Orientation effects in monodomain nematic liquid crystalline polysiloxane elastomers

Article abstract of DOI:10.1039/a705570f

A series of monodomain liquid crystalline (LC) elastomers based on a polysiloxane were synthesised. These elastomers were prepared either with one or two cross-linking agents in the presence of a mechanical field. By using the real-time X-ray facility at

Full text of DOI:10.1039/a705570f

J O U R N A L O F
Orientation effects in monodomain nematic liquid crystalline
polysiloxane elastomers
D. Lacey,a* H. N. Beattie,a† G. R. Mitchellb and J. A. Popleb‡
aSchool of Chemistry, T he University of Hull, Hull, UK HU6 7RX
bDepartment of Physics, T he University of Reading, W hiteknights, Reading, UK RG6 2AF
C H E M I S T R Y
A series of monodomain liquid crystalline (LC) elastomers based on a polysiloxane were synthesised. These elastomers were
prepared either with one or two cross-linking agents in the presence of a mechanical field. By using the real-time X-ray facility at
the University of Reading (AXIS), we have shown that the nematic order parameter ꢀP ꢁ is dependent on both the extension l
value and the degree of cross-linking. We have also shown that the monodomain elastomers, exhibiting permanent alignment and
2
ꢀP ꢁ values of about 0.5, can be prepared by using only one cross-linking agent making the synthesis of these monodomain LC
2
elastomers much more simple and cost effective than that proposed by Kupfer.
¨
Liquid crystalline polymers can be covalently cross-linked to
Results and Discussion
form three dimensional networks, namely, LC elastomers.
Since the synthesis of the first LC elastomer in 1981,1 which
was based on a polysiloxane backbone, a number of different
types of elastomers have been reported. These have included
elastomers containing polyacrylates and polymethacrylates2–6
and work has been extended to slightly cross-linked main
chain as well as combined main-chain–side-chain3,7,8 materials.
These networks are unique in their properties in that they
exhibit rubber elasticity as well as properties associated with
liquid crystals. Provided that the networks have a low cross-
link density the motions of the chain segments are not impaired
and the mesogenic moieties are still free to orientate. Only
near to the cross-link points are the motions of the mesogens
somewhat restricted. Due to cross-linking between chains, the
translational diffusion of the polymer chains is prevented and
therefore the elastomer exhibits shape retention. The field of
LC elastomers has led to a number of ideas which combine
the advantageous properties of LC low molecular mass and
LC polymers as well as rubber elasticity and shape retention.
Certain disadvantages of polymers, e.g. differing chain lengths
leading to slight differences in physical properties amongst
different polymer batches, are favourably lost on cross-linking.
One of the major advantages of LC elastomers is the property
of shape retention thereby allowing mesogenic alignment by
mechanical deformation.9,10
The first successful synthesis of a monodomain polysiloxane
elastomer was achieved by Kupfer25 in 1991 and a schematic
¨
representation of the route adopted by Kupfer is given in
¨
Scheme 1. The network was synthesised in two steps, with the
second cross-linking step being carried out under the influence
of a mechanical field. The different types of active sites on the
two cross-linking agents gave rise to different rates of hydrosi-
lylation of these active sites with the polysiloxane backbone.
It was postulated that the alkene active site (CHNCH ) would
be of the order 100 times faster than that of the methacryloyl-
2
oxy active site [OCOC(CH )NCH ] and therefore the forma-
3
2
tion of the monodomain could be carried out in two distinct
steps. The first involves the formation of a polydomain elasto-
mer involving the cross-linking agent containing the two alkene
active sites. During this process, the second cross-linking agent
would be attached to the polysiloxane backbone via the alkene
active site only, leaving the methacryloyloxy active site
untouched. The second cross-linking step involved only the
methacryloyloxy active site (the bifunctional cross-linking
agent), and because this was carried out under the influence
of a mechanical (stress) field this will result in the formation
of a monodomain elastomer.
