinity. In addition, the
polymer chains have a fully extended chain conforma-
tion, which is different from a folded structure for
flexible polymer chains in lamellar crystals. Therefore,
the topochemically prepared polymer crystals are suit-
able as model crystals to study the structure and
properties of common crystalline polymers. Tashiro and
co-workers25-27 have recently revealed the crystalline
structure and mechanical properties of regularly and
partly crystalline poly(diethyl muconate)s. More re-
cently, we have found a novel feature of polymeric
crystals with an excellently ordered chain structure and
conformation, which are distinguished from common
crystalline polymers. Polymer crystals obtained by the
topochemical polymerization of the 4-bromo- and 4-chlo-
robenzyl esters of (Z,Z)-muconic acid, poly(1) and poly-
(2) in Chart 1, are thermally stable, and their crystal
structures clearly and reversibly change in two steps
according to the temperature conditions. In this paper,
the novel phase transition of the organic polymer
crystals is revealed on the basis of thermal analyses
including thermogravimetric analysis (TG), differential
thermal analysis (DTA), and differential scanning cal-
orimetry (DSC), as well as powder X-ray diffraction
(XRD), single-crystal structure analysis, and IR spec-
troscopy under temperature control.
Phase transitions are important for basic science and
applied technology because they include a noncontinu-
ous change in the structure and the physical properties
of organic materials including crystalline polymers in
the solid state.1-3 Crystalline materials can exist in two
or more polymorphic forms, and the process of trans-
formation from one polymorph to another is a phase
transition.4-11 For the crystals of low-molecular-weight
organic compounds, polymorphs are often found, ac-
cording to a procedure and conditions for a crystalliza-
tion process such as the temperature, solvent, seed, and
crystal growth rate.4-7 Furthermore, the phase transi-
tions of liquid crystals consisting of organic compounds
and polymers are used for many applications in a wide
range of fields such as display, films, optoelectronics,
and photonics.8,9 In contrast, a few cases were reported
as reversible transitions between two different crystal
structures for organic materials in the solid state,
because of the thermal and mechanical instability of
low-molecular-weight organic solids; that is, melting,
sublimation, and decomposition occur upon heating, as
well as the collapse of the crystalline structure. For
crystalline polymers, polymorph is often observed, and
the crystallization or ordering process of polymer chains
has been intensively investigated as well as their
physical properties.10,11 However, many studies have
been carried out using partly crystalline polymer
samples, because of the lack of growth into a single
crystal in a sufficient size for the determination of a
structure and the evaluation of physical properties.
Crystal engineering is the planning and construction
of the structures and properties of crystalline materials
by designing molecular building blocks in a desired
packing structure through intermolecular interac-
* Corresponding author. Fax: +81-6-6605-2981. E-mail:
matsumoto@a-chem.eng.osaka-cu.ac.jp.
† PRESTO-JST.
Experimental Section
General Methods. NMR and UV spectra were
recorded on JEOL JNM A-400 and JASCO V-550
‡ Osaka City University.
10.1021/ma048905a CCC: $27.50 © 2004 American Chemical Society
Published on Web 10/21/2004

Macromolecules, Vol. 37, No. 23, 2004
Phase Transitions of Organic Polymer Crystals 8539
Chart 1
muconate. Yield 4.04 g (84.1%). Bis(4-chlorobenzyl)
(Z,Z)-muconate (2) was also similarly prepared. Yield:
3.87 g (80.5%). Melting point and spectral data are as
follows.
1
1: mp 142.0-142.4 °C (CHCl3); H NMR (400 MHz,
CDCl3) δ 7.92 (m, CHdCHCO2R, 2H), 7.49 (m, C6H4,
4H), 7.25 (m, C6H4, 4H), 6.02 (m, CHdCHCO2R, 2H),
5.13 (s, OCH2, 4H); 13C NMR (100 MHz, CDCl3) δ 165.15
(CdO), 138.49 (CHd), 134.67, 131.74, 129.92, 122.40
(C6H4), 123.86 (CHd), 65.59 (CH2); UV(acetonitrile) λmax
260 nm (ꢀ ) 26 100); IR (KBr) 1710 (νCdC), 1584 (νCdO
)
cm-1
.
spectrometers, respectively, at an ambient temperature.
