Synthesis of novel tri-podal mesogenic alkenes and side-chain polysiloxanes

Article abstract of DOI:10.1016/j.jorganchem.2004.05.019

Low molecular weight tri-podal biphenyl- and benzoate-type mesogens [C₆H₅C₆H₄O(CH₂) ₅SiMe₂CH₂CH₂ SiMe₂]₃CH (4),C₁₁H_23<

Full text of DOI:10.1016/j.jorganchem.2004.05.019

Journal of Organometallic Chemistry 689 (2004) 2606–2613
www.elsevier.com/locate/jorganchem
Synthesis of novel tri-podal mesogenic alkenes and side-chain
polysiloxanes
,1
Tomasz Ganicz , Włodzimierz A. Stanczyk
1
*
´
´
´
Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łodz, Poland
Received 5 April 2004; accepted 17 May 2004
Available online 2 July 2004
Abstract
Low molecular weight tri-podal biphenyl- and benzoate-type mesogens [C6H5C6H4O(CH2)5SiMe2CH2CH2SiMe2]3CH (4),
[C11H23O(C6H4)2O(CH2)5SiMe2]3CH (5) and [MeOC6H4OC(O)C6H4O(CH2)5SiMe2]3CH (6) (C6H4 =1,4-phenylene) were obtained,
from branched silyl substituted methane precursors [CH2‚CH(Me)2Si]3CH (1) and (HMe2Si)3CH (2). The biphenyl-containing
ones (4) and (5) were converted into terminal alkenes, which were subsequently hydrosilylated with poly(methylsiloxanes). The poly-
mer derived from (5) exhibited mesomorphic properties. Such systems have the potential to significantly increase the density of
liquid crystal rod-like structures in side chains of linear polymers (or dendritic liquid crystal polymers).
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Liquid crystalline polymers; Polysiloxanes; Functionalisation of polymers; Nonlinear polymers; Structure–property relationships
1. Introduction
them as free standing films in optical applications. How-
ever, higher molecular weight and higher viscosity of
polymer, lengthen the response time of such materials
to external magnetic or electric fields and this feature re-
stricts many potential applications [3]. Hybrid materials
(oligomers or dendrimers of various generations) have
thus been studied. The latter, often polymers of high
molecular weight, approach spherical geometry at high-
er generations and give materials of relatively low vis-
cosity [4,5]. An especially interesting combination of
properties, viz low viscosity and wide temperature range
for mesophase formation, is shown by polymers with
paired, dimesogenic systems [6], attached to silsesquiox-
ane core [7].
In our search for low melt viscosity liquid crystals,
that form glasses above ambient temperature, as is typ-
ical for oligomeric systems based on cyclic, cubic or star
shape molecules [3,8], we have described a series of
tetrakis-substituted methanes and silanes [9]. The
starting materials [C(SiMe2H)4 and Si(SiMe2H)4] for
the synthesis of star systems seemed to show promise
Liquid crystal polymers, in which rigid, mesogenic
side-chains are attached to polymer backbones via fle-
xible spacers, are a significant class of novel materials
with richly diverse architectures. Their properties can
be adjusted by introducing changes into the structures
of the polymer chain, the flexible spacer or most espe-
cially the mesogen. Other factors, such as molecular
weight and polydispersion play an important role. These
polymer systems are now being considered for applica-
tion in nonlinear optics, pyroelectric detectors and dis-
play devices [1,2]. Compared with low molecular
weight liquid crystals such polymers show enhanced me-
chanical properties and offer possibility of the use of
*
Corresponding author. Tel.: +48-42-6818952; fax: +48-42-
6847126.
E-mail address: tg@bilbo.cbmm.lodz.pl (T. Ganicz).
1
Authors wish to present this paper in memory of the late Prof.
Colin Eaborn FRS.
