Comparing liquid crystalline properties of two epoxy compounds based on the same azoxy group

Article abstract of DOI:10.1080/15421400802305830

Two recently synthesised diepoxy compounds based on the same rigid central segment with carbon chains of different lengths were compared. Microscopic observations, differential scanning calorimetry (DSC) and dielectric measurements confirmed the existence of a mesophase in both compounds and enabled determination of the temperatures of phase transitions. Wide-angle X-ray scattering (WAXS) measurements and optical observations enabled identification of mesophase types. Nematic phase appeared in both compounds; in the material with longer chains smectic A phase was also detected. Lengths of the molecules and average nearest neighbor distances were estimated using the wide-angle X-ray scattering results. Lengths of the molecules were also computed by quantum mechanical methods resulting in very good agreement with the experimental data.

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Comparing Liquid Crystalline
Properties of Two Epoxy
Compounds Based on the Same
Azoxy Group
B. Mossety-Leszczak a , M. Wlodarska b , H. Galina a
& G. W. Bak b
a Department of Industrial and Materials Chemistry,
Rzeszow University of Technology, Rzeszow, Poland
b Institute of Physics, Technical University of Lodz,
Lodz, Poland
Version of record first published: 22 Sep 2010
To cite this article: B. Mossety-Leszczak, M. Wlodarska, H. Galina & G. W. Bak (2008):
Comparing Liquid Crystalline Properties of Two Epoxy Compounds Based on the Same
Azoxy Group, Molecular Crystals and Liquid Crystals, 490:1, 52-66
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Mol. Cryst. Liq. Cryst., Vol. 490, pp. 52–66, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802305830
Comparing Liquid Crystalline Properties of Two Epoxy
Compounds Based on the Same Azoxy Group
B. Mossety-Leszczak1, M. Wlodarska2, H. Galina1,
and G. W. Bak2
1Department of Industrial and Materials Chemistry, Rzeszow
University of Technology, Rzeszow, Poland
2Institute of Physics, Technical University of Lodz, Lodz, Poland
Two recently synthesised diepoxy compounds based on the same rigid central
segment with carbon chains of different lengths were compared. Microscopic
observations, differential scanning calorimetry (DSC) and dielectric measure-
ments confirmed the existence of a mesophase in both compounds and enabled
determination of the temperatures of phase transitions. Wide-angle X-ray
scattering (WAXS) measurements and optical observations enabled identifi-
cation of mesophase types. Nematic phase appeared in both compounds; in
the material with longer chains smectic A phase was also detected. Lengths
of the molecules and average nearest neighbor distances were estimated using
the wide-angle X-ray scattering results. Lengths of the molecules were also
computed by quantum mechanical methods resulting in very good agreement
with the experimental data.
Keywords: epoxy resins; liquid crystals; phase transition
1. INTRODUCTION
Despite more than 30 years of history of liquid crystalline (LC) dis-
plays there is a continuous interest in liquid crystal materials [1]. It
stems from the enormous range of applications where liquid crystals
are utilized for their ability to change their optical properties quickly
in response to various electric or magnetic fields, temperature gradi-
ents, etc. [2]. Nowadays, besides LC monomers there are many other
types of liquid crystal materials (e.g., columnar, discotic, main and
Address correspondence to M. Wlodarska, Institute of Physics, Technical University
of Lodz, 90-924 Lodz, Poland. E-mail: magdaw@p.lodz.pl
52