In our work presented in this paper we have used the real-
time X-ray facility at the University of Reading to examine
more closely the second cross-linking step in the route adopted
The use of X-ray diffraction as a technique for studying and
confirming phase types in LMMLC materials11–14 and in LC
polymers15–20 has been well reviewed. X-Rays can also be used
to define molecular ordering in samples and more quantitative
studies such as the effect of temperature21–23 or external fields,
e.g. magnetic or mechanical,24 on the orientational behaviour
can also be carried out using this technique. The real-time X-
ray equipment at the University of Reading (AXIS, area X-ray
imaging system) allows in situ experiments on orientational
behaviour in LC polymers, and of particular interest to this
work, in LC elastomers, to be carried out and order parameters
by Kupfer et al. in the formation of monodomain polysiloxane
¨
elastomers. A number of elastomers were synthesised in which
the structure of the mesogenic side chain was kept the same,
but the number and structure of the cross-linking agents used
to form the elastomer were varied. The synthesis of the cross-
linking agents and the mesogenic side chain are given in
Schemes 2–4. The formation of the monodomain polysiloxane
elastomer involving both cross-linking agents are shown in
Schemes 5 and 6 with step 2 in Scheme 5 being carried out
under the influence of a mechanical (stress) field. The step
shown in Scheme 6, which outlines the formation of the
monodomains using only one cross-linking agent, involved
initially the normal procedure for the formation of a poly-
domain elastomer, and then the elastomer was subjected to
a mechanical (stress) field to manifest the monodomain
elastomer.
such as ꢀP ꢁ to be calculated.19 X-Rays are scattered from the
electrons within a molecule and therefore the scattering pattern
2
reflects distribution of the regions of electron density. This
method is restricted to the measurement of mesogenic an-
isotropy only and not to the polymer backbone anisotropy.
†Present address: Dow Corning Ltd, Cardiff Road, Barry, South
Glamorgan, Wales, UK CF63 2Y
‡Present address: School of Chemistry, The University of Leeds,
Leeds, UK LS2 9JT
Static X-ray diffraction
The X-ray diffraction pattern of an elastomer based on the
mesogen 2 showed a diffuse outer ring characteristic of a
J. Mater. Chem., 1998, 8(1), 53–60
53

Scheme 1
54
J. Mater. Chem., 1998, 8(1), 53–60

+
+
CH2 CH(CH2)4Br
HO
CO2H
BnO
OH
Cl(CH2)6OH
EtOH
NaOH (aq)
K2CO3
butanone
CH2 CH(CH2)4O
CO2H
BnO
O(CH2)6OH
DCC
POP
CH2Cl2
CH3O
OH
Na
BuOH
HO
O(CH2)6OH
CH2 CH(CH2)4O
CO2
OCH3
2
ClCO2CH3
NaOH (aq)
Scheme 2
O
O
O(CH2)6OH
+
CH2 CH(CH2)4Br
HO
OH
CH3O
CH2 C(CH3)COCl
NEt3
K2CO3
butanone
CH2Cl2
O
CH2 CH(CH2)4O
O(CH2)4CH CH2
O
O(CH2)6OC(O)C(CH3) CH2
CH3O
3
NEt3
Scheme 3
EtOH
nematic phase. The corresponding polymer (g −0.4 N 95 I °C)
was also nematic. In elastomeric samples of low cross-link
density the state of the nematic phase remains unchanged on
cross-linking.1,5,26–28 All the elastomers presented in this paper
exhibit a nematic phase at room temperature.
HO
O(CH2)6OC(O)C(CH3) CH2
DCC
DMAP
CH2Cl2
CH2 CH(CH2)4O
CO2H
Cross-linking effects in elastomers
The data from AXIS for the elastomers, along with their
extension values l and phase behaviour are given in Table 1.
The data from AXIS was used to measure the nematic order
CH2 CH(CH2)4O
CO2
O(CH2)6OC(O)C(CH3) CH2
4
parameter ꢀP ꢁ.19
Elastomers using both cross-linking agents 3 and 4 were
2
Scheme 4
synthesised (a, b and c) as well as elastomers using only cross-
linking agent 3 (d), and cross-linking agent 4 (e and f ). The
maximum value of ꢀP ꢁ for these type of experiments obtained
was 0.56 which corresponded to the elastomer which was
extended the greatest amount.
