Side-chain liquid crystal polymers derived from oxetane monomers containing 2- or 3-fluorophenyl moieties in the core of the mesogen

Article abstract of DOI:10.1039/b009426i

Two series of side-chain liquid crystalline polymers were prepared by cationic ring-opening of oxetane substituted mesogens. Each of the terminally appended side chain polymers prepared had a flexible spacer length of six methylene units separating a meso

Full text of DOI:10.1039/b009426i

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Side-chain liquid crystal polymers derived from oxetane monomers
containing 2- or 3-fluorophenyl moieties in the core of the mesogen{
Stephen J. Cowling,* Kenneth J. Toyne and John W. Goodby
Department of Chemistry, The University of Hull, Hull, UK HU6 7RX
Received 24th November 2000, Accepted 2nd February 2001
First published as an Advance Article on the web 1st May 2001
Two series of side-chain liquid crystalline polymers were prepared by cationic ring-opening of oxetane
substituted mesogens. Each of the terminally appended side chain polymers prepared had a flexible spacer
length of six methylene units separating a mesogenic aromatic core from the polymer backbone. The core unit
was designed to incorporate either a 2-fluoro- or a 3-fluoro-phenyl unit possessing either an (R)-(2)-1-
methylheptyl, (S)-(z)-2-methylbutyl or a 1-propylbutyl terminal chain. The materials produced in this study
were compared with the previously reported unsubstituted parent materials in order to assess the affect of
having a lateral fluoro substituent in the core. Low melting points, smectic C/C* and smectic A/A* phases were
exhibited by most of the monomers. The behaviour of the 3-fluorophenyl monomers was found to be similar to
their unfluorinated parents, whereas the 2-fluoro analogues were shown to have significantly lower transition
temperatures. All of the polymers exhibited smectic C/C* and smectic A/A* phases over wide temperature
ranges and had relatively low Tg values. Some of the polymers were found to exhibit exceptionally large
temperature ranges for the smectic C/C* phase, e.g. from 0.8 ‡C to 190 ‡C.
transmitted polarized light microscopy, exhibited large
Introduction
domains typical of low molar mass materials. The defect
textures formed after very short annealing times thereby
indicating that the polymers had relatively low viscosities. In
this article we report the synthesis and mesomorphism of two
new series of low molar mass oxetanes and their corresponding
Ferroelectric side-chain liquid crystal polymers (SCLCP) have
been an active area of research in liquid crystals since the first
example reported by Shibaev et al.1 in 1984. Most of the early
work on SCLCP’s was based on poly(acrylate)s, although in
1987 Hahn and Percec2 reported the first poly(siloxane) based
material to exhibit a ferroelectric SmC* phase. Both these
polymer backbones have provided the basis for the majority of
work on SCLCP’s even though poly(oxyethylene) materials3
and polymers with more unusual backbones4,5 have also been
reported.
polymers that possess either
a 2-fluorophenyl or a 3-
fluorophenyl moiety (series 1 and 2 in Fig. 1) in their mesogenic
cores. The general structures of these systems are shown in
Fig. 1, with the materials being direct analogues of the
unsubstituted parent system previously described.9
In order to study ferroelectric responses to applied electric
fields, SCLCP’s need to be designed in such a way that the
terminally appended mesogenic core units are separated from
the polymer backbone by a flexible spacer group so that the
motions of the mesogenic units are decoupled from those of the
backbone.6 Hsu et al.7 showed that polymers which exhibit
smectic C phases are typically exhibited by SCLCP’s where the
length of the flexible spacer is greater than six methylene units.
It was also shown that an increase in the flexibility of the
backbone increases the tendency for smectic C phases to be
exhibited.7 Even when a polymer has been designed to exhibit a
chiral smectic C* phase, the flexibility of the polymer backbone
is an important factor in determining the speed of the response
of the polymer to an applied electric field. It has been reported
that polymers with relatively flexible backbones will respond
more quickly to applied fields than polymers with more rigid
backbones,8 and for this reason poly(siloxane)s are found to
respond faster than poly(oxyethylene)s which in turn respond
faster than poly(acrylate)s.
Experimental
Compounds 1, 10, 24 and 1,6-dibromohexane were pur-
chased from Aldrich and compound 21 was purchased from
E. Merck; all of these materials were used without further
purification. The structures of the products and intermedi-
ates were analysed using a range of spectral techniques
including 1H NMR spectrometry (JEOL JNM-LA400 FT
400 MHz spectrometer, where the spectra, unless otherwise
stated, were recorded in CDCl3 using Me4Si as an internal
standard; the J values are given in Hz), infra-red spectro-
metry (Perkin-Elmer 983G infra-red spectrophotometer) and
mass spectrometry (Finnigan-MAT 1020 GC-MS spectro-
meter). The purifications of the intermediates and final
products was achieved using column chromatography over
C60, 230–400 mesh silica gel (Merck). The optical rotations
In previous studies9 we described the synthesis of a series of
SCLCP obtained via the cationic ring-opening polymerisation
of oxetane monomers; the resulting polymers were shown to
exhibit smectic C phases with wide temperature ranges and low
glass transition temperatures in addition to possessing reason-
ably high DP values (y20). The defect textures, observed via
{Electronic supplementary information (ESI) available:
version of Fig. 4. See http://www.rsc.org/suppdata/jm/b0/b009426i/
a colour
Fig. 1 The structure of the monomers in this work.
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This journal is # The Royal Society of Chemistry 2001
DOI: 10.1039/b009426i

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of the chiral intermediates and products was measured using an
Optical Activity AA-10 automatic polarimeter and the [a]D
however the physical properties and the spectral data are
reported.
values are given in 1021 deg cm2 g21
.
Examination of the mesomorphic behaviour and the
determination of transition temperatures of the materials was
achieved using transmitted polarized-light microscopy (Mettler
FP5 temperature controller unit in conjunction with a Mettler
FP52 hot-stage linked to an Olympus BH2 microscope). The
transition temperatures were verified and the enthalpies of
transition were determined by thermal analysis using a Perkin-
Elmer DSC7 differential scanning calorimeter using DSC7/
UNIX software.
The molecular weights of the polymers and polydispersities
were determined via GPC analyses using two mixed D, PL gel
columns, 30 cm60.75 cm, 5 mm, calibrated with polystyrene
standards of a molecular weight of 1000–430 500 amu.
All of the monomeric systems were found to give satisfactory
elemental analyses.
(R)-(2)-1-Methylheptyl 3-fluoro-4-hydroxybenzoate (7)
[a]2D5~233.7 (c 0.03829 in CHCl3). dH: 0.88 (3H, t, J 6), 1.22–
1.40 (8H, m), 1.30 (3H, d, J 6), 1.52–1.78 (2H, m), 5.12 (1H,
sextet, J 6), 6.28 (1H, br s), 7.02 (1H, t, J 9), 7.72–7.76 (1H, m),
7.78 (1H, s). nmax (film)/cm21: 3340, 3020, 2920, 2860, 1700,
1610, 1590, 1510, 1440, 1300, 1210, 900, 760. m/z: 268 (Mz),
156, 139, 112, 58, 43 (100%).
