J. MATER. CHEM., 1994,4(5), 719-727 Liquid-crystalline Polyethers based on Conformational Isomerism Part 33.+-Therrnotropic Polyethers based on a Mesogenic Group containing Rigid and Flexible Units: 1-(4'-Hydroxybiphenyl=4~yl)-2~(4=hydroxyphenyl)propane Virgil Percect Peihwei Chu," Goran Ungar,b Stephen 2. D. Cheng" and Yeocheol Yoon" a Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH 44 106, USA School of Materials and Centre for Molecular Materials, The University of Sheffield, Sheffield, UK SI 3DU " Institute of Polymer Science, The University of Akron, Akron, OH 44325, USA The synthesis of a mesogenic group containing rigid and flexible units: 1-(4'-hydroxybiphenyl-4-yl)-2-(4-hydroxy-pheny1)propane (TPP) is presented. TPP was polyetherified under phase-transfer catalysed conditions with a,o-dibromoalkanes containing 4-20 methylenic units.The resulting polyethers, TPP-x (where x =number of methylenic groups in the spacer), were characterized by a combination of techniques consisting of differential scanning calorimetry, thermal optical polarized microscopy and small- and wide-angle X-ray scattering experiments. All TPP-x polyethers displayed multiple crystalline phases whose nature was determined by the spacer length. TPP-x with x of less than 9 exhibited crystalline phases in which the mesogenic and spacer were intermeshed. Polymers with longer spacers displayed crystalline phases in which the mesogen and spacer were separated in separate layers of different electron densities.TPP-x with x =5, 7, 9 and 11 also exhibited a nematic mesophase. The traditional pathway used in the synthesis of molecular and macromolecular liquid crystals is based on the concept of a rigid-rod-like mesogenic unit. In 1988 we advanced the concept of a flexible rod-like mesogenic unit or rod-like mesogenic unit based on conformational isomerism. This concept was used to synthesize main-chain liquid-crystalline polyethers based on conformational isomerism without' and with2 flexible spacers. It has been demonstrated that this synthetic strategy can be employed to tailor-make linear polymers exhibiting ~ne'-~ or two4 uniaxial nematic, smectic5 and columnar hexagonal mesophases.6 Polyethers based on very flexible mesogenic groups such as 1,2-bis(4-hydroxyphenyl)ethane (BPE)5,6 and 1-(4-hydroxy- pheny1)-2-(2-methyl-4-hydroxypheny1)ethane(MBPE)2.3 and qwdibromoalkanes display mostly virtual, but also mono- tropic and even enantiotropic mesophases.2 Transformation of virtual or monotropic mesophases into enantiotropic mesophases can be accomplished by copolymerization.' Copolymerization experiments can also be used to determine thermal transitions and thermodynamic parameters of the virtual mesophases of the homopolymers.Thermodynamic schemes that explain the interconversion between virtual, monotropic and enantiotropic mesophases have been elabor- ated.7 These schemes suggest that the transformation of a virtual mesophase into an enantiotropic mesophase can also be accomplished by increasing the rigidity and decreasing the degree of order of the macromolecule or of its structural units or by a combination of both. Increased rigidity and decreased degree of order (i.e.increased conformational flexibility) have been used to design the mesogenic unit 1-( 4-hydroxybiphenyl- 4-y1)-2-( 4-hydroxyphenyl) butane (TPB), which, by polyetheri- fication with a,o-dibromoalkanes, leads to soluble polyethers displaying only nematic mesophases.' Polyethers based on TPB and flexible spacers are presently employed as models for main-chain liquid-crystalline polymers in a variety of physical investigations.' At the same time, TPB and its architectural variants are used in molecular engineering of molecular and macromolecular liquid crystals with complex architecture such as macrocyclics'(d~~'Oand dendrimers." Some of these developments have recently been reviewed.12 The polyethers based on TPB and flexible spacers are soluble t Part 32: ref 9(4.in conventional solvents and exhibit only nematic meso-phases.' We are also interested in the design of soluble, main- chain polyethers with more ordered mesophases than the nematic one. In principle, this can be accomplished by increas- ing the cylindrical shape of the TPB-like mesogen. The first aim of this paper is to report the synthesis of such a novel mesogenic unit, this is achieved by replacing the 1,2-substituted butane group of TPB by 1,2-substituteti pro- pane, i.e. l-(4-hydroxybipheny1-4-yl)-2-(4-hydroxyphenyl)-propane (TPP).The second aim of this paper is to describe the synthesis and characterization of polyethers based on TPP and a,w-dibromoalkanes containing 4-20 methylenic groups. Experimental Materials 1,4-Dibromobutane (99"/0), 1,5-dibromopentane (97%), 1,6-dibromohexane (97%), 1,7-dibromoheptane (97%), 1,8-dibromooctane (98YO), 1,9-dibromononane (W%), 1,lO-dibromodecane (97%) and 1,ll-dibromoundecane ( 98%) (all from Aldrich) were used after vacuum distillation. 