IR spectrum was recorded on a JASCO Herschel FT-
IR-670 Plus spectrometer equipped with Irtron IRT-30
and a temperature control unit. The sample was sand-
wiched between KBr plates, pressed, and then measured
for transmittance over the temperature rage 50-250 °C
at a heating and cooling rate of 10 °C/min. The powder
X-ray diffraction profile was recorded on a Rigaku
RINT-2100 with monochromatized Cu KR radiation (λ
) 1.54184 Å, 40 kV, 40 mA, scan speed 2.0°/min, scan
range 3-40°) under temperature control, equipped with
a high-resolution parallel-beam optics system consisting
of a parallel slip analyzer PSA100U and a graded
multiplayer 2960C1. Single-crystal X-ray data were
collected on a Rigaku R-AXIS RAPID Imaging Plate
diffractometer using Mo KR radiation monochromatized
by graphite (λ ) 0.71073 Å). The structures were solved
by a direct method with the program SIR92 and refined
using full-matrix least-squares procedures. All calcula-
tions were performed using the CrystalStructure crys-
tallographic software package. The simultaneous mea-
surement of XRD and DSC was carried out with a
Rigaku RINT-Ultima II equipped with a DSC attach-
ment (Cu KR, 40 kV, 50 mA, scan speed 0.7°/min, scan
range 4-6°, heating and cooling rate 1 °C/min, the flow
rate of dry nitrogen gas 30 mL/min). TG/DTA analysis
was carried out with Seiko TG-6200 in a nitrogen
stream at a heating rate of 10 °C/min over a range from
room temperature to 500 °C. The initial decomposition
temperature (Tinit) was evaluated as the temperature
at which 5 wt % weight loss was observed. The maxi-
mum decomposition temperature (Tmax) was determined
from a differential thermogravimetric curve in TG
analysis. DSC analysis was carried out with Seiko DSC-
6200 in a nitrogen atmosphere at a heating and cooling
rate of 1, 10, or 20 °C/min. Transition temperatures
(T1 and T2) and a melting temperature (Tm) were
determined as the peak temperatures of the DTA or
DSC curve.
1
2: mp 130.8-131.0 °C (CHCl3); H NMR (400 MHz,
CDCl3) δ 7.92 (m, CHdCHCO2R, 2H), 7.32 (m, C6H4,
8H), 6.02 (m, CHdCHCO2R, 2H), 5.14 (s, OCH2, 4H);
13C NMR (100 MHz, CDCl3) δ 165.15 (CdO), 138.46
(CHd), 134.21, 134.15, 129.62, 128.77 (C6H4), 123.86
(CHd), 65.42 (CH2); UV (acetonitrile) λmax 261 nm
(ꢀ ) 24 300); IR (KBr) 1712 (νCdC), 1588 (νCdO) cm-1
.
The monomer crystals were photoirradiated with a
high-pressure mercury lamp (Toshiba SHL-100-2, 100
W, Pyrex filter) at a distance of 10 cm under atmo-
spheric conditions at room temperature. After irradia-
tion, the resulting polymers were isolated by removal
of the unreacted monomer with chloroform. The polymer
yield was gravimetrically determined. For fabrication
of polymer single crystals, monomer single crystals were
cut to an appropriate size and charged into a Pyrex tube,
degassed, and then sealed. γ-Radiation was carried out
with 60Co at room temperature at the Research Institute
for Advanced Science and Technology (RIAST), Osaka
Prefecture University. The irradiation dose was 200
kGy. After irradiation, the quantitative polymer forma-
tion was examined by IR spectroscopy and used for the
X-ray structure analysis.
Crystallographic Data. The summary of the single-
crystal structure analysis of poly(1) at various temper-
atures is as follows.
Temp -70 °C, monoclinic, space group P21/c, a )
5.811(2) Å, b ) 4.857(1) Å, c ) 32.313(9) Å, â )
90.49(2)°, V ) 912.1(4) Å3, Z ) 2, Fcalc ) 1.748 g/cm3,
unique reflections 2086, number observed (I > 2.0σ(I))
1614, R ) 0.077, Rw ) 0.125, GOF ) 1.17, 2θmax ) 55.0°,
R/P ) 12.81.
Temp -50 °C, monoclinic, space group P21/c, a )
5.823(2) Å, b ) 4.864(1) Å, c ) 32.375(7) Å, â )
90.68(2) °, V ) 916.8(4) Å3, Z ) 2, Fcalc ) 1.739 g/cm3,
unique reflections 2099, number observed (I > 2.0σ(I))
1594, R ) 0.073, Rw ) 0.113, GOF ) 1.28, 2θmax ) 55.0°,
R/P ) 12.65.
Materials. Bis(4-bromobenzyl) (Z,Z)-muconate (1)
was prepared by the method described in previous
papers.28,29 To (Z,Z)-muconic acid (1.42 g, 10.0 mmol)
in 10 mL of hexamethylphosphoramide (HMPA) in a 100
mL flask equipped with a calcium chloride tube were
added 4-bromobenzyl bromide (5.03 g, 20.1 mmol) and
potassium carbonate (3.50 g, 25.3 mmol), and the
mixture was stirred at room temperature for 1 day. The
reaction mixture was poured into 500 mL of saturated
brine, and the crude product was extracted with two
portions of 100 mL of chloroform. After the chloroform
solution was washed with water and then dried over
sodium sulfate, the chloroform was evaporated under
reduced pressure, providing a colorless solid. The pre-
cipitated solid was filtered and dried under reduced
pressure; silica gel column chromatography with chlo-
roform as the eluent provided bis(4-bromobenzyl) (Z,Z)-
Temp -30 °C, monoclinic, space group P21/c, a )
5.816(2) Å, b ) 4.855(1) Å, c ) 32.467(8) Å, â )
90.67(1)°, V ) 916.7(4) Å3, Z ) 2, Fcalc ) 1.739 g/cm3,
unique reflections 2083, number observed (I > 2.0σ(I))
1575, R ) 0.069, Rw ) 0.112, GOF ) 1.31, 2θmax ) 55.0°,
R/P ) 12.50.
