GB2304723A - Liquid-crystalline conducting polymers - Google Patents

Abstract

Conducting polymers with conjugated backbones (primirily polyanilines) have mesogenic groups attached their backbones. The resulting liquid-crystallinity observed in certain favourable cases may be used to align the polymer chains and improve the bulk conductivity, or to permit the switching of optical absorption or electronic conductivity by interaction with external electric or magnetic fields.

Description

LIOUID-CRYSTALLINE CONDUCTING POLYMERS Purpose The purpose of this Invention is the synthesis of novel polymers that combine semiconducting properties with switchable liquid crystal units bonded onto a conductive polymer backbone. These materials can exhibit externally variable electrical conductivity and optical properties.

Background Conducting polymers have current applications in rechargeable batteries and conductive coatings, and potential ones as electrochromic materials, chemical sensors and non-linear optical elements. Most such polymers have backbones of conjugated carbon - carbon bonds, normally incorporated into aromatic or heteroaromatic repeat units. The simplest of these, such as polythiophene, polyaniline and polypyrrole, can exhibit near-metallic conductivities when strongly doped p-type by chemical or electrochemical oxidation. However, such materials are usually remarkably amorphous, and their structural disorder severely curtails the electronic mobility, and hence the maximum conductivity which may be attained.

Applications requiring good molecular organisation also require the minimisation of such disorder.

For the simplest aromatic polymers, annealing and stretch-alignment confer little benefit because their glass-transition temperatures are impracticably high. Others, such as pofyacetylene and poly(arylene vinylenes), can be prepared via processible precursor polymers and considerable degrees of chain alignment and/or crystallinity have been obtained in these materials by careful control of the drawing and annealing conditions. However, the fact that processing is necessarily accompanied by pyrolysis of the precursors and effusion of by-products, still restricts both the chemical perfection and particularly the degree of structural control that can be reached before the polymers become too glassy to modify further.For the more stable polyheterocyclics such as Pl", chemical imperfections such as cross-links and deviations from 2,5- linkages are present, but may be reduced by control of the polymerisation conditions and blockage of the 3- and 4-positions. Indeed, 3-substitution with nalkyl groups larger than butyl leads to polymers which are melt and solution processible, and which can achieve significant chain alignment and anisotropic electronic properties after extrusion or drawing. Unfortunately, such processing normally results in some chain scission and poor registry between the aligned chains. This disorder, together with that due to partial head-to-head polymerisation, has prevented such polymers from showing much higher electronic mobilities along their chain axes.

Use of the alignment of liquid crystals (LCs) in electric fields to increase the chain alignment of conducting polymers, is not entirely unknown in the art. Acetylene has been polymerised by a Ziegler-Natta catalyst dissolved in an aligned LC matrix; the resulting polymer showed optical anisotropy, and high conductivity when doped with AsF5. Lyotropic liquid crystalline ordering has been observed in heterocyclic conjugated polymers with alkylsulphonate substituents, and some orientation of the polymer backbone was shown in the presence of applied fields.

For the purpose of this Invention, we have evaluated the effects of attaching magnetically switchable side-chain LCs onto a conjugated polymer backbone; this requires the synthesis of suitable derivatised monomers and their carefully-controlled polymerisation into the desired novel conducting polymers.

Such a synthesis has recently been described in the literature, and shown to be feasible for a simple cyanobiphenyl-polythiophene system, although the workers did not seek to obtain regioselective polymerisation, and reported no detailed properties of the polymerised LC monomer.

The Invention described herein is original both with regard to the (polyaniline) backbone to which the mesogenic groups are attached, and to the nature of the mesogens used, which are required in order to induce LC phase transitions well in excess of the glass-transition temperature of the polymer.

