Macromolecules, Vol. 36, No. 9, 2003
Liquid-Crystalline Elastomers 3321
Ta ble 1. P olym er iza tion a n d P h otolu m in escen ce
P r op er ties
feed
photolumensca
PMHS
A
B
A/(A + B) yield λmax intensb
sample (mmol) (mmol) (mmol) (mol %)
(%) (nm) (×103)
P0
P1
P2
P3
P4
P5
P6
P7
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0
9.00
8.96
8.91
8.82
8.55
8.10
7.20
0.00
0
92
0.023
0.045
0.090
0.225
0.450
0.900
4.500
0.25
0.50
1.00
2.56
5.26
90
90
88
88
87
85
80
494
493
493
494
493
492
493
0.17
0.37
0.73
1.89
3.90
8.21
11.1
100
12.1
a
Obtained from solutions of the samples (0.0050 g) in 50 mL
b
toluene. Calculated by the peak area.
nitrogen atmosphere. Visual observation of liquid crystalline
transitions under cross polarized light was made by a Leitz
Laborlux S polarizing optical microscope (POM) equipped with
a THMS-600 heating stage.
The photoluminescence (PL) spectra of the monomer and
polymers was obtained using a Shanghai Instruments Model-
960 Spectrofluorphotometer.
F igu r e 1. IR spectra for (a) P0, (b) P2, (c) P6, and (d) P7.
Small-angle X-ray scattering (SAXS) measurements were
performed using Cu KR (λ ) 1.542 Å) radiation monochroma-
tized with a Ni filter and a totally reflecting glass block (Huber
small-angle chamber 701). The intensity curves were measured
using a linear position sensitive detector (Mbraun OED-50 M).
Syn th eses. Syn th esis of 2,2′-(1,2-Eth en ed iyl)bis[5-[(4-
u n d ecen oyloxy)p h en yl]a zo]ben zen esu lfon ic Acid . 10-
Undecylenoic acid (18.4 g, 0.1 mol) and thionyl chloride (25.0
g, 0.21 mol) were added into a round flask equipped with an
absorption instrument of hydrogen chloride. The mixture was
stirred at room temperature for 2 h, then heated to 60 °C, and
kept for 3 h in a water bath to ensure that the reaction
finished. The mixture was distilled under reduced pressure
to obtain 12.4 g of 10-undecenoyl chloride at 160-170 °C (20
mmHg) in the yield of 61%.
solution in methanol by the addition of THF. After filtration
and evaporation of the solvent, the product was dried at 80
°C for 2 h under vacuum to obtain 5.03 g of polymer in a yield
of 90%.
IR(KBr, cm-1): 2960-2850 (CH3- and -CH2-); 1608
(NdN); 1738(CdO).
Resu lts a n d Discu ssion
F TIR Sp ectr a . Figure 1 shows the FTIR spectra of
nonionic LC polymer P0, ionic LC polymers P2 and P6,
and ionic polymer P7 recorded at room temperature in
KBr pellets. The disappearance of the Si-H stretching
at 2160 cm-1 indicates successful incorporation of
monomers into the polysiloxane chains. Polymer P6
contains the representative features for all of the ionic
liquid-crystalline elastomers, their characteristic ab-
sorption bands are as follows: 3424 (O-H stretching),
2932, 2857 (C-H aliphatic), 1738 and 1755 (CdO
stretching in two kinds of ester modes), 1608 (NdN
stretching), and 845 cm-1 (dC-H out-of-plane bending).
The FTIR absorption bands of the CdO stretching
vibration (1734 cm-1 in P0; 1757 cm-1 in P7) indicate
different ester linkage.
For organic sulfonic acid, the FTIR absorption range
of the OdSdO asymmetric and symmetric stretching
modes lies in 1100-1260 and 1010-1080 cm-1 respec-
tively. Because of the overlap found for both asymmetric
and symmetric stretching bands of SO2 with C-O and
Si-O stretching bands in the polymers under study, the
NdN stretching mode in bright yellow group is chosen
for identification of ionic groups in the polymers.
Because of the symmetric structure of aromatic groups,
their CdC stretching vibrations are weak. FTIR peaks
at 1600 cm-1 should be regarded as the NdN stretching
mode. Figure 1 compares the FTIR spectra for (a)
nonionic P0, (b) 0.5 mol % ionic content P2, (c) 11.1 mol
% ionic content P6, and (d) ionic polymer P7. While there
is no NdN stretching mode found in nonionic content
P0, such a mode is found as a weak band at 1600 cm-1
for the sample of 0.5 mol % ionic content, and stronger
absorption bands are found at 1597 and 1600 cm-1 for
the samples of P6 and P7. These results clearly indicate
successful incorporation of ionic groups, whose concen-
Brilliant yellow (6.3 g, 0.01 mol) was dissolved in 120 mL
of pyridine to form a solution. 10-undecenoyl chloride (4.1 g,
0.02 mol) was added to the solution and reacted at 80 °C for
6 h, cooled, poured into 500 mL of cold water and acidified
with 6 N H2SO4. The precipitated crude product was filtered
and recrystallized from ethanol/water (1/1) and dried overnight
at 85 °C under vacuum to obtain a brown powder of product
in the yield of 70%. Mp: above 300 °C.
IR (KBr, cm-1): 3420(-OH); 3080(dC-H); 1760(CdO);
1600(NdN); 1500(CdC); 1121(SdO in -SO3H).
Syn th esis of Ch olest-5-en -3-ol(3â)-10-u n d ecen oa te. To
a solution of cholesterol (19.3 g, 0.50 mol) in 100 mL of pyridine
was added 10-undecenoyl chloride (11.0 g, 0.054 mol) and
reacted at reflux temperature for 3 h. The mixture was
dispersed in H2O (500 mL) and acidified with 6 N HCl. The
precipitated crude product was filtered and recrystallized from
ethanol. The product was dried under vacuum to obtain a
white powder, cholest-5-en-3-ol(3â)-10-undecenoate, in a yield
of 80%.
IR (KBr, cm-1): 3050(dC-H); 2965-2854(CH3- and
-CH2-); 1735(CdO).
Syn th esis of th e Ela stom er s. For synthesis of polymers
P0-P7, the same method was adopted. The polymerization
experiments are summarized in Table 1. The synthesis of
polymer P2 was given as an example. 2,2′-(1,2-Ethenediyl)bis-
[5-[(4-undecenoyloxy)phenyl]azo]benzenesulfonic acid (0.042 g,
0.045 mmol, monomer A) was dissolved in 60 mL of dry, fresh
distilled toluene. To the stirred solution were added cholest-
5-en-3-ol(3â)-10-undecenoate (4.92 g, 8.91 mmol, monomer B),
poly(methylhydrogeno)siloxane (0.63 g, 0.30 mmol), and 2 mL
of H2PtCl6/THF (0.50 g hexachloroplatinic acid hydrate dis-
solved in 100 mL of tetrahydrofuran THF), and this mixture
was heated under nitrogen and anhydrous conditions at 65
°C for 48 h. The solvent was removed under reduced pressure,
and the crude polymer was purified by precipitation from