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.05.019

´
T. Ganicz, W.A. Stanczyk / Journal of Organometallic Chemistry 689 (2004) 2606–2613
2607
for the synthesis of polymers, bearing mesogens in side-
chains.
product, [HC(SiMe2Vi)3] (1), was obtained under re-
duced pressure (97 ꢁC/1 mm Hg). Yield: 2.1 g (40.7%);
1H NMR (CDCl3) d: ꢀ0.55 (1H, s, CH), 0.18 (18H, s,
We report here on synthetic methods leading to novel
liquid crystals from ‘‘trisyl’’ type [tris(trimethylsi-
lyl)]methane compounds [10,11], HC(SiMe2Vi)3 (1)
and HC(SiMe2H)3 (2). Some of these can be modified
to give liquid crystal oligomers and polymers.
1
2
SiCH3), 5.75 (2H, m, J=14.7, J=1.45 Hz, CH2‚),
1
2
6.28 (1H, m, J=14.7; J=1.45 Hz, ‚CH); 13C NMR
(CDCl3) d: 1.2 (SiMe), 1.5 (CH), 130.3 (CH2‚), 142.4
(‚CH); 29Si NMR: (CDCl3, INEPT) d: 7.24; Anal. Calc.
for C13H28Si3: C, 58.13; H, 10.51. Found: C, 58.01; H,
10.42%. GC/MS. m/z: 268 [10%, M+], 253 [100%,
M+ ꢀCH3], 241 [95%, M+ ꢀCH‚CH2], 226 [35%,
M+ ꢀCH3 ꢀCH‚CH2], 214 [15%, M+ ꢀ2(CH‚CH2)],
199 [12%, M+ ꢀCH3 ꢀ2(CH‚CH2)], 97 [2%,
(CH3)(CH2‚CH)SiC+], 85 [10%, (CH3)2(CH2‚CH)
Si+], 73 [9%, Me3Si+].
2. Experimental
2.1. Materials and methods
All organometallic syntheses were carried out under
argon with exclusion of moisture by use of Schlenk tech-
niques. Solvents were dried by standard methods and
stored over sodium mirrors or molecular sieves.
Tris(dimethylsilyl)methane [HC(SiMe2H)3] (2) was
synthesised according to [14].
HCBr3 (Aldrich), chlorodimethylvinylsilane (ABCR),
MgSO4 (Aldrich), chlorodimethylsilane (ABCR), Kar-
stedtÕs catalyst (Pt2[(ViSiMe)2O]3, 3.5% sol. in xylenes,
ABCR), LiAlH4 (Aldrich), MeLi (1.6 M sol. in Et2O, Al-
drich), allyl bromide (Aldrich) and poly(methylsiloxane)
(Mn =2150, IP=1.23, ABCR) were used as supplied.
2.2.3. Hydrosilylation of 4-(4-pentenyloxy)biphenyl with
chlorodimethylsilane
A mixture of 4-(4-pentenyloxy)biphenyl (4 g, 16.78
mmol), toluene (20 ml), chlorodimethylsilane (1.59 g,
16.8 mmol) and KarstedtÕs catalyst (20 ll of 3.5% soln.
in xylenes, 2.1·10ꢀ4 mol Pt/mol Si–H) was stirred under
argon at 60 ꢁC for 24 h. The solvent was evaporated to
leave white, solid ClSiMe2(CH2)5OC6H4C6H5 (yield –
5.6 g, 100%).
1H NMR (C6D6) d: 0.22 (6H, s, SiCH3), 0.65 (2H, t,
J=1.0 Hz, Si–CH2), 1.35–1.62 (6H, m, C–(CH2)3–C),
3.67 (2H, t, J=1.90 Hz, OCH2), 6.90, 7.25 (9H, m, aro-
matic protons); Anal. Calc. for C19H25ClOSi: C, 68.54;
H, 7.57. Found: C, 68.34; H, 7.67%.
