Fuller’s earth (lOg) was stirred in dilute H2S04 (50ml) for 12 hours at ambient temperature, then filtered and washed with distilled water until the washings were neutral. The catalyst was then vacuum dried at 100°C. b) o^J-Si-H Functionalised Dimethylsiloxanes. General Proceedure
Octamethylcyclotetrasiloxane (D4), tetramethyldisiloxane (TMDS) and acid activated Fuller’s earth (0.2g) were heated under N2 with stirring for 72
hours at 60°C. The reaction mixture was then cooled and filtered to remove the catalyst. The filtrate was heated under vacuum for 6 hours (150°C, 0.1 torr) to remove low molecular mass cyclic contaminants. The residue was then phase-separated three times from an acetone/water mixture (80/20). The IR and
]H
nmr spectra were consistent with the required structures (see figure 4.6 and 4.7). The molecular weights were determined by GPC and *H nmr (see table 4.1). nominal "n D4 (g, moles. 10’2) TMDS (g, moles. 10’3) (6PC) "n0
H nmr) 1000 20.0, 6*74- 2.70, 20.10 1120 1080 2000 20.0, 6.74- 1.17,8.70
1950 2150 5000 20.0, 6.74; 0.45, 3.35 4750Table 4.1. The polymerisation conditions employed in the preparation of cxjLD-Si-H functionalised dimethylsiloxanes, and the 1
%
data characterising the products obtained.f i gure.4.6 IR spectrum ofcxpSi-H functionalised dimethylsiloxane (nominal
Mn=1 0 0 0).
IR signal (crrrO: 2160(SI-H), 1300-750 (S1-0-S1)
Figure 4.7 >H nmr spectrum of o<,tJ-S1-H functionalised dimethylsiloxane (nominal fin=1 0 0 0).
1H nm r signal (ppm): 0.2 ( 15 3H, s, CH3), 4.75 (2 IH, s, Si-H).
4.2.3.3 cx-5i-H Functionalised Dimethylsiloxanes. Genera) Proceedure259
(see figure 3.3 c)
A 50% solution of hexamethylcyclotrisiloxane (D3) in THF was slowly added to a stirred solution of n-butyllithium in hexane (1.58M.dm“3) at 0°C. After 20 hours the reaction was cooled to -78°C and dimethylchlorosilane (DMCS.10 mole % excess with respect to the moles of n-butyllithium used) was slowly added (see table 4.2). The mixture was allowed to heat to ambient temperature and was then added to water (150ml). The non-aqueous layer was separated and any hexane present was removed under reduced pressure. The product was phase-separated five times from an acetone/water mixture (80/20). The residue was then taken up in acetone, dried (Mg2S04) and filtered. The acetone was then removed under reduced
pressure in order to provide the final product. The IR and jH nmr spectra were consistent with the required structures (see figure 4.8 and 4.9). The molecular weights were determined by GPC and GLC. (see table 4.2)
nominal Mn &3 (g,moles 10"2) BuLi (g,moles 10-2) DMCS (g, moles 10~2) Mn(GPC) MnOH nmr) 5 00 2 0 .0 ,9 .0 3 .3 4 ,5 .2 1 5 .4 2 ,5 .7 3 5 1 0 4 8 0 1000 2 0 .0 ,9 .0 1 .4 5 ,2 .2 6 2 .3 5 ,2 .4 9 9 1 5 8 8 0 1500 2 0 .0 ,9 .0 0 .9 3 , 1.45 1.51, 1.60 1560 1410 2000 2 0 .0 ,9 .0 0.6 8, 1.06 1.11, 1.17 2 1 7 5 2 0 5 0 5 0 0 0 2 0 .0 ,9 .0 0 .2 6 ,0 .4 1 0 .4 3 ,0 .4 5 5 2 0 0 4 6 5 0 N ote:1H nm r spectra recorded on a Bruker W P80. Mn ( nmr ) was calculated by comparison of the signal due to S i-H with the signal due to rest of the molecule.
Table 4.2 The polymerisation conditions employed in the preparation of
oc — functionalised dimethylsiloxanes, and the fin data characterising the products obtained.
Figure 4.8 IR spectrum ofcx-Si-H functionalised dimethylsiloxane (nominal Mn =2000)
IR signal (cm-O: 2160(Si-H), 1300-750 (Si-O-Si)
Figure 49 >H nmr spectrum of <x-Si-H functionalised dimethylsiloxane (nominal Mn=2 0 0 0).
