Molecular design of the polymer forming the complex with metal [I]: Design of the hard-segments of thermoplastic elastomers by using model compounds

Article abstract of DOI:10.1016/S0022-2860(98)00606-1

The six model hard-segments of thermoplastic elastomers containing a pyridine ring were synthesised and the complexation studied with several metal chlorides. It is found that the model compounds containing MPY group (N-pyrid-2-ylmethyl amide) form the stoichiometric 1:1 complex with ZnCl₂ by means of IR. This stoichiometric complexation is caused by the effective formation of the chelate ring between MPY group and ZnCl₂. In addition, the complex structure exhibits strong interaction with each other, so that the melting temperature and enthalpy are remarkably increased. As the result, the MPY-ZnCl₂ complex structure is the most suitable structure as the hard- segment of thermoplastic elastomers.

Full text of DOI:10.1016/S0022-2860(98)00606-1

MOLSTR 10487
Journal of Molecular Structure 477 (1999) 191–199
Molecular design of the polymer forming the complex with metal
[I]: design of the hard-segments of thermoplastic elastomers by
using model compounds
*
Nobuhiro Moriguchi, Toshinori Tsugaru, Shigetoshi Amiya
Analytical Research Center, Kuraray Co., Ltd., Sakazu, Kurashiki, Okayama 710-8691, Japan
Received 25 July 1998; accepted 17 August 1998
Abstract
The six model hard-segments of thermoplastic elastomers containing a pyridine ring were synthesised and the complexation
studied with several metal chlorides. It is found that the model compounds containing MPY group (N-pyrid-2-ylmethyl amide)
form the stoichiometric 1:1 complex with ZnCl2 by means of IR. This stoichiometric complexation is caused by the effective
formation of the chelate ring between MPY group and ZnCl2. In addition, the complex structure exhibits strong interaction with
each other, so that the melting temperature and enthalpy are remarkably increased. As the result, the MPY–ZnCl2 complex
structure is the most suitable structure as the hard-segment of thermoplastic elastomers. ᭧ 1999 Elsevier Science B.V. All rights
reserved.
Keywords: thermoplastic elastomers; model hard-segment; metal coordination; pyridine units; stoichiometric complexation; melting
temperature
A thermoplastic elastomer is polymeric material
with the multi-block structures consisting of a glassy
or semicrystalline ‘hard-segment’ and a rubbery ‘soft-
segment’. Two-phase separation caused by the incom-
patibility of these segments at room temperature leads
to elastic properties [1]. In addition, the hard phase,
which acts as multifunctional cross-links, melts
thermo-reversibly. The degree of the phase separation
and cohesion of the hard-segment significantly influ-
ence the mechanical and thermal properties of ther-
moplastic elastomers. For example, hard domains of
thermoplastic polyurethane elastomers partially melt
on increasing the temperature, so that the elastic prop-
erties decline [2]. The thermoplastic elastomers in
which the hard-segments have a remarkably strong
cohesive and a single size distribution, such as cova-
lent cross-links, is excellent in mechanical and
thermal properties. Usually, four different types of
interaction are considered as the driving force for
the aggregation of hard-segments [3,4]; van der
Waals interaction (in poly (styrene-block-butadiene-
block-styrene) [5]), hydrogen bonding (in thermo-
plastic polyurethane elastomers [6]), crystallization
(in poly (ether ester) thermoplastic elastomers [7])
and ionic interaction (in ionomers [8, 9]). Recently,
the metal coordination interactions and crystallization
of metal complex as the driving force for the hard-
segment aggregation and phase separation have been
reported.
Eisenbach et al. [10–12] synthesized telechelic
polyethers with bipyridine terminal units, which formed
the double-helical complexes of these polymers with
* Corresponding author.
0022-2860/99/$ - see front matter ᭧ 1999 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(98)00606-1

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N. Moriguchi et al. / Journal of Molecular Structure 477 (1999) 191–199
Cu(I). The complexed polymers were phase-separated
at the level of nano to mesoscopic superstructure
consisting of copper-bipyridine complex aggregates
in polyether matrix [11,12]. The mechanical proper-
ties of the complexed polyethers varied with the
composition of the copper. These results indicate
that the potential of the metal coordination interaction
as the driving force for the phase separation of hard
segments is large.