(S)-(z)-2-Methylbutyl 3-fluoro-4-hydroxybenzoate (8)
[a]2D5~z5.18 (c 0.04615 in CHCl3). dH: 0.94 (3H, t, J 6), 1.00
(3H, d, J 6), 1.28 (1H, octet, J 6), 1.53 (1H, octet, J 6), 1.83 (1H,
octet, J 6), 4.14 (2H, m), 6.06 (1H, br s), 7.03 (1H, t, J 9), 7.72–
7.78 (1H, m), 7.79 (1H, t, J 2). nmax (film)/cm21: 3350, 2970,
2880, 1690, 1620, 1600, 1520, 1440, 1310, 1220, 1120, 1090, 980,
900, 840, 770. m/z: 226 (Mz), 156, 139, 82, 70, 43 (100%).
Molecular modelling studies were performed using a Silicon
Graphics workstation (Indigo XS24, 4000) with the programs
Quanta and CHARMm. Within CHARMm, the Adopted
Basis Newton Raphson (ABNR) algorithm was used to locate
the molecular conformation with the lowest potential energy.
1-Propylbutyl 3-fluoro-4-hydroxybenzoate (9)
dH: 0.92 (6H, t, J 6), 1.30–1.48 (4H, m), 1.58–1.76 (4H, m), 5.14
(1H, quintet, J 6), 7.03 (1H, t, J 9), 7.72–7.77 (1H, m), 7.80 (1H,
t, J 2), phenolic proton not observed. nmax (KBr disc)/cm21
3340, 2960, 2880, 1690, 1620, 1600, 1520, 1440, 1300, 1220,
1120, 1090, 950, 900, 840, 770. m/z: 254 (Mz), 139, 111, 98, 83,
43 (100%).
The preparation of intermediate 11 (Scheme 2) has been
reported previously.12
The minimisation calculations were performed until the root
21, which
˚
A
mean square (RMS) force reached 4.184 kJ mol21
:
is close to the resolution limit. The RMS force is a direct
measure of the tolerance applied to the energy gradient (i.e., the
rate of change of potential energy with step number) during
each cycle of minimisation. The calculation was terminated in
cases where the average energy gradient was less than the
specified value. The results of the molecular mechanics
calculations were generated using the programs QUANTA V
4.0 and CHARMm V22.2. The programs were developed and
integrated by Molecular Simulations Inc., Cambridge, UK. The
modelling packages assume the molecules to be a collection of
hard particles held together by elastic forces, in the gas phase at
absolute zero in an ideal motionless state, and the force fields
used are those described in CHARMm V 22.2.
4-Benzyloxy-1-bromo-2-fluorobenzene (12)
The experimental procedure was the same as for the
preparation of compound 2. The following quantities were
used: compound 11, 36.80 g, 0.19 mol; potassium carbonate,
31.74 g, 0.23 mol; benzyl bromide, 35.70 g, 0.21 mol; butanone,
500 ml. Yield 56.20 g (96%), mp 33.2–34.6 ‡C.
dH: 5.05 (2H, s), 6.69 (1H, ddd, J1 10, J2 8, J3 4), 6.77 (1H, dd,
J2 8, J3 4), 7.32–7.42 (6H, m). nmax (KBr disc)/cm21: 1600, 1580,
1480, 1410, 1315, 1260, 1240, 1170, 1000, 960, 830, 760, 730,
690, 650. m/z: 282, 280 (Mz), 191, 189, 91 (100%), 65.
The synthetic scheme for the preparation of intermediates 7–
9 (Scheme 1) has been well documented in the literature by
Parghi et al.10,11 and for brevity will not be reported in detail,
Scheme 1 Synthetic route to 3-fluoro-4-hydroxybenzoates (1MH~1-methylheptyl; 2MB~2-methylbutyl; 1PB~1-propylbutyl).
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Scheme 2 Synthetic route to 2-fluoro-4-hydroxybenzoates.
4-Benzyloxy-2-fluorobenzonitrile (13)
used: compound 14, 8.00 g, 33 mmol; (S)-(z)-octan-2-ol,
4.29 g, 33 mmol; triphenylphosphine, 9.24 g, 35 mmol;
DEAD, 5.74 g, 33 mmol in THF, 40 ml; THF, 150 ml. Yield
8.20 g (69%), [a]2D4~225.32 (c 0.07371 in CHCl3).
dH: 0.82 (3H, t, J 6), 1.20–1.44 (8H, m), 1.31 (3H, t, J 6),
1.50–1.62 (1H, m), 1.66–1.77 (1H, m), 5.04 (2H, s), 5.11 (1H,
sextet, J 6), 6.68 (1H, dd, J1 8, J2 2), 6.77 (1H, dd, J1 8, J2 2),
7.30–7.43 (5H, m), 7.86 (1H, t, J 9). nmax (film)/cm21: 2960,
2930, 2860, 1710, 1620, 1580, 1500, 1450, 1440, 1380, 1280,
1265, 1170, 1140, 1120, 1090, 1025, 890, 820, 740, 700. m/z: 358
(Mz), 338, 229, 138, 110, 91 (100%).
Compound 12 (10.00 g, 35.7 mmol) and copper(I) cyanide
(13.00 g, 71.4 mmol) were suspended in 1-methylpyrrolidin-2-
one (250 ml) and heated under reflux for 24 h. The reaction
mixture was cooled to room temperature and filtered through
‘Hyflo supercel1’. Water (200 ml) was added to the filtrate
which was then washed with ether (26400 ml). The combined
ether extracts were washed with water (26500 ml) and brine
(500 ml) and then dried (MgSO4). The drying agent was filtered
off and the solvent removed in vacuo to yield an off-white solid
which was purified by column chromatography (dichloro-
methane) to yield colourless crystals which were recrystallised
(cyclohexane) and dried in vacuo. Yield 5.79 g (71%), mp 77.7–
79.5 ‡C.
(S)-(z)-2-Methylbutyl 4-benzyloxy-2-fluorobenzoate (16)
dH: 5.10 (2H, s), 6.74–6.87 (2H, m), 7.34–7.42 (5H, m), 7.52
(1H, t, J 9). nmax (KBr disc)/cm21: 2240, 1610, 1570, 1500, 1450,
1380, 1290, 1260, 1110, 1000, 910, 850, 810, 770, 740, 700, 630,
510. m/z: 227 (Mz), 156, 91 (100%), 65.
The experimental procedure was the same as for the
preparation of compound 4. The following quantities were
used: compound 14, 8.00 g, 33 mmol; (S)-(2)-2-methylbutan-
1-ol, 2.90 g, 33 mmol; DEAD, 5.74 g, 33 mmol; triphenylpho-
sphine in THF, 9.24 g, 35 mmol in 40 ml; THF, 150 ml. Yield
9.67 g (93%), [a]D24~z3.58 (c 0.0401 CHCl3).