<H nmr (ppm): O.l (27.5 3H, s, S1-CH3), 0.3 -1.6 (9H, m, nBu), 4.75
(1H, s, S1-H)
Note: the respective ]H nmr and IR signal intensities vary w ith the molecular weight of the sample. Hence, these figures give only the signal positions and the species thereby indicated.
4.2.4 Synthesis of Vinvl Terminated Mesoaens 4.2.4.1 Non-AmphiDhilic Mesoaens (see figure 3.5) a) 4MethoxvDhenvl-4-hvdroxvbenzoate262
A mixture of 4-hydroxybenzoic acid (4.9g, 0.036M) and 4-methoxyphenol (4.96g, 0.04M) in benzene (20ml) containing sulphuric acid (10 drops) was refluxed for six days. Water was removed using a Dean Stark trap. The reaction was monitored by TLC (70% petroleum sp irits/ 30% ethyl acetate). When the 4-hydroxybenzoic acid was consumed, the solid product was filtered off. This residue was dissolved in diethylether (250ml), washed with saturated aqueous sodium bicarbonate three times and dried (Mg2S04).
The diethylether was reduced in volume to 100ml and hexane (100ml) was added. The crude product was filtered off, and was recrystallised from diethylether and hexane to give a white solid (6.80g, 79%), mp 192- 194>C. The *H nmr spectrum was consistent with the required structure (figure 4.10)
Figure 4.10 iH nmr spectrum of 4 methoxyphenyl-4-hydroxybenzoate.
iH nmr signal (d-DMSO); 3.75 (3H, s, OCH3), 7.5 (8H, m, aromatic
H), 10.4 (IH, s, OH). Note: the signal position for ROH may vary with the solvent and the solution concentration.
b) Coupling Vinyl Terminated Spacer to 4-MethoxvDhenv1-4-hvdroxvbenzoate. General Proceedure.
An alkyl bromide (0.028M) was added to a stirred solution of 4-methoxyphenyl-4-hydroxybenzoate (6.8g, 0.028M) and K2C03(5.4g, 0.028M)
in dry acetone, under N2 (see table 4.3). The mixture was refluxed for 48
hours. The reaction was monitored by TLC (90% petroleum s p irits /10% ethyl acetate). The product was obtained by column chromatography (90% petroleum s p irits /10% ethyl acetate). Yields of white solid were about 70%. The ]H nmr spectrum was consistent with the required structures (see figure 4.11 for example spectrum).
Alkvl bromide Value of x in flQiir.e.3,5
iH nmr data (CDCI3 )
allybromide 3 7.6 (8H, m, aromatic H); 6.0 (IH , m, CH); 5.2 (2H, t.-.CH^
45 (2H, t, 0CH2 ); 3.8 (3H, s, 0CH3 )
4-bromo-1-butene 4 7.5 (8H, m, aromatic H); 5.9 (IH . m, CH); 5.2 (2H, t,:CH2)
42 (2H, t, OCH2 ); 3.8 (3H, s, OCH3 ), 2.25 (2H, m, CH2 ) 5-bromo-1-pentene 5 14 (8H. m. aromatic H); 5.7 (IH , m, CH); 5.0 (2H. t.iCh^)
4.0 (2H, t, OCH2 ); 3.8 (3H, s. OCH3 ); 2.0 (4H, m, 2 CH2 ) 6-bromo-l-hexene 6 7.6 (8H, m, aromatic H); 5.8 (1H, m, CH); 5.0 (2H, LiC H ^
4.0 (2H, t, OCH2 ); 3.8 (3H, s, OCH3 ); 1.8 (6H, m. 3 CH2 )
Table 43 The alkyl bromide used In the preparation of non-amphlphlllc mesogens (see figure 3.5), and the !H nmr data characterising these mesogens.