Yang et al. [4,13,14] synthesized the segmented
polyurethane elastomers having pyridine groups.
They investigated the influence of the complexation
between the pyridine group and transition metals on
the elastic properties. The mechanical properties
improved largely when the polyurethanes with the
pyridine groups were blended with a metal acetate,
especially nickel acetate. The formation of coordinate
bonds between the metal and the N atom of the pyri-
dine was confirmed by some spectroscopic methods
such as NMR, FT–IR [13] and EXAFS [14]. They
suggested that these coordinate bonds acting as
cross-links caused the improvement of the material
property.
1.2. Synthesis of 2-MPYAA (bis (N-pyrid-2-ylmethyl)
adipoamide) [15] (1)
2-aminomethylpyridine (25 g) and anhydrous
potassium carbonate (40 g) were dissolved in THF
(150 ml). Adipoyl chloride (12.5 ml) in THF
(150 ml) was added to the solution, and stirred
under a N2 atmosphere at 0ЊC overnight. After the
solvent was evaporated, the residue was washed
with water and methylene chloride. The product was
purified by crystallization from acetone and obtained
as white crystals (yield 71%). 1H–NMR (DMSO–d6):
d1.57 (m, 2H, OyCCH2CH2), d2.22 (t, 2H,
OyCCH2CH2), d4.38 (d, 2H, Py–CH2) d7.23 (m,
2H, pyH–3,5), d7.72 (t, 1H, PyH–4), d8.41, d8.50
(t ϩ d, 2H, NH ϩ PyH–6).
1.3. Synthesis of 2-PYAA (bis (N-pyrid-2-yl)
adipoamide) (2)
2-aminopyridine (23 g) and anhydrous potassium
carbonate (40 g) were dissolved in THF (150 ml).
Adipoyl chloride (12.5 ml) in THF (150 ml) was
added to the solution, and stirred under a N2 atmo-
sphere at 0ЊC overnight. After the solvent was evapo-
rated, the residue was suspended in water and
extracted with methylene chloride. The product was
isolated by crystallization from methanol as white
In the present report, we designed suitable mole-
cular structures as the metal complexed hard-segment
by using some model compounds. The purpose of this
study is to obtain the new type of thermoplastic elas-
tomers with the hard-segment that exhibits the strong
cohesive and remarkable phase separation caused by
the formation of metal complex.
1
crystals (yield 74%). H–NMR (DMSO–d6): d1.66
(m, 2H, OyCCH2CH2), d2.47 (t, 2H, OyCCH2CH2),
d7.08 (t, 1H, pyH–5), d7.76 (t, 1H, PyH–4), d8.12 (d,
1H, PyH–3), d8.30 (d, 1H, PyH–6), d10.42 (s, 1H,
NH).
1. Experimental
1.4. Synthesis of 4-MPYAA (bis (N-pyrid-4-ylmethyl)
adipoamide) (3)
1.1. Materials
Zinc chloride (99.9%), manganese chloride tetrahy-
drate (99.9%), iron(II) chloride tetrahydrate,
cobalt(II) chloride hexahydrate (99.9%), nickel(II)
chloride hexahydrate (99.9%), and copper(II) chloride
dihydrate (99.9%) were purchased from Wako
Chemical Co. and used as received. Tetrahydrofuran
(THF), N,N-Dimethylformamide (DMF) and triethy-
lamine were dried with calcium hydride, distilled and
then stored over molecular sieves 4A. All other
solvents and reagents were used as received from
the commercial distributors except the following
materials.
A procedure similar to that for 2-PYAA was used,
and the product was obtained as white crystals (yield
89%). 1H–NMR (DMSO–d6): d1.58 (m, 2H,
OyCCH2CH2), d2.22 (t, 2H, OyCCH2CH2), d4.31
(d, 2H, Py–CH2) d7.26 (d, 2H, pyH–3,5), d8.44,
d8.50 (d ϩ t, 3H, NH ϩ PyH–2,6).