LC Properties of Two Epoxy Compounds
53
side chain polymers, elastomers) which find new applications in the
industry [3–5]. In any innovative LC device, novel components and
materials play important roles [1].
The epoxy compounds are now commercially used as reagents for
curing because the obtained products of curing have very good mech-
anical properties. Thanks to the lack of side products during proces-
sing, small contraction, and high liquidity, they can be used to make
thin-walled and complex moldings [6]. LC epoxy compounds can also
be used to build larger structures known as LC polymer networks.
Such epoxy precursors with different mesogenic groups have been
synthesized and characterized by several scientific groups [5,7,8].
LC properties of a resin change the physical properties of the
resultant polymer network because of additional ordering of
molecules present both during the reaction and in the cured product.
As an example, excellent transparency and high birefringence of
these networks can be achieved by polymerization of LC monomers
in unidirectional orientation [9]. We also attempt to use the LC
monomers for curing, but to control this process and the properties
of cured materials, knowledge about the properties of pure monomers
is essential [10].
The aim of this article is to compare basic physical properties of two
new diepoxy materials with different carbon chains. The synthesis
route is presented along with the results of optical, dielectric, and
differential scanning calorimetry measurements, which allowed for
precise determination of phase transitions. WXAS measurements con-
firmed the type of the mesophase. Approximate lengths of the mole-
cules and average distances between them were also obtained in
these investigations. The molecular lengths were compared to the
values computed theoretically with the use of ab initio methods
[11,12].
2. MATERIALS
We synthesised two diepoxy compounds based on the same core but
differing in the length of the carbon chains. Their molecular structures
are shown in Fig. 1.
Investigations using ab initio methods [12] resulted in establishing
the geometry of the molecules. The calculations were carried out
for a single molecule, without taking into account any interactions
with other molecules or the surrounding medium. Lengths of the
molecules were estimated as distances between two outermost atoms.
As the studied structures are linear and the terminal atoms are
hydrogens, this approximation should not introduce a significant error.

54
B. Mossety-Leszczak et al.
FIGURE 1 Molecular structure of the investigated compounds.
Geometry optimization was performed following a two-step method
proposed in the article [12] for similar monomers, where details of the
procedure can be found. In the first step, the investigated structures
were split into three segments: the rigid core and two chains, which
were optimized as if they were separate molecules. Subsequently, orig-
inal molecules were reconstructed from the optimized segments (taking
into account several possible orientations of the chains with respect to
the central segment) and underwent final energy minimization. Follow-
ing the article [13], where the geometry of a similar molecule (PAA) was
analyzed, we assumed that the azoxy group of the central segment is
coplanar with the aromatic rings. For both the investigated molecules
the calculations revealed two stable conformations differing in mutual
=
orientation of the C O groups. Both conformations in either pair have
very similar values of energy, which means that they are likely to
coexist in real materials. Length of the molecule is also almost the same
in both isomers, despite the structural differences.
3. EXPERIMENTAL
All starting materials were commercial reagents (Aldrich, Fluka,
Merck) and were used without further purification. The chemical
structure of products was confirmed by 1H-NMR and FTIR
spectroscopy, by using a Bruker AvanceII 500 and a Paragon 1000
FT-IR spectrometer, respectively. The purity of epoxy compounds
was assessed chemically by titration its chloroform solution containing
tetraethylammonium bromide with perchloric acid solution in
anhydrous acetic acid. The procedure described in the standard
ISO 3001–1978 was used. The thus measured epoxy numbers (in
moles of epoxy groups per 100 g) differed from calculated ones by less
than 1%.

