Synthesis and characterization of novel jacketed polymers and investigation of their self assembly and application 3

Chapter Synthesis and characterization of novel terphenyljacketed liquid crystalline polymers 81 3.1 Introduction Side chain LC polymers (SCLCP) with mesogenic groups laterally attached to the polymer backbone represent an interesting series of polymers. Compared with the conventional SCLCPs, polymer architectures with laterally attached groups give rise to the nematic phase 1. Wessflog et al. reported the synthesis of lateral SCLCP in 1984 2, followed by many reports from functional poly(siloxanes), poly(acrylate), poly(norbornenes) derivatives 3-7. In all cases, there are flexible spacers incorporated with the mesogenic units on the polymer backbone. Pugh et al.1, 7-11 demonstrated that smectic layering could be induced in the SCLCPs with laterally attached mesogenic units. The liquid crystalline polynorbornenes with 2, 5-bis[(4’-n-alkoxybenzoyl)oxy]benzyl mesogens can be forced into a smectic mesophase by terminating the alkoxy groups with fluorocarbon segments. Due to the sharp immiscibility between the aliphatic polymer backbone and the n-perfluoroalkane, a layer type organization is formed from the microseparation of the two components. The immiscibility of n-alkanes and perfluoroalkanes is proportional to their lengths. The polynorbornenes require at least eight carbon units in the terminated chains to organize into smectic layers. Microseparation of the two components in these molecules is weak at the minimum lengths required for smectic layers7, 11. Lecommandoux et al.4-5 reported the synthesis of poly(siloxane) derivatives based on phenyl benzoate core terminated with alkyl chains. They demonstrated that the polymer backbone could be segregated between the layers and also present at the middle part of the mesogenic layer, resulting to a smectic C mesophase. In 1987, Zhou et al.12-17 proposed a new side chain liquid crystalline polymers, in which mesogenic units are attached laterally to the backbone with very short spacers and 82 showed properties similar to that of the semi-rigid main chain liquid crystal polymers. The lack of flexible spacers in the polymer lattice increased the range of observed mesophases 16-17. Percec et al.19-21 reported the synthesis of monodendron jacketed side chain liquid crystal polymers. At low degree of polymerization (DP), the conical monodendrons assemble to produce a spherical polymer with a random-coil conformation for the polymer backbone. With the increase of DPs, the monodendritic units are organized into cylindrical structures with extended polymer backbone. The polymers self organize into hexagonal columnar (Φ h) and cubic (Cub) lattice of the thermotropic mesophase. The strategy for making rigid polymers by incorporating many side groups on a flexible polymer backbone is interesting, owing to the interplay of strong steric interaction among the side groups and polymer backbone. Such polymers show properties of semi-rigid main chain liquid crystal polymers with the rigidity can be adopted through tailoring the side-chains. The organization of the rigid side group also allows to synthesize polymer with very narrow molecular weight distribution. This new approach of synthesis of mesogenic polymer offers a rational design for the organized supramolecular materials 4, 22-23 . Here, we report the synthesis of a series of polymers with laterally attached mesogenic units based on terphenyl groups with alkyl chains at the terminal position. The terphenyl aromatic rigid core was used as mesogenic units to incorporate van der Waals interaction and shape effects of substituents on the polymer backbone. At the same time polymers in which the mesogenic units are connected laterally to the polymer backbone without spacer or with very short spacer is expected to induce mesophase properties. 83 3.2 Experimental section 3.2.1 Materials and reagents All reagents and solvents were obtained from commercial sources and used without further purification unless mentioned otherwise. Tetrahydrofuran (THF) was distilled from metal sodium and benzophenone under N2 atmosphere. N,N-dimethylformamide (DMF) was dried with Å molecular sieves (Aldrich). Flash column chromatography was performed using silica gel (60-mesh, Aldrich). Dibenzoyl peroxide (BPO) was recrystallized from chloroform-methanol solution as glistening crystals. 