4-Benzyloxy-2-fluorobenzoic acid (14)
dH: 0.94 (3H, t, J 6), 1.00 (3H, d, J 6), 1.26 (1H, octet, J 6),
1.52 (1H, octet, J 6), 1.83 (1H, octet, J 6), 4.14 (2H, m), 5.10
(2H, s), 6.70 (1H, dd, J1 8, J2 2), 6.78 (1H, dd, J1 8, J2 2), 7.30–
7.42 (5H, m), 7.90 (1H, t, J 9). nmax (film)/cm21: 2960, 2940,
2880, 1710, 1620, 1580, 1500, 1280, 1265, 1175, 1140, 1000,
910, 840, 740, 700. m/z: 316 (Mz), 246, 199, 183, 110, 91
(100%), 65.
Compound 13 (5.70 g, 25 mmol) was suspended in a 2.5 M
sodium hydroxide solution [10.00 g in water (100 ml)] and
heated under reflux for 60 h. The solution was then acidified
with conc. hydrochloric acid to pH 3 and the mixture was then
washed with ether (26100 ml). The carboxylic acid was then
extracted from the combined ether solutions with a saturated
sodium bicarbonate solution (200 ml) and the alkaline extract
was acidified with conc. hydrochloric acid. The mixture was
then washed with ether (400 ml) and the organic washings were
washed with brine (26200 ml) and dried (Na2SO4). The drying
agent was filtered off and the solvent removed in vacuo to yield
a colourless solid which was recrystallised [cyclohexane–ethyl
acetate (95 : 5)]. Yield 3.85 g (58%), mp 165.3–167.6 ‡C.
dH: 5.10 (2H, s), 6.68–6.83 (2H, m), 7.30–7.45 (5H, m), 7.91
(1H, t, J 9), acidic proton was not detected. nmax (KBr disc)/
cm21: 2920, 1700, 1610, 1500, 1440, 1410, 1340, 1270, 1240,
1050, 1020, 900, 840, 740, 650. m/z: 246 (Mz), 229, 139, 127, 91
(100%), 65.
1-Propylbutyl 4-benzyloxy-2-fluorobenzoate (17)
The experimental procedure was the same as for the
preparation of compound 4. The following quantities were
used: compound 14, 9.95 g, 40 mmol; heptan-4-ol, 4.64 g,
40 mmol; DEAD, 6.96 g, 40 mmol; triphenylphosphine in
THF, 11.53 g, 44 mmol in 40 ml; THF, 150 ml. Yield 4.92 g
(40%).
dH: 0.93 (6H, t, J 6), 1.32–1.48 (4H, m), 1.54–1.73 (4H, m),
5.08 (2H, s), 5.15 (1H, quintet, J 6), 6.70 (1H, dd, J1 8, J2 2),
6.78 (1H, dd, J1 8, J2 2), 7.32–7.43 (5H, m), 7.89 (1H, t, J 9).
nmax (film)/cm21: 2960, 2940, 2880, 1710, 1620, 1580, 1505,
1440, 1280, 1270, 1170, 1150, 1130, 1090, 1030, 900, 840, 740,
700. m/z: 344 (Mz), 247, 229, 91 (100%), 65.
(R)-(2)-1-Methylheptyl 4-benzyloxy-2-fluorobenzoate (15)
The experimental procedure was the same as for the
preparation of compound 4. The following quantities were
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(R)-(2)-1-Methylheptyl 4-hydroxy-2-fluorobenzoate (18)
The experimental procedure was the same as for the
preparation of compound 7. The following quantities were
used: compound 15, 8.20 g, 23 mmol; 10% palladium-on-
charcoal, 0.30 g; ethyl acetate, 200 ml. Yield 4.68 g (76%),
[a]2D5~228.39 (c 0.03202 in CHCl3).
dH: 0.86 (3H, t, J 6), 1.20–1.46 (8H, m), 1.30 (3H, d, J 6),
1.54–1.77 (2H, m), 5.12 (1H, sextet, J 6), 6.64 (1H, dd, J1 8, J2
2), 6.70 (1H, dd, J1 8, J2 2), 7.84 (1H, t, J 9), phenolic proton
was not observed. nmax (film)/cm21: 3370, 2930, 2860, 1690,
1620, 1600, 1510, 1460, 1290, 1250, 1230, 1150, 1120, 1090, 980,
920, 855, 775. m/z: 268 (Mz), 157, 139 (100%), 112, 83, 55.
(S)-(z)-2-Methylbutyl 4-hydroxy-2-fluorobenzoate (19)
The experimental procedure was the same as for the
preparation of compound 7. The following quantities were
used: compound 16, 9.67 g, 31 mmol; 10% palladium-on-
charcoal, 0.30 g; ethyl acetate, 300 ml. Yield 5.46 g (78%),
[a]2D5~z6.11 (c 0.1174 in CHCl3).
dH: 0.95 (3H, t, J 6), 1.02 (2H, d, J 6), 1.28 (1H, octet, J 6),
1.58 (1H, octet, J 6), 1.84 (1H, octet, J 6), 4.15 (2H, m), 5.90
(1H, br s), 6.62 (1H, dd, J1 8, J2 2), 6.67 (1H, dd, J1 8, J2 2), 7.86
(1H, t, J 9), phenolic proton not observed. nmax (KBr disc)/
cm21: 3370, 2960, 2940, 2900, 2880, 1700, 1680, 1620, 1595,
1510, 1460, 1390, 1375, 1320, 1300, 1250, 1225, 1140, 1095,
1020, 940, 850, 765, 640. m/z: 226 (Mz), 157, 139 (100%), 111,
83, 70.
1-Propylbutyl 4-hydroxy-2-fluorobenzoate (20)
The experimental procedure was the same as for the
preparation of compound 7. The following quantities were
used: compound 17, 4.92 g, 14 mmol; 10% palladium-on-
charcoal, 0.20 g; ethyl acetate, 200 ml. Yield 3.49 g (98%).
dH: 0.90 (6H, t, J 6), 1.31–1.47 (4H, m), 1.54–1.72 (4H, m),
5.14 (1H, quintet, J 6), 6.64 (1H, dd, J1 8, J2 2), 6.65 (1H, dd, J1
8, J2 2), 7.84 (1H, t, J 9), phenolic proton not observed. nmax
(KBr disc)/cm21: 3330, 2960, 2940, 2880, 1690, 1670, 1620,
1510, 1470, 1330, 1300, 1250, 1140, 1100, 975, 850, 770, 690,
620. m/z: 254 (Mz), 157, 139 (100%), 98, 83, 56.
Scheme 3 Synthetic route to carboxylic acid intermediates.
acid was slowly added until the solution was acidic (pH 6) and
the solution was left to stir for 1 h. The colourless solid formed
was filtered off and washed with copious amounts of water
until the washings were neutral and dried (P2O5). Yield 27.0 g
(84%); K 155.4 N 178.2 Iso liq. ‡C.
dH: 1.32 (3H, s), 1.41–1.54 (4H, m), 1.64 (2H, quintet, J 6),
1.84 (2H, quintet, J 6), 3.48 (4H, s and t, J 6), 3.99 (2H, t, J 6),
4.37 (2H, d, J 6), 4.53 (2H, d, J 6), 6.98 (2H, d, J 8), 7.58 (2H, d,
J 8), 7.64 (2H, d, J 8), 8.14 (2H, d, J 8), acid proton not
observed. nmax (KBr disc)/cm21: 3430, 2940, 2860, 1700, 1670,
1600, 1520, 1490, 1430, 1290, 1250, 1190, 1110, 940, 830. m/z:
398 (Mz), 228, 214 (100%), 197, 83, 55.