1,12-Dibromododecane (technical, Aldrich) was purified by recrystallization from methanol. 1,16-Dibromohexadecane (mp 56-57 "C; Pfaltz and Bauer) and 1,18-dibromooctadecane (K and K Laboratories) were used as received. 1,13-Dibromotride~ane'~(bp 106-162 "C under 0.5 mmHg), 1,14-dibrornotetrade~ane'~(mp 50 "C),1,15-dibromopenta-decane15 (mp 28 "C), 1,17-dibrom~heptadecane~(mp 37-38 "C), 1,19-dibromononade~ane~(~)(mp 49.5 "C) and 1,20-dibromoeicosane'~d~(mp 69 "C) were synthesized as described previously. All other chemicals were commercially available and were used as received.Techniques Proton nuclear magnetic resonance ('H NMR) spectroscopy (200MHz) was carried out by use of a Varian XL-200 spectrometer with TMS as internal standard and CDCI, or [2H,]acetone as solvent. The purity of the products was determined by a combination of thin-layer chromatography (TLC) on silica gel plates (Kodak) with fluorescent indicator and high-performance liquid chromatography (HPLC).Relative molecular weights of the polyethers were determined 720 by gel permeation chromatography (GPC). HPLC and GPC analyses were carried out with a Perkin-Elmer series 10 LC equipped with an LC-100 column oven and a Nelson Analytical 900 series data station. The measurements were made by using a UV detector, CHC1, or THF as solvent (1ml min-', 40 "C), two PL gel columns of 5 x lo2 and 1 x lo4 A and a calibration plot constructed with polystyrene standards. A Perkin-Elmer DSC-7 differential scanning calorimeter was used to measure the thermal transitions. Heating and cooling rates were always 20 "C min-'. Indium was used as a calibration standard. First-order transitions (crystal-crystal, crystal-liquid crystal, liquid crystal-isotropic, etc.) were read at the maxima or minima of the endothermic or exothermic peaks.Glass transition temperatures (T,) were read at the middle of the change in the heat capacity. All heating and cooling scans after the first heating scan were identical. A Carl Zeiss optical polarizing microscope (magnification 100 x) equipped with a Mettler FP 82 hot-stage and a Mettler FP 800 central processor was used to observe the thermal transitions and to characterize the anisotropic textures. X-Ray scattering patterns were recorded using a flat-plate wide-angle (WAXS) vacuum camera (at room temperature and elevated temperatures) or a helium-filled flat-film pinhole- collimated small-angle (SAXS) camera (at room temperature). Ni-filtered Cu-Ka radiation was used.The samples were either in the form of prepared polymers, free-standing powders, fibres or bulk samples in Lindemann thin-walled 1 mm capil- laries cooled from the melt. The temperature stability of the X-ray heating cell was kO.1 "C. WAXS experiments were also carried out with a Rigaku X-ray generator. The point-focused beam was monochromatized with a graphite crystal (Cu-Ka radiation). Diffractograms were recorded as a function of temperature (k0.5 "C cell stability) from polymer films obtained upon melting. Synthesis of 4-Acetoxybiphenyl,2 Compound 2 was prepared by the esterification of 4-phenyl phenol 1 (80 g, 0.47 mol) with acetic anhydride (67 ml, 0.70 mo1).8 The product was recrystallized from 95% ethanol to yield 90 g (89?40) of white crystals.Purity (HPLC) 99.5%; mp 86-88 "C (1it.l6, mp 86-87 "C); 'H NMR (CDCl,, TMS)6,: 2.32 (3 H, s, CH,-), 7.16 (2 H, d, ortho to acetoxy of the substituted phenyl ring, J 8.0 Hz), 7.44 (3 H, m, meta and para of the unsubstituted phenyl ring), 7.56 (2 H, d, meta to acetoxy of the substituted phenyl ring, J 8.0 Hz), 7.59 (2 H, d, ortho of the unsubstituted phenyl ring, J 8.0 Hz). Synthesis of 4-Hydroxyphenylacetic Acid, 4 Compound 4 was prepared by the demethylation of 4-methoxyphenylacetic acid (3) (80 g, 0.30 mol) with hydro- bromic acid (181 ml, 0.99 mol) in 400 ml acetic acid.8 The product was recrystallized from 100ml water to yield 68g (93.5%) of white, needle-like crystals. Mp 146-152 "C (liti7, mp 148 "C); 'H NMR (C2H,]acetone, TMS)GH: 3.50 (2 H, s, -CH,-), 6.79 (2 H, d, ortho to hydroxy of the phenyl ring, J 8.0 Hz), 7.13 (2 H, d, meta to hydroxy of the phenyl ring, J 8.0Hz).The 'H NMR spectrum showed that 4 is free of unreacted methoxy groups. Synthesis of 4Acetoxyphenylacetic Acid, 5 Compound 5 was prepared by the esterification of 4 (75 g, 0.49 mol) with acetic anhydride (93 ml, 0.74 mol) according to the procedure described for the synthesis of 2.8 After washing with water several times and filtration, 76 g (80%) of J. MATER. CHEM., 1994, VOL. 4 a fine white powder was obtained. This was used in the next reaction step without further purification. Mp 105-108 "C (lit.", mp 108-110 "C); 'H NMR (CDCl,, TMS): 6 2.29 (3 H, s, CH,-), 3.64 (2 H, s, -CH2-), 7.06 (2 H, d, ortho to acetoxy of the phenyl ring, J 10.0 Hz), 7.31 (2 H, d, meta to acetoxy of the phenyl ring, J 10.0 Hz).Synthesis of 1-(4-Acetoxybiphenyl-4-y1)-2-(4acetoxyphenyl) ethanone, 7 Compound 7 was prepared by the Friedel-Crafts acylation of 2 with 6. Compound 5 (45g, 0.23mol) and S0C12 (25m1, 0.35 mol) were placed in a 250 ml three-necked flask equipped with a nitrogen inlet-outlet. After adding a few drops of N,N-dimethylformamide (DMF), the reaction mixture was stirred at room temperature for 2 h, and excess SOCl, was removed under reduced pressure to produce a yellow solid, which was used directly in the acylation reaction. The conversion was checked by NMR (-CH2- shift from 3.59 to 4.10).Compound 2 (59 g, 0.28 mol) was dissolved in 250 ml CH,Cl, in a 1000 ml three-necked flask equipped with a nitrogen inlet-outlet, a thermometer and a dropping funnel. The solution was cooled to below 10 "C using an ice-water bath after which time anhydrous AlCl, (110 g, 0.83 mol) was added. 