Temp -10 °C, monoclinic, space group P21/c, a )
5.813(1) Å, b ) 4.856(1) Å, c ) 32.475(7) Å, â )
90.77(1)°, V ) 916.6(4) Å3, Z ) 2, Fcalc ) 1.740 g/cm3,
unique reflections 2084, number observed (I > 2.0σ(I))
1546, R ) 0.066, Rw ) 0.112, GOF ) 1.21, 2θmax ) 54.9°,
R/P ) 12.27.
Temp 10 °C, monoclinic, space group P21/c, a )
5.828(2) Å, b ) 4.855(1) Å, c ) 32.644(8) Å, â )
90.92(1)°, V ) 923.5(4) Å3, Z ) 2, Fcalc ) 1.727 g/cm3,
unique reflections 2093, number observed (I > 2.0σ(I))

8540 Matsumoto and Nakazawa
Macromolecules, Vol. 37, No. 23, 2004
Figure 1. TG/DTA curves of the crystal of (a) poly(1) and (b)
poly(2). A heating rate of 10 °C/min in nitrogen stream.
Figure 2. DSC traces of the crystal of poly(1) (second run).
(a) Heating and cooling rate of 10 °C/min in nitrogen stream.
(b) Effect of the heating rate.
1478, R ) 0.067, Rw ) 0.098, GOF ) 1.19, 2θmax ) 55.0°,
R/P ) 11.73.
Table 1. TG/DTA Data for Poly(1) and Poly(2)
Temp 30 °C, monoclinic, space group P21/c, a )
5.837(2) Å, b ) 4.856(1) Å, c ) 32.742(9) Å, â )
91.05(2)°, V ) 927.8(5) Å3, Z ) 2, Fcalc ) 1.719 g/cm3,
unique reflections 2095, number observed (I > 2.0σ(I))
1456, R ) 0.064, Rw ) 0.091, GOF ) 1.20, 2θmax ) 55.0°,
R/P ) 11.56.
TG
DTA
Tinit
(°C)
Tmax
(°C)
T1
(°C)
T2
(°C)
Tm
(°C)
polymer
poly(1)
poly(2)
298.5
299.2
313.0
309.1
114.4
246.7
186.0
250.9
305.4
296.3
Temp 50 °C, monoclinic, space group P21/c, a )
5.842(2) Å, b ) 4.854(1) Å, c ) 32.845(9) Å, â )
91.17(2)°, V ) 931.2(5) Å3, Z ) 2, Fcalc ) 1.712 g/cm3,
unique reflections 2109, number observed (I > 2.0σ (I))
1391, R ) 0.063, Rw ) 0.088, GOF ) 1.16, 2θmax ) 54.9°,
R/P ) 11.04.
Temp 70 °C, monoclinic, space group P21/c, a )
5.796(2) Å, b ) 4.880(1) Å, c ) 32.6686(8) Å, â )
91.11(2)°, V ) 924.4(4) Å3, Z ) 2, Fcalc ) 1.725 g/cm3,
unique reflections 2112, number observed (I > 2.0σ(I))
1399, R ) 0.068, Rw ) 0.102, GOF ) 1.17, 2θmax ) 55.0°,
R/P ) 11.10.
Temp 90 °C, monoclinic, space group P21/c, a )
5.821(2) Å, b ) 4.869(1) Å, c ) 32.886(8) Å, â )
91.19(1)°, V ) 931.9(4) Å3, Z ) 2, Fcalc ) 1.711 g/cm3,
unique reflections 2091, number observed (I > 2.0σ(I))
1307, R ) 0.064, Rw ) 0.086, GOF ) 1.12, 2θmax ) 54.7°,
R/P ) 10.37.
Temp 110 °C, monoclinic, space group P21/c, a )
5.824(2) Å, b ) 4.857(2) Å, c ) 32.96(1) Å, â )
91.04(1)°, V ) 932.0(5) Å3, Z ) 2, Fcalc ) 1.711 g/cm3,
unique reflections 2064, number observed (I > 2.0σ(I))
1232, R ) 0.063, Rw ) 0.090, GOF ) 1.16, 2θmax ) 54.5°,
R/P ) 9.78.
to their extremely high crystallinity: Tm ) 305 and 296
°C for poly(1) and poly(2), respectively. In their DTA
traces, small endothermic peaks were observed at 114.4
and 186.0 °C for poly(1), and 246.7 and 250.9 °C for poly-
(2) due to any transitions below the melting points or
the onset temperature of decomposition. Therefore, we
further investigated the transitions by DSC analysis.