The present invention concentrates on systems having the polyaniline backbone because of its exceptional environmental stability, its comparatively high conductivity and its well-known chromic properties. A simple representation of the repeating unit in the intended type of polymer system is shown below, although it should be understood that the polyaniline backbone is shown in its unprotonated and fully-reduced (insulating) state for simplicity; as is well known in the art, the conductivity will be at a maximum when half of the nitrogen atoms are protonated and the structure is half-oxidised (i.e. to a polybenzeneamine-imine or "emeraldine" structure):

where m = r/4, and r is an integer.

The groups R1 to R12 may variously equal either H (a hydrogen atom), an alkyl chain H(CH2)y- (where y = 1 to 25), an alkoxy group or polyether chain (such as CH,O- or CH3O.CH2.CH2O-), or L; where L represents a liquid crystal functionality comprising a mesogenic moiety, one of certain types known in the art (see below), attached to a flexible spacer group such as -(CH2)n- or -O-(CH2)a-O- or -02C-(CH2)n-O- (3 < n < 25).

Not all possible combinations of R will lead to a polymer having LC properties, and for example if RI to R12 are all equal to H, or if Rl to R4 = CH3O- and R5 to R12 = H, the material is a simple polyaniline of a kind known in the prior art.

The following are the principal favourable combinations of substituents leading to liquid crystalline homopolymers within the scope of the present invention: Type A: R1 to R4 = L; R5 to R8 = H or an alkyl or alkoxy group; R9 to R12 = H.

Type B: Rl to R8 = L; R9 to R12 = H Type C: R1 to R8 = H or an alkyl or alkoxy group; R9 to R12 = L Co-polymers in which some of the liquid crystal units L in the above list are replaced by H or an alkyl or alkoxy group may in some cases also be liquid-crystalline. This substitution should preferably be regular, in order to maintain a high degree of order in the material; an example of such a co-polymer related to type A above is given below: Rl and R3 = L; R2, R4 and R5 to R8 = H or an alkyl or alkoxy group; R9 to R12 = H.

There is preferably a maximum of one LC unit per aniline residue in the backbone, its effect on the electronic and optical properties being dependent on the type of mesogen attached. These will preferaHFbe selected on the basis of their high polarisability, to make them susceptible to orientation in electric or magnetic fields. In general, the simplest mesogens used in non-polymeric thermotropic liquid crystals (such as the 4-cyano-1,1'-biphenyl group) are not found to confer LC properties on the polymer ; this is because the glass transition temperature of the polyaniline backbone is higher than the potential LC transition temperature.It is found to be necessary to use more "hightemperature" mesogens such as those based on terphenyl or on three-ring esters, and examples of synthetic methods for polyanilines with such groups in their side-chains are given below. In addition a major factor is the effect of spacer length in determining the influence of the mesogen on the conducting backbone. It is important to attach the mesogen quite closely to the polymer backbone so that when the LC moiety generates its own order, this will be imposed on the polymer chain, which will result in changes in conductivity. If the spacer length is too short a LC.phase may not be generated, but if it is too long, flexing of the spacer when the LC units align may significantly reduce their effect on the polymer backbone and hence on conductivity and optical properties.

Further benefit, for the purpose of this Invention, is to be obtained by incorporating mesogens that contain chiral moieties as pendant groups, these being chosen to induce strong ferroelectric or antiferroelectric ordering.

Some polymers of the kinds defined in this Description will have the advantage of easier processing into an aligned state with freer chargecarrier mobility than conventional conducting polymers. The maximum benefit is obtained if the the polymers are heated above their glass transition temperatures during processing, and a magnetic or electric field is applied; this can induce favourable molecular organisation. The magnetic field should remain applied until the polymers have been cooled below their glass transition temperatures, so that the molecular organisation is "frozen" into the solid polymers.In cases where the glass transition is below ambient temperature, the optical and electrical properties of the polymers may be repeatedly and reversibly "switched" by the application of external magnetic or electric fields at ambient temperature. (Electric fields may only be used when the polymers are not in the metallic state.) This property may be used for example in electrochromic optical displays, or for magnetically-induced electric switching.