1
The H, 13C and 29Si NMR spectra were recorded in
CDCl3 or C6D6 solutions with Bruker AC 200 or DRX
500 spectrometers. The progress of hydrosilylation was
followed by the disappearance of the Si–H absorption
(at 2160 cmꢀ1 for poly(methylsiloxane), 2105 cmꢀ1 for
HSiMe2Cl and C6H5C6H4O(CH2)5SiMe2H, 2120 cmꢀ1
for HC(SiMe2H)3) by use of an ATI Mattson spectrom-
eter. Mass spectra were obtained using ThermoQuest
Finnigan GC/MS. Thermal behaviour was studied by
differential scanning calorimetry (DSC) using a DuPont
DSC-910 instrument. Phase transitions were verified by
optical microscopy and X-ray diffraction studies.
2.2.4. Synthesis of 4-biphenyloxypentyldimethylsilane (3)
The product from the preceding experiment 4-biphe-
nyloxypentyldimethylchlorosilane (16.78 mmol) was dis-
solved in dry diethyl ether (20 ml), then LiAlH4 (0.65 g,
17.13 mmol) was added and the mixture was heated un-
der reflux for 6 h.
2.2. Syntheses
2.2.1. Rod-like alkenes
4-(4-Pentenyloxy)biphenyl [CH2‚CH(CH2)3OC6H4-
C6H5],
[CH2‚CH(CH2)3OC6H4C(O)OC6H4OCH3] and 40-un-
decanyloxy4-(4-pentenyloxy)biphenyl [CH2‚CH(CH2)3
OC6H4C6H4OC11H23] were made by the literature meth-
ods [12,13].
The solvent was removed under vacuum and the
black, solid residue dissolved in hot toluene (30 ml).
The solution was filtered and the solvent removed under
vacuum to give white crystals of HSiMe2-
40-methoxyphenyl-4-(4-pentenyloxy)benzoate
1
(CH2)5OC6H4C6H5 (3). Yield: 3.45 g (70%); H NMR
(C6D6) d: 0.05 (6H, d, J=3.71 Hz, SiCH3), 0.55-
1
2
(2H, m, J=1.0; J=3.10 Hz, Si–CH2), 1.25–1.75 (6H,
m, C–(CH2)3–C), 3.65 (2H, t, J=1.90 Hz, O–CH2),
4.15 (1H, m, J=3.71 Hz, Si–H), 6.95, 7.15 (9H, m, aro-
matic protons); Anal. Calc. for C19H26OSi: C, 76.47; H,
8.79. Found: C, 76.21; H, 8.85%.
2.2.2. Silyl-substituted methanes
A solution of HCBr3 (2.4 ml, 0.028 mol) in 10 ml of dry
THF was added dropwise during 1 h to a stirred mixture
of chlorodimethylvinylsilane (11.4 ml, 0.084 mol), mag-
nesium turnings (2.2 g, 0.09 mol) and dry THF (50 ml).
The mixture was heated under reflux for 2 h, then cooled
to room temperature. Ice (40 g) was added slowly. The
mixture was filtered and the organic phase separated,
washed twice with 15 ml of cold water, then dried over
MgSO4 and filtered. Solvent was distilled off and the
2.2.5. Hydrosilylation of tris(dimethylvinylsilyl)methane
(1) with 4-biphenyloxypentyldimethylsilane (3)
A mixture of tris(dimethylvinylsilyl)methane (1) (0.76
g, 2.83 mmol) and KarstedtÕs catalyst (20 ll of 3.5% so-
lution in xylenes, 5.1·10ꢀ4 mol Pt/mol Si–H) was added
to 4-biphenyloxypentyldimethysilane (3) (2.1 g, 7.0

´
T. Ganicz, W.A. Stanczyk / Journal of Organometallic Chemistry 689 (2004) 2606–2613
2608
mmol) in toluene (10 ml). The mixture was stirred at 60
ꢁC for 72 h and the solvent evaporated to leave a brown
solid that was extracted with CH2Cl2. The extract was
filtered and the solvent evaporated to leave white solid,
which was recrystallised from hot methanol (30 ml) to
give HC[Si(Me)2(CH2)2Si(Me)2(CH2)5OC6H4C6H5]3 (4)
(2.01 g, 74%); 1H NMR (CDCl3) d: ꢀ0.59 (1H, s,
CH), ꢀ0.12 (18H, s, HC–SiMe2), 0.18 (18H, s, H2C–
carbon atoms); 29Si NMR: (C6D6 INEPT) d: 6.3; Anal.