Figure 4.11 iH nmr spectrum of 4'-methoxyphenyl-4-pent-1-enoxybenzoate
(i.e. the non-amphiphilic mesogen incorporating a pentyl spacer group). !H nmr signal (ppm); 2.0 (2 2H; m, 2 CH2), 3.6 (3H, s, OCH3), 3.95 (2H, t, OCH2), 5.0 (2H, t, CH2), 5.75 (IH, m, CH), 7.5 (8H, m, aromatic H). • 10
4.2.42 Protection of the Carboxvl Group of 10-Undecenoic acid. Synthesis of Trim ethvlsilvl 10-Undecenoate244
Trimethylchlorosilane (54.47g, 0.5M, 10% mole excess with respect to moles of acid) in dichloromethane (40ml) was added to a stirred solution of 10-undecenoic acid (84g, 0.456M, freshly distilled at 110°C, 0.2 mmHg)) in dichloromethane (30ml). After refluxing under N2 for 4 hours, the reaction
mixture was cooled to -78°C and a solution of triethylamine (50.6g, 0.5M) in dichloromethane, was slowly added. The mixture was refluxed for a further 16 hours. The extent of reaction was followed by monitoring the disappearance of the -COOH IR stretching band (2900-3500 cm '1). When reaction was complete the mixture was cooled, and filtered under N2 to
remove the solid triethylamine hydrochloride. The filtra te was evaporated under reduced pressure to remove the solvent. The residue was dissolved in petroleum spirits and a second fraction of triethylamine hydrochloride removed by filtra tio n under N2. The solvent was removed under reduced pressure and the ester (a colourless liquid) obtained by vacuum distillation (72°C, 0.3 mm Hg) (yield 85.4g, 73%). The IR and ]H nmr spectra were consistent with the required structure (see figures 4.12 and 4.13).
4.2.5 Coupling of Mesoaens and Siloxanes. General Procedure246*249
Catalyst solutions of hexachloroplatinic acid in dry THF were prepared in a dry box under N2 and used immediately. All apparatus was flame dried under
N2 and wrapped in foil. The appropriate Si-H functionalised siloxane and
alkene terminated mesogen (10% molar excess w ith respect to the Si-H content of the siloxane) were dissolved in THF (50% solution). An aliquot of catalyst solution was added, such that the alkene/catalyst molar ratio was I:10~4 The mixture was stirred at 50°C for up to 5 days. The extent of
reaction was followed by IR, the disappearance of an adsorption band at 2060-2080 cm" 1 (Si-H stretching) indicated complete reaction (see figure
4.14)
Figure 4.12 IR spectrum of trim ethylsilyl 10-undecenoate.
IR signal (cm-1): 2900 (CH2), 1720 (C=0), 1300-750 (Si-O-Si). Note the absence of OH at 3000-3500 crrr1.
Figure 4.13 <H nmr spectrum of trimethylsilyl undecenoate.
1H nmr signal (ppm); 0.2 (9H, s, Si-CH3), 1.0-2.3 (16H, m, CH2), 4.8 (2H, t, CH2), 5.6 (IH, m, CH)
1
I
iir,®
I
BW^SrfWS
Figure 4.14 IR spectra of coupling reaction of methyl undecenoate and 1,3,5,7 tetrahydrocyclotetrasiloxane (hydrogenmethyl D4), after A) 30 minutes and B) 48 hours.
Note: absence of Si-H at 2160 cm- 1 in B) indicating complete
4.2.6 Isolation of Products
The work up and isolation of products varied according to the nature of the backbone and the mesogen.
4.2.6.1 Cyclic Non-AmphiDhilic Oligomers
The cyclic non-amphiphilie oligomers were isolated by 6PC using a
Shephadex LH-20 gel and THF as the eluting solvent. The column was monitored by TLC (90% petroleum s p irits /10% ethyl acetate). The solvent was removed under reduced pressure, and the polymer dried under vacuum as the isotropic liquid. The IR and ]H nmr spectra were consistent with the required structures (see figures 4.15 and 4.16).
100 —l-lOOi Him ...L r-t-i-i-..."“s': i ' lobo (CM-*) ‘ 800 3500 (CM ") 3000 2500 2000 TJ3ZT 4000 1200 6 0 0
Figure 4.15 IR spectrum of D4C6 (see figure 8.1 for key to nomenclature).
IR signal (cm-'): 2950 (CH), 1725 (C=0), 1600 (C=C), 1300-750 (Si-O-Si).
Figure 4.16 >H nmr spectrum of D4C6 (see figure 8.1 for key to nemenclature).