LC Properties of Two Epoxy Compounds
55
The textures of the compounds were observed using a polarising
microscope Zeiss at a magnification of 80ꢀ. The temperature was
controlled by means of a Linkam TMS 91 hot stage. The measure-
ments were carried out in cells of two kinds, one composed of parallel
glass plates covered with conducting layers and the others in which
the electrodes were also covered with thin polyimide film with anti-
parallel rubbing. This additional coating enforced planar orientation
of LC samples. The sample thickness was 5 ꢁ 10ꢂ6 m in the cell with
polyimide layer.
DSC measurements were performed with the use of a Mettler
Toledo DSC822e instrument under nitrogen atmosphere. The thermo-
grams recorded at heating and cooling rate of 2 deg=min allowed for
determination of phase transitions.
WAXS measurements were conducted using a rotating anode
(Rigaku 18 kW) X-ray beam with a pinhole collimation and a two-
dimensional detector (Siemens) with 1024 ꢀ 1024 pixels. A double
graphite monochromator for the CuKa radiation (k ¼ 0.154 nm) was
used. The beam diameter was about 0.5 mm and the sample to detector
distance was 80 mm. Measurements were performed in various tem-
peratures for samples molten in glass capillaries.
Temperature-dependent dielectric measurements were performed
using the experimental set-up of Novocontrol. The system was
equipped with Alpha high-resolution dielectric analyzer, Quatro
v.4.0 temperature controller. The AC voltage applied to the capacitor
was 0.5 V, and the frequency for the static dielectric constant was
10 kHz, the samples were in sandwich-type cells. The temperature
was controlled using a nitrogen-gas cryostat and the temperature
stability of the sample was better than 0.1 K.
Ab initio calculations were conducted using restricted Hartree–Fock
(RHF) method with the standard 6–31Gꢁ basis set. The structures of all
molecules were optimised to a minimum of energy using Berny algor-
ithm [14]. The optimization procedure was described in detail (for other,
but similar materials) in [12]. All the computations were carried out
using Gaussian 03 program suite [11] running on a PC workstation.
4. RESULTS AND DISCUSSION
4.1. Synthesis
4.1.1. Synthesis of 4,40-Dihydroxyazobenzene
The synthesized epoxy compounds were derivatives of 4,40-
dihydroxyazobenzene (1). The synthesis of 4,40-dihydroxyazobenzene
was earlier described in literature [15,16]. In this work, we use the

56
B. Mossety-Leszczak et al.
way similar to the method described by P. Vanoppen et al. [15]. 4,40-dihy-
droxyazobenzene was obtained by azo coupling of diazonium salt of 4-
hydroxyaniline with phenol dissolved in solution of sodium hydroxide.
4-hydroxyaniline (5.46 g, 0.05 mol) was dissolved in dilute hydro-
chloric acid (12 cm3 37% aq. HCl þ 40 cm3 of water) and cooled to
0–3ꢃC. To this mixture an aqueous solution of sodium nitrite (3.45 g,
0.05 mol in 18 cm3 of water) was slowly added dropwise under
continues stirring. Next the obtained diazonium salt was diluted with
200 cm3 of precooled ethanol. Separately phenol (4.7 g, 0.05 mol) was
dissolved in 42 cm3 10% NaOH and 50 cm3 of ethanol, and this
mixture was also cooled to 0–3ꢃC. The phenolate solution was added
dropwise under stirring to the diazonium salt and the dark-red
solution was obtained. Azo coupling was continued for 4 h in 5ꢃC, and
then the solution was neutralized with dilute hydrochloric acid. The
yielded red solid was filtered, washed with water and dried. The crude
material was recrystallised from methanol to give 5.2 g (49%) dark-red
solid of mp 215–216ꢃC.
1H-NMR (acetone-d6), d (ppm); 8.9 (2H, s, OH), 7.85 (4H, d, J ¼
9.0 Hz, arom.), 6.95 (4H, d, J ¼ 9.0 Hz, arom.).
FTIR (KBr), n (cmꢂ1); 3458–3193 (-OH), 3017, 1608–1591, 1507–1430,
844 (arom.), 1251–1105 (C-O).
4.1.2. Esterification
To 0.1 mol of mesogenic diol 1 (2.14 g) and 0.02 mol of 4-pentenoic
acid 2a (2.00 g) or 10-undecenoic acid 2b (3.76) in 80 cm3 of dry
dichloromethane, 0.022 mol (4.54 g) of N,N-dicyclohexylcarbodiimide