1.5. Synthesis of 2-MPWA (N-pyrid-2-ylmethyl
valeroamide) (4)
A procedure similar to that for 2-PYAA was used.
The product was purified by chromatography on silica

N. Moriguchi et al. / Journal of Molecular Structure 477 (1999) 191–199
193
gel using ethyl acetate/methanol (95/5 (v/v)), and
obtained as clear liquid (yield 75%). 1H–NMR
(DMSO–d6): d0.87 (t, 3H, CH2CH3), d1.28 (m, 2H,
CH2CH3), a1.52 (m, 2H, OyCCH2CH2), d2.18 (t, 2H,
OyCCH2CH2), d4.36 (d, 2H, Py-CH2), d7.23 (m, 2H,
pyH–3,5), d7.74 (t, 1H, PyH–4), d8.39, d8.49 (t ϩ d,
2H, NH ϩ PyH-6).
filtered off and washed by methanol. In the cases of
2-MPYAA, 2-PYAA, 4-MPYAA and 2-MPYHDI,the
complexes were quantitatively obtained by using this
method.
1.8.2. Method B
The model compound (1 mol) in methanol (10 ml)
and appropriate concentration of metal chloride in
methanol (10 ml) was mixed and reflexed for 1 h.
The solvent was evaporated, then the complex was
obtained.
1.6. Synthesis of 2-MPYHDI (bis (N-pyrid-2-
ylmethyl)-N0-1 6-hexyldiurea) (5)
2-aminomethylpyridine (25 g) and was dissolved in
DMF (200 ml). 1,6-hexamethylene diisocianate
(16 ml) in DMF (70 ml) was added to the solution,
and stirred under a N2 atmosphere at 0ЊC overnight.
The reaction mixture was poured into water. The
precipitate was filtered off and washed by water.
The product was obtained as white crystals (yield
94%). 1H–NMR (DMSO–d6): d1.27 (m, 2H,
NHCH2CH2CH2), d1.36 (m, 2H, NHCH2CH2CH2),
d2.98 (m, 2H, NHCH2CH2CH2), d4.28 (d, 2H, Py–
CH2) d6.10 (t, 1H, NHCH2CH2CH2), d6.39 (t, 1H,
NHCH2–Py), d7.23 (m, 2H, pyH–3,5), d7.73 (t, 1H,
PyH–4), d8.47 (d, 1H, PyH–6).
1.9. General procedure
The FT-IR measurements were performed on a
JEOL JIR–5500. The infrared spectrum was obtained
directly (liquid sample) or from powders in KBr
medium (solid sample). Each spectrum was generated
by signal averaging 10 scans at resolution of
2.0 cmϪ1
.
The differential scanning calorimetry (DSC)
measurements were performed on a Perkin-Elmer
DSC–7 differential scanning calorimeter. Each
sample (ca. 5 mg) was measured under a N2 atmo-
sphere with a DSC-scan rate of 10 K/min. Indium
was used as a calibration standard.
1.7. Synthesis of 2-MPYAE (bis (N-pyrid-2-ylmethyl)
adipate) (6)
The differential thermal analysis (DTA) measure-
ments were performed on a Rigaku TAS–200 thermal
analysis system. Each sample (ca. 10 mg) was
measured under a N2 atmosphere with a DTA-scan
rate of 10 K/min.
2-hydroxypyridine (25 g) and anhydrous potassium
carbonate (40 g) were dissolved in THF (150 ml).
Adipoyl chloride (12.5 ml) in THF (150ml) was
added to the solution, and stirred under a N2 atmo-
sphere at 0ЊC overnight. After the solvent was evapo-
rated, the residue was suspended in water and
extracted with methylene chloride. The product was
isolated by crystallization from acetone/hexane as
2. Results and discussion
2.1. Molecular design of hard segment
1
white crystals (yield 68%). H–NMR (DMSO–d6):
In general, free metal ions prevent the formation of
the hydrogen bonding or crystallization, thus leading
to disaggregate the hard segments of the thermoplastic
elastomers. In addition, some metal salts cause the
decline of mechanical properties by taking up water.