The results of DSC data obtained under various scan-
ning conditions are summarized in Table 2. The transi-
tion temperatures observed in the first run (T1 ) 115.1
°C and T2 ) 186.6 °C) were consistent with the DTA
results (Table 1), when the polymers were used in the
form as polymerized after removing the unreacted
monomer with chloroform at room temperature. This
T1 value in the first run was higher than that observed
for those in the second and third runs (T1 ) 105.9 and
105.7 °C, respectively). These thermodynamic changes
in the DSC traces were reversible, but the transition
was always observed at a lower temperature in the
cooling process than that in the heating process; endo-
thermic and exothermic peaks were observed at 105.9
and 186.6 °C (∆H ) 6.1 and 5.4 mJ/unit, respectively)
upon heating, and 86.5 and 182.6 °C (∆H ) -5.3 and
-5.4 mJ/unit, respectively) upon cooling, as shown in
the thermogram for poly(1) (Figure 2). The results of
DSC experiments with different heating rates (1, 10,
and 20 °C/min) indicate that this transition process is
independent of the measurement conditions such as the
scanning rate (Figure 2b and Table 2).
Results and Discussion
Thermal Analyses. Thermogravimetric (TG) and
differential thermal analyses (DTA) were carried out for
poly(1) and poly(2) at a heating rate of 10 °C/min in a
nitrogen stream. The results are shown in Figure 1 and
Table 1. Both polymer crystals were thermally stable
and neither decomposed nor melted under approxi-
mately 300 °C. They showed a clear melting point due
XRD and Single-Crystal Structure Analysis. To
reveal the structural change due to the phase transi-
tions, powder X-ray diffraction (XRD) patterns were

Macromolecules, Vol. 37, No. 23, 2004
Phase Transitions of Organic Polymer Crystals 8541
Figure 3. Change in powder X-ray diffraction profiles of poly(1) on (a) heating and (b) cooling. The temperature was changed
stepwise in the range 30-250 °C. X-ray radiation conditions: Cu KR, 40 kV, 40 mA, scan speed 2.0°/min, scan range 3-40°.
Table 2. DSC Data for Poly(1)
on heating
on cooling
rate
T1
∆H1
T2
∆H2
rate
T1
∆H1
T2
∆H2
run
first
(°C/min)
(°C)
(mJ/unit)
(°C)
(mJ/unit)
(°C/min)
(°C)
(mJ/unit)
(°C)
(mJ/unit)
10
1
10
20
10
115.1
106.4
105.9
108.6
105.7
4.54
6.08
6.05
6.10
6.03
186.6
186.6
186.6
188.6
186.6
4.53
5.37
5.38
5.42
5.41
10
10
10
88.0
86.5
86.5
-5.54
-5.28
-5.11
182.5
182.6
182.7
-5.71
-5.42
-5.51
second
third
recorded at various temperatures. Figure 3 shows the
diffraction profiles of poly(1) recorded over the temper-
ature range of 30-250 °C. When the polymer crystals
were heated stepwise from 30 to 250 °C, the diffraction
profiles changed in two steps. For example, the intensity
of the peak observed at 2θ ) 5.42°, which corresponds
to d ) 16.30 Å, decreased, and simultaneously another
peak appeared at the smaller angle side upon heating.
No original peak was observed at 180 °C, and a further
increase in the temperature induced another structural
change in the crystals, as is clearly shown in the
expanded diffractions of XRD in Figure 4. This process
was reversible as shown by changes in the diffraction
patterns on cooling (Figure 3b and Figure 4b). Similar
reversible phase transitions were also observed for poly-
(2) (Figure 5).
The simultaneous measurement of both XRD and
DSC was carried out with the same sample to confirm
a direct relationship between the thermodynamics and
the structural change during the phase transitions of
the crystals. The XRD diffraction was recorded in the
range of 2θ ) 4-6° at a heating and cooling rate of 1
°C/min. During the heating process, endothermic peaks
were observed at 113.8 and 188.9 °C, at which temper-
atures a drastic change in the XRD profile was detected
(Figure 6). On cooling from 250 °C to room temperature,
a similar structural change was observed accompanying
the exothermic peaks at 185.5 and 92.4 °C in a DSC
trace. This strongly supports that the thermodynamic
behavior is related to the structural change in the
crystal lattice of the polymer. It was confirmed that a
change in the XRD profile was always observed over a
certain temperature range at the peak temperature in
DSC analysis, just the same as those observed in
Figures 3 and 4. Phase transitions are generally affected
by not only thermodynamic but also kinetic factors.