LC Properties of Two Epoxy Compounds
57
(DCC), and a catalytic amount (8 ꢄ 10ꢂ4 mol, 0.0977 g) of 4-dimethyla-
minopyridine (DMAP) were added. The reaction mixture was stirred
for 24 h, then N,N-dicyclohexylurea (DHU) was filtered off and,
after removal of the solvent, crude products were crystallised from
methanol. Yields 52% of 3a, 47.5% of 3b.
3a: 1H-NMR (CDCl3), d (ppm); 7.9 (4H, d, J ¼ 8.9 Hz, arom.), 7.2 (4H,
=
=
d, J ¼ 9.0 Hz, arom.), 5.85 (2H, m, CH ), 5.1 (4H, m, CH2), 2.55 (8H,
m, -(CH2)2-).
FTIR (KBr), n (cmꢂ1); 3082, 1600–1495, 861 (arom.), 2999–2856
=
=
(CH2), 1744 (C O), 1643, 916 (C Caliph.), 1234–1095 (C-O).
3b: 1H-NMR (CDCl3), d (ppm); 7.9 (4H, d, J ¼ 8.8 Hz, arom.), 7.2 (4H,
=
=
d, J ¼ 8.9 Hz, arom.), 5.75 (2H, m, CH ), 4.95 (4H, m, CH2), 2.55 (4H, m,
-CH2-), 2.15 (4H, m, -CH2-), 1.8 (4H, m, -CH2-), 1.45 (20H, m, -(CH2)5-).
FTIR (KBr), n (cmꢂ1); 3079, 1589–1470, 858 (arom.), 2923–2851
=
=
(CH2), 1747 (C O), 1641, 914 (C Caliph.), 1245–1097 (C-O).
4.1.3. Epoxidation
Under continuous stirring, 8.13 g (0.033 mol, 70%) of m-chloroper-
oxybenzoic acid (MCPBA) was added to a solution of 0.01 mol of diole-
fin (3.78 g of 3a or 5,46 g of 3b) in 80 cm3 of dichloromethane. The
mixture was refluxed for 48 h (the reaction was monitored by TLC).
After cooling and subsequent filtration, the mixture was washed with
100 cm3 of aqueous 5% Na2SO3, 100 cm3 of aqueous 5% NaHCO3,
40 cm3 of aqueous 30% NaCl. The dichloromethane layer was dried
over MgSO4 and evaporated. Recrystallization from methanol yielded
the final products: 73% of 4a, epoxy number (EN) ¼ 0.465 (calcd.
0.469), and 78% of 4b EN ¼ 0.334 (calcd. 0.337).
4a: 1H NMR (CDCl3), d (ppm); 8.25 (4H, m, arom.), 7.2 (4H, m,
arom.), 3.0 (2H, m, CH of epoxy), 2.75 (4H, m, CH2 of epoxy), 2.55
(4H, m, -CH2-), 1.9 (4H, m, -CH2-).
FTIR (KBr), n (cmꢂ1); 3114–3057, 1610–1469, 860 (arom.), 2991–
=
2928 (CH2), 1752 (C O), 1410, 1307–1293 (N!O), 1222–1102 (C-O),
914, 841 (epoxide).

58
B. Mossety-Leszczak et al.
4b: 1H NMR (CDCl3), d (ppm); 8.25 (4H, m, arom.), 7.2 (4H, m, arom.),
2.95 (2H, m, CH of epoxy), 2.75 (2H, m, CH2 of epoxy), 2.55 (4H, m,
-CH2-), 2.45 (2H, m, CH2 of epoxy), 1.8 (4H, m, -CH2-), 1.4 (24H, m,
-(CH2)6-).
FTIR (KBr), n (cmꢂ1), 3055, 1610–1466, 859 (arom.), 2924–2850
=
(CH2), 1759 (C O), 1414, 1318–1293 (N!O), 1200–1105 (C-O), 912,
843 (epoxide).
4.2. Physical Properties
Phase transitions in the investigated materials were analyzed using
DSC, polarizing microscope, and dielectric measurements. Example
DSC diagrams for compound 4b are shown in Fig. 2 (for both heating
and cooling). The phase transitions solid=mesophase and mesophase=
isotropic liquid are clearly seen, but there are also small peaks
between the two main transitions, which suggest existence of two
different mesophases (having similar molecular arrangement). In
the material 4a, only one mesophase is observed.
The optical microscopy observations (Fig. 3) enabled identifi-
cation of the DSC peaks with solid–liquid crystal phase transitions.
The investigated materials were placed between plates covered
with ordering layers (enforcing a homogenous planar orientation,
Fig. 3a).
FIGURE 2 Example of an exothermic DSC thermogram of compound 4b,
recorded at heating and cooling rate of 2ꢃC=min. Visible peaks correspond to
phase transitions detected. See Table 1 for details.