comparable to elastomer c. Therefore it seems that the chemical
structure of the elastomer has limited influence on the value of
2
ꢀP ꢁ up to extensions of 38% (l=1.38) during the second step
of the cross-linking reaction. The elastomer which was extended
2
Low values of ꢀP ꢁ are a consequence of the maximum
extension not being attained. It must be pointed out that all
2
the most (l=1.68) gave the largest ꢀP ꢁ value (elastomer b,
0.56). Correspondingly the elastomer which was extended the
2
the elastomers undergo an additional strain process which is
extremely difficult to quantify. Initially, the elastomer is in a
swollen state at the beginning of the stretching procedure. The
toluene then evaporates out of the network and the sample
shrinks exerting additional strain on the elastomer. Finally,
the elastomer relaxes as the experiment proceeds releasing
some of the strain. Elastomers with a much higher order
parameter can be synthesised using a constant load rather
than strain. Fig. 1 of sample (b) was recorded which shows a
high degree of orientation of the mesogenic side chains.
least gave the smallest ꢀP ꢁ value (elastomer e, 0.40).
So that a direct comparison could be made between the
different elastomers the time taken to reach 90% of the value
2
of the maximum ꢀP ꢁ value for each elastomer was estimated
from the plot of the orientation function coefficient against
time. The shape of the plots of orientation function coefficient,
2
i.e. ꢀP ꢁ, versus time for elastomers a–f are all similar and the
plot for elastomer d is given in Fig. 2 for illustration. Initially
2
a large increase in order parameter is observed which eventu-
ally levels off to a plateau with time. The initial rate of change
of orientation of elastomers is different which corresponds to
the response of the network to strain. Initially the network is
relatively lightly cross-linked and the gradient of the graph is
steep. As the percentage of cross-linking agent increases within
the network, the gradient of the graph decreases until eventu-
ally after 3 or 4 h there was virtually no more mesogenic
alignment of the mesogenic side chains.
A comparison between the elastomers which contain cross-
linking agents 3 and 4 (a, b and c), showed that, on increasing
the extension, the order parameter ꢀP ꢁ increased. Using only
cross-linking agent 3 (elastomer d) and extending the elastomer
2
during the synthesis to 30% (l=1.30) a ꢀP ꢁ value of 0.50 0.03
was obtained which is comparable to elastomer c. For elastomer
2
f, prepared with only cross-linking agent 4, a ꢀP ꢁ value of 0.48
2
was obtained on extension of 38% (l=1.38), which is also
J. Mater. Chem., 1998, 8(1), 53–60
55

Scheme 5
The three elastomers prepared using both cross-linking
agents took the longest length of time to obtain 90% of their
the second step of the cross-linking process were varied, and
the results were noted. The plots of orientation function
maximum ꢀP ꢁ value. It has been observed in similar previous
experiments that the rate of evaporation of toluene from
coefficient (ꢀP ꢁ) vs. time (see Fig. 2) are all of similar shape;
the steepness of the curve corresponds to the response of the
2
2
network to strain. Other factors such as rate of evaporation
of solvent and cross-link density after the first step of the
monodomain synthesis, must also be taken into account whilst
elastomers containing dissimilar cross-linking agents is differ-
ent. The rate of evaporation, for example, from the elastomer
containing cross-linking agent 4 (elastomers e and f ) is much
slower than that from the elastomer containing only cross-
linking agent 3 (elastomer d). The rate of evaporation must
also be taken into account when discussing the results from
these experiments as it would seem likely that a rapid removal
of solvent would swell the elastomer and therefore increase the
rate of reaction of the second cross-linking agent.
discussing the results. A comparison of ꢀP ꢁ values was made
and the values for these elastomers ranged from 0.40–0.56.
These experiments on cross-linking effects in polysiloxane
2
elastomers show that the nematic order parameter ꢀP ꢁ is
dependent on the extension, l. This is as predicted by the
2
Landau–de Gennes theory.29–34 The value of the nematic order
parameter ꢀP ꢁ also depends on the degree of cross-linking
which has taken place prior to extension. A relatively high
Re-examination of the elastomers by AXIS was carried out
after 4 to 5 days to check that the orientation of the mesogenic
side chains had remained unchanged. Alignment of the meso-
genic side chains is permanent in all of the elastomers prepared,
showing that the second cross-linking process is effective.