The preparation of intermediates 22,13 2314 and 2515
(Scheme 3) have been reported previously.
Methyl 4’-[6-(3-methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-
4-carboxylate (26)
Compound 23 (29.6 g, 0.13 mol), compound 25 (34.7 g,
0.13 mol), potassium carbonate (35.9 g, 0.26 mol) and potas-
sium iodide (5.00 g, 30 mmol) were dissolved in butanone
(700 ml) and heated under reflux overnight. On completion of
the reaction (analysis by TLC), the reaction solution was
cooled to room temperature, poured into water (200 ml) and
stirred for 2 h. The resulting colourless precipitate was filtered
off, washed with water and dried in vacuo (P2O5). Yield 32.8 g
(62%), mp 146–147.3 ‡C.
dH: 1.32 (3H, s), 1.40–1.54 (4H, m), 1.62 (2H, quintet, J 6),
1.82 (2H, quintet, J 6), 3.46 (4H, s and t, J 6), 3.91 (3H, s), 3.99
(2H, t, J 6), 4.35 (2H, d, J 6), 4.51 (2H, d, J 6), 6.99 (2H, d, J 8),
7.56 (2H, d, J 8), 7.62 (2H, d, J 8), 8.08 (2H, d, J 8). nmax (KBr
disc)/cm21: 3400, 2940, 2860, 1710, 1600, 1525, 1490, 1290,
1250, 1200, 1110, 830. m/z: 412 (Mz), 228 (100%), 197, 139,
115, 83, 55.
(R)-(2)-4-(1-Methylheptyloxycarbonyl)-2-fluorophenyl 4’-[6-(3-
methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-carboxylate
(M1) (Scheme 4)
N,N’-Dicyclohexylcarbodiimide (DCC) (0.64 g, 3.10 mmol)
and 4-(dimethylamino)pyridine (DMAP) (0.10 g, 0.10 mmol)
were added to a stirred solution of compound 27 (1.23 g,
3.10 mmol) and compound 7 (0.83 g, 3.10 mmol) in dichloro-
methane. The reaction mixture was left stirring at room
temperature for 72 h until completion. The dicyclohexylurea
formed was filtered off and the solvent removed in vacuo to
yield a viscous colourless oil which was purified by column
chromatography (ethyl acetate). The colourless material was
then recrystallised from ethanol by cooling to 260 ‡C, filtered
off and dried in vacuo (P2O5). Yield 1.83 g (91%), [a]2D4~222.3
(c 0.02997 in CHCl3); K v270 SmC* 40.0 SmA* 61.6 Iso liq.
‡C. Elemental analysis for C39H49F1O7: calculated C 72.18%;
H 7.62%; found C 72.02%; H 7.57%. dH: 0.88 (3H, t, J 6), 1.29
(3H, s), 1.21–1.41 (8H, m), 1.34 (3H, d, J 6), 1.42–1.54 (4H, m),
1.64 (4H, quintet, J 6), 1.83 (2H, quintet, J 6), 3.48 (2H, t, J 6),
3.50 (2H, s), 4.04 (2H, t, J 6), 4.37 (2H, d, J 6), 4.52 (2H, d, J 6),
5.17 (1H, sextet, J 6), 7.00 (2H, d, J 8), 7.34 (1H, dd, J1 9, J2 1),
7.58 (2H, d, J 8), 7.70 (2H, d, J 8), 7.85–7.94 (2H, m), 8.22 (2H,
4’-[6-(3-Methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-
carboxylic acid (27)
10 M Sodium hydroxide (30 ml) was added to a solution of
compound 26 (32.8 g, 0.080 mol) in ethanol–water (1 : 5) (1.6 l)
and the mixture was heated under reflux for 1 h. The reaction
mixture was cooled in an ice–salt bath and 2 M hydrochloric
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Scheme 4 Synthetic route to the oxetane monomers and polymers. m~number of repeat units.
d, J 8). nmax (film)/cm21: 2940, 2860, 1740, 1715, 1600, 1505,
1450, 1430, 1290, 1260, 1180, 1110, 1060, 1015, 900, 830, 770.
m/z: 648 (Mz), 479, 381 (100%), 196, 139, 55.
dH: 0.94 (6H, t, J 6), 1.28 (3H, s), 1.28–1.52 (8H, m), 1.60–
1.72 (6H, m), 1.81 (2H, quintet, J 6), 3.45 (2H, s), 3.48 (2H, t, J
6), 4.03 (2H, t, J 6), 4.36 (2H, d, J 6), 4.46 (2H, d, J 6), 5.16 (1H,
quintet, J 6), 7.01 (2H, d, J 8), 7.39 (1H, t, J 9), 7.64 (2H, d, J 8),
7.75 (2H, d, J 8), 7.88–7.93 (2H, m), 8.23 (2H, d, J 8). nmax
(film)/cm21: 2940, 2870, 1750, 1715, 1605, 1500, 1430, 1255,
1180, 1115, 1060, 1015, 950, 900, 830, 760. m/z: 634 (Mz), 382
(100%), 352, 279, 197, 139.
(S)-(z)-4-(2-Methylbutyloxycarbonyl)-2-fluorophenyl 4’-[6-(3-
methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-carboxylate
(M2)
The experimental procedure was the same as for the
preparation of compound M1. The following quantities were
used: compound 27, 1.31 g, 3.30 mmol; compound 8, 0.75 g,
3.30 mmol; DCC, 0.68 g, 3.30 mmol; DMAP, 0.10 g,
0.10 mmol; dichloromethane, 50 ml. Yield 1.50 g (75%),
[a]2D5~z1.0 (c 0.01227 in CHCl3); K 0.8 SmC* 51.9 SmA*
89.6 N* 95.5 BP III 99.0 Iso liq. ‡C. Elemental analysis for
C36H43F1O7: calculated C 71.25%; H 7.15%; found C 71.32%;
H 7.13%.
dH: 0.97 (3H, t, J 6), 1.02 (3H, d, J 6), 1.31 (3H, s), 1.40–1.56
(6H, m), 1.63 (2H, quintet, J 6), 1.83 (3H, quintet, J 6; and
octet, J 6), 3.47 (2H, s), 3.48 (2H, t, J 6), 4.01 (2H, t, J 6), 4.19
(2H, m), 4.36 (2H, d, J 6), 4.52 (2H, d, J 6), 7.01 (2H, d, J 8),
7.36 (1H, dd, J1 9, J2 1), 7.61 (2H, d, J 8), 7.70 (2H, d, J 8),
7.86–7.94 (2H, m), 8.24 (2H, d, J 8). nmax (film)/cm21: 2940,
2870, 1730, 1710, 1605, 1510, 1460, 1360, 1270, 1220, 1180,
1115, 1055, 1015, 980, 890, 830, 765. m/z: 606 (Mz), 381
(100%), 351, 197, 139, 55.