LC Properties of Two Epoxy Compounds
59
FIGURE 3 Textures of the investigated compounds, observed in a polarizing
microscope between crossed polaroids. Sample placed between glass plates
covered with rubbed polyimide layers, enforcing planar orientation of the
molecules: (a) nematic phase of compound 4b, T ¼ 98ꢃC; (b) changes in the
texture, smectic A phase in compound 4b, T ¼ 90ꢃC.
The microscopic observations in liquid crystal cell with parallel
rubbing suggest the existence of a nematic mesophase below 110ꢃC
in both compounds (the images are almost the same and look like
the one shown in Fig. 3a), and compound 4a retains a similar texture
up to temperatures slightly exceeding 140ꢃC. In the case of compound
4b, a noticeable change occurs in the microscopic image of the sample
during cooling below 97ꢃC, which remains stable in the further course
of the cooling (Fig. 3b). We can conclude from this observation that a
smectic phase appears in cooling. In the course of the heating, some
changes are also visible in the sample, but they are not distinctive
enough to allow for clear conclusion whether or not a smectic–nematic
transition exists here. The microscopic observations in the cell without
rubbing show a homeotropic texture for both compounds. In this case,
there are no visible changes between the two mesophases of compound
4b during cooling, i.e., the smectic phase also has a homeotropic tex-
ture. Smectic A phases have been found to be optically uniaxial and
frequently show such textures [17]. Smectic type C, where molecules
are tilted within the layers, cannot have this texture [18–21]. It could
appear in smectic type B, but high degree of molecular alignment
within the layers in that phase would result in much stronger DSC
peak for smectic–nematic transition than the one observed in our case.
The existence of two mesophases in compound 4b was confirmed by
dielectric observations. The results for both compounds are shown in
Fig. 4. The static dielectric permittivity depends on the phase of the

60
B. Mossety-Leszczak et al.
FIGURE 4 Changes in the dielectric constant corresponding to phase transi-
tions in the materials: (a) cooling of compound 4a; (b) heating; and (c) cooling
of compound 4b.