3.2.2 Instrumentation Fourier transform Infrared (FT-IR) spectra were obtained using a Perkin-Elmer 1616 FTIR spectrophotometer as KBr mulls. H NMR, 13 C NMR spectra were recorded on a Bruker ACF 300 MHz spectrometer. MS spectra were obtained using a Finnigan TSQ 7000 spectrometer with ESI or EI ionization capabilities. Thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC) were conducted using a TASDT2960 and a TA-DSC 2920 at a heating rate of 10 °C min-1 under N2 environment. Gel permeation chromatographic (GPC) analyses were done with a Waters 2696 separation module equipped with a Water 410 differential refractometer HPLC system and Waters Styragel HR 4E columns using THF as eluent and polystyrene as standard. The XRD patterns were recorded on a powder diffractometer with a graphite monochromator using 1.54 Å Cu Kα wavelength at room temperature (scanning rate: 0.05 o/s; scan range 1.5-30o). A Zeiss Axiolab polarized optical microscope equipped with a Linkam LTS 350 hot stage was used to observe anisotropic textures. 84 3.2.3 Synthesis Poly (4, 5’, 4”-trimethoxy [1, 1’, 4’, 1”] terphenyl-2’-yl acrylate) (P1-C1), poly(4, 4”dibutoxy-5’-methoxy [1, 1’, 4’, 1”] terphenyl-2’-yl acrylate) (P1-C4), poly(4, 4”didecyloxy-5’-methoxy [1, 1’, 4’, 1”] terphenyl-2’-yl acrylate) (P1-C10), poly(1, 3-bis(4, 5’, 4”-trimethoxy[1, 1’, 4’,1”]terphenyl-2’-yloxy)-2-propyl acrylate) (P2-C1), poly(1, 3bis(4, 4”-dibutoxy-5’-methoxy [1, 1’, 4’, 1”] terphenyl-2’-yloxy)-2-propyl acrylate) (P2C4), and poly(1, 3-bis(4, 4”-didecyloxy-5’-methoxy [1, 1’, 4’,1”] terphenyl-2’-yloxy)-2propyl acrylate) (P2-C10) were synthesized using the following route shown in Scheme 3.1. OH OBn OBn Br K2CO3/DMF Br Br Br BnBr CH3I NaOH/Ethanol Br Br OH OH OCH3 Br B(OH)2 n-BuLi B(O-i-Pr)3 THF 1M HCL OR1 OBn Br Br OCH3 OBn R1O Pd(PPh3)4/Toluene/EtOH OR1 4-C1 R1= CH3 5-C1 4-C4 R1= C4H9 5-C4 4-C10 R1= C10H21 5-C10 OR1 H3CO 2M K2CO3 (aq) 6-C1 6-C2 6-C10 85 O OH Pd/C H2 O O OR1 R1O Cl R1O OR1 Et3N H3CO OCH3 7-C1 8-C1 7-C4 8-C4 7-C10 8-C10 n BPO/THF O O R1O OR1 P1-C1 R1=CH3 P1-C4 R1=C4H9 P1-C10 R1=C10H21 H3CO OH R1O OH OR1 OH O Br Br K2CO3/DMF H3CO OR2 OR2 O O Et3N OR2 OR2 7-C1 9-C1 10-C1 7-C4 9-C4 7-C10 9-C10 10-C4 10-C10 P2-C1 R2 = H3CO O OCH3 H3CO n BPO/THF O Cl P2-C4 R2 = C4H9O OC4H9 H3CO OR2 OR2 P2-C10 R2 = C10H21O C10H21 H3CO Scheme 3.1. Synthesis route for monomers and polymers 86 4-Methoxyphenyl boronic acid (5-C1) In a 500 ml RB flask with a magnetic stirring bar was placed 9.35 g (50 mmol) of 4-C1 and 150 ml dry THF. The solution was cooled to -78 °C and a 1.6 M solution of butyl lithium in hexanes (93 ml, 0.15 mol) was added slowly under nitrogen atmosphere. The solution was warmed to RT and cooled to -78 °C, followed by the dropwise addition of triisopropyl borate (46 ml, 0.2 mol) during a period of h. After complete addition, the mixture was warmed to RT, stirred overnight, and mixed with L of deionized water. The organic phase was collected, dried with MgSO4, filtered, and concentrated under reduced pressure. The light yellow solid was recrystallized from acetone. Yield: 5.2 g (68.4 %). 1H NMR (300 MHz, DMSO-d6, δ ppm) 7.84 (s, B-OH, H), 7.74-6.87 (m, ArH, H), 3.75 (s, Ar-O-CH3, H). 13 C NMR (75.4 MHz, DMSO-d6, δ ppm) 160.8, 135.7, 112.8,108.3 (ArC), 54.7 (O-CH3). MS (ESI): m/z: 152, 134. Mp: 196 °C. 4-Butoxyphenyl boronic acid (5-C4) Compound 5-C4 was synthesized according to the procedure described for 5-C1. Yield: 10.3 g (44.2 %). 1H NMR (300 MHz, DMSO-d6, δ ppm) 7.80 (s, B-OH, H), 7.73-6.85, (m, ArH, H), 3.97 (t, J = 6.3Hz, Ar-O-CH2-, H), 1.67 (p, J = 8.4Hz, R(O)-CH2-, H), 1.42 (p, J = 8.1 Hz, -CH2-, H), 0.92 (t, J = 7.2 Hz, H). 13 C NMR (75.4 MHz, DMSO- d6, δ ppm) 160.3 136.8, 115.6, 113.5 (ArC), 66.7 (O-CH2-), 30.6, 18.6 (-CH2-), 13.6 (CH3). MS (ESI): m/z: 194.0, 166.1. Mp: 167.5 °C. 4-Decyloxyphenyl boronic acid (5-C10) Compound 5-C10 was synthesized according to the procedure described for compound 5C1. 14.1g (45 mmol) of 1-bromo-4-decyloxybenzene (4-C10), 85 ml (0.135 mol) of 1.6 M butyllithilium in hexane and 41.4 ml (0.18 mol) of triisopropylborate were used and 87 the targeted compound was obtained as light yellow powder. Yield: 11.8 g (31.4%). 1H NMR (300 MHz, DMSO-d6, δ ppm) 7.70 (d, J = 8.1 Hz, ArH, 2H), 7.56 (s, B-OH, 2H), 6.78 (d, J = 8.2 Hz, ArH, 2H), 3.92 (t, J = 6.3Hz, Ar-O-CH2-, H), 1.72 (p, J = 6.3Hz, R(O)-CH2-, 2H), 1.24 (b, -CH2-, 14H), 0.84 (t, J = 6.0 Hz, 3H). 