Therefore, the time dependence of the XRD patterns was
examined in the range of temperatures where the two
phases simultaneously coexist. Consequently, however,
we observed the constant ratio, independent of the time,
of the peak intensities of two components in XRD
diffractions observed around the DSC peak tempera-
ture. This means that the composition of both structural
components is a function of the temperature and that
the two phases are in equilibrium with a fast structural
change. This conclusion agrees well with the results for
the DSC experiments in Figure 2b, indicating that a
kinetic factor is not important during the phase transi-
tion of these polymer crystals.
We fully assigned XRD data shown in Figures 3 and
5 on the basis of the single-crystal structures of poly(1)
and poly(2). The results of the analysis of XRD diffrac-
tions are summarized in Table 3. Figure 7 shows the
single-crystal structure of poly(1) determined at 30 °C.

8542 Matsumoto and Nakazawa
Macromolecules, Vol. 37, No. 23, 2004
Figure 4. Expanded powder X-ray diffraction profiles of poly(1) on (a) heating and (b) cooling. The temperature was changed
stepwise in the range 30-250 °C.
12.81, R ) 0.077, Rw ) 0.125, GOF ) 1.17. For the
structure determined at 30 °C, monoclinic, space group
P21/c, a ) 5.837(2) Å, b ) 4.856(1) Å, c ) 32.742(9) Å, â
) 91.05(2)°, V ) 927.8(5) Å3, Fcalc ) 1.719 g/cm3, Z ) 2,
reflections measured 6690, unique reflections 2095,
number observed (I > 2σ(I)) 1456, parameter ratio 11.56,
R ) 0.064, Rw ) 0.091, GOF ) 1.20. All the cell
parameters continuously change over the range from
-70 to +110 °C (see Experimental Section). We also
attempted to determine the single-crystal structure of
poly(1) at a higher temperature, but it failed due to the
collapse of single-crystal structure. We are continuing
an effort to determine the single structures for the high-
temperature phases by the careful measurement and
analysis of diffractions below and over the phase transi-
tion temperature.
Structural Change in Phase Transition. Using eq
1, we evaluated cell lengths on the basis of the d-spacing
in the XRD.
Figure 5. Temperature dependence of X-ray-diffraction pro-
file for poly(2) on heating and cooling. The temperature was
1
1
h2 k2 sin2 â l2 2hl cos â
changed stepwise in the range 30-250 °C.
)
+
+
-
(1)
2
(
)
sin2 â a2
b2
c2
ac
dhkl
Molecular packing and chain conformations in the poly-
(1) crystals were very similar to those for poly(2)
previously reported.23 Crystallographic data for both
polymers are shown in Table 4. Figure 8 shows the XRD
profile calculated from the results of the single-crystal
structure analysis of poly(1) at 30 °C, as well as the
observed diffraction profiles before and after a heating
and cooling process, as was already shown in Figure 3.
These diffraction profiles agree well with each other.
The XRD diffractions in Figure 5 were also assigned as
is shown in Table 3 in a similar way, on the basis of
the single-crystal structure of poly(2).
DSC, XRD, and single-crystal structure analysis
confirmed no occurrence of phase transition below room
temperature to -70 °C, differing from the observation
in a higher temperature region. For example, the
obtained crystal parameters are as follows: for the
structure determined at -70 °C, monoclinic, space group
P21/c, a ) 5.811(2) Å, b ) 4.857(1) Å, c ) 32.313(9) Å, â
) 90.49(2)°, V ) 912.1(4) Å3, Fcalc ) 1.748 g/cm3, Z ) 2,
reflections measured 6805, unique reflections 2086,
number observed (I > 2σ (I)) 1614, parameter ratio
First, a c-axis length was determined from the d002
values at various temperatures. As has already been
shown in Figure 4, the diffraction noncontinuously
changes depending on the temperature, and in the
boundary regions, two phases are simultaneously ob-
served in the temperature ranges of 130-170 and 200-
230 °C. A change in the c-axis length is shown in Figure
9a. Similarly, a- and b-axis lengths were estimated