Calc. for C64H81O12Si3: C 68.18; H, 7.34. Found: C,
67.98; H, 7.20%.
2.2.7. Functionalisation of silyl-substituted methanes (4)
and (5) by reaction with methyl lithium and allyl bromide
Compound (4) or (5) (0.76 mmol) in dry THF (10 ml)
was added dropwise to a solution of MeLi (2 mmol) in
THF (10 ml) at room temperature. The reaction mixture
was heated under reflux for 5 h to give a deep red solu-
tion of the lithium derivative.
The mixture was cooled to 0 ꢁC and allyl bromide (0.12
ml, 0.8 mmol) was added dropwise. The mixture was stir-
red for 4 h at 0 ꢁC and the solvent evaporated under vac-
uum at 0 ꢁC to leave red, semi-solid product, that was
partly extracted with toluene (20 ml). The extract was fil-
tered and the solvent evaporated to leave a yellow solid
that was recrystallised from hot ethanol (15 ml).
Allyl derivatives: CH2‚CHCH2C[SiMe2(CH2)2Si-
SiMe2(CH2)5OC6H4C6H5]3 (7) and CH2‚CHCH2C[Si-
[SiMe2(CH2)5OC6H4C6H4O(CH2)10CH3]3 (8) were
obtained, respectively, in 88% (0.81 g) and 73% (0.63
g) yield.
1
2
SiMe2–CH2), 0.35 (12H, m, J=1.40; J=7.70 Hz, Si–
CH2–CH2–Si), 0.56 (6H, m, 1J=7.70, 2J=1.0 Hz,
Si–CH2(CH2)4), 1.28–1.45 (18H, m, C–(CH2)3–C), 4.05
(6H, t, J=1.90 Hz, O–CH2), 6.90, 7.25 (27H, m, aromat-
ic protons); 13C NMR (CDCl3) d: ꢀ5.2 (CH), ꢀ3.9
(HC–SiMe2), 0.6 (CH2–SiMe2–CH2), 7.7 (CH2–Si–
CH), 11.1 (–(CH2)5–Si–CH2), 14.8 ((CH2)4–CH2–Si),
23.8, 29.1, 30.1 (–C–CH2–C), 68.1 (O–CH2), 114.8,
126.6, 126.7, 128.1, 128.7 (aromatic carbon atoms);
29Si NMR (CDCl3, INEPT) d: 2.77 (Si–(CH2)5), 4.00
(Si–CH); Anal. Calc. for C70H106O3Si6: C, 72.25; H,
9.19. Found: C, 72.39; H, 9.08%.
2.2.6. Hydrosilylation of mesogenic alkenes with tris(di-
methylsilyl)methane
The general procedure is described below:
(7) 1H NMR (CDCl3) d: ꢀ0.17 (18H, s, SiMe2–
(CH2)5), ꢀ0.05 (18H, s, SiMe2–CH), 0.23 (12H, m,
1J=7.70; 2J=1.0 Hz, Si–CH2–CH2–Si), 0.38 (6H, m,
J=1.0 Hz, (CH2)4–CH2–Si), 1.28–1.45 (18H, m, C–
(CH2)3–C), 3.35 (2H, m, 1J=1.40; 2J=1.0 Hz, CH2–
C‚C), 3.91 (6H, t, J=1.25 Hz, O–CH2), 4.95 (2H, m,
KarstedtÕs catalyst (10 ll of 3.5% solution in xylenes,
5.5·10ꢀ4 mol Pt/mol Si–H) was added to a mixture of
the mesogenic alkene (3.2 mmol) and tris(dimethylsi-
lyl)methane (2) (0.2 g, 1.04 mmol) in dry toluene. The
mixture was stirred at room temperature for 12 h, then
for 92 h at 60 ꢁC. The product was separated by multiple
precipitation from dichloromethane/methanol and sol-
vent removed under vacuum.