LC Properties of Two Epoxy Compounds
61
material because of changing in mean orientation of molecular dipoles
(or induced dipoles in non-polar molecules). During the phase tran-
sition from isotropic liquid to liquid crystal, the dielectric permittivity
can increase or decrease depending on the alignment in the sample
(and the direction of dipole moment of the molecule), and during
crystallization the dielectric permittivity mostly decreases. So the
self-ordering in mesophase causes that the phase transition is
observed in dielectric measurements in almost all liquid crystals. In
the case of compound 4b, the phase transition between the meso-
phases is also clearly seen (Fig. 4b,c) because of different arrangement
of molecules in the smectic phase (layer formation affects the
molecular interactions). The summarized results of measurements
are presented in Table 1.
The above conclusions were confirmed by WAXS measurements
performed for samples in thin capillaries. In temperatures below
110ꢃC similar patterns were obtained for both compounds (Fig. 5a).
The diffraction images show two pairs of crescent-shaped, diffuse
reflections positioned at different scattering angles. This type of pat-
tern is typical for nematics [22]. The lack of any other diffraction max-
ima and strong diffusion of the reflections (for both wide and small
angles) indicates that there is no higher-level ordering. The diffraction
pattern changes noticeably for compound 4b after cooling below 97ꢃC
(Figs. 5b, 6). The basic feature of the image (two pairs of reflections)
remains visible, but in the lower temperature the intensity of the
small-angle reflections is much larger, which indicates stronger corre-
lation in molecular arrangement along the mean direction of their
axes (a different mesophase) and is therefore in accordance with
optical observations. Below 80ꢃC, the pattern is typical for solid state
(Fig. 6).
Images similar to those acquired in temperatures below 110ꢃC have
been obtained by other authors (e.g., [19]) for different nematic mate-
rials. The appearance of arcs rather than rings reflects orientation of
the sample, induced by interaction between the molecules and the
TABLE 1 Phase Transitions in the Investigated Compounds, According to
DSC, Dielectric, and Optical Analysis
Materials
Temperatures of phase transitions [ꢃC]
Comments
First
compound (4a)
Second
Cr 105 N 143 I
Cr 93 N 141 I
Cr 90 SmA 97 N 110.5 I
Cr 80 SmA 97 N 110 I
heating
cooling
heating
cooling
compound (4b)

62
B. Mossety-Leszczak et al.
FIGURE 5 Examples of WAXS 2D patterns: (a) material 4b, T ¼ 103ꢃC; the
diffraction pattern (two diffuse rings) is typical for nematics; (b) material
4b, T ¼ 87ꢃC; the diffraction pattern (two rings, sharp small-angle ring) is
typical for smectics A.
FIGURE 6 The plot of X-ray scattering intensity vs. scattering vector s for
material 4b. Two diffraction maxima are visible in the isotropic and nematic
phase; the peaks at small values of s are much stronger and narrower in
smectic A phase; a different pattern can be observed in the solid state.

LC Properties of Two Epoxy Compounds
63
capillary walls. The director n of the structure is perpendicular to the
imaginary line connecting the centres of both wide-angle arcs [23,24].
Formation of smectic layers creates positional correlation in the
system, which gives rise to diffraction maxima at small angles. As
the smectic phase is approached on cooling from the nematic phase
the diffuse spots in the nematic structure factor sharpen and eventu-
ally become the quasi-Bragg peaks of the smectic phase [22]. We can
see similar behavior in our case, where below 97ꢃC the intensity of
the small angle peaks for compound 4b becomes much stronger
(Fig. 6). The wide-angle diffraction pattern exhibits two crescent-
shaped maxima in equatorial positions, similar to those observed in
the nematic phase, which means that there is no two-dimensional lat-
tice formation inside the layers (Figs. 5, 6). In liquid-like layers of both
smectics A and C, a diffuse ring was also observed by other authors
[22,24]. However, the pairs of wide-angle and small-angle reflections
in smectics C are not perpendicular to each other, as in the case of
smectics A (and our samples). WAXS results are therefore consistent
with other results indicating formation of smectic A phase in our case.
Considering the scattered intensity as a function of the scattering
vector s (s ¼ 2sinh=k, where h is the scattering angle and k is the wave-
length [22]) it is possible to obtain the approximate values of several
parameters of the measured system. The repeat distance l correspond-
ing to sm (the value of scattering vector s at a diffraction maximum)
may be computed as l ¼ 1=sm [24]. This value, computed for small-
angle peaks, may be directly interpreted as the approximate length
of a molecule in nematics and as the layer width in smectics. The pos-
ition sm of wide-angle reflections is related to intermolecular distance
d, but this relation depends on the three-dimensional geometry of the
system. For ordered nematics (as well as for smectics A and C), the
geometry of random packing of parallel cylinders seems to be appropri-
ate, which results in the formula d ¼ 1.12=sm [23,24].
The experimental results from WAXS measurements (the values of
the scattering vector sm corresponding to the diffraction peaks and the
calculated structural parameters) are presented in Table 2 and com-
pared to the lengths of the molecules obtained by ab initio methods,
for the most extended conformers of the molecules.
The experimental values are close to those obtained from quantum
mechanical calculations. The observed differences for the nematic
phase are less than 10% of the calculated values. The simplest expla-
nation of this difference is that the long axes of the molecules in
nematics are not aligned strictly with the global director n. Instead,
they may be tilted by some angle b from ꢂt1he direction of n. We can
then identify the correlation length sm obtained from WAXS