4-Acetoxyphenylacetyl chloride (6') dissolved in 200 ml anhy- drous CH,Cl, was added dropwise maintaining the reaction temperature below 10 "C. After completing the addition, the deep-red solution was stirred at the same temperature for 3 h. The reaction mixture was poured into a mixture containing 120ml concentrated HCl, 1OOOml iced water and 600ml CHCl,. The organic layer was separated and washed twice with 500 ml water, dried over MgSO,, filtered and the solvent was removed on a rotary evaporator.The product was recrystallized from 1000 ml toluene to yield 63 g (70%) white crystals. Purity (HPLC) 99.5%; mp 196-198 "C; 'H NMR (CDCl,, TMS)GH: 2.29 (3 H, S, CH3COO--Ph-CH,-), 2.33 (3 H, s, CH,C00-biphenyl), 4.30 (2 H, s, -CH,-), 7.07 (2 H, d, ortho to acetoxy of the monophenyl ring, J 8.0 Hz), 7.20 (2 H, d, ortho to acetoxy of the biphenyl ring, J 8.8 Hz), 7.31 (2 H, d, meta to acetoxy of the monophenyl ring, J 8.0 Hz), 7.65 (2 H, d, meta to acetoxy of the biphenyl ring, J 8.8 Hz), 7.65 (2 H, d, meta to carbonyl of the biphenyl ring, J 8.0 Hz), 8.08 (2 H, d, ortho to carbonyl of the biphenyl ring, J 8.0 Hz). Synthesis of 1-(4-Methoxybiphenyl-4yl)-2-( Cmethoxyphenyl) propanone, 8 Compound 7 (20 g, 0.052 mol), iodomethane (10 ml, 0.16 mol) and tetrabutylammonium hydrogen sulfate (TBAH; 5.4 g, 0.016 mol) were dissolved in 300 ml THF in a 1000 ml three- necked flask equipped with reflux condenser.NaOH (300 ml, 50%) was quickly added at 40 "C and the reaction was stirred for 50min. During the reaction the colour of the solution changed from orange to light yellow. The reaction mixture was poured into 800 ml water and 600 ml CHCl,, after which time the organic layer was separated, stirred for 30 min with 300 ml dilute HCl, washed with 300 ml water and dried over MgSO,. The solvent was removed on a rotary evaporator to give a yellow solid, which was recrystallized from 95% ethanol to yield 7.8 g (44%) light-yellow crystals.The dimethylated compound was eliminated by recrystallization. Purity (HPLC) 99.5%; mp 128-132 "C. 'H NMR (CDCl,, TMS)G,: 1.52 (3 H, d, CH,-CH-, J 7.4 Hz), 3.76 (3 H, S, CH3O-Ph), 3.85 (3 H, s, CH,O-biphenyl), 4.66 (1 H, q, CH,-CH-), 6.84 (2 H, d, ortho to methoxy of the monophenyl ring, J 8.4 Hz), 6.97 (2 H, d, ortho to methoxy of the biphenyl ring, J 8.8 Hz), 7.23 (2 H, d, meta to methoxy of the monophenyl ring, J 8.4 Hz), J. MATER. CHEM., 1994, VOL. 4 7.55 (2 H, d, meta to methoxy of the biphenyl ring, J 8.8 Hz), 7.55 (2 H, d, meta to carbonyl of the biphenyl ring, J 8.4 Hz), 8.00 (2 H, d, ortho to carbonyl of the biphenyl ring, J 8.4 Hz). Synthesis of 1-( 4-Methoxybiphenyl-4yl)-24Qmethoxyphenyl)propane, 9 Compound 9 was prepared by the reduction of 8 with LiAlH,-AlCl,.AlCl, (35 g, 0.26 mol) was placed in a 200 ml three-necked flask equipped with a dropping funnel and a nitrogen inlet-outlet, and cooled in an ice-water bath, after which time 95 ml anhydrous diethyl ether was added dropwise. LiAlH, (4.0 g, 0.12 mol) was placed in a 250 ml three-necked flask equipped with a dropping funnel and a nitrogen inlet-outlet, and cooled in an ice-water bath. To the flask containing LiAlH, were added successively 95 ml anhydrous diethyl ether, AlC1,-diethyl ether complex solution, 95 ml anhydrous CHCl, and then the solution of 8 in 95 ml anhy- drous CHCl, was added dropwise to the reducing agent solution at 0 "C. The reaction mixture was stirred at room temperature for 5 h, after which time 30% HC1 (290 ml) was added dropwise with stirring to decompose the LiAlH,-AlCl, complex. The product was extracted with 400ml CHCl,, washed twice with 100 ml water and dried over MgS0,.After filtration, the solvent was evaporated off to yield a light- yellow solid, which was recrystallized from 1100 ml ethanol to produce 13 g (88%) of white, needle-like crystals. Purity (HPLC) 99.5%; mp 128-129 "C;'H NMR (CDCl,, TMS)G,: 1.24 (3 H, d, CH,-CH-, J 7.2Hz), 2.67-2.94 (3 H, m, -CH,-CH-), 3.79 (3 H, S, CH3O-Ph), 3.85 (3 H, S, CH30-biphenyl), 6.83 (2 H, d, ortho to methoxy of the monophenyl ring, J 9.1 Hz), 6.96 (2 H, d, ortho to methoxy of the biphenyl ring, J 9.2 Hz), 7.12 (2 H, d, ortho to methylene of the biphenyl ring, J 8.7 Hz), 7.12 (2 H, d, meta to methoxy of the monophenyl ring, J 9.1 Hz), 7.42 (2 H, d, meta to methoxy of the biphenyl ring, J 9.2Hz), 