using the d102 and the d111h values. For the determination
of the latter, experimentally obtained values of the angle
â were used for the calculation below 110 °C, and the
value at 110 °C was used for the estimation of â angles
at a higher temperature. The change in the a- and b-axis
lengths is shown in Figure 9b,c, respectively. The
temperature dependence of the b-axis length and its
change accompanied by the transitions were smaller
than for the other two axes. This is because of the
presence of the covalent chains and intermolecular
halogen-halogen interactions along the b-axis. As
clearly shown in Figure 7, in the crystals of poly(1), the
columns of polymer chains are tightly linked by weak

Macromolecules, Vol. 37, No. 23, 2004
Phase Transitions of Organic Polymer Crystals 8543
Table 3. XRD Data for Poly(1) and Poly(2)a
polymer
temp (°C)
30
hkl
002
2θ (deg) (calcd)
d (Å) (calcd)
height
intensity (%) (calcd)
half-line width
poly(1)
5.417 (5.399)
10.84 (10.81)
16.24 (16.22)
18.42 (18.47)
18.86 (18.84)
21.77 (21.72)
22.53 (22.51)
22.77 (22.80)
23.93 (23.96)
25.10 (25.12)
26.09 (26.12)
26.44 (26.46)
27.31 (27.36)
27.61 (27.65)
28.51 (28.52)
28.84 (28.82)
30.81 (30.82)
31.20 (31.23)
32.90 (32.77)
34.65 (34.63)
35.41 (35.37)
36.16 (36.09)
36.66 (36.63)
38.64 (38.68)
38.95 (38.92)
4.874
16.300 (16.368)
8.155 (8.184)
5.453 (5.465)
4.813 (4.803)
4.703 (4.711)
4.079 (4.176)
3.944 (3.930)
3.902 (3.900)
3.715 (3.714)
3.545 (3.545)
3.412 (3.411)
3.369 (3.369)
3.262 (3.259)
3.228 (3.227)
3.128 (3.129)
3.093 (3.098)
2.900 (2.901)
2.864 (2.867)
2.720 (2.733)
2.587 (2.590)
2.533 (2.537)
2.481 (2.489)
2.449 (2.454)
2.328 (2.328)
2.310 (2.314)
18.116
9447
555
1162
175
1957
321
303
485
220
1220
457
2099
1005
340
296
196
198
221
699
424
163
250
255
347
188
1796
396
72
100 (100)
5.2 (3.7)
16.5 (51.9)
2.1 (9.6)
18.4 (57.5)
2.9 (0.5)
2.4 (8.1)
5.1 (18.3)
2.4 (13.5)
13.8 (71.3)
8.7 (25.1)
19.9 (55.4)
13.5 (12.7)
2.6 (17.0)
3.1 (9.2)
1.6 (9.9)
6.3 (5.8)
12.4 (4.5)
9.4 (10.4)
7.3 (10.9)
2.4 (2.4)
5.4 (4.0)
5.5 (4.6)
5.9 (1.7)
1.7 (5.8)
100.0
0.146
0.147
0.238
0.235
0.120
0.155
0.121
0.167
0.207
0.160
0.207
0.158
0.174
0.141
0.184
0.165
0.244
0.391
0.210
0.163
0.290
0.432
0.312
0.243
0.176
0.142
0.146
0.153
0.155
0.224
0.212
0.161
0.186
0.139
0.255
0.135
0.149
0.215
0.145
0.277
0.226
0.390
0.141
0.126
0.112
0.133
0.154
0.137
0.189
0.146
0.139
0.127
0.112
0.134
0.140
0.178
0.096
0.170
0.384
0.165
0.136
0.169
0.213
0.233
0.205
0.226
0.225
0.233
0.201
0.159
0.201
0.227
0.311
0.215
0.240
004
102
011
104
008
106
015
111h
113h
114h
017
115h
115
018
116h
117
202
204
119
0,1,11
1,0,12
1,0,12
024
1,1,11
002
004
102
poly(1)
180
9.756
9.059
20.5
14.66
6.039
3.2
16.26
5.447
144
196
141
372
175
138
112
225
280
220
82
10.0
17.02
5.204
12.2
18.78
4.722
10.9
19.13
4.635
24.9
008
19.67
4.509
11.4
20.75
4.277
5.8
22.10
4.019
8.3
111h
23.51
3.781
9.4
24.55
3.623
16.3
25.06
3.550
12.7
26.95
3.306
3.2
204
29.54
3.021
134
68
42
10.0
33.84
2.647
7.4
34.67
2.586
4.3
poly(1)
250
002
004
102
4.697
18.80
1283
577
95
100.0
9.395
9.405
41.4
14.12
6.267
6.1
16.57
5.346
63
5.1
17.06
5.193
117
155
125
573
253
146
206
351
141
391
265
93
11.1
17.37
5.100
10.5
008
18.89
4.712
13.6
19.36
4.580
40.7
19.64
4.516
26.2
20.62
4.304
11.0
22.20
4.001
20.7
111h
23.20
3.831
25.3
23.66
3.757
9.5
24.74
3.596
59.9
25.11
3.543
30.9
26.34
3.380
12.0
28.19
3.163
82
28.9
204
28.48
3.132
151
154
87
10.4
30.07
2.969
11.7
32.60
2.745
6.1
33.33
2.686
65
11.1
poly(2)
30
002
004
100
102h
104h
013
014
008
106h
110
016
113
5.527 (5.51)
11.01 (11.03)
15.59 (15.60)
16.54 (16.54)
19.11 (19.11)
20.01 (20.06)
21.30 (21.36)
22.12 (22.16)
22.81 (22.80)
24.07 (24.09)
24.68 (24.74)
25.47 (25.53)
15.978 (16.048)
8.031 (8.024)
5.569 (5.680)
5.355 (5.360)
4.640 (4.643)
4.433 (4.427)
4.169 (4.159)
4.016 (4.012)
3.894 (3.901)
3.694 (3.694)
3.605 (3.598)
3.494 (3.490)
430
219
1053
3379
2924
102
127
711
563
125
429
1378
13.2 (6.4)
5.9 (1.0)
31.3 (55.4)
100.0 (44.0)
89.6 (63.3)
2.7 (9.2)
2.7 (7.5)
18.8 (2.1)
16.8 (5.4)
5.1 (10.7)
