Thermal properties of liquid-crystalline diols and corresponding bis-urethanes with mesogenic groups of various structures in side chains

Article abstract of DOI:10.1080/15421400390193954

The liquid-crystalline dials with mesogenic groups of different structures were synthetized and their temperature behavior and existence of mesophases were determined. These compounds were also reacted with phenylisocyanate to form bis-urethanes at the ra

Full text of DOI:10.1080/15421400390193954

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Thermal Properties of
Liquid-Crystalline Diols and
Corresponding Bis-Urethanes
with Mesogenic Groups of
Various Structures in Side
Chains
M. Kašpar a , V. Hamplová a , V. Novotná a , M.
Studenovský b & M. Ilavský b c
a Institute of Physics , Academy of Sciences of the
Czech Republic , Na Slovance 2, Prague 8 , 182 21 ,
Czech Republic
b Institute of Macromolecular Chemistry , Academy
of Sciences of the Czech Republic , Prague 6 , 162
06 , Czech Republic
c Faculty of Mathematics and Physics , Charles
University , Prague 8 , 180 00 , Czech Republic
Published online: 18 Oct 2010.
To cite this article: M. Kašpar , V. Hamplová , V. Novotná , M. Studenovský & M.
Ilavský (2003) Thermal Properties of Liquid-Crystalline Diols and Corresponding Bis-
Urethanes with Mesogenic Groups of Various Structures in Side Chains, Molecular
Crystals and Liquid Crystals, 392:1, 17-30, DOI: 10.1080/15421400390193954
To link to this article: http://dx.doi.org/10.1080/15421400390193954
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Mol. Cryst. Liq. Cryst., Vol. 392, pp. 17–30
Copyright # 2003 Taylor & Francis
1542-1406/03 $12.00+.00
DOI: 10.1080/15421400390193954
THERMAL PROPERTIES OF LIQUID-CRYSTALLINE
DIOLS AND CORRESPONDING BIS-URETHANES
WITH MESOGENIC GROUPS OF VARIOUS
STRUCTURES IN SIDE CHAINS
´
´
M. Kasˇpar, V. Hamplova, and V. Novotna
Institute of Physics, Academy of Sciences of the
Czech Republic, Na Slovance 2, 182 21 Prague 8,
Czech Republic
´
M. Studenovsky
Institute of Macromolecular Chemistry, Academy of
Sciences of the Czech Republic, 162 06 Prague 6,
Czech Republic
´
M. Ilavsky
Institute of Macromolecular Chemistry, Academy of
Sciences of the Czech Republic, 162 06 Prague 6,
Czech Republic
Faculty of Mathematics and Physics, Charles University,
180 00 Prague 8, Czech Republic
The liquid-crystalline diols with mesogenic groups of different structures were
synthetized and their temperature behavior and existence of mesophases were
determined. These compounds were also reacted with phenylisocyanate to
form bis-urethanes at the ratio of reactive groups [OH]=[NCO] ¼ 1=1. The
changes of phase transition temperatures due to the change of H–O–H to H–
N–H interactions have been investigated. Generally, the introduction of a
phenylurethane group into the molecule suppresses the occurence of meso-
phases; in the case of simple mesogens the mesophases disappear completely.
Stiff substituents bound to mesogen as end groups (such as the phenyl group,
alkoxy group, etc.) stabilize the mesophases to such a degree that the negative
influence of urethane group is compensated and the LC properties are
recovered.
Keywords: liquid-crystalline diols; phenylisocyanate; mesophases; phenylurethanes
Financial support of the Grant Agency of the Academy of Sciences of the Czech Republic
(grant A4112901) is gratefully acknowledged.
17