13 C NMR (75.4 MHz, DMSO-d6, δ ppm) 158.2, 132.2, 116.3, 112.5 (ArC), 68.2 (O-CH2-), 31.8, 29.5, 29.4, 29.3 29.1, 25.9, 22.6, 22.0 (-CH2-), 13.8 (-CH3). MS (ESI): m/z: 278.2, 223.2, 210.2. Mp: 82.5 °C. 5’-Benzyloxy-4, 2’, 4”-trimethoxy [1, 1’, 4’, 1”] terphenyl (6-C1) 24 A 250 ml round-bottomed flask equipped with a condenser was charged with 4.0g (11 mmol) of 1-benzyloxy-2, 5-dibromo-4-methoxybenzene and 4.3 g (28 mmol) of 4methoxyphenyl boronic acid, 60 ml toluene, 20 ml methanol and 60 ml 2M sodium carbonate solution. The mixture was degassed thoroughly, before the catalyst of 0.5g tetrakis(triphenylphosphine) palladium (2 mol%) was added in dark under argon atmosphere. The reaction mixture was degassed once more and heated to 100 °C for 48 h in argon atmosphere, cooled to RT, and filtered. The liquid layer was separated with a separation funnel, and the aqueous layer was extracted with toluene (100 ml × 2), toluene fractions were combined, washed with × 100 ml water, dried over MgSO4 and filtered. After the removal of solvent under reduced pressure, the crude product obtained was purified using column chromatography on silica gel with hexane and dichloromethane (4:1) mixture as eluant. Yield: 4.1g (44.3%). 1H NMR (300 MHz, DMSO-d6, δ ppm) 7.60 - 6.97 (m, ArH, 15 H), 4.99 (s, Ar-CH2-, H), 3.86 (s, Ar-O-CH3, H), 3.80 (s, Ar-OCH3, H). 13 C NMR (75.4 MHz, DMSO-d6, δ ppm) 158.7, 130.5, 130.4, 129.5, 129.4, 128.3, 127.5, 127.1, 117.4, 114.5, 114.2, 113.5, 113.4, 112.4 (ArC), 71.8 (O-CH2-), 56.2, 88 55.2 (O-CH3), 30.8 (O-CH3). MS (EI): m/z: 426.2, 335.1, 304.2, 277.1, 189.1. Mp: 148 °C. 5’-Benzyloxy-4, 4”-dibutoxy-2’-methoxy [1, 1’, 4’, 1”] terphenyl (6-C4) The synthesis of compound 6-C4 was performed according to the procedure for compound 6-C1. From 6.4 g (17.2 mmol) of compound and 10 g (51.6 mmol) of compound 5-C4, the desired product was obtained as a white powder. Yield: 7.2 g (81.9 %). 1H NMR (300 MHz, CDCl3, δ ppm) 7.63 - 7.00 (m, ArH, 15 H), 5.02 (s, Ar-CH2-, H), 4.05 (t, J = 3.3 Hz, Ar-O-CH2-, H), 3.82 (s, Ar-O-CH3, H), 1.84 (b, -CH2-, H), 1.55 (b, -CH2-, H), 1.06 (t, J = 2.8 Hz, -CH3, H). 13C NMR (75.4 MHz, CDCl3, δ ppm) 158.3, 151.1, 149.68, 137.4, 130.6, 130.5, 129.6, 129.5, 129.4, 129.3, 128.3, 127.5, 127.1, 118.5, 117.4, 115.3, 115.1, 114.3, 114.0, 113.3, 113.0 (ArC), 71.8 (O-CH2-Ar), 67.6 (OCH2-), 56.8 (O-CH3), 31.8, 19.2 (-CH2-), 13.8 (-CH3). MS (EI): m/z: 510.2, 419.2, 363.2, 307.1, 292.1, 199. Mp: 103 °C. 5’-Benzyloxy-4, 4”-didecyloxy-2’-methoxy [1, 1’, 4’, 1”] terphenyl (6-C10) The synthesis of compound 6-C10 was performed according to the procedure for compound 6-C1. From 4.1 g (11.0 mmol) of compound and 9.2 g (33 mmol) of compound 5-C10 was obtained the desired product as a white powder. Yield: 6.1 g (81.7 %). 1H NMR (300 MHz, CDCl3, δ ppm) 7.60-6.98 (m, ArH, 15 H), 5.00 (s, Ar-CH2-O, H), 4.02 (t, J = 3.6 Hz, Ar-O-CH2-, H), 3.80 (s, Ar-O-CH3, H), 1.84 (p, J = 4.8, -CH2-, 4H), 1.34 (b, -CH2-, 28H), 0.92 (t, J = 6.0 Hz, -CH3, 6H). 13C NMR (75.4 MHz, CDCl3, δ ppm) 158.3, 151.1, 149.7, 137.4, 130.6, 130.5, 130.2, 129.4, 128.3, 127.5, 117.4, 115.1, 114.0, 112.9 (ArC), 71.8 (O-CH2-Ar), 67.9 (O-CH2-), 56.8 (O-CH3), 31.8, 29.5, 29.4, 89 29.3, 29.2, 26.0, 22.6, 19.2 (-CH2-), 13.8 (-CH3). MS (EI): m/z: 678.4, 588.4, 447.3, 308.1, 293.1, 247.0, 199. Mp: 77 °C. 4, 5’, 4”-Trimethoxy [1, 1’, 4’, 1”] terphenyl-2’-ol (7-C1) To a 100 ml round-bottom flask containing 10 % Pd/C (2.0 g) in 50 ml THF was added compound 6-C1 (3.8 g, 8.9 mmol). The flask was purged with nitrogen, and a balloon filled with H2 was fitted to the flask. The nitrogen was briefly evacuated from the flask, and the H2 was charged above the solution. The reaction mixture was stirred for 24 h at ambient temperature and then filtered. The solid was washed with THF (3 × 25 ml), the organic phases were combined and the solvent was then removed under reduced pressure to yield a white powder. The resulting crude product was purified using column chromatography on silica gel with hexane and ethyl acetate (1:4) as the eluants. Yield: 2.8 g (93.4 %). 1H NMR (300 MHz, CDCl3, δ ppm) 7.63 - 6.85 (m, ArH, 10 H), 4.93 (s, Ar-OH, H), 3.88 (s, Ar-O-CH3, H), 3.78 (s, Ar-O-CH3, H). 