12.1 (10.1)
43.5 (100)

8544 Matsumoto and Nakazawa
Macromolecules, Vol. 37, No. 23, 2004
Table 3 (Continued)
polymer
temp (°C)
hkl
017
108
115h
018
116
117h
2θ (deg) (calcd)
d (Å) (calcd)
height
intensity (%) (calcd)
half-line width
poly(2)
26.66 (26.72)
27.19 (27.25)
27.76 (27.84)
28.78 (28.85)
29.34 (29.41)
30.04 (31.06)
31.96 (31.98)
33.46 (33.43)
34.88 (34.93)
35.82 (35.89)
37.09 (37.11)
3.341 (3.336)
3.277 (3.272)
3.211 (3.205)
3.099 (3.095)
3.042 (3.037)
2.879 (2.880)
2.798 (2.791)
2.676 (2.680)
2.570 (2.568)
2.505 (2.502)
2.422 (2.423)
2671
482
2485
429
410
75
805
2056
354
349
970
92.8 (69.5)
19.3 (5.1)
74.1 (25.0)
13.7 (9.7)
12.6 (15.5)
2.5 (2.8)
22.3 (0.4)
61.5 (10.9)
11.8 (9.0)
12.0 (4.2)
28.0 (4.2)
0.264
0.305
0.227
0.243
0.233
0.251
0.211
0.227
0.253
0.262
0.220
1,0,10
204h
119h
0,1,11
1,0,12
1,1,11
39.26 (39.31)
2.293 (2.292)
1770
61.9 (5.4)
0.266
a The values in parentheses are those calculated on the basis of the single-crystal structures of poly(1) and poly(2).
Figure 6. XRD and DSC simultaneous measurements of poly(1). Heating and cooling rate of 1 °C /min in a nitrogen stream.
X-ray radiation conditions: Cu KR, 40 kV, 50 mA, scan speed 0.7°/min, scan range 4-6°.
hydrogen bonds between halogen atoms to form two-
dimensional polymer sheets. The distance for close
contact between the nonbonding chlorine atoms was
3.64 Å, being very similar to that for the monomer
crystals (3.63 Å),23 and shorter than the sum of the
corresponding van der Waals radii.30,31 The polymer
sheets are further linked to each other through weak
hydrogen bond interaction between the carbonyl carbon
and the olefinic hydrogen in the polymer main chain.
The axis lengths for the three phases are summarized
in Table 5. Upon heating, the c- and a-axis lengths
increased by 11 and 4% in the phase transitions from
the original to the second, and from the second to the
third phases, respectively. In contrast, the b-axis prob-
ably implies less change in the length because of the
presence of the rigid polymer chains and halogen zigzag
chains. During the cooling process, similar transitions
were observed and the identical cell parameters were
obtained. A similar reversible phase transition was also
observed in poly(2), but not in other polymers with other
substituents such as an alkoxy group. This suggests the
contribution of interchain halogen-halogen interactions
for the reversible structural change in the polymer
crystals.
We also investigated the temperature dependence of
the vibrational modes of the chemical bonds by IR
spectroscopy. The absorption bands around 1000 and
1180 cm-1 showed extraordinary temperature depen-
dence (Figure 10). On cooling, a reverse change was also
observed as was expected. Recently, Nakamoto et al.25
successfully revealed the mechanical deformation be-
havior of a giant single crystal of poly(diethyl muconate).
IR and Raman spectra were measured as a function of
tensile stress for the polymer crystal, which was ten-
sioned along the chain axis. The structural data were
analyzed on the basis of normal-modes calculation under
a quasi-harmonic approximation, allowing the estimat-
ing of the microscopic deformation mechanism of the
polymer chain under tension. Similarly, the absorption
bands shown in Figure 10 in the present work are
assigned to the vibrational stretching due to several
C-C and C-O bonds. The peaks observed around 1000

Macromolecules, Vol. 37, No. 23, 2004
Phase Transitions of Organic Polymer Crystals 8545
Table 5. Comparison of Axis Lengths of Poly(1) Crystals
for Three Phasesa
temp
(°C)
a-axis length
b-axis length
c-axis length
(Å)
(Å)
(Å)
30
180
250
30
5.83 (5.83)
6.45 (6.44)
6.69
4.89 (4.88)
4.73 (4.72)
4.72
32.61 (32.69)
36.24 (36.19)
37.60
5.837b
4.856b
32.742b
a Axis lengths were evaluated from d002, d102, and d111h spacings
by XRD. Values in parentheses indicate an axis length observed
during a cooling process from 250 to 30 °C. b Determined by single-
crystal structure analysis.