2
1
1J=1.40; J=1.80 Hz, CH2‚C), 5.95 (1H, m, J=1.40;
2J=1.80 Hz, CH‚), 6.90, 7.25 (27H, m, aromatic pro-
tons); 13C NMR (CDCl3) d: ꢀ2.1 (SiMe2–(CH2)5), 0.7
(SiMe2–CH), 7.9 (CH2–Si–CH), 11.2 ((CH2)5–Si–CH2),
14.8 ((CH2)4–CH2–Si), 23.8, 29.1, 30.1 (–C–CH2–C),
47.3 (CH2–C‚C), 68.1 (O–CH2), 114.8, 126.6, 126.7,
128.1, 128.7 (aromatic carbon atoms), 138.6 (CH2‚),
142.4 (CH‚); 29Si NMR (CDCl3) d: 2.1 (Si–(CH2)5),
7.8 (CH2‚CH–C–Si); Anal. Calc. for C73H110O3Si6: C,
72.84; H, 9.22. Found: C, 72.60; H, 9.07%.
Tri-podal methanes (5) and (6) with, respectively, 40-
undecanyloxybiphenyl-4-(4-pentenyloxy) and 40-meth-
oxyphenyl-4-(4-pentenyloxy)benzoate moieties were
obtained, in 76% (0.83 g) and 74% (0.89 g) yield.
(5) 1H NMR (C6D6) d: ꢀ0.25 (1H, s, CH), 0.08 (18H,
1
2
s, SiCH3), 0.68 (6H, m, J=1.0; J=7.25 Hz Si–CH2),
0.96 (9H, t, J=1.0 Hz, C–CH3), 1.20–1.75 (12H+48H,
m, Si–C–(CH2)2–C+O–C–C–(CH2)8CH3), 1.78–1.81
(12H, m, –CH2–C–O), 3.95, 4.02 (6H+6H, t, OCH2),
6.95, 7.1, 8.15, (24H, m, aromatic protons); 13C NMR
(C6D6) d: ꢀ5.8 (HC), 2.0 (SiCH3), 12.6 (C–CH3), 18.7
(CH2Si), 25.3–31.4 (–C–CH2–C), 69.1, 71.4 (CH2
CH2O), 76.5, 77.1 (CH2O), 115.5–134.5 (aromatic car-
bon atoms); 29Si NMR: (C6D6 INEPT) d: 6.2; Anal.
Calc. for C91H142O6Si3: C, 77,17; H, 9.22. Found: C,
77.02; H, 9.05%.
(8) –1H NMR (CDCl3) d: ꢀ0.16 (18H, s, SiMe2–
(CH2)5), ꢀ0.04 (18H, s, SiMe2–CH), 0.22 (12H, m,
1J=7.70; 2J=1.0 Hz, Si–CH2–CH2–Si), 0.37 (6H, m,
J=1.0 Hz, (CH2)4–CH2–Si), 0.92 (9H, t, J=1.0,
C–CH3), 1.28–1.49 (18H+48H, m, C–(CH2)3–C+O–C–
C–(CH2)8CH3), 3.34 (2H, m, 1J=1.40; 2J=1.0 Hz,
CH2–C‚C), 3.91, 3.93 (6H+6H, t, J=1.25 Hz, O–
CH2), 4.94 (2H, m, 1J=1.40; 2J=1.80 Hz, CH2‚C),
1
2
5.92 (1H, m, J=1.40 J=1.80 Hz, CH‚), 6.91, 7.26
(27H, m, aromatic protons); 13C NMR (CDCl3) d: ꢀ2.2
(SiMe2–(CH2)5), 0.8 (SiMe2–CH), 7.7 (CH2–Si–CH),
11.3 ((CH2)5–Si-CH2), 14.8 ((CH2)4–CH2–Si), 23.8–32.4
(–C–CH2–C), 47.3 (CH2–C‚C) 68.1, 69.2 (O–CH2),
115.6–132.8 (aromatic carbon atoms), 138.9 (CH2‚),
142.2 (CH‚); 29Si NMR (CDCl3) d: 1.9 (Si–(CH2)5),
7.2 (CH2‚CH–C–Si); Anal. Calc. for C94H146O6Si3: C,
77.84; H, 10.11. Found: C, 77.61; H, 9.98%.