18
M. Kasˇpar et al.
INTRODUCTION
Thermotropic liquid crystalline (LC) polymers with alternating rigid
(mesogenic) and flexible (spacer) units in the chain have attained con-
siderable attention in literature [1,2]. Systems such as polyesters, poly-
ethers, polycarbonates, etc. have been investigated. Less attention was
devoted to LC polyurethanes, as their LC=isotropic transition is located at
high temperatures. In LC polyurethanes the mesogenic groups were usually
introduced into polyols or polyisocyanates [3,4]. Recently LC networks
(LCNs) also have been investigated [5,6]. In the isotropic state the LCNs
exhibit the mechanical behavior of conventional networks, whereas in the
LC state a complex behavior reflecting a coupled response of ordered
mesogens to the applied force has been found [7,8]. Both types of the
LCNs, with mesogens in the main or in the side chains, have been inves-
tigated. The DSC measurements of polyurethanes having the mesogenic
part in the main chain revealed that the transition temperatures in LC
polyurethanes qualitatively corresponded to those in LC diols [8]. The
advantage of LCNs prepared from polyols with mesogens in side chains is in
their lower melting temperatures, so that the behavior corresponding to
classical elastomers can be obtained. A modification of the structure of
initial reactants could influence the thermal and mechanical properties of
the corresponding polyurethane systems.
We have synthetised LC diols of various structures with two or three
aromatic rings in the side chain. We investigated the relation between the
type of the side substituent (structure of mesogen and=or spacer) and the
mesogenic behavior of the diols.
By the reaction of diols with phenylisocyanate in the stoichiometric
ratio of reactive groups ([OH]=[NCO] ¼ 1) bis-urethanes were prepared.
The mesomorphic properties of the bis-urethanes have been estab-
lished and compared with those of corresponding diols. The aim was to
find a bis-urethane with a wide temperature range of mesophase, over-
lapping the mesophase range of the corresponding diol, that could be
used for preparation of LC polyurethanes by the polymerization in
LC state.
EXPERIMENTAL
Structure of Diols and Related Phenylisocyanates
A series of diols, with two or three aromatic rings in the side chain bound to
the two terminal hydroxy groups in the main chain, have been synthesized
(compounds 1–6, Y ¼ OH). All these diols were reacted with phenyliso-
cyanate at the ratio [OH]=[NCO] ¼ 1. In this way a series of bis-urethanes

Liquid-Crystalline Diols and Bis-Urethanes
19
has been prepared where both the –OH groups have been substituted by
phenylisocyanate groups (compounds 1–6, Y ¼ OCONHphenyl).
n ¼ 5, 6; X ¼ H, O2N, NC, H13C6O, H15C7O, H17C8O, H21C10O, or phenyl;
Y ¼ OH or OCONHphenyl
Synthesis of Diols
The synthesis of materials was carried out according to the Scheme 1.
Starting phenols (7) were obtained by diazotation and copulation of cor-
responding anilins with phenol.

20
M. Kasˇpar et al.
SCHEME 1 Synthesis of diols with mesogenic groups.
Preparation of 2-(6-bromhexyl)-1,3-propandiol (8)
30 g (1.3 M) of sodium was dissolved in 500 ml of absolute ethanol under
cooling. Then 260 g (1.625 M) of dried diethylmalonate and 407 g (1.668 M)
of dried 1,6-dibromhexane were added under vigorous stirring and refluxed
for 90 min. The mixture was cooled down and distilled under reduced
pressure. Boiling point of the product was 145–150ꢀC=1.5 mm. The yield
was 198.5 g, n20 ¼ 1.4600. For the next reaction, 185 g of this compound
was dissolved in 4000 ml of methanol and heated to the boiling point.