Figure 7. Crystal structure of poly(1) determined by single-
crystal structure analysis at 30 °C: the view along the
crystallographic a and b axes in the top and bottom, respec-
tively. Dotted lines represent intermolecular halogen-halogen
interaction.
Table 4. Crystallographic Data of Poly(1) and Poly(2)
Figure 8. Comparison of observed and calculated XRD
profiles: (a) before a heating and cooling process; (b) after a
heating and cooling process; (c) calculated from the single-
crystal structure.
compound
poly(1)
poly(2)
formula
(C20H16O4Br2)n
480.15
monoclinic
P21/c
(C20H16O4Cl2)n
391.25
monoclinic
P21/c
formula weight
crystal system
space group
a, Å
b, Å
c, Å
the local molecular structure of the polymer side chain
at an initial stage, followed by a change accompanied
by heat flow and then a drastic change in the crystal
structures. It has already been revealed that the car-
bonyl groups interact with weak acidic hydrogens to
cause C-H‚‚‚O intermolecular interaction (weak hy-
drogen bond) in the polymer crystals of 1 or the other
related benzyl ester compounds.23,28,32 In this case,
carbonyl interaction in a direction along the crystal-
lographic a-axis becomes weaker upon heating, and
rotation or any other change in the conformation around
the ester groups would be induced. This local structural
change may further induce a change in the crystal
structure. A delay or difference in the structural changes
observed between vibrational spectroscopy and diffrac-
tion data has been reported for the crystallization of
flexible chain polymers, the phase transition of crystal-
line polymers, and polymerization processes.3,33-36 The
monitoring of a physical process by different measuring
methods is very important to clarify the mechanisms
of the phase transitions of polymer crystals.
5.837(2)
4.856(1)
32.742(9)
91.05(2)
927.8(5)
2
5.6796(3)
4.8631(1)
32.097(1)
90.185(2)
886.54(5)
2
â, deg
V, Å3
Z
F
calc, g/cm3
1.719
1.466
total reflections
unique reflections
number observed
parameter ratio
R
6690
5572
2095
2098
1456 (I > 2σ(I))
11.56
1838 (I > 2σ(I))
12.94
0.064
0.066
Rw
GOF
2θmax, deg
temp, °C
ref
0.091
0.170
1.20
1.70
54.9
54.9
30
23
23
this work
and 1180 cm-1 are produced by ν(C3-C5) + ν(C5-O7) +
ν(O7-C8) and ν(C2-C3) + ν(O7-C8) + ν(C8-C9), respec-
tively (Figure 11).
The IR spectrum changed continuously from a tem-
perature lower than the phase-transition temperatures
observed by DSC or XRD experiments. Especially, the
absorption bands related to the ester groups of the
polymer side chain greatly changed as shown in Figure
10, in contrast to no significant change in peak position
and shape in the bands due to the other bonds. These
results suggest that the transition of the polymer crystal
structure is first induced by conformational change in
In conclusion, we have demonstrated a novel phase
transition of organic polymer crystals, which were
directly fabricated by the topochemical polymerization
of the corresponding diene monomers in the crystalline
state. The highly regular crystalline structure of the
polymer crystals has provided a new insight into organic
crystalline materials on behalf of the thermal stability

8546 Matsumoto and Nakazawa
Macromolecules, Vol. 37, No. 23, 2004
Figure 11. Numbering of constituent atoms of poly(1).
crystals other than the muconate polymer crystals.
However, topochemical polymerization implies the great
potential to provide useful organic materials with
sophisticated and completely regular structures of the
polymer chains and crystals.
Acknowledgment. We gratefully thank Prof. Kohji
Tashiro, Osaka University, for invaluable discussion,
Rigaku Corp. for powder X-ray diffraction/DSC simul-
taneous measurements, JASCO Corp. for FT-IR mea-
surements, and Prof. Kunio Oka, Osaka Prefecture
University, for his kind assistance with the γ-radiation
experiment. This work was supported by PRESTO-JST
(Conversion and Control, 2000-2003) and the Grant-in-
Aid Scientific Research on Priority Areas (Molecular
Nano Dynamics, No. 16072215) from the MEXT, Japan.
Supporting Information Available: Single-crystal X-ray
diffraction of poly(1) (CIF). The material is available free of
charge via the Internet at http://pubs.acs.org.
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Figure 9. Change in axis lengths of poly(1) crystal during a
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