(6) 1H NMR (C6D6) d: ꢀ0.25 (1H, s, CH), 0.07 (18H,
1
2
s, SiCH3), 0.65 (6H, m, J=1.0; J=7.25 Hz, Si–CH2),
1.25–1.70 (12H, m, Si–C–(CH2)2–C), 1.85 (6H, m,
–CH2–C–O), 3.75 (9H, s, OCH3), 4.05 (6H, m, J=1.25
Hz, CH2–O), 6.95, 7.1, 8.15, (24H, m, aromatic pro-
tons); 13C NMR (C6D6) d: ꢀ5.6 (HC), 2.1 (SiCH3),
18.6 (CH2Si), 25.3, 35.2 (–C–CH2–C), 55.8 (OCH3),
69.1 (CH2CH2O), 76.5 (CH2O), 115.5–134.5 (aromatic

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T. Ganicz, W.A. Stanczyk / Journal of Organometallic Chemistry 689 (2004) 2606–2613
2609
2.2.8. Synthesis of side-chain linear polysiloxanes (9) and
(10)
7.40–7.56 (27H, aromatic hydrogen atoms); 29Si
NMR (C6D6) d: ꢀ21.5 (Si–O), 2.9 (Me3Si end
groups), 4.1 (Si–(CH2)5), 7.0 (C–Si–(CH2)3).
A precursor (7) or (8) (0.67 mmol) was dissolved in
toluene (10 ml) and poly(methylsiloxane) (Mn =2150)
(0.36 g, 0.6 mmol of Si–H) and KarstedtÕs catalyst (10
ll of 3.5% solution in xylenes, 1.5·10ꢀ3 mol Pt/mol
Si–H) were added. The mixture was stirred under argon
at 60 ꢁC for 96 h and the solvent evaporated to leave
white, semi-solid product. This was purified by multiple
precipitation from CH2Cl2/MeOH and the solvent re-
moved under vacuum.
1
(10) H NMR (CDCl3) d: 0.08 (18H, s, –C–SiMe2–
C–), 0.12 (3H, s, O–Si–Me from main chain), 0.45
(12H+2H, s, SiCH2), 0.81 (9H, m, CH3), 1.21–1.29
(4H+6H, m, Si–CH2(CH2)2C+SiMe2CH2CH2), 1.32–
1.35 (6H+30H, m, SiMe2CH2CH2CH2 +OCH2CH2
(CH2)5), 1.71–1.83 (6H+6H, m, O–CH2CH2), 3.76,
3.89 (6H+6H, m, OCH2), 6.79–6.91, 7.0–7.12, 8.05–
8.13 (27H, aromatic hydrogen atoms); 29Si NMR
(CDCl3) d: ꢀ21.7 (Si–O), 3.9 (Me3Si end groups), 7.1
(Me2Si).
The polysiloxanes (9) and (10) were obtained, respec-
tively, in 59% (0.45 g) and 61% (0.64 g) yield.