An additional advantage is the potential laser-alignment capability of the materials. Laser-induced side-group alignment is a phenomenon which has been well established in side-chain LC polysiloxanes and polyacrylates. A low power (-20 mW) laser focussed onto a thin film of such materials, can produce a planar alignment of the side-groups and confer order on the backbone. A translation of this phenomenon to the polymers described herein, would permit the fabrication of thin conducting tracks within a comparatively insulating, non-aligned bulk material.

Embodiments of the Invention Synthetic Routes: The detailed synthetic examples will be confined to polymers of Type A, as defined above. This is because the corresponding monomers have been found to polymerise relatively easily, and thus polymers of good regularity and high average molecular mass may be obtained by those skilled in the arL Type B monomers may be synthesised by analogous routes, but with poorer yields and less regular structures; the latter fact is particularly damaging to liquid crystalline ordering of the resulting polymers. Type C polymers may be prepared by the direct reaction of LC units whose spacer groups are terminated by bromine atoms with a polyaniline (emeraldine) chain, but the yield and chemical regularity are liable to be poor.

A convenient synthetic approach for Type A, which is used as the basis of the examples cited herein, involves the following stages to produce a polymer based on aniline units with side-chain mesogenic groups:1. The mesogenic group is synthesised (if necessary) and coupled to an alkyl or alkoxy chain, or similar "spacer group", as is common in the synthesis of simple thermotropic liquid crystals. The spacer group must retain a functional moiety such as a terminal bromine atom, to permit its attachment to the polymerisable unit.

2. As aniline molecules are easily oxidised, it is convenient to start by synthesising a substituted nitrobenzene, for example by Williamson etherification of 2-nitrophenol with the bromine atoms of the spacer group.

3. Once a spacer group terminating in a suitable mesogen has been attached to the nitrobenzene in the ortho-position, this is then hydrogenated to yield the corresponding 2-substituted aniline; the latter is often liquid-crystalline in its own right, but is also polymerisable to form a conducting polymer.

4. The 2-substituted aniline monomer is polymerised by oxidation in a Brönsted acid medium to form a side-chain liquid-crystalline polymer with a semiconducting backbone.

The method of hydrogenation adopted depends on the susceptibility of the LC side-group to reduction. It should be emphasised that other synthetic routes are available for these types of compounds. Careful attention must be paid to the regiochemical control of the polymerisation reactions: otherwise the resulting disorder is liable to vitiate the beneficial effects of the mesogen.

[For thiophene monomers, the normal oxidative coupling leads to a large amount of random head-tohead linkage, and hence disorder. For the anilines, this is only a serious problem if the pH is uncontrolled, and is allowed to rise above a value of about 2.0 .] The polymers produced will be in their conductive protonated [emeraldine salt] form.

Firstly, (Scheme 1) a series of Smethoxyphenyl 4- $[x-(2-nitrophenoxy)alkoxy]benzoate molecules [or a-(methoxyphenyl4oxybenwate)-(2-nitrophenoxy)alkanesJ were synthesised, in order to study the influence of the number of methylene units (x) in the bridging group (x = 2-10) on the liquid crystal transition temperatures of the nitro-aromatic precursors. Hydrogenation of some of these molecules to form ortho-substituted aniline compounds was carried out. After polymerisation, no mesogenic properties were revealed, but the effect of a large ortho-substituent on the polymer backbone glass transition temperature (tug) was established. In fact, the Tg decreased slightly as the ortho-group increased.

Syntheses of molecules with higher liquid crystal transition temperatures and with fixed spacer groups (Scheme 2) were therefore devised, in order to form polymers with liquid crystalline properties above their Tg. Polymerisation of the anilines was performed by oxidative chemical polymerisation in a Brönsted acid medium. Typically, this led to a predominantly nara-linked head-to-tail polymer which was partly protonated at the nitrogen atoms (Scheme 3). Introduction of large ortho-substituents on the aniline monomers rendered them insoluble in aqueous acidic media. A method was thus developed, using a surfactant (4-dodecylbenzenesulfonic acid) to disperse a chloroform solution of the monomers in aqueous HCI 1M. This will be described below.