A way to solve these problems is to construct the hard
segment capable of forming the stoichiometric
complex with a metal in a polymer system. Therefore,
we designed the hard segment with the following
strategy; 1. introduction of a ligand which coordinate
with a metal, 2. formation of a chelate ring so as to
form the complex effectively, 3. introduction of a
d1.75 (m, 2H, OyCCH2CH2), d2.45 (t, 2H,
OyCCH2CH2), d5.22 (s, 2H, Py–CH2) d7.22 (t, 1H,
pyH–5), d7.35 (t, 1H, PyH–3), d7.69 (d, 1H, PyH–4),
d8.58 (d, 1H, PyH–6).
1.8. Preparation procedure of metal-model compound
complex
1.8.1. Method A
The model compound (1 mol) in methanol (10 ml)
and metal chloride (1 mol) in methanol (10 ml) was
mixed and refluxed for 1 h. The precipitate was

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N. Moriguchi et al. / Journal of Molecular Structure 477 (1999) 191–199
pyridine ring (Fig. 2). While 2-MPYAA (1) and 2-
MPYVA (4) consist of MPY group, 2-PYAA (2)
consist of PY group. 4-MPYAA (3), in which 4-
carbon of pyridine is bound with a methylene spacer,
is impossible to form a chelate ring. 2-MPYHDI (5)
and 2-MPYAE (6) consist of urea and ester groups,
respectively, instead of the amide group. Only 2-
MPYVA is obtained as liquid, and other derivatives
are solid.
Fig. 1. Structures of the group designed as the hard-segment
forming of the metal complex. PY (1) and MPY (2).
functional group so that the hard segment obtained is
easily introduced to a polymer. According to the
above-mentioned strategy, we adopt the two types
of structures, PY (N-pyrid-2-yl amide) and MPY (N-
pyrid-2-ylmethyl amide) as shown in Fig. 1. While 2-
carbon of pyridine is directly connected with an amide
group in PY, there is a methylene spacer among 2-
carbon of pyridine and the amide group in MPY. We
intend that one metal atom coordinated to both the
pyridine and the amide group, as a result, the chelate
ring is formed. In order to investigate that these struc-
tures act as the metal complexed hard-segment effec-
tively, we synthesized six model compounds with a
2.2. IR study
Fig. 3 shows the IR spectra of 2-MPYAA and 2-
MPYAA-ZnCl2 complex obtained by the method A.
The absorption bands at 1473 cmϪ1 (pyridine ring
stretching), 600 cmϪ1 (in-plane pyridine ring defor-
mation) and 405 cmϪ1 (out-of-plane pyridine ring
deformation) of 2-MPYAA are respectively shifted
to 1485 cmϪ1, 619 cmϪ1 and 418 cmϪ1 by forming
the complex with ZnCl2. These shifts are suggested
that a Zn atom of ZnCl2 coordinates to a N atom of
pyridine ring [16,17]. In addition, the absorption
Fig. 2. Structures of pyridine-containing model compounds. 2-MPYAA (1), 2-PYAA (2), 4-MPYAA (3), 2-MPYVA (4), 2-MPYHDI (5), 2-
MPYAE (6).

N. Moriguchi et al. / Journal of Molecular Structure 477 (1999) 191–199
195
Fig. 3. IR spectra of 2-MPYAA(a) and 2-MPYAA-ZnCl2(b) complex obtained by method A.
bands at 3290 cmϪ1 (N–H stretching), 1639 cmϪ1
(CyO stretching) and 1545 cmϪ1 (C–N stretching)
are respectively changed to 3261 cmϪ1, 1608 cmϪ1
and 1570 cmϪ1 in the complex of ZnCl2. These results
indicate that a Zn atom coordinates to an O atom of
the amide group [18].
also 2-MPYHDI, the absorption bands at 1616 cmϪ1
(CyO stretching), 600 cmϪ1 (in-plane pyridine ring
deformation) and 398 cmϪ1 (out-of-plane pyridine
ring deformation) are completely shifted to
1606 cmϪ1, 627 cmϪ1 and 417 cmϪ1, respectively.