(R)-(2)-4-(1-Methylheptyloxycarbonyl)-3-fluorophenyl 4’-[6-(3-
methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-carboxylate
(M4)
The experimental procedure was the same as for the
preparation of compound M1. The following quantities were
used: compound 27, 1.23 g, 3.1 mmol; compound 18, 0.83 g,
3.1 mmol; DCC, 0.64 g, 3.1 mmol; DMAP, 0.10 g, 0.1 mmol;
dichloromethane, 50 ml. Yield 1.09 g (55%), [a]2D4~217.4 (c
0.00826 in CHCl3); SmC* 63.9 SmA* 77.8 Iso liq.
‡C. Elemental analysis for C39H49F1O7: calculated C 72.18%;
H 7.62%; found C 71.69%; H 7.48%.
dH: 0.88 (3H, t, J 6), 1.24–1.52 (14H, m), 1.31 (3H, s), 1.38
(3H, d, J 6), 1.65 (2H, quintet, J 6), 1.83 (2H, quintet, J 6), 3.35
(2H, s), 3.36 (2H, t, J 6), 4.02 (2H, t, J 6), 4.35 (2H, d, J 6), 4.52
(2H, d, J 6), 5.18 (1H, sextet, J 6), 7.01 (2H, d, J 8), 7.09–7.15
(2H, m), 7.60 (2H, d, J 8), 7.69 (2H, d, J 8), 8.01 (1H, t, J 9),
8.22 (2H, d, J 8). nmax (film)/cm21: 2940, 2870, 1740, 1710,
1610, 1520, 1500, 1430, 1250, 1195, 1140, 1060, 1020, 930, 870,
735, 700. m/z: 648 (Mz), 381 (100%), 351, 278, 197, 139, 55.
4-(1-Propylbutyloxycarbonyl)-2-fluorophenyl 4’-[6-(3-
methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-carboxylate
(M3)
(S)-(z)-4-(2-Methylbutyloxycarbonyl)-3-fluorophenyl 4’-[6-(3-
methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-carboxylate
(M5)
The experimental procedure was the same as for the
preparation of compound M1. The following quantities were
used: compound 27, 1.25 g, 3.15 mmol; compound 9, 0.76 g,
3.15 mmol; DCC, 0.65 g, 3.15 mmol; DMAP, 0.10 g,
0.10 mmol; dichloromethane, 50 ml. Yield 1.60 g (80%); SmC
10.3 Iso liq. ‡C. Elemental analysis for C38H47F1O7: calculated
C 71.89%; H 7.47%; found C 72.12%; H 7.59%.
The experimental procedure was the same as for the
preparation of compound M1. The following quantities were
used: compound 27, 1.31 g, 3.30 mmol; compound 19, 0.75 g,
3.30 mmol; DCC, 0.68 g, 3.30 mmol; DMAP, 0.10 g,
1594
J. Mater. Chem., 2001, 11, 1590–1599

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0.10 mmol; dichloromethane, 50 ml. Yield 1.24 g (62%),
[a]2D4~z2.3 (c 0.02627 in CHCl3); K 60.4 SmC* 123.6 SmA*
140.5 Iso liq. ‡C. Elemental analysis for C36H43F1O7:
calculated C 71.25%; H 7.15%; found C 71.02%; H 7.04%.
dH: 0.96 (3H, t, J 6), 1.02 (3H, d, J 6), 1.31 (3H, s), 1.41–1.50
(6H, m), 1.63 (2H, sextet, J 6), 1.83 (3H, octet, J 6; sextet, J 6),
3.48 (2H, s), 3.49 (2H, t, J 6), 4.02 (2H, t, J 6), 4.20 (2H, m),
4.35 (2H, d, J 6), 4.51 (2H, d, J 6), 7.01 (2H, d, J 8), 7.10–7.15
(2H, m), 7.60 (2H, d, J 8), 7.71 (2H, d, J 8), 8.04 (1H, t, J 9),
8.22 (2H, d, J 8). nmax (KBr disc)/cm21: 2940, 2880, 1730, 1710,
1610, 1530, 1500, 1435, 1300, 1280, 1250, 1190, 1130, 1060,
1020, 970, 900, 830, 770, 725, 700. m/z: 606 (Mz), 381 (100%),
279, 197, 139, 55.
Poly{(S)-(z)-4-(2-methylbutyloxycarbonyl)-2-fluorophenyl 4’-
[6-(3-methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-
carboxylate} (P2)
The experimental procedure was the same as for the
preparation of compound P1. The following quantities were
used: compound M2, 0.800 g, 1.320 mmol; SARCAT KI 85,
0.022 g, 2 mol%, 0.026 mmol. Yield 0.500 g (63%), [a]2D4~z3.5
(c 0.00683 in CHCl3); Tg 1.9 SmX* 161.5 SmC* 178.7 SmA*
192.7 Iso liq. ‡C.
dH (CD2Cl2): 0.91 (3H, s), 0.94 (3H, d, J 6), 0.99 (3H, t, J 6),
1.21–1.32 (2H, br m), 1.36–1.60 (6H, br m), 1.73–1.88 (3H, br
m), 3.21 (4H, s), 3.25 (2H, s), 3.35 (2H, br t), 3.92 (2H, br t),
4.14 (2H, m), 6.91 (2H, d, J 8), 7.31 (1H, t, J 8), 7.52 (2H, d, J
8), 7.63 (2H, d, J 8), 7.80–7.90 (2H, m), 8.13 (2H, d, J 8).
4-(1-Propylbutyloxycarbonyl)-3-fluorophenyl 4’-[6-(3-
methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-carboxylate
(M6)
Poly{4-(1-propylbutyloxycarbonyl)-2-fluorophenyl 4’-[6-(3-
methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-carboxylate}
(P3)
The experimental procedure was the same as for the
preparation of compound M1. The following quantities were
used: compound 27, 1.25 g, 3.20 mmol; compound 20, 0.80 g,
3.20 mmol; DCC, 0.67 g, 3.20 mmol; DMAP, 0.10 g,
0.10 mmol; dichloromethane, 50 ml. Yield 1.08 g (54%); K
42.6 (SmA 30.4) Iso liq. ‡C. Elemental analysis for
The experimental procedure was the same as for the
preparation of compound P1. The following quantities were
used: compound M3, 0.800 g, 1.260 mmol; SARCAT KI 85,
0.021 g, 2 mol%, 0.025 mmol. Yield 0.600 g (75%); Tg 10.5
SmC 94.3 Iso liq. ‡C.
dH (CD2Cl2): 0.92 (9H, br m), 1.30–1.50 (8H, br m), 1.50–
1.70 (6H, br m), 1.72–1.82 (2H, br m), 3.22 (4H, s), 3.25 (2H, s),
3.36 (2H, br t), 3.93 (2H, br t), 5.15 (1H, br quintet), 6.93 (2H,
br d), 7.33 (1H, br t), 7.54 (2H, br d), 7.65 (2H, br d), 7.87 (2H,
br m), 8.16 (2H, br d).