Liquid-Crystalline Diols and Bis-Urethanes
21
During 2 h, 183 g (4.82 M) of natriumborohydride were added slowly under
stirring. After cooling of the mixture, 2000 ml of water was added and
vigorously stirred for 1 h. Methanol was distilled under reduced pressure,
and the remaining water phase was extracted three times by diethylether.
Sixty one g of yellowish oil was dissolved in 500 ml of heptane and 400 ml of
ethyl acetate and cooled down to ꢁ80ꢀC. Crystals were separated on
cooled fritted glass. After heating to laboratory temperature they melted
into yellow viscous liquid (8), yield 27 g.
1
Products were characterized by H-NMR spectroscopy using a Varian
NMR spectrometer Gemini 200 at 25ꢀC.
1H-NMR (CDCl3, 200 MHz): 3.70 dd and 3.55 dd (2Hþ2H, CH2OH); 3.34
t (2H, CH2Br); 3.22 s (2H, OH); 1.79 quint (2H, CH2CH2Br); 1.65 m (1H,
CH); 1.1–1.4 m (8H, CH2).
Acetal (9) was prepared from 1.1 M (132 g) of 1,1,1-tris(hydroxy-
methyl)ethane, 1 M (30 g) paraformaldehyde, and 30 g CaCl2 in 100 ml
dioxane, with 1 ml HCl used as a catalyst. The mixture was refluxed for
10 h, and then the organic layer was separated, dried by calcium chloride,
and distilled. Boiling point of the product was 103ꢀC=10 mm.
Preparation of acetal (10)
Twenty three g of sodium was pulverized in 300 ml of xylene. After
cooling to 100ꢀC, 150 g of acetal (9) was added dropwise under vigorous
stirring. The mixture was then stirred for 2 h under the reflux. After cooling
to room temperature, 200 ml of dioxane, 488 g of 1,6-dibromhexane, and
2 ml 15-crown-5 were added. The reaction mixture was stirred for 1 h at
room temperature and then slowly heated to boiling point. Then the mix-
ture was refluxed for 2 days and left to stand overnight. The precipitated
natrium bromide was separated by filtration and extracted by hot dioxane.
Then the dioxane was evaporated and the yellow residue was distilled (b.p.
145–150ꢀC=3 mm) to obtain 110 g of colorless liquid (10).
1H-NMR (CDCl3, 200 MHz): 4.9 and 4.65 dd (2H, -O-CH2-O-); 3.8 and 3.4
dd (4H ,C-CH2-O); 3.45 m (6H, CH2Br and CH2OCH2); 1.85 quint. (2H,
CH2CH2Br); 1.58 quint. (2H, CH2CH2O); 1.40 m (4H, CH2); 0,85 s (3H,
CH3).
Preparation of diol (11)
Hydrolysis of very stable acetal ring was carried in two steps: Acetal (10)
(50 g) was mixed with an excess of acetanhydride and 1 ml of concentrated
sulphuric acid. The resulting solution was heated in a water bath for 10 h.
The acetanhydride was removed by evaporation under reduced pressure
and the residue was diluted by ethanol. Then the solution was refluxed for
several hours and evaporated under reduced pressure to dryness. Then the