2
nematic order parameter ꢀP ꢁ value of about 0.5 was obtained
using a modified and improved method of synthesis of monodo-
2
mains developed by Kupfer et al.1 From the data it can be
¨
clearly observed that the results for ꢀP ꢁ are the same within
experimental error. Therefore it can also be concluded that
2
Conclusions
there is little difference whether one cross-linking agent is used
or two. It is possible to form a monodomain polysiloxane
elastomer with permanent alignment by just using one cross-
linking agent which makes the synthesis much more simple
and cost effective. The time taken for the mesogenic side chains
to align, during the second step of the cross-linking reaction,
The cross-linking effects and ꢀP ꢁ values of six different
elastomers were compared (elastomers a–f ) to find out how
factors such as extension during the second step of the cross-
linking reaction and chemical structure affected ꢀP ꢁ values.
The cross-linking agents used and the extension ratios during
2
2
56
J. Mater. Chem., 1998, 8(1), 53–60

Scheme 6
was found to be between 4 and 6 h. For all monodomain
elastomers synthesised in the LC phase, during the second step
of the reaction, the alignment was permanent.
the internal standard, unless otherwise stated. The multiplicities
of absorptions are denoted by singlet (s), doublet (d), triplet
(t), quartet (q) and multiplet (m). Infrared (IR) spectra were
obtained using either a Perkin Elmer 983G or a Perkin Elmer
487G spectrometer. The samples were prepared as thin films
in potassium bromide discs. Mass spectra were obtained on a
Finnigan MAT 1020 GC–MS spectrometer: M+ represents the
molecular ion and the base peak is indicated by 100%. Optical
microscopy was performed using an Olympus microscope
BH2, in conjunction with a Mettler hot-stage FP52 and a
Mettler controller FP5. Differential scanning calorimetry
Experimental
Physical techniques
1H Nuclear magnetic resonance spectra (NMR) were obtained
using a JMN GX270 FT spectrometer (270 MHz). Deuterated
chloroform was used as the solvent and tetramethylsilane as
J. Mater. Chem., 1998, 8(1), 53–60
57

Table 1a
phase
behaviour/°C
elastomer
ꢀP ꢁ
2 max
ꢀP ꢁ
2 90%
t
/s
l
90%
(a)E .253,4
0.51
0.56
0.47
0.50
0.40
0.48
0.46
0.50
0.42
0.45
0.36
0.43
18 000 1.56 g −8.8 N 75 I
12 000 1.68 g −7.7 N 80 I
15 000 1.30 g −5.8 N 75 I
10 000 1.30 g −6.1 N 83 I
12 000 1.18 g −5.6 N 85 I
8000 1.38 g −9.5 N 87 I
m
(b)E .253,4
m
(c)E .253,4
m
(d)E .253
m
(e)E .254
m
(f )E .254
m
aꢀP ꢁ
2 max
maximum ꢀP ꢁ value respectively, t
90%
and l is the extension where extension is defined as the final
and ꢀP ꢁ
are the maximum ꢀP ꢁ value and 90% of the
2 90%
2
is the time taken to reach
2
ꢀP ꢁ
2 90%
length of the elastomer divided by the initial length of the elastomer.
Fig. 3 Schematic representation of AXIS
was indium. Analytical thin layer chromatography (TLC) was
performed on aluminium sheets coated in Kieselgel silica gel
60 F . All references to column chromatography signify flash
254
column chromatography using Sorbsil C60 (40–60 mm) as the
stationary phase. The column was put under pressure by the
use of air or nitrogen from a laboratory line or a blowing ball.
High performance liquid chromatography (HPLC) was used
to measure the purity of samples by using reverse phase
chromatography on a silica gel column (5 mm pore size,
Fig. 1 High degree of orientation of mesogenic side groups in
elastomer b as shown by AXIS
25×0.46 cm, Dynamax Microsorb C18 column) and
a
Spectroflow 757 UV detector (l=254 nm) with data handling
facilities. Melting points of the solids were measured using a
Gallenkamp melting point apparatus with adjustable heating
rates.
X-ray diffraction equipment (AXIS). The apparatus used at
the University of Reading is shown in Fig. 3. The data collected
˚
for wide angle X-ray is on the scale of 1 to 100 A and therefore
of the order of a few repeat units of the polymer chain. In
order to examine the orientational behaviour of samples on
the application of a mechanical stress, the elastomers were
mounted in a tensiometer (Rosand Precision Ltd.) which was
placed in the path of the X-ray beam and extension ratios
were measured. Cu-Ka radiation was used in conjunction with
a graphite monochromator and a pinhole collimator was used
to provide a 1 mm2 collimated beam at a wavelength of
0.154 nm.