7.51 (2 H, d, meta to methylene of the biphenyl ring, J 8.7 Hz).Synthesisof 1-(4-Hydroxybiphenyl-4yl)-2-( Qhydroxyphenyl) propane, 10 Compound 10 was prepared by the demethylation of 9. To a 500 ml three-necked flask equipped with a dropping funnel and a nitrogen inlet-outlet and placed in a dry ice-acetone bath, were added 100 ml anhydrous CH,Cl,, BBr, (1.0 mol 1-l in CH2C12, 97 ml, 0.096 mol), followed by 9 (13.34 g, 0.04 mol) dissolved in 177 ml anhydrous CH2C1, at -78 "C. After addition, the reaction mixture was stirred at room temperature for 16 h, after which time 100ml water and 400ml diethyl ether were added.The organic layer was separated, washed with 100 ml water twice, dried over MgSO,, filtered and the solvent evaporated off. The product was purified by column chromatography (silica gel, diethyl ether) and the white product recrystallized twice from toluene to yield 9.1 g (74.5%) of white, needle-like crystals. Purity (HPLC) ~99.5%; mp 189-189.5 "C; 'H NMR (CDCl,, TMS)S,: 1.24 (3 H, d, CH,-CH-, J 8.0 Hz), 2.71-3.04 (3 H, m, -CH,-CH-), 4.57 (1 H, s, hydroxy of the monophenyl ring), 4.73 (1 H, s, hydroxy of the biphenyl ring), 6.76 (2 H, d, ortho to hydroxy of the monophenyl ring, J 8.0Hz), 6.89 (2 H, d, ortho to hydroxy of the biphenyl ring, J 8.0 Hz), 7.09 (2 H, d, ortho to methylene of the biphenyl ring, J 8.0 Hz), 7.09 (2 H, d, meta to hydroxy of the monophenyl ring, 2d, J 208.0 Hz), 7.44 (2 H, d, meta to hydroxy of the biphenyl ring, J 8.0 Hz), 7.44 (2 H, d, meta to methylene of the biphenyl ring, J 8.0 Hz). 721 Synthesis of Polyethers Conventional liquid-liquid two-phase (organic solvent-aqueous NaOH solution) phase-transfer-catalysed polyether-ification conditions were used for the preparation of polyethers.2(") The polyetherifications were accomplished under a nitrogen atmosphere at 80 "C in an o-dichloro-benzene-10 mol 1-' NaOH two-phase system (10-fold molar excess of NaOH versus phenol groups) in the presence of TBAH as phase-transfer catalyst. The molar ratio of nucleophilic to electrophilic monomers was always 1.0 : 1.0.An example of the polyetherification is as follows.To a 25 ml single-necked flask equipped with a condenser and a nitrogen inlet-outlet were successively added 0.60 mmol (0.1826 g) of monomer TPP (lo),1.2 ml of o-dichlorobenzene, 0.60 mmol (0.1632 g) of 1,8-dibromooctane, 1.2 ml of 10 mol I-' NaOH and 1.24 mmol (0.0815 g) of TBAH. The reaction mixture was stirred at 1100 rpm with a magnetic stirrer at 80 "C. After 3 h of reaction the organic and aqueous layers were diluted with CHC1, and water and the aqueous layer separated off. The organic layer was washed once with water, once with dilute HCl and three times with water. The polymer solution was precipitated into methanol to yield 0.2412 g (97%) of white fibrous material. The polymer was further purified by four successive precipitations from CHC1, solution into acetone, then once from CHCl, solution into methanol and finally twice from THF solution into water.Results and Discussion Synthesis and Thermal Characterization Scheme 1 presents the synthesis of racemic TPP (10). The synthesis of TPP was accomplished via a synthetic route similar to that employed in the preparation of TPB.' As illustrated in Scheme 2, TPP has a stereocentre. However, the sequence of reactions outlined in Scheme 1 leads to the racemic mixture of the two enantiomers of TPP. The individ- ual enantiomers of TPP can be prepared via the same procedure as that used in the synthesis of the two enantiomers of TPB.~o(~) There are a few details for the preparation of TPP that we should mention here.Although 4 is commercially available, we prefer to prepare it from 3 since this route is less expensive, The alkylation of 7with ethyl iodide leads to a mixture of C- and 0-alkylated products. Their separation was difficult. The 0-alkylated product was cleaved in situ and then was realkyl- ated with ethyl iodide to increase the overall yield of the C-alkylated product.' In the alkylation of 7 with ethyl iodide only low amounts of 0-alkylated and C-dialkylated products are obtained. The pure compound 8 can be separated from the C-dimethylated and 0-methylated products by recrys- tallization from 95% ethanol. The reduction of 8 to 9 was performed with LiAlH,-AlCl,~Et,O in CHCl,." For reasons discussed previously,' it is essential that complete reduction is accomplished at this step.The demethylation of 9 to 10 was most conveniently performed with BBr, in CHC1, 2o The synthesis of the polyethers of TPP with a,u-dibromoalkanes (TPP-x) was performed under phase-transfer catalysed polyetherification conditions developed in our labor- atory' (Scheme 2). As illustrated in Scheme 2 the resulting TPP-x polyethers are in fact copolyethers derived from the four constitutional and stereoisomers of TPP. TPP-x contain- ing even number x is soluble only at high temperature in chlorobenzene, THF or chloroform. TPP-x with odd number x is soluble at room temperature. TPP-x with x=4, 