22
M. Kasˇpar et al.
procedure of addition of new portion of alcohol, refluxing, and evaporating
was repeated three times. The residue was diluted with water (100 ml) and
extracted twice with ether. The combined extracts were dried over anhy-
drous potassium carbonate. The ether was evaporated. The product (11) is
yellow viscous liquid (yield 41 g).
1H-NMR (CDCl3, 200 MHz): 3.5–3.7 dd (4H, CH2OH); 3.4 m (6H, CH2Br,
CH2OCH2), 1.8 quint (2H, CH2CH2Br); 1.55 quint. (2H, CH2CH2O); 1.40 m
(4H, CH2), 0.8 s (3H, CH3).
Preparation of final diols
Diols (1) were obtained by heating of corresponding phenols to the
temperature of 60ꢀC with fivefold excess of 1,5-dibrompentane resp. 1,6-
dibromhexane in the excess of anhydrous potasium carbonate in acetone
for 48 h. Products were crystallized from acetone and then heated with
excess of diethylamine in isopropanol for 48 h at 85ꢀC. The final diols (1)
were crystallized twice from toluene.
1H-NMR (CDCl3, 200 MHz):
diol 1 (X ¼ CN, n ¼ 6, Y ¼ OH): 7.89 d (4H, HAr ortho to –N); 7.73 d
(2H, HAr ortho to CN); 6.95 d ( 2H, HAr ortho to –OR); 3.99 t (2H,
CH2OAr), 3.65 t (4H, CH2OH); 2.60 t (4H, CH2CH2O); 2.49 t (2H, CH2N);
1.77 quint (2H, CH2CH2OAr); 1.3–1.46 m (6H, CH2).
diol 1 (X ¼ NO2, n ¼ 5, Y ¼ OH): 8.28 d (2H, HAr ortho to NO2), 7.88 m
(4H, HAr ortho to –N); 6.93 d (2H, HAr ortho to –OR); 3.99 t (2H,
CH2OAr); 3.55 t (4H, CH2OH); 2.59 t (4H, CH2CH2O); 2.50 t (2H, CH2N);
1.77 quint (2H, CH2CH2OAr); 1.45 m (4H, CH2).
Diols (2) were obtained by heating of corresponding phenols with 1.1
excess of (8) in acetone in excess of dried potassium carbonate at 60ꢀC for
48 h. The final diol (2) was filtered and recrystallized from toluene.
1H-NMR (CDCl3, 200 MHz):
diol 2 (X ¼ C6H5, n ¼ 6, Y ¼ OH): 7.06–7.89 m (13H, HAr); 4.05 (2H,
CH2OAr); 3.4 dd (4H, CH2OH); 3.1 t (2H, –OH); 1.72 m (1H, CH); 1.23–
1.44 (10H, CH2).
The final diols (3), (4), (5), and (6) were obtained by reaction with
mesogenic phenols in acetone in the presence of anhydrous potassium
carbonate and potassium iodide as catalysts. Mesogenic phenols were
ˇ
synthesized by usual methods or by the method described in Kaspar et al.
[9]. All products were crystallized from acetone and purified by column
chromatography on silica gel (Kieselgel 60, Merck Darmstadt) using CH2Cl2
with 5% of ethanol as an eluent. The purity of products was determined by
HPLC carried out with chromatograph Ecom using Tessek C18 column with
mixture of methanol and toluene (90:10) as the eluent and detection of
eluting products by UV-VIS detector (l ¼ 290 nm).
1H-NMR (CDCl3, 200 MHz):