1
(9) H NMR (C6D6) d: 0.04 (s, SiMe3 polymer end
groups), 0.12 (3H, s, O–Si–Me from main chain), 0.24
(18H, s, Si–C–SiMe2), 0.29 (18H, s, CH2Si(Me)2CH2),
0.40 (12H, s, SiCH2CH2Si), 0.51–0.61 (8H, m, SiCH2
(CH2)4 +O–Si–CH2), 0.73–0.78 (8H, m, O–SiCH2CH2
CH2C+Si–CH2CH2–(CH2)3), 1.36–1.55 (8H, O–SiCH2
CH2CH2C+Si–(CH2)2–CH2–(CH2)2), 1.70 (6H, m,
O–CH2CH2), 3.73 (6H, m, OCH2), 6.71, 6.93, 7.24,
3. Results and discussion
There appears to be a growing demand for multi-
podal mesogens as a way of increasing density of
liquid crystal moieties attached to polymer backbones.
Such taper-shaped side groups, based on 3,4,5
HSiMe2Cl
+
Br3CH
+
ClSi(Me)2CH=CH2
Mg
O(CH2)3CH=CH2
[Pt] toluene
THF
HC[Si(Me)2CH=CH2]3
O(CH2)5SiMe2Cl
LiAlH4
(1)
(1)
O(CH2)5SiMe2H
+
(3)
[Pt]
toluene,
60 ˚C
O(CH2)5SiMe2CH2CH2SiMe2
CH
3
(4)
MeLi 0 ˚C,
THF
BrCH2CH=CH2
O(CH2)5SiMe2CH2CH2SiMe2
CCH2CH=CH2
3
(7)
Me
Si
toluene,
60 ˚C
[Pt]
O
n
H
Me
Me3SiO Si
(CH2)3
O
SiMe3
(9)
n
Scheme 1. Synthetic pathway leading to side-chain polysiloxane (9).

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T. Ganicz, W.A. Stanczyk / Journal of Organometallic Chemistry 689 (2004) 2606–2613
2610
Mg
(2)
HC(SiMe2H)3
+ ClMe2SiH
HCBr3
THF
[Pt], toluene,
60 deg. C
(CH2)3O
C
O
O
OCH3
(CH2)3O
H23
OC11
(CH2)5O
HC SiMe2
(CH2)5O
HC SiMe2
OC11H23
C O
O
OCH3
3
3
(6)
(5)
MeLi
BrCH2CH=CH2
0 deg C
THF
(8)
(CH2)5O
CH2=CHCH2C
SiMe2
OC11H23
3
Me
toluene,
60 ˚C
[Pt]
Si
H
O
n
Me
Me3SiO Si
(CH2)3
O
SiMe3
n
(10)
Scheme 2. Synthetic pathway leading to side-chain polysiloxane (10).
Fig. 1. MHz 1H NMR and 29Si NMR of side-chain polysiloxane (9).
substituted benzene rings, have recently been attached
to polymethylmethacrylate backbone [15]. The synthe-
ses involve, however, 11-steps and the short flexible
spacers leave little freedom to individual mesogens at
branching point.
Such problems are avoided in the syntheses of the
branched multi-rod type side-chain polymers described
here (Schemes 1 and 2). The tri-functional methanes –
[CH2‚CH(Me)2Si]3CH (1) and (HMe2Si)3CH (2), can
be easily made by Grignard type coupling reactions

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2611
and the longer spacer between the mesogenic rods and
the polymer backbone allows more flexibility for orien-
tation of the mesogenic fragments. Longer spacers (8–10
atoms separating polymer chain from a mesogen) usual-
ly better decouple motions of the mesogens from the
polymer backbone [16]. The simplest model mesogenic
rod-like alkene, 4-(4-pentenyloxy)biphenyl, was modi-
fied by hydrosilylation with chlorodimethylsilane to give
Cl(Me)2 Si(CH)5OC6H4C6H5, which was subsequently
reduced with LiAlH4 to 4-biphenyloxypentyldimethylsi-
lane (3) with an overall yield of 70%. A simple hydrosi-
lylation of (1) with a threefold excess of (3) gave the
tri-podal substituted methane (4) (Scheme 1). The acid
C–H moiety in methane (4) [11] was quantitatively lith-
iated (MeLi) and the lithium salt functionalised by reac-
tion with allylbromide. The substituted branched alkene
(7) was attached to commercially available poly(methyl-
siloxane) (Mn =2150, IP=1.23) by the addition of
Si–H bonds in the polymer across allyl functions in
the methane. The new polymer (9) has branched side-
chain substituents at each silicon atom along the silox-
ane chain (see 1H NMR and 29Si NMR, Fig. 1). Neither
(7) nor the side-chain polysiloxane (9) exhibits liquid
crystalline properties. The simple biphenyl rod-like sys-
tem is known to be a rather ineffective mesogen
[17,18], but it was used here as a model to prove the
effectiveness of the individual steps of the synthetic
pathway.