13C NMR (75.4 MHz, CDCl3, δ ppm) 159.3, 158.7, 150.5, 146.4, 130.4, 130.2, 129.3, 126.6, 117.8, 114.6, 113.5, 112.5 (ArC), 56.3 (O-CH3), 54.3 (O-CH3). MS (EI): m/z: 336.1, 289.1, 261.0, 247.1, 213.1, 185.1. Mp: 161 °C. 4, 4”-Dibutoxy-5’-methoxy [1, 1’, 4’, 1”] terphenyl-2’-ol (7-C4) Compound 7-C4 was synthesized according to the procedure described for compound 7C1. From 7.0 g (13.7 mmol) of 6-C4 was obtained the product as a white powder. Yield: 5.4 g (93.6 %). 1H NMR (300 MHz, CDCl3, δ ppm) 7.52 - 6.94 (m, ArH, 10 H), 5.16 (s, Ar-OH, H), 4.03 (t, J = 4.8 Hz, Ar-O-CH2-, H), 3.74 (s, Ar-O-CH3, H), 1.83 (b, CH2-, H), 1.54 (b, -CH2-, H), 1.02 (t, J = 6.3 Hz, -CH3, H). 13C NMR (75.4 MHz, CDCl3, δ ppm) 158.8, 158.3, 150.5, 146.4, 130.4, 130.1, 129.0, 126.6, 117.4, 115.2, 90 Monomer 10-C10 was synthesized according to the procedure described for monomer 8C1. From 1.2 g (1 mmol) of compound 9-C10, 0.3 ml (3 mmol) of acryloyl chloride was obtained the desired monomer as oil. Yield: 0.7 g (54.4 %). 1H NMR (300 MHz, CDCl3, δ ppm) 7.47 - 6.79 (m, ArH, 20 H), 6.28 (d, J = 10.6 Hz, C=CH2, H), 6.04 (q, J =10.5 Hz, C=CH-, H), 5.79 (d, J = 12.2 Hz, C=CH2, H), 5.30 (t, J = 4.8 Hz, -CH(O)-, H), 4.09 (b, J = 4.8 Hz, O-CH2-, H), 4.03 (m, O-CH2-C, H), 3.77 (s, Ar-O-CH3, H), 1.80 (b, -CH2-, H), 1.29 (b, -CH2-, H), 0.90 (t, J = 6.0, -CH3, 12 H). 13C NMR (75.4 MHz, CDCl3, δ ppm) 168.1 (C=O), 158.0, 151.2, 150.4, 130.4, 130.1, 129.9, 129.5, 128.9, 127.8, 118.0, 115.3, 114.3 (ArC), 70.5 (O-CH2-), 69.6 (O-CH2-C), 56.3 (O-CH3), 31.8, 29.5, 29.4, 29.3, 29.2, 26.0, 22.6, 18.6 (-CH2-), 13.9 (-CH3). MS (ESI): m/z: 1286.2, 644.5, 588.4. Poly(4, 5’, 4”-trimethoxy [1, 1’, 4’, 1”] terphenyl-2’-yl acrylate) (P1-C1) A 25 ml RBF containing a stirring bar was charged with 1.0 g (2.6 mmol) compound 8C1, 0.01 g (1 wt%) of BPO and ml THF and sealed with a rubber septum. The solution was subjected to freeze-pump-thaw cycles, then stirred at 70 ºC for 48 h. the crude reaction mixture was precipitated from MeOH. The resulted solid was redissolved in THF, precipitated from methanol several times and dried under high vacuum. Yield: 0.7 g (70 %). 1H NMR (300 MHz, CDCl3, δ ppm) 7.48 - 7.17 (b, ArH, 10 H), 3.85-3.71 (b, OCH3, H), 1.92 (b, -CH-, H), 1.27 (b, -CH2-, H). FT-IR (KBr, cm-1): 3055 (ArH stretching), 2929 (-CH2- stretching), 1714 (ester C=O stretching), 1600, 1514, 1479 (Ar, C=C stretching), 1249, 1164, 1096 (C-O-C stretching). Mw: 0.9 × 104, Mn: 0.6 × 104, PD: 1.7. Poly(4, 4”-dibutoxy-5’-methoxy [1, 1’, 4’, 1”] terphenyl-2’-yl acrylate) (P1-C4) 96 Polymerization of 8-C4 was performed according to the procedure described for P1-C1. From 1.0 g (2.1 mmol) of compound 8-C4 and 0.01 g (1 wt%) of BPO was obtained 0.6 g (60%) of the desired polymer. 1H NMR (300 MHz, CDCl3, δ ppm) 7.55 - 6.62 (b, ArH, 10 H), 4.01 - 3.60 (b, O-CH3 or O-CH2-, H), 1.92 (b, -CH-, H), 1.57-1.05 (m, -CH2-, 10 H), 0.92 (b, -CH3, H). FT-IR (KBr, cm-1): 3039 (ArH stretching), 2957 (-CH2stretching), 1748 (ester C=O stretching), 1608, 1524, 1489 (Ar, C=C stretching), 1291, 1177, 1026 (C-O-C stretching). Mw: 1.76 × 104, Mn: 1.04 × 104, PD: 1.7. Poly(4, 4”-didecyloxy-5’-methoxy [1, 1’, 4’, 1”] terphenyl-2’-yl acrylate) (P1-C10) Polymerization of 8-C10 was performed according to the procedure described for P1-C1. From 0.85 g (1.3 mmol) of monomer 8-C10 and 0.008 g (1 wt%) of BPO was obtained 0.5 g (58.8 %) of the desired polymer. 1H NMR (300 MHz, CDCl3, δ ppm) 7.55 - 6.50 (b, ArH, 10 H), 4.01 -3.50 (b, O-CH3 or O-CH2-, H), 1.90 (b, -CH-, H), 1.58-1.03 (m, CH2-, 34 H), 0.89 (b, -CH3, H). FT-IR (KBr, cm-1): 3038 (ArH stretching), 2924 (CH2- stretching), 1749 (ester C=O stretching), 1610, 1524,1491 (Ar, C=C stretching), 1243, 1178, 1049 (C-O-C stretching). Mw: 0.65× 104, Mn: 0.63 × 104, PD: 1.1. Poly(1, 3-bis (4, 5’, 4”-trimethoxy [1, 1’, 4’, 1”] terphenyl-2’-yloxy)-2-propyl acrylate) (P2-C1) Polymerization of 10-C1 was performed according to the procedure described for P1-C1. From 0.64 g (0.8 mmol) of monomer 10-C1 and 0.006 g (1 wt%) of BPO was obtained 0.4 g (62.5 %) of the desired polymer. 1H NMR (300 MHz, CDCl3, δ ppm) 7.64 - 7.00 (b, ArH, 24 H), 5.45 (b, -CH(O)-, H), 4.18 (b, O-CH2-, H), 3.96 - 3.72 (b, O-CH3 , 18 H), 1.73 (b, -CH-, H), 1.27 (b, -CH2-, H). FT-IR (KBr, cm-1): 3034 (ArH stretching), 97 2931 (-CH2- stretching), 1730 (ester C=O stretching), 1609, 1521, 1491 (Ar, C=C stretching), 1292, 1179,1031 (C-O-C stretching). Mw: 1.46× 104, Mn: 1.07 × 104, PD: 1.4. Poly(1, 3-bis (4, 4”-dibutoxy-5’-methoxy [1, 1’, 4’, 1”] terphenyl-2’-yloxy)-2-propyl acrylate) (P2-C4) Polymerization of 10-C4 was performed according to the procedure described for P1-C1. From 0.65 g (0.68 mmol) of monomer 10-C4 and 0.006 g (1 wt%) of BPO was obtained 0.4 g (61.5 %) of the desired polymer. 