6 and 8 is so sparingly soluble that the molecular weight could not be determined by GPC.TPB-x with both odd and even x is very soluble even at room temperature.8 J. MATER. CHEM., 1994, VOL. 4 DSC traces of the first, second and subsequent heating scans are shown in Fig. l(u), (b) and (c).The phase-transition temperatures reported in Table 1were collected from the DSC traces of Fig. 1 and were assigned by a combination of thermal optical polarized microscopy and X-ray scattering experi- ments. Both these experiments will be discussed in a later section of this paper. The DSC traces from Fig. 1 demonstrate that TPP-x presents multiple phase transitions during both heating and cooling. All TPP-x are crystalline polymers with polymorphic crystalline phases. Only TPP-x with x=5, 7, 9 and 11 exhibit above their highest crystalline melting trans- ition also an enantiotropic nematic mesophase. The highest phase-transition temperatures of TPP-x present an odd-even dependence on spacer length regardless of whether this trans- ition refers to the melting of a crystal or of a liquid-crystalline phase into an isotropic liquid [Fig.2(b)]. With increasing 1 5 spacer length this dependence disappears. The second highest melting temperature is almost independent of spacer length [Fig. 2(u)]. Fig. 2(b) shows a plot of the highest transition PMF(i.e., isotropization) and the nematic-crystalline transition 2 6 7 CH31, TBAH, NaOH(aq)-THF, 40OC1 8 9 BBr&H2CI2 or HBr-CH,CO~BAH1 Scheme 1 Synthesis of TPP Table 1summarizes the yields, molecular weights and phase- transition temperatures together with the corresponding thermodynamic parameters of all TPP-x.Although the mol- ecular weights reported are only relative to polystyrene stan- dards, they are all larger than the values below which they become molecular-weight dependent.s temperatures for TPP-x with odd number x. There is a continuous increase of the nematic-crystalline and a continu- ous decrease of the isotropization transition temperatures. At x= 13 these two dependences intercept each other and there- fore, for x> 13 the nematic mesophase of TPP-x disappears. X-Ray Characterizationof TPP-XPolymers In agreement with the DSC data, the X-ray diffraction experi- ments showed a clear difference in the behaviour of TPP-x polymers with x=even and x=odd.As was expected, this difference was most pronounced in polymers with short spacers. With increasing spacer length the phase behaviours of even and odd polymers gradually converged. This trend was in agreement with that observed by using DSC [Fig. 2(u)]. Polymers With Odd-numbered Spacers x <9 X-ray scattering experiments confirmed that TPP-x (x=odd) polymers with short spacers, i.e. TPP-5, TPP-7 and TPP-9, are crystalline with a nematic phase at higher temperatures. The two main DSC peaks (Fig. 1) were thus identified as crystal-nematic(N) and nematic-isotropic(1) transitions, respectively. The powder pattern of the crystalline state is dominated by two intense, closely spaced reflections in the wide-angle range and no clear diffraction features at lower angles.For TPP-5 the Bragg spacings corresponded to the two wide-angle reflections 4.77 and 4.54 A, at room tempera- ture. On slow cooling from the nematic melt and after further annealing, additional weak diffraction features appeared. At 123 "C,i.e. between the temperatures of melting from the first DSC scan [i.e. 53 "C;see Table 1 and Fig. l(u)] and the small DSC endotherm at 148 "C, the pattern thus recorded had the same global appearance as that at room temperature prior to annealing, with th,e two strong reflections corresponding to 4.80 and 4.635 A. However, ic addition there were two weak reflections at 4.98 and 5.11 A. Upon cooling below the weak solid-solid transition the distribution of the satellite reflections on the low-angle side of the main wide-angle doublet changed into a short series of equidistant lines.In addition a very weak diffractjon feature developed at lower angles, corresponding to 20.5 A. The position of the dominant wide-angle doublet did not seem to change discontinuously at the solid-solid transition. The main features of the fibre pattern of TPP-5 are shown schematically in Fig. 3. The two dominant reflections are seen to be on the same row line, one of the reflections being equatorial. The maximum annealing temperature was only 80 "C, which did not produce resolvable satellite reflections J. MATER. CHEM., 1994, VOL. 4 Br -(CH&-Br C d Scheme 2 Synthesis of polyethers based on 1-(4-hydroxybiphenyl-4-y1)-2-(4-hydroxyphenyl) propane and a,w-dibromoalkanes containing x methylenic units (TPP-x) Table 1 Characterization of polyethers based on TPP and a,w-dibromoalkanes (TPP-x) with different numbers of methylenic units Ix). Data collected from first heating, cooling (both on first line) and second heating DSC (on the second line) scans thermal transitions/"C and corresponding enthalpy changes/kJ mru- ' in parentheses" x yield(Yo) 04")GPC (wv/M")GPC heating coo1in