Detailed examples of svnthetic methods are now given. for the Production and polymerisation of 2-substituted anilines in accordance with the Dresent Invention.

[Some physical properties of the intermediates are given, for the assistance of those wishing to reproduce the synthetic processes.] i) 2-(x-Bromoalkoxv)nitrobenzenes (or &alpha;-bromo-#-(2-nitrophenoxy)alkanes} ; compounds [1] - [9] . A mixture of 2-nitrophenol (15.02 g, 108 mmol), anhydrous potassium carbonate (71.59 g, 518 mmol) and the appropriate a,bdibromo-n-aLkane (378 mmol) was heated under reflux in cyclohexanone (150 ml) with constant stirring for 4h. On cooling, the precipitated salts were filtered off and washed with cyclohexanone. The solvent was removed from the combined filtrate and washings by rotary evaporation and the product was purified by vacuum distillation to yield an orange liquid.

ii) Ethyl 4-[x-(2-Nitrophenoxy)alkoxy]benzoates (or a-(4ethvlbenzoate-oxv)-o (2-nifrovbenoxv)alkanes) ; compounds [11] - 119] A mixture of ethyl-$hydroxybenzoate (2.74 g, 16.5 mmol), anhydrous potassium carbonate (10.95 g, 79.2 mmol) and the appropriate 2-(x-bromoalkoxy)nitrobenzene (16.5 mmol) was heated under reflux in cyclohexanone (80 ml) with constant stirring under an atmosphere of nitrogen for 3.5h. On cooling, the precipitated salts were filtered off and washed with cyclohexanone. The solvent was removed from the combined filtrate and washings by rotary evaporation and the brown solid obtained was purified by recrystallisation from methylated spirit to yield an off-white crystalline solid.

iii) 4-Tx-(2-Nitrophenoxv)alkoxylbenzoic acids (or a-(4benzoic acid-oxy)-#- (2-nitrophenoxy)alkanes , compounds [21] - [291 The appropriate ester [11]-[191 (12.9 mmol) was added to potassium hydroxide (2.19 g, 39 mmol) in 80% aqueous ethanol (100 ml) and the mixture was heated under reflux for 3h. The reaction mixture was cooled, diluted with water (100 ml), and acidified with concentrated hydrochloric acid. The precipitate was filtered off, and purified by recrystallisation from methylated spirit to yield a white solid.

All products showed the expected spectroscopic and analytical data, and typical values of the melting points and yields of compounds [1] - [29] are shown in Table 1.

iv) 4Methoxvphenvl Q [x-(2-Nitrophenoxy)alkoxy]benzoates (or oc-(4methoxv phenyl-4-oxybenzoate)-#-(2-nitrophenoxy)alkanes} ; compounds [31] - [39] 4-methoxyphenol (1.38 g, 11.1 mmol) was added to a stirred mixture of the appropriate acid [21]-[29] (11.1 mmol) and trifluoroacetic anhydride (2.73 g, 13 mmol) in dry dichloromethane (120 ml) contained in a flask fitted with a CaCl2 guard tube. The mixture was stirred for 3 days. The solvent was removed by rotary evaporation, and the product was purified by column chromatography on silica gel, eluting with a mixture of toluene: ethyl acetate (3:1). The ester was then recrystallised from methylated spirit to yield a white crystalline solid.