1H NMR (300 MHz, CDCl3, δ ppm) 7.64 - 6.93 (b, ArH, 24 H), 5.30 (b, -CH(O)-, H), 4.06 (b, O-CH2-, H), 3.96-3.65 (b, O-CH3 and OCH2-, 14 H), 1.67 (b, -CH-, H), 1.56-0.95 (m, -CH2-, 18 H), 0.88 (b, -CH3, 12 H). FTIR (KBr, cm-1): 3038 (ArH stretching), 2958(-CH2- stretching), 1748 (ester C=O stretching), 1609, 1524, 1491 (Ar, C=C stretching), 1242, 1177, 1048 (C-O-C stretching). Mw: 0.98× 104, Mn: 0.63× 104, PD: 1.6. Poly(1, 3-bis (4, 4”-didecyloxy-5’-methoxy [1, 1’, 4’, 1”] terphenyl-2’-yloxy)-2-propyl acrylate) (P2-C10) Polymerization of 10-C10 was performed according to the procedure described for P1C1. From 0.6 g (0.47mmol) of monomer 10-C10 and 0.006 g (1 wt%) of BPO was obtained 0.46 g (76.7 %) of the desired polymer. 1H NMR (300 MHz, CDCl3, δ ppm) 7.90 - 6.85 (b, ArH, 20 H), 5.34 (b, -CH(O)-, H), 4.00 (b, O-CH2-, H), 3.98 - 3.65 (b, O-CH3 and O-CH2-, 14 H), 1.66 (b, -CH-, H), 1.50-1.08 (m, -CH2-, 66 H), 0.88 (b, CH3, 12 H). FT-IR (KBr, cm-1): 3037 (ArH stretching), 2924 (-CH2- stretching), 1734 (ester C=O stretching), 1609, 1524, 1493 (Ar, C=C stretching), 1244, 1178,1056 (C-O-C stretching). Mw: 1.67× 104, Mn: 1.04× 104, PD: 1.6. 98 3.3 Results and Discussion 3.3.1 Synthesis of polymers The polymers were synthesized through radical polymerization from the appropriate monomers. The concentration of initiator BPO was 1.0 mol % based on the amount of the monomer used. The structures of all monomers and polymers prepared in our work were characterized by 1H NMR and FTIR. Figure 3.1 illustrates two representative 1H NMR spectra of monomer 8-C4 and polymer P1-C4. In the 1H NMR spectra of monomer 8-C4, for example, the signals appearing in the range of δ 7.51- 6.92 correspond to those in aromatic protons. The signals at δ 3.82 are assigned to protons of methoxy groups while the multiplets at δ 4.00 correspond to the protons of –OCH2- in alkyl chains. The triplets at δ 6.42, 6.17 and 5.71 are characteristic of acrylic carbon double bond protons. It is noted that in the spectrum of polymer P1-C4, these three signals disappears. The absence of a C=C band at 1640 cm-1 in the FTIR spectrum of P1-C4 also indicates that the monomer has reacted to form a polymer. 3.3.2 Thermal characterization The thermal stability of polymers in nitrogen was investigated by thermogravimetric analysis (TGA) and the results are depicted in Figure 3.2. The polymers show a weight loss at 285 °C for P2-C4, 287 °C for P1-C4, 296 °C for P1-C1 and 307 °C for P2-C1, 306 °C for P1-C10, 312 °C for P2-C10. This may be due to the similar structure of the polymer backbone. Thermally induced phase transition behaviors of the polymers were evaluated using differential scanning caloritry (DSC) in nitrogen atmosphere. The DSC traces are shown in Figure 3.3. 99 Figure 3.1. 1H NMR spectra of monomer 8-C4 and polymer P1-C4 in CDCl3 P1-C1 p2-C1 P1-C4 P2-C4 P1-C10 P2-C10 100 weight percent (%) 80 60 40 20 0 100 200 300 400 500 600 700 800 o Temperature ( C) Figure 3.2. TGA traces of P1-C1, P1-C4, P1-C10, P2-C1, P2-C4, P2-C10 measured in a nitrogen atmosphere at a heating rate 10 °C /min. 100 o o Tg-19.7 ( C) o Tg24.8 ( C) Heat flow (mW) o Tn 57.4 ( C) Tiso 76.2 ( C) o Tiso 81.1 ( C) P2-C10 P1-C10 o Tg20.4 ( C) P2-C4 o Tg 64.8 ( C) T 156.4 (oC) iso o Tg 63.1 ( C) P2-C1 o P1-C1 Tg 77.2 ( C) -50 50 P1-C4 100 150 200 250 o Temperature ( C) Figure 3.3. Second heating differential scanning calorimetry curves for P1-C1, P1-C4, P1-C10, P2-C1, P2-C4, P2-C10 measured in a nitrogen atmosphere at a heating rate 10 °C /min. P1-C1 exhibits a glass transition (Tg) at 77.2 °C. With the increase of the flexible alkyl chains in the terminal position on the terphenyl rigid rod, the glass transition temperatures of P1-C4 and P1-C10 decrease to 64.8 °C and 24.8 °C, respectively. Similarly, P2-C1 shows a glass transition at 63.1 °C whereas the Tgs of P2-C4 and P2-C10 decrease to 20.4 and –19.7 ºC. It is noted that besides the glass transition, polymer P1-C4, P1-C10 and P2-C10 exhibit mesophase properties at different temperatures. P1-C4 undergoes an isotropization at 156.4 °C whereas P1-C10 shows a mesophase change at 81.1 °C. P2C10 exhibits a small thermal transition at 57.4 °C, and then undergoes an isotropization 101 at 76.2 °C. The decrease of the isotropization temperatures is proportional to the increase of the alkyl chain length on mesogenic units. 