morphic properties. We therefore proceeded with syn-
theses of derivatives bearing rod-like moieties already
shown to give mesomorphic properties in the expecta-
tion that these would be strengthened on transfer to
polymer systems.
Synthetic routes to polymers containing the
established mesogenic groups [19], 40-methoxyphenyl-
4-(4-pentenyloxy)benzoate and 40-undecanyloxy-4-(4-
pentenyloxy)biphenyl, were simplified (Scheme 2). The
use of (HMe2Si)3CH (2) as a precursor in the place
of [CH2‚CH(Me)2Si]3CH (1) made it possible to syn-
thesize mesogenic alkenes by direct hydrosilylation,
without reaction with HMe2SiCl and subsequent reduc-
tion with LiAlH4 (Scheme 1). Two low molecular
weight branched mesomorphic derivatives (5) and (6)
were made (Scheme 2), and the following phase transi-
tions: K 98 ꢁC N 124 ꢁC I (5) and K 6 ꢁC SmA 40 ꢁC I
(6) (where K, N, SmA and I denote crystal, nematic,
smectic A and isotropic phases, respectively) were es-
tablished by DSC (Fig. 2) and X-ray diffraction stud-
ies. A limitation, on the incorporation of mesogen (6)
into polymer systems, arises from the sensitivity of its
ester bond towards MeLi. A search for an alternative
route is under way. Mesogen (5), on the other hand,
can be readily attached to linear poly(methylsiloxane)
via the mesomorphic alkene (8) (K 101 ꢁC N 126 ꢁC
I) to give the liquid crystalline side-chain polymer
(10) (K 85 ꢁC SmA 98 ꢁC I) (DSC, Fig. 3). The meso-
phase temperature range for this novel polymer is nar-
rower than the one of the parent alkene (8). However,
due to the flexibility of polysiloxane chain a mesophase
We considered that the crowded branched structure
of methane derivative (7) or (8) can be responsible for
the poor alignment of the ‘‘rods’’ and hence weak meso-
Fig. 2. DSC trace of low molecular branched mesomorphic methane (6), heating, 5 deg/min.

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2612
Fig. 3. DSC trace of side-chain polysiloxane (10), heating, 5 deg/min.
of higher order is generated (SmA) at a temperature
lower by almost 20 ꢁC.
and simple mesogenic groups should be easily attached
to polymer systems (e.g., dendritic polysiloxanes
[20,21] or polycarbosilanes [22]) in which the number
of available sites is limited.
4. Conclusions
Acknowledgement
Three novel model tri-podal methane derivatives
(4–6) were made by hydrosilylation of [CH2‚CH(Me)2-
- Si]3CH (1) with H(Me)2Si(CH2)5OC6H4C6H5 or hy-
We thank the Polish Committee for Research (KBN)
for financial support within grants PBZ-KBN 15/09/
T09/99/01c (T.G.), PBZ-KBN 01/CD/2000 (W.A.S.).
drosilylation
O)OC6H4OCH3
of
CH2‚CH(CH2)3OC6H4C(O)O-
or CH2‚
CH(CH)3C6H4C6H4OC11H23 with (HMe2-Si)3CH (2).
Compounds (4) and (5) were further converted into ter-
minal tri-podal alkenes and the mesogenic groups were
attached to linear poly (methylsiloxane).
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