g 4 5 6 97.7 94.8 93.3 -11,200 - -2.53 - K 65(0.5) K 144(2.68) K 280(21.77) I G 46 K 150(2.95) K 282(20.55) I K 53(0.35) K 148(3.57) N 183(7.52) I G 48 K 149( 3.08) N 183(4.56) I K 59(1.25) K 126(2.22) K 249(20.35) I I272(-18.7) K 134(-3.22) K 34 (; I 173(-4.76) N lox(-3.05) K 39 G I 234(- 19.36) K 121(-0.44) K 7 8 9 10 11 12 13 97.5 97.5 99.0 91.2 91.3 90.2 97.5 25,000 -29,500 19,700 3 1,800 18,300 29,200 2.60 -2.30 3.32 1.68 2.90 2.00 G 38 K 135(0.56) K 249( 19.97) I K 49(0.48) K 150(5.0) N 178(5.88) I G 37 K 150(5.11) N 178(5.31) I K 55(0.33) K 141(2.16) K 221(19.51) I K 146(2.52) K 213 K 221(19.15) I K 48(0.56) K 154(7.43) N 173(6.69) I G 37 K 154(7.35) N 173(6.57) I K 52(0.5) K 145(12.19) K 204(20.51) I K 144( 12.08) K204(20.73) I K 49(0.5) K lll(9.9) K 155(8.7) N 165(6.2) I K lll(9.75) K 155(8.6) N 165(6.24)I K 51(0.6) K 144( 12.78) K 187( 19.54) I G 31 K 144( 13.48) K 186( 19.8) I K 50( 1.1) K 108( 15.86) K 162( 18.84) I I 167(-5.81) N 126(-4.08) K 33 <i I 207(- 18.63) K 135(- 1.79 ) K I 161(-7.32) N 133(-5.36) K 27 <; I 186(-21.94) K 120(-12.67) K I 156(-8.0) N 136(-6.7) K 95(-9.27) K I 166(-19.48) K 131(-12.77) K 19 G I 147(-7.0) K 140(-10.3) K 97(-14.14) K 28 G 14 15 16 17 18 92.3 93.3 93.1 95.2 96.7 16,500 20,900 28,700 34,500 23,500 2.03 2.02 3.42 1.89 2.92 G 26 K 108( 15.48) K 162( 18.25) I K 50(0.68) K 143( 17.12) K 176(21.56) I G 30 K 143(22.2) K 176(22.24) I K 49(0.66) K 118( 19.93) K 158(20.41) I G 27 K llg(21.7) K 158(19.48) I K 49(0.82) K 140(19.96) K 170(21.8) I G 27 K 142(22.99) K 170(21.9) I K 47(0.65) K 121(22.81) K 154(23.84) I G 23 K 122(26.2) K 154(23.51) I K 50(0.94) K 137(23.47) K 159(19.65) I I 161(-21.92) K 132(-18.49) K 32 G I 137(- 18.77) K 105(-21.03) K 23 G I 151(-21.67) K 129(-22.41) K 32 G I 132(-23.31) K 108(-24.91) K 21 G I 135(- 19.57) K 124(-23.9) K 30 G 19 89.4 23,100 2.01 G 27 K 137(24.98) K 158( 19.54) I K 47(0.73) K 119(23.98) K 156(23.86) I I 137(-23.0) K 108(-25.05) K 23 G 20 92.0 37,300 2.28 G 26 K 120(26.54) K 157(23.35) I K 50( 1.14) K 135(23.54) K 156(23.76) I G 29 K 137(27.63) K 157(23.41) I I 139(-22.66) K 126(-28.06) K 31 G ~~ " mru = molecular repeat unit.J. MATER. CHEM., 1994, VOL. 4 I I I I I -20 30 80 130 180 230 280 3 3 -20 30 80 130 180 230 280 3 TIT 77°C I I I I I -20 30 80 130 180 230 280 3 0 T/"C Fig. 1 First heating (a), first cooling (b), and second heating (c) DSC thermograms (20 "C min-l) of polyethers based on TPP and a,w-dibromoalkanes containing x methylenic units (TPP-x) or the 20.5 A feature.A sharp laxer-line streak was present sitional correlation. This correlatiyn greatly improves on slow with the meridional spacing of 6.0 A (indicated in Fig. 3). This melt crystallization. The 20.5 A periodicity which thus was attributed to a maximum in the molecular structure factor. develops corresponds reasonably well with the calculated A summary interpretation of the diffraction data on TPP-5 extended monomer length of 23.5 A. The solid-solid transition is that the crystal structure is based on a distorted hexagonal at 143 "C appears to be associated with axial shift between packing of tilted chains, with initially poor interchain tran- neighbouring chains. J. MATER. CHEM., 1994, VOL. 4 P 0 4 8 12 16 20 24 it-200 100 K K G 0 8,111 temperatures-of TPP-x as a function of x.Data collected from second heating scans. U, T,; 0,T,; 0,TK-N; A, TI;and (b)dependence of the transition temperatures of TPP-x with x containing an odd number of methylenic groups as a function of x. Data collected from cooling scans. A, TPNor TbK; 0, TN-K; .,TG;and a, TK-K I I I I I I r Fig.3 Main features of the X-ray diffractogram pattern of TPP-5 GI..., fGh,-qv;c T,a,-t;p,,ll In TPP-5 the departure from the hexagonal chain cross- section remained approximately constant with temperature, as judged by the constant splitting of the dominant, wide- angle reflection. In some TPP-x (x =odd) homopolymers with larger x, as well as in some copolymers of TPP with two different spacers (which will be described in a subsequent paper), the splitting decreased with temperature.This is illustrated in Fig. 4for TPP-9. Here, with increasing tempera- ture the cross-section of the unit cell perpendicular to the chain direction became progressively closer to the hexagonal. This may be associated with a reduction in the chain tilt. Polymers With Odd-numbered Spacers x 3 11 TPP-x homopolymers with x 3 13 behaved quite differently from those described above, with TPP-11 being an intermedi- ,,I ,,,,l,llll,,*ll,,,,l1,,,l1111 i,,, 5 10 15 20 25 30 35 2B/degrees Fig. 4 X-Ray diffractograms of TPP-9 (powder) as a funcr.ion of temperature. Temperature of each thermogram/"C: (a)rt; (b)40.