However, in cases of 2-PYAA and 4-MPYAA, the
complete shifts of the absorption bands from amide
groups such as the model compounds having the
MPY- groups are not detected. These results indicate
the unique and the stoichiometric structure is not
formed for these complexes. For 4-MPYAA, the 4-
carbon atom of pyridine connects with the methylene
spacer bound to an amide group, so that a chelate ring
is impossible to form with a Zn atom. Therefore, the
partial shifts of the bands suggest that the formation of
the chelate ring causes the unique complex structure.
In the case of 2-PYAA, there is not the methylene
spacer, therefore the distance between the N atom of
pyridine and the Zn atom is closer than that of 2-
MPYAA. The results of IR studies indicate that the
presence of a methylene spacer is very important for
the formation the unique and the stoichiometric
complex structure.
By elemental analysis,
a
2-MPYAA-ZnCl2
complex consists of one 2-MPYAA and two ZnCl2s
(Found; H 4.01%, C 36.08%, N 9.26%, Cl 23.37%, Zn
19.9%, Calc.; H 3.70%, C 36.09%, N 9.35%, Cl
23.67%, Zn 21.8%,), which suggests that a 1:1
complex is formed between the MPY group and
ZnCl2. This supposition is confirmed by the IR
measurement of the 2-MPYAA-ZnCl2 complex with
various ratios of ZnCl2 to MPY prepared by the
method B as shown in Fig. 4. When ZnCl2 is less
than the MPY group, the absorption bands from the
pyridine ring and the amide group are partially
shifted, and a doublet signal from comlexed and
uncomplexed 2-MPYAA is detected. Then the IR
spectrum of the complex that consisted of a 1:1 ratio
of ZnCl2 to MPY is corresponded with the IR spec-
trum of the 2-MPYAA-ZnCl2 complex obtained by
the method A (Fig. 3).
Table 1 also shows the IR spectra of a 2-MPYVA-
ZnCl2 complex prepared in the various ratios of
ZnCl2 to 2-MPYVA by the method B. The uncom-
plexed 2-MPYVA is liquid. Since no hydrogen
Table 1 shows the characteristic IR wavenumbers
of six model compounds with pyridine rings and their
complexes of ZnCl2 prepared by the method A. For

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N. Moriguchi et al. / Journal of Molecular Structure 477 (1999) 191–199
2.3. Thermal analysis
As described in IR studies, the MPY group forms
the stoichiometric complex with ZnCl2. These
complexes have unique thermal properties. Fig. 5
shows the DTA profiles of the 2-MPYAA-ZnCl2
complex prepared in the various ratios of ZnCl2 to
2MPYAA by the method B. The uncomplexed 2-
MPYAA has the endothermic peak from the melt at
136ЊC. On increasing the amounts of ZnCl2, this peak
becomes smaller, and finally disappears in the 1:1
molar ratio of ZnCl2 to MPY. In addition, the new
endothermic peak of the 2-MPYAA-ZnCl2 complex
appears at 324ЊC. However, this endothermic peak
disappears by adding of an excess of ZnCl2.
Table 2 shows the melting temperatures and the
enthalpies of three model compounds containing of
the MPY group and their complexes of ZnCl2 by the
DSC measurements. The 1:1 complexes of 2-MPYAA
and ZnCl2 prepared by both method A and method B
indicate the same melting temperature, which
suggests that both structures are same in being
supported by IR studies. As shown in Table 2, the
stoichiometric 1:1 complexes of the model
compounds that contain of the MPY group such as
2-MPYAA, 2-MPYVA and 2-MPYHDI have the
melting temperature and enthalpy. Furthermore,
these melting temperature and enthalpy are remark-
able high compared with uncomplexed model
compounds. Especially the melting temperature of
the 2-MPYVA-ZnCl2 complex is higher than that of
the uncomplexed by 129ЊC. And the enthalpy of the
complex is also increased about two orders of magni-
tude over that of the umcomplexed. These results
suggest that the formation of the MPY-ZnCl2 complex
give rise to strong interaction, which leads to the
increase in the melting temperature.