Liquid-Crystalline Diols and Bis-Urethanes
23
diol 3 (X ¼ C6H13O, n ¼ 6, Y ¼ OH): 8.15 d (2H, HAr ortho to –COO);
7.50 m (4H, HAr); 7.25 d (2H, HAr ortho to –OCO); 6.98 d (4H, HAr ortho
to –O–); 4.00 m (4H, CH2OAr); 3.60 q (4H, –CH2OH); 3.42 m (4H,
CH2OCH2); 2.3 brs (2H, OH); 1.8 m (4H, CH2 CH2OAr); 1.2–1.6 m (12H,
CH2); 0.9 t (3H, CH3); 0.8 s (3H, CH3).
diol 4 (X ¼ C8H17O, n ¼ 6, Y ¼ OH ): 7.45 d (4H, HAr meta to –O–); 6.95 d
(4H, HAr ortho to –O–); 4.0 t (4H, CH2OAr); 3.5–3.7 dd (4H, CH2OH);
3.44 m (4H, CH2OCH2), 2.2 brs (2H, OH); 1.8 quint (4H, CH2CH2OAr); 1.2–
1.7 m (16H, CH2); 0.9 t (3H, CH3); 0.8 s (3H, CH3).
diol 4 (X ¼ C7H15CO, n ¼ 6, Y ¼ OH): 8.0 d (2H, HAr ortho to –CO);
7.6 dd (4H, HAr); 7.0 d (2H, HAr ortho to –O); 4.0 t (2H, CH2OAr); 3.5–
3.7 q (4H, CH2OH); 3.42 m (4H, CH2OCH2); 2.95 t (2H, CH2CO); 2.4 brs
(2H, OH); 1.8 quint (2H, CH2CH2OAr); 1.2–1.6 m (14H, CH2); 0.9 t (3H,
CH3); 0.8 s (3H, CH3).
diol 6 ( X ¼ C6H13O, n ¼ 6, Y ¼ OH): 7.85 d (4H, HAr ortho to N); 7.0 d
(4H, HAr ortho to –O); 4.0 t (4H, CH2OAr); 3.5–3.7 q (4H, CH2OH); 3.4 m
(4H, CH2OCH2); 2.7 brs (2H, OH); 1.8 quint (H, CH2CH2OAr); 1.2–1.6 m
(12 H, CH2); 0.9 t (3H, CH3); 0.8 s (3H, CH3).
Preparation of bis-urethanes
Corresponding diols were refluxed in toluene with twofold excess of
phenylisocyanate for 60 min. After cooling down, the precipitate was fil-
tered and crystallized from toluene.
1H-NMR (CDCl3, 200 MHz):
bis-urethane 1 (X ¼ NO2, n ¼ 6, Y ¼ OCONHC6H5): 8.29 d (2H, HAr
ortho to NO2); 7.23 m (7H, HAr); 6.93 m (5H, HAr); 4.19 t (4H, CH2OCO);
3.96 t (2H, CH2OAr); 2.76 t (4H, CH2CH2OCO); 2.52 t (2H, CH2N); 1.73
quint (2H, CH2CH2OAr); 1.28–1.43 m (6H, CH2).
bis-urethane 2 (X ¼ C6H5, n ¼ 6, Y ¼ OCONHC6H5): 7.06–7.89 m (23H,
HAr); 4.26 dd (4H, –CH2OCO); 3.99 t (2H, CH2OAr); 1.72 quint (1H, CH);
1.23–1.44 m (10H, CH2).
bis-urethane 3 (X ¼ C6H13O, n ¼ 6, Y ¼ OCONHC6H5): 8.15 d, (2H, HAr
otho to –COO); 7.50 m (4H, HAr); 7.3 m (10 H, HAr ortho to –OCO, HAr
meta and ortho to NH); 7.0 m (6H, HAr ortho to –O–, HAr para to –NH);
6.6 s (2H, NH); 4.15 m (4H, CH2OCONH); 4.0 m (4H, CH2CH2OAr); 1.2–
1.6 m (12H, CH2); 1.0 s (3H, CH3); 0.9 t (3H, CH3).
Methods of Measurements
Phase transition temperatures and the sequence of mesomorphic phases
were determined from characteristic textures and their changes were
observed under a polarizing microscope Eclipse E-600 Nikon. The samples
were filled into glass plates in the isotropic state. For temperature control

24
M. Kasˇpar et al.
the heating stage Linkam was used. The temperature changed usually at a
rate of 2–5 K=min.
Most of materials were also studied by differential scanning calorimetry
carried out by Perkin-Elmer DSC-7 equipment using the 5–10 K=min
heating and cooling rate.
RESULTS AND DISCUSSION
Phase transition temperatures established from texture changes during
observation in polarizing microscope are in good agreement with the
positions of peaks in DSC plots. Data for all studied materials are sum-
marized in Table 1. In the starting diols as well as in the bis-urethanes the
existence of mesophases depends strongly on the type of substituent X.
For diols 1 with X ¼ H the mesophases do not occur. If X ¼ CN, the nitril
group increases the longitudinal dipole moment of the molecule, which
causes higher intermolecular interactions and the smectic mesophase
appears on cooling. This mesophase partially crystallizes during heating
(see Figure 1). All bis-urethanes 1 with X ¼ H or X ¼ CN did not have any
mesophase and went into an amorphic phase during cooling.
TABLE 1 Phase Transition Temperatures for Diols and Bis-Urethanes
Diol
Bis-urethane
N
Formula
X
n
m.p. Iso
N
Sm
Cr m.p. Iso
Cr
1
1
1
1
1
1
1
1
2
3
4
4
5
6
6
H–
H–
5
6
5
6
5
6
5
6
6
6
6
6
6
6
6
77
92
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
–
–
–
–
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
–
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
–
–
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
–
–
–
ꢂ
ꢂ
ꢂ
56
77
ꢂ
ꢂ
x
x
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
77
78
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
–
–
–
–
–
–
–
xx
xx
xx
xx
xxx
xxx
ꢂ
NC–
NC–
103
102
90
106
97
(99)
(59)
69
101
86
O2N–
O2N–
128
130
114
146
180
125
123
52
105
82
102
1
68
C8H17O–
Phꢁ
ꢁ18
133
164
102
105
89
100
55
50
48
137
168
105
117
96
138
168
126
152
ꢂ
ꢂ
–
–
–
ꢂ
ꢂ
ꢂ
ꢂ
Ph–
121
118
116
48
121
< 20
23
ꢂ
C6H13O–
C8H17O–
C7H15CO
ꢂ
120
112
174
171
163
ꢂ
(46)
140
78
x
C
10H21O–
C6H13O–
10H21O–
107
129
120
156
139
152
94
149
86
153
159
138
ꢂ
114
107
ꢂ
C
75
75
ꢂ
x Material partially crystalizes during heating.
xx Material does not crystallize and continuously goes into an amorphic phase.
xxx Decomposition.
ꢂPhase exists.