All products showed the expected spectroscopic and analytical data, and typical yields and purities are given for compound [35] (x=6): yield 94% ; purity 99.9 per cent.

v) 4-Bromo-4'-[6-(2-nitrophenoxy)hexoxy]biphenyls {or &alpha;-(4-bromobiphenyl-4'- oxg)-#-(2-nitrophenoxy)hexane} ; compound [40] A mixture of 4-bromo-4'-hydroxybiphenyl (5.01 g, 20.1 mmol), anhydrous potassium carbonate (13.5 g, 97.7 mmol) and 2-(6-bromohexoxy)nitrobenzene (6.15 g, 20.4 mmol) was heated under reflux in cyclohexanone (150 ml) with constant stirring under an atmosphere of nitrogen overnight. On cooling, the precipitated salts were filtered off and washed with cyclohexanone. The solvent was removed from the combined filtrate and washings by rotary evaporation and the product was crystallised from methylated spirit.The solid obtained was purified by column chromatography on silica gel, eluting with a mixture of dichloromethane: petroleum spirit 6e80"C (1:1) and then recrystallised from methylated spirit to yield a white crystalline solid (6.43 g, 68%), purity 99 per cent.

vi) 4-Ethoxyphenylboronic acid ;compound [41] n-Butyllithium (1.6 mol dm-3 in hexane, 31.5 cm 3, 50.4 mmol) was added dropwise to a stirred, cooled (-78 C) solution of 4-bromophenetole (10.05 g, 50 mmol) in dry THF (50 ml) under dry nitrogen. The reaction mixture was maintained under these conditions for 3.5 h and then a previously cooled solution of tri-isopropyl borate (18.75 g, 99.7mmol) in dry THF (50 ml) was added dropwise at -78 C. The reaction was allowed to warm to room temperature overnight and then stirred for 2 h with 10% hydrochloric acid (50 ml). The product was extracted into dichloromethane (3 times), and the combined chlorinated extracts were washed with water and dried (MgSO4).The solvent was removed in vacuo by rotary evaporation and the product was recrystallised from hexane to yield a white crystalline solid (5.07 g, 61%); m.p. 165-167 C.

vii) 4-Cyano-4'-[x-(2-nitrophenoxy)alkoxy]biphenyls {or &alpha;-(4-cyanobiphenyl-4'- oxv)-(nitroyhenoxv)alkanes) ; compounds [50] - [51] A mixture of 4-cyano-4'-hydroxybiphenyl (3.01 g, 15.4 mmol), anhydrous potassium carbonate (10.21 g, 73.9 mmol) and the appropriate 2-(x-bromoalkoxy)nitrobenzene (15.4 mmol) was heated under reflux in cyclohexanone (90 ml) with constant stirring under an atmosphere of nitrogen for 4h. On cooling, the precipitated salts were filtered off and washed with cyclohexanone. The solvent was removed from the combined filtrate and washings by rotary evaporation and the product was crystallised from methylated spirit.The solid obtained was purified by column chromatography on silica gel, eluting with a mixture of toluene:ethyl acetate (3:1) and then recrystallised from methylated spirit to yield a white crystalline solid.

All products showed the expected spectroscopic data and typical yield and purity for compound [51] (x=6) is: yield 89% ; purity 99.9 per cent.

viii) 4-Biphenyl-[6-(2-nitrophenoxy)hexoxy]carboxylic acid {or &alpha;-(4-biphenyl carboxvlic acid-4'-oxv)-o-(2nitrophenoxy)hexure) ; compound [60] 4-cyano-4'-[6-(2-nitrophenoxy)hexoxy]biphenyl (3 g, 7.2 mmol) was added to a mixture of 50% (w/w) aqueous sulfuric acid (30 ml) and glacial acetic acid (75 ml). After heating under gentle reflux for 16hrs, the solution was poured into ice-cooled distilled water (150 ml). The solid was filtered off and washed with water followed by a small amount of icecooled methylated spirit to yield a white solid (2.75 g; 88%), purity 99.9 per cent.