Fig. 4. IR spectra of 2-MPYAA-ZnCl2 complex with various ratio
of ZnCl2 to MPY group prepared by method B. The mole ratio of
MPY/ZnCl2 is indicated at the left of each spectrum.
bonding of an amide group is formed in 2-MPYVA,
the CyO stretching (1651 cmϪ1) of 2-MPYVA is
higher wavenumbers than that of 2-MPYAA
(1639 cmϪ1). No complex of 2-MPYVA is isolated
by the method A. However, the stoichiometric 1:1
complex is obtained as a solid by the method B
when an equivalent ZnCl2 to the MPY group is
added. For 2-MPYAE, a Zn atom is coordinated
with the only N atom of pyridine, which indicate
that an O atom of an ester group is too week as a
Lewis base to coordinate with the Zn atom.
However, no extra high endothermic peak from
melting is observed in any DTA profile with various
ratios of the Zn atom to the pyridine ring for the 4-
MPYAA-ZnCl2 complex as shown in Fig. 6. This
result suggests the increase in the melting temperature
is caused by the formation of the chelate ring with the
MPY- group and ZnCl2. This suggestion is confirmed
by the fact that no endothermic peak is revealed for
the 2-MPYAE-ZnCl2 complex that is impossible to
form the chelate ring because of the low Lewis basi-
city of the O atom as presented in IR studies.

N. Moriguchi et al. / Journal of Molecular Structure 477 (1999) 191–199
197
Table 1
Characteristic IR wavenumbers (cmϪ1) of various model compounds of the hard-segment and their ZnCl2 complexes. d(ip): in-plane of pyridine
ring deformation. d(oop): out-of-plane pyridine ring deformation. ND: not detected
Amide group
Pyridine ring
n(N–H)
n(C ˆ O)
n(C–N)
n(py)
d(ip)
d(oop)
2-MPYAA
2-MPYAA-ZnCl2
2-PYAA
3290
3261
3255
3271
3232
3328
3325
3292
3261
3334
3315
3379
3300
ND
1639
1608
1701
1720
1654
1641
1657
1651
1608
1616
1545
1507
1522
1540
1481
1554
1533
1547
1570
1579
1473
1485
1473
1441
600
619
613
644
405
418
413
419
2-PYAA-ZnCl2
4-MPYAA
4-MPYAA-ZnCl2
2-MPYVA
2-MPYVA-ZnCl2
2-MPYHDI-ZnCl2
1498
ND
1475
1485
1479
600
621
611
619
600
ND
ND
403
418
398
2-MPYHDI-ZnCl2
1606
1579
1495
627
417
2-MPYAE
2-MPYAE-ZnCl2
1730
1730
ND
ND
1481
1491
627
650
403
417
ND
By thermal analyses, we conclude that the MPY
group has possibilities to form a complex with
ZnCl2, which shows a much higher melting tempera-
ture than that of the umcomplexed.
2.4. The complex with other metal halides
The MPY group has possibilities to form a complex
with various metal halides. In the cases of MnCl2,
CoCl2, FeCl2, NiCl2 and CuCl2, the complex of the
MPY to the metal is formed in the 1:0.5 molar ratio.
No stoichiometric complex is formed from 2-
MPYAA and CuCl2. These findings suggest that the
coordination number of ZnCl2 is 4, while those of
MnCl2, CoCl2, FeCl2 and NiCl2 are 6. Table 3 shows
Table 2
Melting temperature (Tm), enthalpy (DHm) and entropy (DSm) of
various model compounds containing of MPY group and their
ZnCl2 complexes by DSC measurement
Tm(ЊC)
DHm(J/mol)
DSm(J/K·mol)
2-MPYAA
2-MPYAA-ZnCl2
2-MPYVA
2-MPYVA-ZnCl2
2-MPYHDI
2-MPYHDI-ZnCl2
136
324
Ϫ70
159
193
249
3.2 × 104
5.8 × 104
5.6 × 102
1.4 × 104
6.5 × 104
7.2 × 104
2.8
97
2.8
32
140
139
Fig. 5. DTA profiles of 2-MPYAA-ZnCl2 complex with various
ratio of ZnCl2 to MPY group prepared by method B. The mole ratio
of MPY/ZnCl2 is indicated at the right of each spectrum.