C38H47F1O7: calculated
C 71.89%; H 7.47%; found C
71.60%; H 7.29%.
dH: 0.94 (6H, t, J 6), 1.32 (3H, s), 1.40–1.58 (8H, m), 1.59–
1.75 (6H, m), 1.83 (2H, quintet, J 6), 3.47 (2H, s), 3.48 (2H, t, J
6), 4.03 (2H, t, J 6), 4.36 (2H, d, J 6), 4.53 (2H, d, J 6), 5.20 (1H,
quintet, J 6), 7.01 (2H, d, J 8), 7.08–7.15 (2H, m), 7.60 (2H, d, J
8), 7.71 (2H, d, J 8), 8.04 (1H, t, J 9), 8.21 (2H, d, J 8). nmax
(film)/cm21: 2940, 2870, 1740, 1710, 1610, 1530, 1500, 1430,
1280, 1250, 1190, 1120, 1060, 1015, 900, 830, 770, 700. m/z: 634
(Mz), 520, 382, 352, 197, 139, 55 (100%).
Poly{(R)-(2)-4-(1-methylheptyloxycarbonyl)-3-fluorophenyl 4’-
[6-(3-methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-
carboxylate} (P4)
The experimental procedure was the same as for the
preparation of compound P1. The following quantities were
used: compound M4, 0.800 g, 1.230 mmol; SARCAT KI 85,
0.021 g, 2 mol%, 0.025 mmol. Yield 0.430 g (52%),
[a]2D4~216.8 (c 0.00997 in CHCl3); Tg 20.3 SmC* 123.1
SmA* 137.3 Iso liq. ‡C.
Poly{(R)-(2)-4-(1-methylheptyloxycarbonyl)-2-fluorophenyl 4’-
[6-(3-methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-
carboxylate} (P1){
Compound M1 (0.800 g, 1.230 mmol) and photoinitiator
(SARCAT KI 85) (0.021 g, 2 mol%, 0.025 mmol) were
dissolved in dichloromethane (approx. 5 ml) and pipetted
onto a sheet of glass over an area of 190 cm2 (19610 cm). The
solvent was evaporated off in an oven (80 ‡C) over 30 minutes.
The polymerisation mixture was then sandwiched by a second
sheet of glass and cooled to room temperature under nitrogen
and with exclusion of light. The polymerisation mixture was
exposed to UV light for 1 h with cooling (a N2 gas stream
cooled by liquid nitrogen) and then cured in an oven (80 ‡C) for
1 h. The polymer was then cooled to room temperature and
dissolved in dichloromethane (approx. 250 ml) and washed
with water (150 ml). The organic solution was then dried
(Na2SO4). The drying agent was filtered off and the solvent
removed in vacuo to yield the crude polymer which was purified
by precipitation from dichloromethane with hexane. This
precipitation process was repeated 3 times to ensure removal of
all unreacted monomer. The polymer was then dissolved in
dichloromethane and filtered through a 0.45 mm filter. The
solvent was removed in vacuo and the polymer dried in vacuo
(P2O5). Yield 0.260 g (33%), [a]2D5~220.1 (c 0.00416 in CHCl3);
Tg 10.3 SmC* 127.9 SmA* 147.6 Iso liq. ‡C.
dH (CD2Cl2): 0.88 (3H, br t), 0.93 (3H, s), 1.23–1.35 (13H, br
m), 1.35–1.65 (6H, br m), 1.70–1.84 (2H, m), 3.23 (4H, s), 3.25
(2H, s), 3.38 (2H, br t), 3.98 (2H, t), 5.15 (1H, br sextet), 6.97
(2H, br d), 7.05–7.15 (2H, br m), 7.58 (2H, br d), 7.72 (2H, br
d), 8.00 (1H, br t), 8.18 (2H, br d).
Poly{(S)-(z)-4-(2-methylbutyloxycarbonyl)-3-fluorophenyl 4’-
[6-(3-methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-
carboxylate} (P5)
The experimental procedure was the same as for the
preparation of compound P1. The following quantities were
used: compound M5, 0.800 g, 1.320 mmol; SARCAT KI 85,
0.022 g, 2 mol%, 0.026 mmol. Yield 0.520 g (65%), [a]2D4~z1.2
(c 0.00999 in CHCl3); Tg 0.8 SmC* 190.1 SmA* 222.2 Iso liq.
‡C.
dH (CD2Cl2): 0.91 (3H, s), 0.93 (3H, d, J 6), 0.96 (3H, t, J 6),
1.19–1.31 (2H, m), 1.33–1.59 (6H, br m), 1.69–1.89 (3H, br m),
3.20 (4H, s), 3.23 (2H, s), 3.36 (2H, br t), 3.97 (2H, br t), 4.14
(2H, m), 6.95 (2H, br d), 7.03–7.18 (2H, br m), 7.56 (2H, br d),
7.68 (2H, br d), 7.99 (1H, br t), 8.15 (2H, br d).
d
H (CD2Cl2): 0.87 (3H, br t), 0.92 (3H, s), 1.23–1.34 (12H, br
Poly{4-(1-propylbutyloxycarbonyl)-3-fluorophenyl 4’-[6-(3-
methyloxetan-3-ylmethoxy)hexyloxy]biphenyl-4-carboxylate}
(P6)
m), 1.34–1.63 (7H, br m), 1.65–1.82 (2H, br m), 3.21 (4H, s),
3.25 (2H, s), 3.36 (2H, br t), 3.93 (2H, br t), 5.11 (1H, br sextet),
6.93 (2H, br d), 7.33 (1H, br t), 7.55 (2H, br d), 7.65 (2H, br d),
7.86 (2H, br m), 8.16 (2H, br d).
The experimental procedure was the same as for the
preparation of compound P1. The following quantities were
used: compound M6, 0.800 g, 1.260 mmol; SARCAT KI 85,
0.021 g, 2 mol%, 0.025 mmol. Yield 0.250 g (30%); SmC 165.4
SmA 185.6 Iso liq. ‡C.
{The IUPAC names for polymers P1–P6 are poly(oxy{2-methyl[2-(6-
{4’-[4-alkoxycarbonyl-2- or -3-fluorophenoxycarbonyl]biphenyl-4-
yloxy}hexyloxymethyl]trimethylene}).
J. Mater. Chem., 2001, 11, 1590–1599
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Table 1 Transition temperatures (‡C) and enthalpies of transition (J g21) for monomers M1–M6 and the parent monomers I–III
ð1Þ
Transition temperature/‡C
Mpa/‡C
Iso
(DHtransition/J g21) liq.
SmA/
SmA*
SmC/
SmC*
Compound
no.
R
x
y
BPI
—
.
BPIII
—
—
—
—
.
N*
SmX* Recrysta
I
1-MH* H H 34.5 (24.2)
2-MB* H H 36.6 (24.5)
1-PB H H 35.7 (34.6)
1-MH* F H v270
.
.
.
.
.
.
.
.
.
102.1 (4.0)
134.1 (4.6)
64.9 (3.1)
61.6 (2.0)
99.0 (0.4)c
10.3 (0.7)
77.8 (2.0)
140.5 (4.9)
[30.4 (0.3)
—
—
—
—
—
— —
— —
— —
— —
.