3.3.3 Polarized optical microscopy study The mesophase was identified using polarized optical microscope investigation. Polymers (P1-C4, P1-C10 and P2-C10) showed the homotropic textures. POM microphotographs of the mesomorphic textures of these novel polymers are shown in Figure 3.4. When the isotropic liquid of P2-C10 was cooled to 56 °C, a branched fan texture was observed. According to the literatures 25-26, the texture is considered of SmB phase. The micrograph Figure 3(b) was taken after heating the mesophase to 75 °C, and the observed fibrous textures indicate the formation of nematic mesophase. Polymer P1-C10 showed a typical focal-conic fan texture of smectic A phase 26 when cooled to 72 °C from an isotropic melt of P1-C10 (Figure 3.4 c), whereas Schlieren texture was observed for P1C4 (Figure 3.4 d) while cooling the isotropic melt to 125 °C, and no other mesophases were observed on prolonged cooling. No birefringent textures were found from the P1C1, P2-C1 and P2-C4 during cooling. a b 102 c d Figure 3.4. Polarized optical micrographs of the textures observed on cooling of (a) P2C10 to 56 °C; (b) P2-C10 to 75 °C; (c) P1-C10 to 72 °C; and (d) P1-C4 to 125 °C from the isotropic liquid with a cooling ratio of 0.5 °C /min. From DSC and POM results, it is noted that the polymer P1-C10 and P2-C10 form a lamellar layer structure in the mesophase while P1-4 only shows a nematic phase. It is also reporteded that the side chain liquid crystalline polymers with mesogenic groups laterally attached to the polymer backbone prefer to form nematic mesophases 12-14. The steric crowding of the side chains forces the backbone into an extended conformation with the mesogens organizing parallel to the polymer backbone. Therefore the centers of the mesogenic units are staggered inside the polymer lattice to form a nematic phase. The terphenyl aromatic rigid cores are attached to the polymer backbone without any spacer, therefore the rigid mesogenic units are not only force the polymer backbone to take an extended conformation, but also organize close to the backbone, and form a rigid core. This enhances the rigidity of the polymer backbone, and the micro-separation between rigid core and the flexible alkyl chains is the main driving force for the polymers to pack in a more ordered pattern 27-28. The DSC results show that the long alkyl chains at 103 the terminal position on the rigid aromatic core are necessary to form a layer structure. P1-C1 and P2-C1 with methyl groups on the side chain didn’t exhibit any mesophase, whereas P1-C4 showed a nematic phase12-15. Only polymer with terminal alkyl chains such as P1-C10 and P2-C10 showed a smectic lattice. 3.3.4 X-ray diffraction analysis XRD measurements were carried out to collect more information on self-organization and the packing modes of the novel polymers. The polymers were annealed in the oven at about 60 °C for two days then cooled down quickly to room temperature before measurement. X-ray diffraction patterns for all polymers are shown in Figure 3.4, The dspacing distance was derived using the Bragg’s law d = nλ/2sin(θ) (λ = 1.54 Å). The reflection angle 2θ and the space distance d are listed in Table 3.1. Table 3.1. Peak Angles in degree and d Spacings in Å for the Polymers Polymer 2θ1°/ d1Å 2θ2°/ d2Å 2θ3°/ d3Å 2θ4°/ d4Å P2-C10 4.16/21.2 8.32/10.6 10.25/8.6 19.7/4.5 P1-C10 4.74/18.6 10.40/8.5 21.14/4.2 P1-C4 7.84/11.3 10.50/8.4 20.08/4.4 P2-C4 20.2/4.4 P2-C1 20.0/4.4 P1-C1 20.56/4.3 104 ο 21.2 A o 10.6 A o 8.6 A o Relative intensity (a.u) 18.6 A P2-C10 o 8.5 A P1-C10 o 11.3 A o 8.4 A P1-C4 P2-C4 P2-C1 P1-C1 12 16 20 24 2-theta(degree) Figure 3.5. X-ray diffraction patterns for the jacketed liquid crystalline polymers at room temperature. The XRD diffraction pattern of P2-C10 shows three sharp reflections in small and middle angle regions at a 2θ value of 4.16, 8.32 and 10.2°, from which d spacings of 21.2Å, 10.6 Å and 8.6 Å are derived. It is noted that polymer P2-C10 affords two X-ray diffraction peaks in small angle with d spacings ratio of 1:1/2. This d spacing