ix) 4-Cyanophenyl-4'-[6-(2-nitrophenoxy)hexoxy]biphenyl-4-carboxylate -{or &alpha;-[(4-cyanophenyl-biphenyl-4-carboxylate)-4'-oxy]-#- (2-nitrophenoxy)hexane} ; compound [70] The 4-hydroxybenzonitrile (0.68 g, 5.74 mmol) was added to a stirred mixture of the carboxylic acid [60] (2.50 g, 5.74 mmol) and trifluoroacetic anhydride (1.90g, 9 mmol) in dry dichloromethane (170 ml) contained in a flask fitted with a CaCl2 guard tube. This mixture was stirred for 5 days. The water was then removed slowly by distillation (Dean and Stark apparatus) over 2 days. The remaining solvent was removed by rotary evaporation, and the residue purified by column chromatography on silica gel, eluting with a mixture of chloroform:ethyl acetate (9:1).

Recrystallisation from methylated spirits yielded a white solid (2.11 g; 69%), purity 99.5 per cent.

x) 4-Methoxyphenyl-4-[6-(2-nitrophenoxy)hexoxy]biphenyl-4'-carboxylate {or &alpha;-[(4-methoxyphenyl-biphenyl-4-carboxylate)-4'-oxy]-#- (Onitronhenoxv)hexanel; compound [80] 4-Methoxyphenol (0.287 g, 2.31 mmol) was added to a stirred mixture of the carboxylic acid [60] (1 g, 2.30 mmol) and trifluoroacetic anhydride (0.89 g, 4.25 mmol) in dry dichloromethane (70 ml) contained in a flask fitted with a CaCl2 guard tube. This mixture was stirred for 5 days. The solvent was removed by rotary evaporation to yield an orangebrown oil which was purified by column chromatography on silica gel, eluting with a mixture of chloroform:ethyl acetate (9:1). Recrystallisation from methylated spirit yielded a white solid (0.423 g; 34%), purity 99.6 per cent.

xi) 4-Ethoxy-4"-[6-(2-nitrophenoxy)hexoxy]terphenyl ; compound [90] A solution of compound [41] (1.38 g, 8.3 mmol) in ethanol (40 cm-3) was added to a stirred mixture of compound [40] (3.01 g, 6.4 mmol) and tetrakis(triphenylphosphine) palladium(0) (0.25 g, 0.21 mmol) in toluene (50 cm-3) and aqueous sodium carbonate (2 mol dm-3 ; 50 cm 3) at room temperature under dry nitrogen. The stirred mixture was heated under reflux for 24 h (i.e. until tlc analysis revealed a complete reaction). The product was extracted into dicholoromethane (twice) and the combined chlorinated extracts were washed with brine and dried (MgSO4). The solvent was removed in vacuo and the residue was purified by column chromatography on silica gel, eluting with toluene followed by chloroform, and then recrystallised from a mixture of toluene:ethyl acetate:methylated spirit (3:2:2) to yield a white crystalline solid (2.70 g, 83%), purity 99.5 per cent.

xii) 4'Cvanobiyhenvl(2-nitronhenoxv)hexoxvl nhenvl-carboxvlate {or &alpha;-[(4'-cyanobiphenyl-phenyl-4-carboxylate)-4-oxy]-#- (2-nitronhenoxv)hexane) ; compound [100] 4-cyano-4'-hydroxybiphenyl (1.625 g, 8.3 mmol) was added to a stirred mixture of the carboxylic acid [25] (3.0 g, 8.3 mmol) and trifluoroacetic anhydride (8.18 g, 38.9 mmol) in dry dichloromethane (250ml) contained in a flask fitted with a CaCl2 guard tube. This mixture was stirred for 1 day. The solvent was removed by rotary evaporation, and the residue purified by column chromatography on silica gel, eluting with chloroform. Recrystallisation from methylated spirit yielded a white solid (4.16 g; 93%), purity 99.5 per cent.