.
58.3
(0.2)
90.6
(0.2)
49.5
(0.2)
40.0
(0.1)
51.9
(v0.1)
—
.
.
—
—
v270
II
130.7
—
[13.3 (0.2) .]b v270
III
M1
M2
M3
M4
M5
M6
—
—
—
—
—
—
—
.
.
—
—
—
—
—
—
—
—
—
—
—
—
—
—
v270
v270
v270
v270
v270
v270
v270
—
.
.
2-MB* F H 0.8 (9.8)
1-PB F H v270
—
95.5
(0.4)c
—
.
89.6
(1.2)
.
.
—
—
—
—
—
— —
— —
— —
— —
—
.
.
1-MH* H F v270
—
—
—
—
63.9
(0.5)
123.6
(v0.1)
—
.
2-MB* H F 60.4 (56.3)
—
.
.
1-PB H F 42.6 (3.2)
—
.]
—
aThe melting points and the recrystallisation temperatures were determined by DSC. bTransition in square brackets shows a monotropic transi-
c
tion. The enthalpy values for the BPIII and N* transition are combined due to overlapping peaks.
d
H (CD2Cl2): 0.91 (3H, s), 0.94 (6H, br t), 1.25–1.47 (6H, br
stabilities of the 3-fluoro compounds are higher than for the 2-
fluoro analogues.
m), 1.47–1.72 (8H, br m), 1.75–1.84 (2H, m), 3.20 (4H, s), 3.23
(2H, s), 3.34 (2H, br t), 3.90 (2H, br t), 5.17 (1H, br quintet),
6.97 (2H, br d), 7.09–7.18 (2H, br m), 7.58 (2H, br d), 7.68 (2H,
br d), 8.02 (1H, br t), 8.19 (2H, br d).
Monomers M1, M2, M4 and M5 were all found to exhibit
SmA* and SmC* phases, and the monomers with the achiral 1-
propylbutyl chain gave either SmC (M3) or SmA (M6) phases.
Monomer M2 is particularly interesting because, not only does
it have a low melting point of 0.8 ‡C and exhibits SmA* and
SmC* phases, it is the only compound in the series to show
BPIII and a chiral nematic phase.
Results and discussion
Comparisons of the transition temperatures for the mono-
mers synthesised in these studies with those of the parent
analogues, I–III, show some interesting differences related to
the effect of either the 2- or the 3-fluoro substitution. For the 2-
fluoro compounds, there is, without exception, a reduction in
mesophase stabilities and melting points in comparison with
those obtained for the parents (compare I and M1; II and M2;
and III and M3); the reductions range from 18.3 to 41.1 ‡C with
greater relative reductions for the smectic A* phase.
Mesomorphic behaviour of the monomers
The transition temperatures for compounds M1–M6 and the
analogous parent systems, I–III,9 are given in Table 1.
Monomers M1–M6 are all mesogenic with the 3-fluoro
compounds (M4–M6) generally showing higher melting
points than the 2-fluoro analogues (M1–M3) (however, it
should be noted that a melting point could not be detected for
M4). Similarly, where comparisons are possible, the mesophase
Fig. 2 Structure and transition temperatures of two series of compounds with n-alkoxy chains which behave similarly to compounds I–III and M1–
M6.
1596
J. Mater. Chem., 2001, 11, 1590–1599

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results and the differences between the two fluoro systems are
consistent with those found for some similar n-alkoxy
compounds, see Fig. 2.
The similarity of the transition temperatures of the 3-fluoro
compounds with those of the parents can be attributed to the
space-filling of the fluorine atom but, more importantly by
maintaining the linearity of the core, allowing the molecules to
pack in such a way as to encourage the formation of the
lamellar type ordering that is required for smectic phase
formation. The 2-fluoro systems have reduced transition
temperatures compared to the parent system and this might
be attributed to the interaction of the fluorine atom and the
inner carbonyl of the ester group. The interaction between the
fluorine and the carbonyl may be a repulsive interaction,
causing an internal twist in the core which depresses smectic
phase formation. Indeed, modelling of the 2-fluoro and 3-
fluoro substituted 1-methylheptyl esters M1 and M4 shows that
the rotation about the central ester linkage is severely restricted
for the 2-fluoro analogue in comparison to the 3-fluoro
material. The restricted rotation has the effect of positioning
the carbonyl moiety of the central ester group (for a good
portion of its time) on the opposing side of the molecule to the
2-fluoro substituent, see Fig. 3(a). This leads to the possibility
of the dipoles associated with the carbonyl group and the
fluoro substituent opposing one another. The opposing
strongly polar groups located at the heart of the central core
of the 2-fluoro materials probably lead to reduced lateral
interactions of the molecules thereby resulting in reduced
stability of the smectic state in comparison to the 3-fluoro
analogues (Fig. 3(b)).
Mesomorphism and molecular weight of the polymers
The polymerisation of the monomers occurred in varying
yields, but typically the polymers were obtained in yields
w50%, with polymers P1 (33%) and P6 (30%) as the
exceptions. Table 2 summarises the molecular weight results
determined by GPC analysis and shows that the monomers
M1–M3 give polymers of higher DP than monomers M4–M6.
This suggests that the termination rate is faster for polymer-
isation of compounds M4–M6 which have the 3-fluoro
substituent. Polymers P1–P3 have higher molecular weights
than P4–P6 but they also have greater degrees of polydisper-
sity.
The transition temperatures for polymers P1–P6 and the
parent polymers PI–PIII are shown in Table 3. All of the
polymers exhibit smectic C/C* phases which are typically
exhibited over a very wide temperature range, e.g., from below
room temperature up to 190.1 ‡C for P5, and the phases which
arise for the polymers are almost precisely the same as those
Fig. 3 (a) The minimised space filling molecular structure of M1, (b)
the minimised space filling molecular structure of M4.
The introduction of a 3-fluoro substituent into the mesogenic
core gives a much less coherent picture with respect to
property–structure correlations. For the following pairs of
analogues, II and M5 and III and M6, the 3-fluoro materials
have higher melting points, but for I and M4 the melting point
of the 3-fluoro monomer is significantly lower. The patterns for
the changes in mesophase stabilities are also somewhat erratic;
comparison between III and M6 shows a reduction in smectic
A stability, I and M4 shows an increase in smectic C* and a
decrease in smectic A* stabilities, and II and M5 shows an
increase in both smectic C* and A* stabilities so that the
clearing point for M5 is higher than for II. Thus, the overall
Table 2 Molecular weight and DP values of polymers P1–P6 and polymers PI–PIII determined by GPC
ð1Þ
Compound No
R
x
y
Mn
Mw
Mw/Mn
DP
PI
1-MH*
2-MB*
1-PB
1-MH*
2-MB*
1-PB
1-MH*
2-MB*
1-PB
H
H
H
F
F
F
H
H
H
H
H
H
H
H
H
F
14575
10998
13700
9122
13757
9828
7121
30449
21497
20674
14052
30550
16734
9393
2.0
2.0
1.5
1.5
2.2
1.7
1.3
1.3
1.2
23
19
22
14
23
16
11
9
PII
PIII
P1
P2
P3
P4
P5
P6
F
F
5074
5131
7058
6096
8
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Table 3 Transition temperatures (‡C) and enthalpies of transition (J g21) for polymers P1–P6 and the parent polymers PI–PIII
ð1Þ
Transition temperature/‡C (DHtransition/J g21
)
a
Tg
Compound no.