(c) 60 (d) 80; (e) 100; cf) 110 6)120; (h) 130; (i) 140; (j)150; (k) 160; r,l) 170 (m) 180; (n) 190; (0)200; (p) 210; (4)220. ate case. The x3 13 polymers did not exhibit the nematic phase although, as the thermograms showed, they underwent a strong transition below the final isotropization temperature. This, however, was a crystal-crystal transition and the poly- mers did not show a liquid-crystal phase at all (Figs. 1 and 2). Neither of the two crystal forms was isomorphous with those described above. For illustration, Fig. 5 shows the temperature evolution of the diffractogram of TPP- 13. The low-temperature form was characterized by a number of intense Bragg peaks in the wide-angle region and by three orders of layer reflections at lower angles.The structure was clearly of lower symmetry than those described so far. On the other hand, the scattering pattern of the high- temperature form was rather simple and was dominated at wide angles by a strong maximum with a medium-intensity reflection on either side of it. The strong low-angle funda- mental was retained, but the higher orders were weakened, compared with the low-temperature form. The lowest angle reflection in both forms closely corresponded to the monomer spacings calculated for the extended monomer units. The considerable intensity was in contrast with the extremely weak or non-existent low-angle diffraction intensity of the TPP-x polymers with x=5, 7 and 9. A strong layer reflection in the long spacer polymers suggested that aromatic mesogens and aliphatic spacers were segregated into separate layers of different electron densities.On the other hand, the absence of strong reflections in the low-angle region, as in polymers with 5 <x <9, signified full or partial intermeshing.21 Polymers TPP-15, TPP-17, TPP-19 and TPP-20 displayed 5 10 15 20 25 30 35 2Wdegrees Fig.5 X-Ray diffractograms of TPP-13 (powder) as a function of temperature. Temperature of each thermogram/"C: (a) 30; (b) 40; (c) 60; (d) 80 (e) 100; cf) 110; (g) 120; (h) 130; (i) 140; (j)150; (k) 160; (I) 170; (m)180; (n)190; (0)200; (p) 210; (4) 220. the same two crystal forms as TPP-13, and melted without undergoing a liquid-crystal phase transformation.As will be shown further below, the present high-temperature crystal phase was also found in TPP polymers with long even spacers (x 10). TPP-11 showed three strong first-order transitions. X-Ray scattering from the highest temperature phase (156-166 "C) consisted only of diffuse scattering and confirmed the nematic assignment made by optical polarized microscopy. The lowest temperature phase was isomorphous in the low-temperature crystal form of higher odd-numbered polymers ( 13<x <19). The phase in the intermediate temperature region, between 113 and 156 "C, was a new high symmetry crystal form. The powder diffraction pattern ?as dominated by one intense wide-angle reflection at !.70 A and one medium-intensity low- angle reflection at 22.1 A.In addition, there were several weab bands on both the wide- and low-angle side of the 4.70A reflection. The appearance of these side bands, particularly the low-angle ones, suggested that the structure was a tilted hexagonal, i.e. either Crystal-G or Crystal-H.22 This intermediate phase could be rapidly quenched, partially or completely. Even at room temperature, the formation of the low-symmetry low-temperature phase was rather slow. Similarly, precipitation from solution resulted in a mixture of Crystal-G and Crystal-H and the poorly developed low- temperature crystal form, which had disappeared at 48 "C during the first DSC heating scan. Polymers with Even-numbered Spacers x d 8 The even-numbered spacer polymers also showed a break in their phase behaviour around the same spacer length as the odd-numbered spacer polymers.This was already suggested by the appearance of DSC thermograms (Fig. 1). For TPP-x J. MATER. CHEM., 1994, VOL. 4 polymers with x <8 the low-temperature transition endotherm was small whereas for polymers with x 2 10 it was considerably larger (Fig. 1, Table 1). X-Ray diffraction patterns of TPP-6 and TPP-8 were recorded as a function of temperature. Both the low- and the high-temperature phases ?ere characterized by a strong sharp diffraction peak at 4.6A. The low-temperature phase had additional weak reflections on the high-angle side and one reflection at lower angles, corrFsponding >o approximately half the monomer repeat: 12 A (=24/2 A) for TPP-8, as compared with the extended monomer length of 27A.The observed reflections for TKP-8 could b? indexed on a hexag- onal unit cell with a= 5.31 A and c =21 A, as shown in Table 2. The discrepancy between the measured (12.0) and calculated ( 10.5) dooz spacing is not understood. Attempts at producing well oriented fibres were unsuccessful. A significant feature of the low-temperature phase is the absence of the 001 reflection, indicating the existence of a glide plane parallel to the chain axis. Thus neighbouring chains are translated by half the monomer length with respect to each other. This seems to be a rather general feature of the main-chain polymers with shorter spacers and also parallels the behaviour of the TPP-x (x=odd) polymers.In the high-temperature phase only the strong sharp 100 hexagonal reflection remains. At lower angles two very weak diffractioq