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N. Moriguchi et al. / Journal of Molecular Structure 477 (1999) 191–199
Fig. 7. DTA profiles of the 2-MPYAA (a) and 2-MPYAA
complexes with MnCl2(b), CoCl2(c) and ZnCl2(d).
Fig. 6. DTA profiles of 4-MPYAA-ZnCl2 complex with various
ratio of ZnCl2 to MPY group prepared by method B. The mole ratio
of MPY/ZnCl2 is indicated at the right of each spectrum.
coordinate bond energy or stability. On the other
hand, the IR wavenumbers of CyO stretching of the
amide group change with the coordinated metals in
the order of Zn Ͻ Cu Ͼ Ni Ͼ Co, Fe, Mn. The lower
wavenumber indicate the formation of the stronger
coordinate bond between the metal and the O atom
of the amide CyO [18]. The order of the strength of
metal coordinate bonds to the O atom of the amide
group and the N atom of pyridine is the opposite. We
speculate that the competitions of the O atom of amide
group and the N atom of pyridine take place in
coordinating with metal atom. So the metal which
coordinate strongly with pyridine form the weak
coordinate bond with the amide group.
the characteristic IR wavenumbers of the complexes
of 2-MPYAA with various metal halides. The magni-
tudes of the shifts of the IR absorption bands from
pyridine ring deformation change in the order of
Mn Ͻ Fe Ͻ Co Ͻ Ni, Cu Ͼ Zn, which is parallel to
the well-known Irving-Williams order. Schmidt et al.
[19] reported that this order is related with the
Table 3
Characteristic IR wavenumbers (cmϪ1
) of various model
compounds of the hard-segment and their metal complexes. d(ip):
in-plane of pyridine ring deformation. d(oop): out-of-plane pyridine
ring deformation
Fig. 7 shows the DTA profiles of the 2-MPYAA
complex with MnCl2, CoCl2 and ZnCl2. In the cases
of FeCl2, NiCl2 and CuCl2, no endothermic peak is
observed because of an acceleration of thermal
decomposition. The melting temperature of the
complex is higher in the order of Zn Ͼ Mn Ͼ Co.
From these results, the MPY-ZnCl2 complex is the
most suitable structure as the hard-segment of thermo-
plastic elastomers. Because this complex has the
n(C ˆ O)
n(C–N)
d(ip)
d(oop)
2-MPYAA
1639
1614
1610
1612
1620
1646
1545
1567
1576
1576
1564
1512
1551
1570
600
621
623
623
623
624
405
418
426
430
438
436
2-MPYAA-MnCl2
2-MPYAA-FeCl2
2-MPYAA-CoCl2
2-MPYAA-NiCl2
2-MPYAA-CuCl2
2-MPYAA-ZnCl2
1608
619
418

N. Moriguchi et al. / Journal of Molecular Structure 477 (1999) 191–199
199
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force for hard-domain aggregation and phase separa-
tion, it also has thermal stability.
3. Conclusions
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In the present studies, the six model compounds were
synthesized and investigated in relation to their thermal
properties and complexation with several metal chlor-
ides. In the IR spectroscopic studies, we found that the
MPY group, with a methylene spacer between the 2-
position of pyridine and the amide group is able to
form the stoichiometric strong complex with ZnCl2.
So the melting temperature and the enthalpy are
remarkably increased. From these results, we
conclude that the MPY-ZnCl2 complex is the most
suitable structure as the hard-segment of the thermo-
plastic elastomer. In a further report, we will study a
polymer containing this complex group.
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