Liquid-Crystalline Diols and Bis-Urethanes
25
FIGURE 1 DSC plots for diol 1 (X ¼ CN, n ¼ 6, Y ¼ OH). Heating (cooling) rate is
5–10 K=min.
The nitro group as a substituent polarizes mesogenic core of the mole-
cule even stronger. In addition, the nematic phase appears and the tem-
perature range of mesophases is expanded. Unfortunately after
substitution of the –OH groups of diols by phenylurethanes, the decom-
position of materials occurs after melting. The strong oxidation effect of
nitro group also contributes to this decomposition. Therefore, the nitro and
cyano groups have not been introduced as the substituents to the molecule
of more complicated compounds having three aromatic rings. We
observed for diol 1 substituted by nitro group two mesophases in contra-
diction to diol 1 substituted by CN group. Similar behavior was observed in
a case of terminally substituted mesogens with azo group in mesogenic core
[10]. The author mentioned nematic mesophase for compound substituted
by CN group whereas we found smectic mesophase. This different behavior
may be connected with the fact that compounds in Petrov and Shimizu [10]
had no free hydroxy groups. The mesogenic behavior of diol 1 (X ¼ NO2)
corresponds to the compounds with terminal NO2 group that were
described before [10,11].
Longer alkoxy substituent in the compound 1 leads to expected
decrease of melting point due to lowering of the dipole moment of the
molecule. However, mesophases of corresponding bis-urethane dis-
appeared in spite of the fact that the starting diol had smectic mesophase,
which crystallizes at very low temperature (see Figure 2), and the liquid
crystalline behavior existed within the temperature range of about 130
degrees. Introduction of a nonsubstituted phenyl ring into the X position of
the compound 1 stabilized the mesophases, and a nematic phase also

26
M. Kasˇpar et al.
FIGURE 2 DSC plots for diol 1 (X ¼ C8H17O, Y ¼ OH). Heating (cooling) rate is 5–
10 K=min.
appeared in the corresponding bis-urethane in spite of the fact that a
partial decomposition of the material takes place.
Compound 2 differs from compound 1 by the diol type. When the phenyl
ring was used in the X position of the diol 2, similar behavior of monotropic
phases was observed at higher temperatures than in the case of the diol 1.
Bis-urethane with the structure 2 has the nematic phase in the tempera-
ture range that is much narrower than that for the bis-urethane 1.
Modification of diol structure using more branched alkyl chain (formulas
3 and 4) did not lead to a substantial widening of the temperature range of
mesophases. For both, diol 3 and bis-urethane 3 mesophases disappeared.
For the diols 4 with biphenyl moiety in the core, only a nematic phase was
observed. It differs from similar amphiphilic biphenyl derivatives with
another type of diol unit described by Tschierske et al. [12] that exhibited
smectic C and smectic A phases. The diol of similar structure having
biphenyl mesogenic core was also studied by Akiyama and Koide [13]. Their
diol had methoxy group in para position and less branched alkyl chain.
They observed one enantiotropic mesophase for diol and one or two
mesophases for related polyurethanes. The corresponding bis-urethanes 4
did not have any mesophase. The compound was relatively stable, and no
symptoms of decomposition were observed even after multiple heatings.
The longitudinal dipole moment of mesogene for aliphatic X ¼ RO is very
low, and the differences in electron densities on aromatic rings are probably
not sufficient to create strong enough donor–acceptor interactions that
could create ordered structure. The strong hydrogen bonds of urethane
groups dominate and probably disturb parallel ordering of molecules.
Even increasing of the molecule polarity due to introduction of a keto
group to the molecule of formula 4 (X ¼ C7H15CO) did not bring