ratio is indicative of a smectic structure, corresponding to first- and second-order Bragg reflections from smectic layers 29,30. P1-C10 affords two sharp reflections in the small and middle angle region at 2θ = 4.74 o and 10.4o, from which d spacings of 18.6 and 8.5 Å are derived. The existence of long-range order in the polymer lattice rules out the possibility of the nematic phase formation and reinforces the smectic lattice structure. For P1-C4, the diffraction patterns exhibits one sharp reflection at 2θ = 7.84 o and small peak at 2θ = 10.5 o, from which d spacings of 11.3Å and 8.4Å are derived. The profiles of the P1-C1, 105 P2-C1 and P2-C4 are similar, the diffraction patterns exhibits one broad halo at about 2θ = 20 o, and no sharp reflections were observed, which indicate an amorphous lattice. It is noteworthy that the polymers P2-C10, P1-C10 and P1-C4 all offer a sharp reflection in middle angle region. According to the literature31, 32, when the substituted groups are much larger than the repeating units, a steric hindrance is exerted on the polymer backbone, making the polymer chain to take an extended conformation with an overall cylindrical symmetry. The sharp reflection on X-ray diffraction pattern was assigned to a packed cylindrical polymer chain32. The alkyl chain on the rigid core of P1-C4 is so short that the micro-separation between the flexible alkyl chains and rigid units may be insignificant and the full polymer chain adopts a cylindrical geometry, whereas, in P2C10 and P1-C10, the backbone and mesogenic units form the rigid core and the long flexible alkyl chains organize in between them. A diffuse halo at wide angle 20 o for all the polymers can be attributed from the disordered arrangement of mesogenic groups 29 and lack of short-range order in the lattice. From the DSC, POM and X-ray diffraction data, the following scheme for the observed smectic mesophase was suggested (Figure 3.6): in the layer structure of the jacketed liquid crystalline polymers, the rigid part comprised of aromatic units and the polymer backbone confined to a thin two-dimensional layer. The alkyl chains in the terminal position on the aromatic rings stretch out to fill the middle zone of the mesogenic layers. 3.3.5 AFM study The self-assembly of the liquid crystalline polymers on a substrate was examined using atomic force microscopy (AFM). Polymer solution in toluene was deposited on mica substrate and left to evaporate in a solvent-saturated atmosphere to form a thin film for 106 AFM studies. Toluene is a good solvent for both rigid and flexible units of polymers, so the morphology of polymer is expected to be governed by the self-assembling characteristics of the polymer chains rather than the phase separation in solution. A typical AFM micrograph for P2-C10 is shown in Figure 3.7. Figure 3.6. Schematic representation of lamellar structures of the novel jacketed polymer, d1 is the Smectic layer distance, and d2 is the diameter of the cylindrical core, which comprised of mesogenic units and the backbone of the polymers. a b Figure 3.7. AFM images (contact mode) of film on mica by slowly evaporating from a solution of P2-C10 (0.5 mg/ml) in toluene (a) 2D 10× 10 µm; (b) 3D 10× 10 µm 107 Spherical aggregates of about 200-300 nm in diameter were observed. However, a precise self-assembling mechanism could not be derived due to the big gap between the measured scale level in AFM image (about 200-300 nm) and the cylinder diameter derived from X-ray diffraction (below 10 nm). 3.4 Conclusion A series of novel liquid crystalline polymers, in which laterally attached terphenyl aromatic rigid core with alkyl chains on the terminal position on the polymer backbone, were synthesized. The structural aspects on the chemical and physical properties of the polymers were investigated using GPC, TGA, DSC, POM and XRD. 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Soc. 2003, 125, 6854-6855. 111 [...]... with a mixture of hexane and dichloromethane (2 :3) as eluents Yield: 2.2 g (67.1 %) 1H NMR (30 0 MHz, CDCl3, δ ppm) 7.52 - 6.89 (m, ArH, 20H), 4.24 (q, J = 5.7 Hz, -CH(O)-, 1H), 3 (d, J = 5.2 Hz, OCH2-C, 4H), 3. 86 (s, Ar-O-CH3, 3H), 3. 78 (s, Ar-O-CH3, 3H), 3. 77 (s, Ar-O-CH3, 3H), 2.20 (b, -C-OH, 1H) 13 C NMR (75.4 MHz, CDCl3, δ ppm) 158.7, 151.2, 149.4, 131 .4, 130 .4, 129.7, 129 .3, 114.6, 1 13. 5, 112.5 (ArC),... 