Fractionation of polysiloxane backbone. Preparative GPC
was carried out at the University of York on a commercially
available polysiloxane backbone (DC1107, Dow Corning) in
order to fractionate the polydisperse polymer into relatively
monodisperse fractions. The instrument at the University of
York is fitted with two preparative columns 1.2 m long (from
Waters Associates Ltd.), with an internal diameter of 0.06 m
and each packed with Styragel (a polystyrene based gel).
Column A is used for the fractionation of low molecular mass
polymers up to 5×104 g mol−1. It has a nominal porosity of
500 nm and is estimated to have a plate count of ca. 7000
plates m−1. Column B is used for the fractionation of higher
molecular mass polymers up to 1×106 g mol−1. This Styragel
column has a nominal porosity of 1000 nm. After the fractions
were collected, the toluene was removed by distillation under
Fig. 2 Plot of the orientation function coefficient vs. time for
elastomer d
(DSC) was carried out using a Perkin Elmer DSC 7, with TAC
7/PC instrument interface and controlled cooling accessory.
Heating and cooling rates were usually 10 °C min−1 and a
nitrogen atmosphere was maintained in the furnace. The
reference sample used was gold and the calibration sample
reduced pressure and the polymer samples collected. The M ,
9
M and M /M were then determined using analytical GPC.
w
9
For a more detailed account of the method used, see ref. 35.
9
9
n
w
n
58
J. Mater. Chem., 1998, 8(1), 53–60

The fraction 2 was used for this work which had a DP value
of 234 and a DPI value of 1.1.
4-(6-Hydroxyhexyloxy)phenol. 1-Benzyloxy-4-(6-hydroxy-
hexyloxy)benzene (12 mmol) was dissolved in butanol (100 ml)
and heated under reflux. Sodium (12 mmol) was added slowly.
After all the sodium had completely reacted, water (15 ml) was
added carefully followed by hydrochloric acid (15 ml, 20%
v/v). The product was extracted into diethyl ether (100 ml)
and the ether solution was washed with water (3×100 ml) and
Preparation of mesogenic side chain 2 (Scheme 2)
4-(Hex-5-enyloxy)benzoic acid. 4-Hydroxybenzoic acid
(0.5 mol) was dissolved in ethanol (300 ml). Sodium hydroxide
(1 mol) and water (150 ml) were added and the solution was
brought to reflux. 6-Bromohex-1-ene (0.6 mol) was added
dropwise and the resulting solution was heated under reflux
for 24 h. The ethanol was removed and the residue was diluted
with water (300 ml). The cooled reaction mixture was acidified
with concentrated hydrochloric acid and the crude product
was filtered off and washed with water. The product was
purified by recrystallisation (ethanol, 50% v/v aq.). The purity
of the product was confirmed by TLC (dichloromethane, single
spot). Yield, 92%, K 101 N 140 I °C. d (CDCl ), 8.05 (d, 2H),
dried (MgSO ). The product was purified by recrystallisation
4
(ethanol). The purity of the compound was confirmed by TLC
(dichloromethane, single spot). Yield, 55%, mp, 69–70 °C. d
(CDCl ), 6.7–6.8 (s, 4H), 4.4–4.45 (s, 1H), 3.85–3.9 (t, 2H),
3.6–3.7 (m, 2H), 1.4–2.85 (m, 8H), 1.2–1.35 (s, 1H); n
H
3
max
(KBr)/cm−1, 3350–3360, 2880–2940, 1510, 1470, 1450, 1370,
(100%), 83, 65, 55.