!H nmr signal (ppm): 0.1 (12H, s, Si-CH3), 0.6 (8H, t, Si-CH2), 1.5
(32H, m, CH2), 3.8 (12H, s, 0CH3), 4.0 (8H, t, 0CH2), 7.5 (32H, m,
aromatic H). ^
42.6.2 Cyclic Amphiphilic Oligomers
After removal of the solvent, the excess monomeric amphiphile was distilled off (100°C, 0.3mm.Hg, 4 hours). The residue was stirred in ethanol (4 hours at 50°C) to liberate the carboxylic acid groups. The ethanol was removed under reduced pressure, and the product obtained by phase-separation from acetone/water (80/20) 7 times. Finally, an acetone solution of the product was dried (Mg2S04), filtered and evaporated to give
the final product, which was then dried under vacuum. The 1H nmr spectra were consistent with the required structures (see figures 4.17).
Figure 4.17 iH nmr spectrum of the acid form of the cyclic amphiphilic tetramer.
iH nmr signal (ppm); 0.05 (12H, s, Si-CH3), 0.5 (8H, t, Si-CH2),
1.3 (48H, m, CH2), 1.65 (8H, m, CH2-C-acid), 2.35 (8H, m,
42.6.3 Linear Amphiphilic Polymers
After removal of the solvent, the product was isolated by phase-separation from acetone/water (80/20) seven times. The residue was stirred in ethanol (4 hours at 50°C) to liberate the carboxylic acid groups. After the ethanol was removed, the product was taken up in acetone, dried (Mg2S04)
and filtered. The acetone was removed under reduced pressure and the product was dried under vacuum. The IR and nmr spectra were consistent with the required structures (see figures 4.18 and 4.19).
S^'Wp3<55a>
Figure 4 18 IR spectrum of linear amphiphilic polymer (nominal Mn= 1000). IR signal (cm-1): 3500-3000 (COOH), 2950 (CH), 1710 (CO),
C H 31 C H 2) 31 SI C H 32 C SI C H 32 0I 13 CS IC H3 2C H2 10 CO aB lC H2 1 3I S IC H 32 (S IC H 32 0) 13 (S IC H 32 C H 2 1 0C OO H) I
Figure 4.19 ]H nmr spectrum of the linear amphiphilic polymer (nominal Mn=1 0 0 0).
1H nmr signal (ppm): 0.0 (1 0 0H, m, SI-CH3), 0.47 (4H, m,
SI-CH2), 1.2 (18H, m, CH2), 1.55 (2H, m, CH2-C-ac1d),2.25 (2H, t, CHo-acid)4.
p i) S X V .U '
4.2.7 Salts of the Amphiphilic Siloxanes. General Procedures 4.2.7.1 Sodium salts
a) Cyclic Oligomers.
Ethanolic solutions of the acid functionalised cyclic oligomers (2g in 20ml) were neutralised with ethanolic NaOH (0.025M.dm-3). The precipitated sodium salts were filtered off, triturated with hot acetone and dried under reduced pressure (yield approximately 85%). The IR and nmr spectra were consistent with the required structure (see figures 4.20 and 4.21).
2000 WOO 1100 WOO
Figure 4.20 IR spectrum of the sodium salt of cyclic amphiphilic tetramer. IR signal (crrH): 2950 (CH), 1560 (C=0), 1300-750 (Si-O-SI). Note: due to misalignment of the recording chart, peaks appear at 50 crrr1 above actual. Therefore, subtract 50 cm-1 from chart
reading to obtain true wavenumber.
Figure 4.21 1H nmr spectrum of the sodium salt of the cyclic tetramer.
nmr signal (ppm): 0.1 (12H, s, Si-CH3), 0.6 (8H, t, Si-CH2), 1.3 (48H, m, CH2), 1.55 (8H, m, CH2-O s a lt), 2.15 (8H, t, CH2-salt).
PP
b) Linear Polymers
Ethanolic solutions of the acid terminated linear polymers (2g in 20ml) were neutralised with ethanolic NaOH (0.025M.dnrr3). The end-point was monitored by change in pH as a function of added NaOH using a pH meter. The solutions were reduced in volume, under reduced pressure, to their solubility lim it and then excess acetone was added. Clear, viscous gums were deposited and the liquors were decanted off. The products were triturated in hot acetone and dried under vacuum. The IR and ]H nmr spectra were consistent with the required structure (see figures 4.22 and 4.23). The molecular weights were determined by GLC (see table 4.4).
nominal Mn of siloxane segment plus butyl tail
observed Mn of siloxane segment ( 1H nm r) observed Mn*o t molecule as a whole ( 1H nm r) 5 0 0 5 1 0 7 17 1 0 0 0 9 6 0 1167 a) 1500 1530 1737 2 0 0 0 2 2 0 0 2 4 0 7 b) 2 0 0 0 2 1 0 0 2 3 0 7
* 1H nm r spectra recorded on a Bruker 5 6 0 spectrometer. M n calculated by comparison of signal due to Siloxane w ith signal due to rest of the molecule.