4.00 (t, J =3. 9 Hz, O-CH2-, 4H), 3. 82 (s, Ar-O-CH3, 3H), 1.79 (p, J = 6.9 Hz, R(O)-CH2-, 4H), 1.54 (p, J= 6.0 Hz, -CH2-, 4H), 0.99 (t, J= 7.5 Hz, -CH3, 6H) 13 C NMR (75.4 MHz, CDCl3, δ ppm) 161.2 (C=O), 158.7, 158.2, 151.2, 150.4, 130 .4, 129.7, 129 .3, 128.9, 127.8, 118.0, 115 .3, 114 .3 (ArC), 69.6 (O-CH2-), 56 .3 (O-CH3), 31 .8, 29.5 (-CH2-), 13. 4 (-CH3) MS (EI): m/z: 474.4, 420 .3, 36 4 .3, 30 7.2, 247.1,... = 3. 9 Hz, Ar-O-CH2-, 4 H), 92 3. 83 (s, Ar-O-CH3, 3 H), 1.82 (q, J = 6.6 Hz, -CH2-, 4H), 1.28 (b, -CH2-, 28 H), 0.91 (t, J = 6.6 Hz, -CH3, 6 H) 13C NMR (75.4 MHz, CDCl3, δ ppm) 164.8 (C=O), 158.6, 158.4, 154.2, 140.9, 133 .4, 132 .1, 130 .4, 129.9, 129.8, 129.6, 129.4, 127.7, 124.5, 115 .3, 114.2, 114.0 (ArC), 68.0 (O-CH2-), 56 .3 (O-CH3), 31 .8, 29.5, 29.4, 29 .3, 29.2, 26.0, 22.6, 18.6 (-CH2-), 13. 9 (-CH3)... %) 1H NMR (30 0 MHz, CDCl3, δ ppm) 7.52 - 6.84 (m, ArH, 10 H), 4.94 (s, Ar-OH, 1 H), 4.02 (t, J = 5.2 Hz, Ar-O-CH2-, 4 H), 3. 77 (s, Ar-OCH3, 3 H), 1. 83 (p, J = 6.6 Hz, -R(O)-CH2-, 4 H), 1.54 (b, -CH2-, 28 H), 0.91 (t, J = 6.6 Hz, -CH3, 6 H) 13C NMR (75.4 MHz, CDCl3, δ ppm) 159 .3, 158 .3, 150.5, 146.4, 130 .7, 130 .4, 130 .1, 129.0, 117.7, 115.2, 114.0, 1 13. 6 (ArC), 68.0 (O-CH2-), 56 .3 (O-CH3), 31 .8, 29.5,... NMR (30 0 MHz, CDCl3, δ ppm) 7.51 - 6.84 (m, ArH, 20 H), 4.22 (q, J = 3. 4 Hz, -CH(O)-, 1 H), 4.04 -3. 95 (m, O-CH2-, 12 H), 3. 78 (s, Ar-O-CH3, 6 H), 2.28 (d, -C-OH, 1 H) 13CNMR (75.4 MHz, CDCl3, δ ppm) 158.7, 158.2, 151.2, 150.4, 130 .4, 128.9, 127.8, 118.0, 115 .3, 114 .3 (ArC), 70.5 (O-CH2-), 69.6 (O-CH2-C), 56 .3 (O-CH3), 36 .8, (-CH-OH), 31 .8, 29.5, 29.4, 29 .3, 29.2, 26.0, 22.6, 18.8 (-CH2-), 13. 4 (-CH3)... 1.4 g ( 43. 3 %) 1H NMR (30 0 MHz, CDCl3, δ ppm) 7.51 - 6.88 (m, ArH, 20 H), 4.22 (q, J = 4.7 Hz, -CH(O)-, 1 H), 4.04 (q, J = 3. 1 Hz, O-CH2-, 8 H), 3. 95 (d, J = 4.2 Hz, O-CH2-C, 4 H), 3. 78 (s, Ar-O-CH3, 6 H), 2.80 (d, -C-OH, 1 H) 13C NMR (75.4 MHz, CDCl3, δ ppm) 158.7, 158.2, 151.2, 150.4, 130 .4, 128.9, 127.8, 118.0, 115 .3, 114 .3 (ArC), 70.5 (O-CH2-), 69.6 (O-CH2-C), 56 .3 (OCH3), 36 .8, (-CH-OH), 32 .9, 19.2... 112.5 (ArC), 70.5 (O-CH2-), 56 .3, 55.2 (O-CH3), 36 .8, (-CH-OH) MS (EI): m/z: 728 .3, 670.2, 39 2.2, 33 6.1, 289.0, 2 13. 0, 185.1 Mp: 178 °C 1, 3- Bis (4, 4”-dibutoxy-5’-methoxy [1, 1’, 4’, 1”] terphenyl-2’-yl) propan-2-ol (9-C4) 93 Compound 9-C4 was synthesized according to the procedure described for compound 9C1 From 3. 1 g (0.74 mmol) of compound 7-C4, 0 .37 ml (3. 6 mmol) of 1, 3- dibromopropan-2-ol was obtained... with hexane and ethyl acetate (1:1) as eluents to yield the monomer Yield: 1.4 g (80.4 %) 1H 91 NMR (30 0 MHz, CDCl3, δ ppm) 7.51 - 6.89 (m, ArH, 10 H), 6.90 (d, J = 14.0 Hz, C=CH, 1 H), 6.17 (q, J = 6.9 Hz, R=CH-, 1 H), 5.88 (d, J = 10.5 Hz, C=CH, 1 H), 3. 78 (s, Ar-OCH3, 9H) 13CNMR (75.4 MHz, CDCl3, δ ppm) 165.2 (C=O), 158.7, 150.6, 149 .3, 138 .1, 137 .8, 130 .9, 130 .7, 130 .5, 130 .4, 129.4, 129 .3, 128.7,... Polymerization of 8-C10 was performed according to the procedure described for P1-C1 From 0.85 g (1 .3 mmol) of monomer 8-C10 and 0.008 g (1 wt%) of BPO was obtained 0.5 g (58.8 %) of the desired polymer 1H NMR (30 0 MHz, CDCl3, δ ppm) 7.55 - 6.50 (b, ArH, 10 H), 4.01 -3. 50 (b, O-CH3 or O-CH2-, 7 H), 1.90 (b, -CH-, 1 H), 1.58-1. 03 (m, CH2-, 34 H), 0.89 (b, -CH3, 6 H) FT-IR (KBr, cm-1): 30 38 (ArH stretching),... (0.47mmol) of monomer 10-C10 and 0.006 g (1 wt%) of BPO was obtained 0.46 g (76.7 %) of the desired polymer 1H NMR (30 0 MHz, CDCl3, δ ppm) 7.90 - 6.85 (b, ArH, 20 H), 5 .34 (b, -CH(O)-, 1 H), 4.00 (b, O-CH2-, 4 H), 3. 98 - 3. 65 (b, O-CH3 and O-CH2-, 14 H), 1.66 (b, -CH-, 1 H), 1.50-1.08 (m, -CH2-, 66 H), 0.88 (b, CH3, 12 H) FT-IR (KBr, cm-1): 30 37 (ArH stretching), 2924 (-CH2- stretching), 1 734 (ester . Ar-O-CH 3 , 3 H). 13 C NMR (75.4 MHz, CDCl 3 , δ ppm) 159 .3, 158.7, 150.5, 146.4, 130 .4, 130 .2, 129 .3, 126.6, 117.8, 114.6, 1 13. 5, 112.5 (ArC), 56 .3 (O-CH 3 ), 54 .3 (O-CH 3 ). MS (EI): m/z: 33 6.1,. 4H), 3. 86 (s, Ar-O-CH 3 , 3H), 3. 78 (s, Ar-O-CH 3 , 3H), 3. 77 (s, Ar-O-CH 3 , 3H), 2.20 (b, -C-OH, 1H). 13 C NMR (75.4 MHz, CDCl 3 , δ ppm) 158.7, 151.2, 149.4, 131 .4, 130 .4, 129.7, 129 .3, 114.6,. 151.2, 150.4, 130 .4, 129.7, 129 .3, 128.9, 127.8, 118.0, 115 .3, 114 .3 (ArC), 69.6 (O-CH 2 -), 56 .3 (O-CH 3 ), 31 .8, 29.5 (-CH 2 -), 13. 4 (-CH 3 ). MS (EI): m/z: 474.4, 420 .3, 36 4 .3, 30 7.2, 247.1,