1290, 1230, 1100, 1040, 820, 730; m/z, 209 (M+), 101, 91
1-(Methoxycarbonyloxy)-4-(6-hydroxyhexyloxy)benzene. 4-
(6-Hydroxyhexyloxy)phenol (26 mmol) was added, with vigor-
ous stirring, to a solution of sodium hydroxide (75 mmol) in
water (250 ml), maintained at 0 °C. Methyl chloroformate
(43 mmol) was added slowly to the resulting suspension,
keeping the temperature at 0 °C. The resulting reaction mixture
was allowed to stir at room temp. for a further 4 h. The
reaction was adjusted to pH 5 (universal indicator paper) by
the addition of a mixture of concentrated hydrochloric acid
and water (151). The product was extracted into diethyl ether
and the ether solution was washed with saturated sodium
H
3
6.9 (d, 2H), 5.85 (m, 1H), 5.0 (t, 2H), 4.05, (m, 2H), 2.15 (m,
2H), 1.85 (m, 2H), 1.62 (m, 2H); n
3860–3980, 1690, 1610, 1510, 1430, 1260, 845; m/z, 220 (M+),
(KBr)/cm−1, 3400,
max
138, 121, 82, 67, 55 (100%).
4-Methoxyphenyl 4-(hex-5-enyloxy)benzoate 2. 4-(Hex-5-
enyloxy)benzoic acid (0.02 mol), 4-methoxyphenol (0.02 mol)
and 4-pyrrolidin-1-ylpyridine (POP) (0.02 mol) were dissolved
in dichloromethane (100 ml). Dicyclohexylcarbodiimide
(DCC) (0.02 mol) was dissolved in dichloromethane (30 ml)
and added to the mixture dropwise. The resulting solution was
stirred at room temp. for 12 h. The resulting product was
purified by column chromatography (dichloromethane) and by
recrystallisation (acetonitrile). The purity of the product was
confirmed by TLC (dichloromethane, single spot) and HPLC
chloride solution and dried (MgSO ). The product was purified
by column chromatography (dichloromethane–ethyl acetate,
4
80520). The purity of the product was confirmed by TLC
(dichloromethane, single spot). Yield, 74%. d (CDCl ), 7.0–7.2
(d, 2H), 6.8–6.9 (d, 2H), 3.75–3.95 (m, 5H), 3.6–3.7 (m, 2H),
H
3
1.2–1.85 (m, 8H); n
1760, 1595, 1505, 1440, 1200–1270, 1000–1060, 830, 730; m/z,
110 (100%), 93, 81, 65, 55.
(KBr)/cm−1, 3260–3500, 2860–2980,
(acetonitrile), >99%. Yield, 70%, K 64.3 (N 58) I °C. d
max
H
(CDCl ), 7.25 (d, 2H), 6.8 (d, 2H), 8.25 (d, 2H), 6.95 (d, 2H),
3
5.85 (m, 1H), 5.05 (m, 2H), 4.05 (t, 2H), 3.8 (s, 3H), 2.25 (m,
2H), 1.85 (m, 2H), 1.6 (m, 2H); n
1740, 1165; m/z, 326 (M+), 203, 196, 135, 121 (100%), 76.
(KBr)/cm−1, 3060, 2930,
max
1-Methoxycarbonyloxy-4-(6-methacryloyloxyhexyloxy)ben-
zene. Methacryloyl chloride (19 mmol) was added to
1 - (methoxycarbonyloxy) - 4 - (6 - hydroxyhexyloxy) benzene
(19 mmol), which was heated under reflux in dichloromethane
(75 ml). Triethylamine (25 ml) was added dropwise into the
stirred reaction mixture. After completion the reaction mixture
was heated under reflux for a further 4 h. The reaction mixture
was cooled and the organic phase washed with hydrochloric
acid (10% v/v, 3×75 ml) and then with saturated sodium
chloride solution until free of acid (universal indicator paper).
Preparation of cross-linking agent 3 (Scheme 3)
1,4-Bis(hex-5-enyloxy)benzene 3. A stirred suspension of 6-
bromohex-1-ene (0.06 mol), potassium carbonate (0.15 mol)
and hydroquinone (0.03 mol) in dry butanone (100 ml) was
heated under reflux for 24 h. When cooled, the potassium
carbonate was filtered off and the butanone was removed by
distillation under reduced pressure. The product was purified
by column chromatography (dichloromethane), followed by
recrystallisation (dichloromethane). The purity of the product
was confirmed by TLC (dichloromethane, single spot) and
The organic layer was dried over MgSO . The product was
purified by column chromatography (dichloromethane–ethyl
4
acetate, 80520). The purity of the product was confirmed by
TLC (dichloromethane, single spot). Yield, 76%. d (CDCl ),
7.0–7.1 (d, 2H), 6.8–6.9 (d, 2H), 6.05 (s, 1H), 5.5, (s, 1H),
HPLC (acetonitrile, >99%). Yield, 70%, mp 34–36 °C. d
(CDCl ), 6.8–6.85 (s, 4H), 5.75–5.9 (m, 2H), 4.95–5.1 (t, 4H),
H
3
H
3
4.05–4.35 (m, 2H), 3.8–3.95 (m, 5H), 1.2–2.35 (m, 11H); n
(KBr)/cm−1, 2880–2940, 1760, 1710, 1630, 1500, 1440, 1250,
3.85–3.95 (t, 4H), 2.05–2.15 (m, 12H); n
2860–2940, 1640, 1505, 1230, 1110, 1070, 1040, 995, 910, 830;
(KBr)/cm−1,
max
max
830; m/z, 336 (M+), 168 (100%), 124, 109, 83, 69.