R
x
y
Iso liq.
SmA/SmA*
SmC/SmC*
SmX*
PI
1-MH*
2-MB*
1-PB
1-MH*
2-MB*
1-PB
1-MH*
2-MB*
1-PB
H
H
H
F
F
F
H
H
H
H
H
H
H
H
H
F
.
.
.
.
.
.
.
.
.
167.8 (1.7)
227.8 (9.2)
146.5 (5.0)
147.6 (5.5)
192.7 (6.5)
94.3 (2.9)
137.3 (1.3)
222.2 (4.1)
185.6 (0.5)
.
.
.
.
.
—
.
.
.
150.2 (0.3)
190.3 (v0.1)
134.5 (0.1)
127.9b
178.7 (0.1)
—
123.1 (0.6)
190.1 (0.4)
165.4 (v0.1)
.
.
.
.
.
.
.
.
.
—
—
—
—
—
—
—
—
.
—
—
—
—
11.8
PII
PIII
P1
P2
P3
P4
P5
P6
19.0
11.2
10.3
1.9
10.5
20.3
0.8
161.5 (0.3)
—
—
—
—
F
F
—
aDetermined by DSC. bNo enthalpy value determined because the transition occurs as a shoulder on a very broad SmA*–Iso liq. transition.
found for the monomers; the only exceptions being that the
nematic phase of M2 is suppressed for the polymer, and a
smectic C phase was induced for polymer P6.
Comparison of polymers P3 and P6 shows that P3 has a
higher clearing point than P6, whereas for the monomers, M3
had a lower clearing point than M6. This observation can be
attributed to the difference in the DP values of the polymers;
P3 has a DP value double that of P6. One of the most
important points that can be made about all of the polymers is
that during microscopy, very little annealing time is required to
obtain a well-defined defect texture. Typically, the annealing
time to create a defect texture, of the type normally exhibited
by low molar mass materials, is about 5 minutes compared to
the few hours or maybe longer required for structurally similar
acrylates or polysiloxanes (often these systems only produce
poorly defined, sandy textures). The polymer textures that are
shown in Fig. 4 for P2, a polymer with a DP of 23, arise after
annealing in the SmA* phase for five minutes, 5 ‡C below the
clearing point.
Polymer P2 exhibited an unidentified mesophase below the
SmC* phase; the textures of both the SmC* phase and the
SmX* phase are shown in Fig. 4. The SmX* phase can be
confirmed as being a tilted phase because a schlieren texture is
observed, however, the schlieren brushes are small and are
difficult to focus upon; typically the bulk of the texture of the
smectic phase of the polymer tends to be made up of focal–
conic domains.
On examination of the DSC results, a small peak (0.3 J g21
)
representing the SmC*–SmX* transition was observed which
was larger than the SmA*–SmC* transition (0.1 J g21). As a
result it is inconclusive whether the SmX* phase is an
antiferroelectric SmCA* phase or a higher ordered smectic
phase, such as smectic I*.
The Tg values for all the polymers are low, and lie within the
range 20.3 to 10.5 ‡C, and for P6 a Tg value could not be
detected.
Comparison of the results for the polymers in this work with
those for the polymers with the parent core (see Table 2) shows
that DP values for P1–P3 are similar to those for PI–PIII,
except in the case of P2 which has a DP value 4 units higher.
The transition temperatures for all of the polymers with a 2-
fluoro substituent (P1–P3) are much lower than for the parent
polymers and the Tg values are also lower. P4 exhibits
transition temperatures which are comparable with P1, but
the transition temperatures of P5 are similar to those of the
parent system, which is quite remarkable especially as the DP
value is approximately 10 units lower that PII. Polymer P6 is
the only fluoro-substituted polymer from those presented
which exhibits transition temperatures that are at higher
temperatures compared to the analogous parent system (PIII).
This increase of transition temperatures is most unexpected
since P6 has the lowest DP of all of the presented polymers,
being approximately 14 units lower than PIII; all other
examples show reduced transition temperatures compared to
the parent system.
Conclusion
In this article we have reported the synthesis of two series of
liquid-crystalline monomers with oxetane terminal groups and
their resulting polymerisation to give side-chain liquid crystal-
line polymers. The monomeric materials exhibit both smectic
A/A* and smectic C/C* mesophases which are preserved upon
polymerisation. The polymers formed are of low viscosity as
Fig. 4 Photomicrographs of the textures of P2; (a) SmC* phase at
178 ‡C, (b) SmX* at 161 ‡C.1{
1598
J. Mater. Chem., 2001, 11, 1590–1599

View Article Online
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4
5
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9
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indicated by their ability to anneal quickly and to give excellent
mesophase textures seen through optical microscopy.
The series of monomers (M4–M6) and polymers (P4–P6)
with a 3-fluoro substituent, in some cases, show superior liquid
crystal properties with respect to the parent systems, particu-
larly with respect to the smectic C/C* temperature ranges, while
the materials which incorporate a 2-fluoro substituent show
reduced smectic C/C* stabilities. All of the monomers have low
melting points, and the polymers show low Tg values. The
suitability of these materials for potential applications is being
assessed by measuring their electrooptical properties (Ps, tilt
angles and response times).
10 D. D. Parghi, S. M. Kelly and J. W. Goodby, Ferroelectrics, 1998,
212, 349.
11 D. D. Parghi, S. M. Kelly and J. W. Goodby, Mol. Cryst. Liq.
Cryst., 1999, 332, 2823.
Acknowledgements
This work is published with the permission of the Controller of
Her Britannic Majesty’s Stationery Office and was supported
by DERA (Malvern). The authors would like to thank Total
for the donation of the photoinitiator used in this work. We
would also like to thank Mrs B. Worthington, Mr A. Rendell
and Mr A. Roberts for the analytical services.
12 G. W. Gray, C. Hogg and D. Lacey, Mol. Cryst. Liq. Cryst., 1981,
67, 1.
13 B. A. Jones, J. S. Bradshaw, M. Nishiota and M. L. Lee, J. Org.
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14 B. Fieser, J. Am. Chem. Soc., 1936, 58, 1738.
15 M. Motoi, H. Suda, K. Shimamura, S. Hagahara, M. Takei and
S. Kanoh, Bull. Chem. Soc. Jpn., 1988, 61, 1653.
16 D. J. Young, Ph.D Thesis, University of Hull, 1989.
17 S. Takehara, T. Fujiwara, Y. Arai and S. Kurokawa, EP 188.222,
JP 85-1.791, JP 85-71.628, JP 85-81.688, JP 85-90.676 (1986).
18 M. Hird, J. W. Goodby, K. J. Toyne, H. Gleeson, I. Buxton and
A. J. Seed, presented at the 18th International Liquid Crystal
Conference, Sendai, Japan, 24–28 July 2000, abstract no. 27E-37-P.
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