features were observed, which correspond to 11.5 and 14.8 A. As in the loy-temperature form, no reflection was observed in the 20-30A region, which would correspond to monomer periodicity. Had it not been for the two weak reflections, the high-temperature phase would have been described as hexagonal columnar. It may be that these were not true Bragg reflections but rather sharp molecular trans- formation maxima, in which case the description of the phase as columnar would have been valid. Further attempts to prepare well oriented fibres of TPP-8 and TPP-6 are planned, with a view to resolving this question.Polymers with Even-numbered Spacers x 3 10 The main feature of the powder diffractograms of the low- temperature phase of the polymers with longer even-numbered spacers was common to the whole series from TPP-10 to TPP-18. There were a number of strong reflections at wide angles, indicating low crystal symmetry (see Fig. 5). In addition, there was always a reasonably strong low-angle reflection corresponding closely to monomer periodicity, as well as its second- and sometimes third-order. For example, for TPY-12 the observed reflections corresponded to 26.3 and 26.5/2 A, respectively, compared with the calculated extended monomer length of 32.2A. The appearance of the strong reflection in the region of the full monomer repeat suggests that mesogens and spacers form separate layers, in contrast to the observation with shorter-length spacer TPP polymers.The overall situation was similar to the odd-numbered spacer TPP series, except that the actual crystal structure was different in the two series. With increasing temperature some diffraction peaks shifted Table 2 Observed reflections of TPP-8 spacinglii reflection measured calculated 100 4.60 4.60 101 4.48 4.49 103 3.86 3.84 104 3.43 3.46 002 12.0 10.5 J. MATER. CHEM., 1994, VOL. 4 considerably, leading to merging of certain reflections [Fig. 6(d)and (e)].This was associated with a heat capacity anomaly, which became apparent as a broad shoulder in the DSC traces of some of the polymers in the present group, e.g.in TPP-16 at ca. 100 “C. Above the main transition, associated by the lower of the two large DSC endotherms (Fig. l), the powder pattern was greatly $mplified, leaving one dominant wide-angle reflection at 4.70A and a weaker reqection on either side; these corre- sponded to 5.16 and 4.23 A (data for TPP-12). In addition, two orders of low-angle reflections remained, although they were shifted to somewhat smaller fundamFnta1 spacing. For TPP-12 the shift was from 26.4 to 24.2 A. Thus, the high- temperature phase in TPP-N polymers with long, even-numbered spacers x 210 was isomorphous with the high- temperature form of the polymers having long odd-numbered spacers with x 3 13.It was not surprising that the convergence of the structures of x =even- and x =odd-numbered polymers should occur for long spacers and at high temperatures. Increasing both spacer length and temperature reduced the probability of finding the spacer in its minimum-energy conformation. The fact that the spacers were conformationally disordered in the high-temperature phase was suggested by the abov5-mentioned average monomer shrinkage of more than 2A upon the transition from the low-temperature form to the high-temperature form. For a long disordered spacer, orientational correlation between its terminal bonds became too low for the even-odd variation to determine mutual orientation of successive mesogens and hence influence crystal structure.The nematic mesophase of TPP-x polymers with x =5, 7, 9 and 11 exhibited characteristic schlieren textures. I\ -5 10 15 20 25 30 35 2Bldegrees Fig.6 X-Ray diffractograms of TPP-18 (powder) as a function of temperature. Temperature of each thermogram/”C: (a) 30; (b) 40; (c) 60; (d) 80; (e) 100; (f) 110; (g) 120; (h) 130; (i)140; (j)150; (k) 160; (I) 170; (m) 180; (n) 190; (0)200; (p) 210; (4)220. Conclusions The TPP-x polymers described in this paper provided a very complex and comprehensive system in which the structure of the polymers was strongly influenced by their spacer length. This system contrasted with the TPB-x polymers, which showed only a nematic, and/or a nematic and a crystalline phase.Since some of the phases of TPP-x polymers exhibited various hexagonal or distorted hexagonal crystalline phases, they could be of great potential for the molecular design of polymers displaying a columnar hexagonal liquid-crystalline phase by suitable copolymerization experiments. Financial support by the National Science Foundation, Materials Research Group DMR-9122227 and NATO is gratefully acknowledged. References 1 V. Percec and R. Yourd, Macromolecules, 1988,21,3379. 2 (a) V. Percec and R. Yourd, Macromolecules, 1989, 22, 524; (b) V. Percec and Y. Tsuda, Macromolecules, 1990,23,5; (c)V Percec and Y. Tsuda, Macromolecules, 1990, 23, 3229; (d)V. Percec and Y. 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Paper 3/06318F; Received 20th October, 1993