m/z, 274 (M+), 192, 110 (100%), 93, 81, 67.
4-(6-Methacryloyloxyhexyloxy)phenol. 1-Methoxycarbonyl-
oxy-4-(6-methacryloyloxyhexyloxy)benzene (14 mmol) was
stirred at room temp. for 90 min in a mixture of ammonia and
ethanol (153, 75 ml). The reaction was monitored by TLC
(dichloromethane). The ammonia and ethanol were removed
under reduced pressure and the product was washed with
hydrochloric acid (10% v/v, 3×75 ml), followed by saturated
sodium chloride solution (3×75 ml) until free of acid. The
Preparation of cross-linking agent 4 (Scheme 4)
1-Benzyloxy-4-(6-hydroxyhexyloxy)benzene. The method
used to prepare 1-benzyloxy-4-(6-hydroxyhexyloxy)benzene
was similar to that outlined for the preparation of 1,4-bis(hex-
5-enyloxy)benzene (previous section), but using 6-chlorohex-
anol (0.05 mol), potassium carbonate (0.3 mol) and 4-(benzyl-
oxy)phenol (0.05 mol) in dry butanone (130 ml). The product
was purified by recrystallisation (ethanol) and the purity of
the product was confirmed by TLC (dichloromethane, single
spot). Yield, 50%, mp, 82–83 °C. d (CDCl ), 7.3–7.45 (m, 5H),
organic layer was dried over MgSO . The purity of the product
4
was confirmed by TLC (dichloromethane, single spot). Yield,
77%. d (CDCl ), 6.7–6.8 (s, 4H), 6.1 (s, 1H), 5.05 (s, 1H),
H
3
H
3
6.85–6.95 (m, 4H), 5.0–5.05 (s, 2H), 3.85–3.95 (t, 2H), 3.6–3.7
5.2–5.3 (s, 1H), 4.05–4.3 (m, 2H), 3.8–3.9 (m, 2H), 1.45–2.35
(KBr)/cm−1 3380–3430, 2860–2940, 1710, 1505,
65, 55.
(t, 2H), 1.35–1.85 (m, 8H), 1.15 (s, 1H); n
3290–3340, 2860–2940, 1605, 1380, 1240, 1120, 1080, 1040,
(KBr)/cm−1,
(m, 11H); n
1450, 1230, 1155, 830, 750; m/z, 279 (M+), 110 (100%), 83, 69,
max
max
820, 740; m/z, 300 (M+), 209, 122, 91 (100%), 55.
J. Mater. Chem., 1998, 8(1), 53–60
59

4-(6-Methacryloyloxyhexyloxy)phenyl 4-(hex-5-enyloxy)b-
enzoate. 4-(Hex-5-enyloxy)benzoic acid (15 mmol), 4-(6-
methacryloyloxyhexyloxy)phenol (14 mmol) and 4-dimeth-
ylaminopyridine (DMAP) (2 mmol) were dissolved in
dichloromethane (100 ml). Dicyclohexylcarbodiimide (DCC)
(15 mmol) was dissolved in dichloromethane (30 ml) and
added to the mixture dropwise. The resulting solution was
allowed to stir at room temp. for 12 h. The resultant product
was purified by column chromatography (dichloromethane)
and recrystallisation (dichloromethane). The purity of the
compound was confirmed by TLC (dichloromethane, single
spot) and HPLC (acetonitrile, >99%). Yield, 29%, K (N 41)
48 I °C. d (CDCl ), 8.1–8.2 (d, 2H), 7.05–7.15 (d, 2H),
University of York for their assistance in the fractionation of
the polysiloxane.