Liquid-Crystalline Diols and Bis-Urethanes
27
improvement. In spite of the fact that diol 4 exhibits a nematic phase, bis-
urethane 4 has no mesophase and low melting point.
Since the best results were obtained for the compounds 1 and 2 with
the substitution by phenyl ring, we prepared and studied materials
containing three aromatic rings connected by ester group in the mesogenic
core (formulas 5 and 6). It is known that the presence of the ester group in
molecule for some type of LC compounds could lead to a decrease of the
phase transition temperatures [9,14] and simultaneously could disturb
compensation of the dipole moment by a symmetric substitution by the
alkyl groups (formula 4, X ¼ RO). All the three studied diols with formulas
5 and 6 show wide mesophase temperature ranges. After the addition of
phenylisocyanate to the diol 5, the smectic mesophase disappears and only
the narrow nematic phase remains. The bis-urethanes derived from the
structure 6 have nematic phases in wide temperature range regardless of
the alkyl chain length. This fact confirms that the presence of three aro-
matic rings is substantial for formation of mesophases in bis-urethanes.
Photos of a texture in smectic phase of diol 5 (X ¼ C10H21O) and in
mesophase of corresponding bis-urethane 5 (X ¼ C10H21O) are shown in
Figures 3 and 4 respectively. We cannot distinguish the type of the smectic
FIGURE 3 Texture of the diol 5 (X ¼ C10H21O, Y ¼ OH) in smectic phase at the
temperature 150ꢀC. (See Color Plate I).

28
M. Kasˇpar et al.
FIGURE 4 Texture of the bis-urethane 5 (X ¼ C10H21O, Y ¼ OCONHC6H5) in a
mesophase at the temperature 147ꢀC. (See Color Plate II).
FIGURE 5 DSC plots for bis-urethane 6 (X ¼ C10H21O, Y ¼ OCONHC6H5). Heating
(cooling) rate is 5–10 K=min.

Liquid-Crystalline Diols and Bis-Urethanes
29
mesophase from observed texture for diols 5 and 6. It seems to be partially
homeotropically aligned. Bis-urethane 6 (X ¼ C10H21O) shows a postponed
crystallization, which takes place during heating after the phase transition
(Figure 5). This phenomenon has not been studied in detail so far.
CONCLUSION
Great differences in mesogenic behavior of diols and bis-urethanes are
caused by the distinct character of inter- and intra-molecular hydrogen
bonds [15,16,17]. Hydrogen bond O . . . H . . . O supports a stronger aggre-
gation of molecules of diols and by this the existence of mesophases
instead of weaker bonds N . . . H . . . N in bis-urethanes. We have found
promising materials for preparation of grafted LC polyurethanes with
urethane group in the main chain. Bis-urethanes 6 with three phenyl rings
in the core and the long alkyl chains as substituents (X ¼ C6H13O or
X ¼ C10H21O) have wide mesophase temperature ranges (about 80
degrees) that overlap with those of the mesophases of the corresponding
diols. We assume that in the middle of these intervals the whole system
could not pass to the crystalline or isotropic state during polymerization.
The physical properties of such LCN polyurethanes are now under study.
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