64
B. Mossety-Leszczak et al.
TABLE 2 Molecular Lengths (l)ꢁ and Average Intermolecular Distances (d)ꢁ
Calculated from the Positions of WAXS Maxima (sm). For Comparison, the
Molecular Lengths Obtained from ab initio Calculations (lc) are also Presented
WAXS – wide angle
WAXS – small angle
Ab initio
lc [nm]
Molecule
sm [nmꢂ1
]
d [nm]
sm [nmꢂ1
]
l [nm]
l=lc
(4a) nematic
(4b) nematic
smectic A
2.21
2.25
2.30
0.51
0.50
0.49
0.45
0.26
0.245
2.22
3.85
4.08
2.33
3.90
0.95
0.98
1.05
ꢁValues of l are computed as l ¼ 1=sm; values of d are computed as d ¼ 1.12 smꢂ1
assuming the model of random packing of cylinders for both the nematic and smectic
A phases.
measurements with the mean projection ln of molecular length l
along the director. For the average value of b ꢅ 30ꢃ, which is quite
reasonable for nematics, this model gives ln ꢅ 0.9 l [24], which is very
close to our results. It is noteworthy that at higher temperatures
non-all-trans conformations also exist, which may lead to smaller
values of measured layer width. There are also other factors which
may influence the results. The diffraction peaks are not very sharp,
which makes it difficult to determine the maximum accurately. The
ab initio calculations were carried out in vacuo, without taking into
consideration any intermolecular interactions. Taking all of this into
account, we may conclude that the results are in good accordance
with theoretical data. The value obtained for the smectic A phase
(compound 4b) is slightly larger than for the nematic phase and close
to the calculated length of the molecule. This is an additional argu-
ment that smectic A is formed, as molecules do not appear to be
tilted within the layers.
Another quantity obtained from WAXS results (Table 2) is the near-
est neighbour distance, which is little above 0.5 nm for all the mole-
cules considered. Similar values were found for a wide variety of
compounds [24].
5. CONCLUSIONS
. A two-stage method of synthesis of diepoxy compounds has been
used to obtain two new compounds. A mesophase was observed in
both cases. The temperatures of phase transitions were determined
with DSC, polarising microscope, and dielectric spectroscopy. The
mesophase types were verified by means of WAXS technique.

LC Properties of Two Epoxy Compounds
65
. The compound 4a has a nematic phase in wide range of tempera-
tures (100ꢃC–140ꢃC) in both heating and cooling.
. The compound 4b is isotropic liquid above 110ꢃC and its range of
mesophase is narrower. Except the nematic phase, a smectic A
phase was also observed in this case, which appears in a narrow
temperature range (90ꢃC–97ꢃC) during heating and in a wider range
(97ꢃC–80ꢃC) during cooling.
. As we expected, connecting the same mesogen with longer carbon
chains resulted in a lower temperature of the transition to isotropic
phase. Extending the chains also led to the appearance of a second,
smectic mesophase, but at a cost of much smaller range of the
nematic phase.
. Lengths of the molecules obtained experimentally from WAXS
results are in agreement with those obtained in quantum mechan-
ical calculations (RHF method with 6–31Gꢁ basis set).
6. ACKNOWLEDGMENTS
Part of this work was supported by the Polish Committee of Scientific
Research (KBN), grant N205 060 31=2543.
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