xiii) Hedrosenation: The required nitro-compound was dissolved in a minimum quantity of the appropriate solvent (dimethylformamide (DMF) for compounds [70], [80] & [90]; ethanol for all others) in a glass-lined autoclave;and a catalytic amount of 16% palladium on charcoal was added. This was subjected to a moderate pressure of hydrogen (10-20 bar) at the appropriate temperature (40 C for DMF; 95 C for ethanol) with constant agitation during the required time (24 h for DMF; 3-5 h for ethanol). On cooling, the catalyst was filtered off and the solvent was removed by rotary evaporation to yield the appropriate aniline. The compounds were purified by recrystallisation from methylated spirit to give one spot by tlc.They were polymerised immediately in order to avoid the generation of impurities arising from reaction with atmospheric dioxygen.

Yields averaging 80-90% were obtained with ethanol as solvent, and 60% with DMF.

xiv) Emulsion Polymerisation of Aniline Monomers: The monomers were dissolved in the required solvent (chloroform or acetone). The solution was emulsified with an equal volume of a mixture of 10% aqueous surfactant (dodecylbenzenesulfonic acid 1M) and 90% HCI (1M). A few mg of iron (II) chloride tetrahydrate were added, and the resulting mixture was cooled and stirred during the addition of a solution of ammonium persulfate (1 equiv.) in 5-10 ml of HCl (1M). This was stirred continuously for at least 24 h after the appearance of a dark precipitate of polymer. This mixture was then poured into water (200 ml) to deactivate the surfactant. The precipitate was filtered off and washed with HCI (1M) to yield a black solid which was dried in a vacuum oven.

Yields averaging 90% were obtained.

Pronerties of the Liquid Crvstalline Materials Synthesised as Described Above: A) Monomers: Transition temneratures A series of 4-methoxyphenyl-4-[x-(2-nitrophenoxy)alkoxy]benzoates was synthesised (see Scheme 1), in order to study the influence of the spacer length (x=2 to 10) on their liquid crystal behaviour.

The mesomorphic properties of these compounds were investigated by hot-stage optical polarizing microscopy and differential scanning calorimetry. The resulting liquid crystal transition temperatures are shown in Table 2.

The series shows a strong odd-even effect. With the exception of the pentyl homologue, the melting points exhibit a regular alternation on increasing x, the even-numbered spacers causing the higher values. The nematic-isotropic (N- > I) transition temperatures show a dramatic odd-even effect of varying chain length. The molecules with even spacers were liquid crystalline (Schlieren and homeotropic textures of the monotropic nematic phase), whereas the odd members were not.

Hydrogenation of some of these molecules resulted in similar liquid crystal behaviour to their nitro analogues, with a similar range of transition temperatures. These are not quoted here, since oxidation of the aniline group occurred easily when the amines were warmed, making the transition temperatures variable and unreliable.

The substituted polyanilines initially prepared exhibited no mesogenic properties, apparently because the backbone Tg was higher than the expected liquid crystal transition temperatures. The preparation of molecules with higher mesogenic transition temperatures (Scheme 2) was therefore undertaken, and data for the relevant nitro-compounds are shown in Table 3. The spacer length in these materials (x=6) was chosen on the basis of the work on compounds [31] - [39], in the hope of conferring a convenient liquid crystalline range on the subsequent polymers.

Compound [51] exhibits Schlieren and homeotropic textures of a monotropic nematic phase.

Compound [60] shows the Schlieren texture of a nematic phase as well as a focal-conic fan texture of the Sc phase and an arced-fan texture of an as-yet unidentified Sl phase. Compounds [70], [80] and [100] exhibit a homeotropic texture of the nematic phase, and compound [80] a homeotropic texture of the smectic A phase in addition to two possible higher order phases. Molecule [90] exhibits reversible phases under DSC but microscopic investigation revealed rigid phases (K1 to K3) which could be crystalline or very high order smectic phases.

These nitro compounds were hydrogenated to generate the aniline monomers which showed similar behaviour to their nitro analogues, with a similar range of transition temperatures.