References
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H
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6.85–6.95 (d, 4H), 6.1 (s, 1H), 5.75–5.9 (m, 1H), 5.5–5.55 (s,
1H), 4.9–5.05, (t, 2H), 3.9–4.2 (3×t, each 2H), 1.2–2.2 (m,
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(KBr)/cm−1, 2840–2960, 1730, 1650, 1610, 1510,
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10 H. Finkelmann and G. Rehage, Adv. Polym. Sci., 1984, 60/61, 99.
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Preparation of the elastomers (Schemes 5 and 6). The syn-
thesis of the elastomers follows the well-known procedure of
the hydrosilylation reaction with polysiloxanes in the presence
of a Pt catalyst36 and is based on the spin-cast technique
15 J. H. Wendorff, H. Finkelmann and H. Ringsdorf, ACS Symp. Ser.,
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developed by Finkelmann.1
A solution of monomer 2
16 J. H. Wendorff, L iquid Crystalline Order in Polymers, Acad. Press,
NY, 1978.
(0.8 mmol), cross-linking agent 3 and/or cross-linking agent
4, polysiloxane backbone 1 (DP=234, DPI=1.1) [60 mg
(1 mmol)] and Pt-catalyst SLM86003 (Wacker Chemie,
Burgenhausen) (8 ml) in absolute toluene (1 ml). The reaction
mixture was then filtered through a PTFE membrane filter
(0.5 mm pore size) into the cylindrical vessel, with a diameter
of 5 cm and a height of 1 cm, which was lined with Teflon film.
The vessel was sealed and fitted onto the top of a specially
adapted centrifuge, placed in an oven at 60 °C and spun at
4000 rpm for 4 h. After cooling the vessel, the swollen elastomer
was removed and placed into a tensiometer. The sample was
then extended (between 18 and 56%) and the second step of
the cross-linking reaction was monitored in situ in the X-ray
beam of AXIS (area X-ray imaging system). Data were collected
continually over a period of 12 h. Finally graphs were plotted
17 H. Finkelmann and D. Day, Makromol. Chem., 1979, 180, 2269.
18 L. Z. Azaroff, Mol. Cryst. L iq. Cryst., 1987, 145, 31.
19 (a) G. R. Mitchell and A. H. Windle, Developments in Crystalline
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20 G. R. Mitchell, Comprehensive Polymer Science, Pergamon,
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¨
1991, 12, 717.
26 F. J. Davis, J. Mater. Chem., 1993, 3(6), 551.
27 J. Kupfer, Ph D T hesis, Freiburg, Germany, 1993.
of orientation function coefficient (ꢀP ꢁ) against time (s). The
2
¨
axis of orientation (°) versus time was also plotted for the
28 S. Disch, C. Schmidt and H. Finkelmann, Macromol. Rapid
Commun., 1994, 15, 303.
29 P. G. de Gennes, Mol. Cryst. L iq. Cryst., 1971, 12, 193.
30 P. G. de Gennes, T he Physics of L iquid Crystals, Claredon Press,
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corresponding experiments to observe the orientation process
of the mesogenic side chains on application of a mechanical
field. The axis of orientation is defined as the dissection line
of the orientation arcs in the X-ray diffraction picture. In the
equatorial sector the axis of orientation is equal to 0°. In the
meridonal sector the axis of orientation is equal to 90°. The
data from this work are summarised in Table 1.
34 M. Warner, Side-Chain L iquid Crystal Polymers, ed. C. B. McArdle,
Blackie, Glasgow, London, 1989.
35 H. N. Beattie, Thesis, University of Hull, 1994.
36 G. W. Gray, Side-Chain L iquid Crystal Polymers, ed.
C. B. McArdle, Blackie, Glasgow, London 1989.
We would like to thank the EPSRC for funding (H.N.B.). We
would like to express our sincere thanks to Professor
Finkelmann and Dr Kupfer for their valuable assistance in the
¨
development of the procedure for the synthesis of LC elasto-
mers at Hull, and to Dr Semlyen and his colleagues at the
Paper 7/05570F; Received 31st July, 1997
60
J. Mater. Chem., 1998, 8(1), 53–60