Table 4.4 Mn of the sodium salts of a) cx- and b)cx,uMunctionalised linear dimethylsiloxanes.
Figure 4.22 IR spectrum of the sodium salt of cx- functionalised linear dimethylsiloxane (nominal Mn=1 0 0 0).
IR Signal (cm-i): 2950 (CH), 1570 (C=0), 1300-750 (Si-0-51). Note: due to misalignment of the recording chart, peaks appear at 50 cnrr1 above actual. Therefore, subtract 50 cnrr1 from chart
reading to obtain true wavenumber. 505882
i X X C4 m m x
Figure 4.23 'H nmr spectrum of the sodium salt of c<-functionalisea linear dimethylsiloxane (nominal Mn=1 0 0 0).
'H nmr signal (ppm); 0.0 (72H, s, Si-CBj), 0.45 (4H, m, Si-CH2), 0.8 (3H, t, CH3), 1.2 (18H, m, CH2), 1.45 (2H, m, CH2-C-salt), 2.05
42.7.2 The Calcium Salts a) The Cyclic Tetramer154
The tetrakis sodium salt of the cyclic tetramer (0.5g, 4.7 10~4M) was
dissolved in deionised water (20ml) at 50 °C. Excess, saturated aqueous CaCl2 was added while stirring and a white, solid product precipitated out
of solution. After centrifugation and filtration, the product was triturated in acetone, filtered and dried under vacuum (yield 0.39g, 79%).
b) The<x-Functionalised Linear Polymer (nominal Mn=500)
A solution of the acid cX-terminated linear dimethylsiloxane (0.5g) in acetone (50ml) was stirred at 50°C over excess CaOH2 for 4 hours. The
solvent was removed under reduced pressure. The residue was then taken up in ethanol, filtered and the ethanol was removed under reduced pressure. The product was then dried under vacuum (yield 0.45g, 90%).
APPENDIX 4.1
This contains the 6CMS data for the commercial mixture of cyclic
hydrogenmethylsiloxanes obtained from Petrach Systems. All data was acquired using the following conditions:
The gas chromatograph of the mixture, along w ith the structures subsequently assigned to the individual peaks, is shown in figure 4.24. Figures 4.25 to 4.29 show the mass spectra obtained for each of the major peaks in the chromatograph. Only the ions of particular importance have been referenced on the individual mass spectra, although the unmarked fragments do agree w ith the proposed structures. In all spectra 'M' represents the molecular ion.
Equipment Injection temperature Inlet lines Column Initial temperature Final temperature Temperature gradient Carrier gas
Electron beam energy
lOC.min-1 Helium 16 lbs.in2 70eV 60°C 200°C 225°C 200°C VG 305 Mass spectrometer 1.25% Dexil 300
H Me D CD □
□
QFigure 4 2 4 Gas chromatograph of the commercially available m ixture of cyclic hydrogenmethylsiloxanes. RE TE NT IO N TI M E
FT
Z
--
Figure 4.25 Mass spectrum of the compound corresponding to scan 15, i.e.
the cyclic hydrogenmethyltetrasiloxane (hydrogenmethyl D4).
MA
SS
N
2f
l
S
Figure 4.26 Mass spectrum of the compound corresponding to scan 28, i.e.
the cyclic hydrogenmethylpentasiloxane (hydrogenmethyl D5).
MA
SS
,N
2
L£ 3 > - L lJ cc > CC o < ' LJ \A OD- CM u>- CM o I/) 0 100 80 60 40 20 Ol (/) on <
Figure 427 Mass spectrum of the compound corresponding to scan N9 36, i.e.
the linear hydrogenmethylsiloxane impurity:
(CH3)3SiO-C-SiO-)2-SKCH3 )3
23
3
Figure 4.28 Mass spectrum of the compound corresponding to scan N5 54, i.e. the cyclic hydrogenmethylhexasiloxane (hydrogenmethyl D6).
MA
SS
N
CM
20 0
Figure 429 Mass spectrum of the compound corresponding to scan N9 57, i.e.
the linear hydrogenmethylsiloxane impurity:
H
(CH3)3SiO-(-SiO-)3-Si(CH3 )3