B) Polymers: The polymers formed as described above were insoluble in the most common organic solvents. They were soluble only in a limited range of polar aprotic solvents such as DMF and DMSO (dimethyl sulfoxide). Hence, processing of the polyanilines from solution was not very convenient, as these solvents did not easily evaporate.

The molecular weights of the polyanilines have been investigated by gel permeation chromatography in DMF. Some samples ranging from poly(2-methoxyaniline) to poly(2-pentoxyaniline) were used for comparison purposes. Gel permeation chromatography clearly showed that the side-chain polymers had a wide range of molecular weights, [from oligomers (r = 2 to 15) to higher polymers, a smaller proportion having a very large number of repeat units]. The resulting fairly low average molecular weights are believed to be due to the polymers readily precipitating out of solution as the chain length increases. Study of these oligomers under polarized light on the hot-stage microscope, and by DSC, revealed evidence of liquid crystalline behaviour in two polymer systems prepared from the nitro compounds number [60] and [70]. In both cases, a Schlieren texture was observed, which flashed when subjected to mechanical stress, providing evidence of liquid crystalline behaviour. These polymers had to be annealed for about one hour on the hot-stage before the liquid crystal textures developed fully. The glass transition temperatures Tg and the clearing temperatures of these polymers were determined by DSC. In the case of the carboxylic acid T,, was equal to 139"C and the nematic to isotropic transition temperature was 225"C, and for the 3 ring ester, the Tg was equal to 105"C and the nematic to isotropic transition was at 133-140"C. The liquid crystalline textures exhibited by the polymers remained when they were cooled below Tg.

Preliminary 2-electrode measurements on pressed powder pellet samples showed an increase in electronic conductivity for the carboxylic acid polymer with increasing temperature (at 20 C a = 10 Siemens per metre, and at 220 C o = 10 3 Sm-1), but the high liquid crystal transition temperatures of these molecules resulted in the loss of HCl protonation above 1300C. In the case of the esterfunctionalised polymer, the room temperature conductivity of the partly protonated, as-prepared material was 10-3 Sm~l.

The conductivities of the polymers may be increased by their exposure to strong magnetic or electric fields above their glass transition temperatures, the fields being maintained until the polymers have been cooled to temperatures at least 50 C below Tg. After this processing, it is generally necessary to re-protonate the polymers (for example by exposure of thin polymer films to 1 atmosphere of HCI gas for several hours) in order to return them to their most highly conductive state.

x Compounds [1] - [9] Compounds 111] -[19] Compounds [21]-[29] b.p.( C) / yield m.p.( C) / yield m.p.( C) / yield 2 145-150/0.3mmHg 100.5-102.5 206.0-208.0 56% 69% 89% 3 104-109/0.05mmHg 81.8-82.1 178.7-179.9 57% 76% 93% 4 152-157/0.2mmHg 78.9-80.1 180.2-182.4 66% 89% 93% 5 155-165!0.25mmHg 62.5-63.7 150.0-152.0 76% 63% 84% 6 152-155/0.1mmHg 90.0-91.0 165.0-167.0 63% 88% 94% 7 180-185/0.35mmHg 64.1-64.6 111.1-112.5 69% 81% 90% 8 195-205/0.3mmHg 56.4-56.5 148.0-149.0 77% 83% 93% 9 180-187/0.15mmHg 49.5-50.7 106.0-108.0 71% 60% 91% 10 202-206/0.2mmHg 44.746.0 129.0-131.0 69% 77% 90% TABLE 1 : Data for compounds [1]-[9], [11]-[19] and [21]-[29].

x TCI/ C TNI/ C TIC/ C TNC/ C #HCIkJmol-1 2 119.4 62 60 43 3 104 < -35 44 4 108.9 58.4 46 42 5 107.2 < -60 51.2 6 88.3 56.5 35 48.5 7 77.5 36.1 52.9 8 82.2 55.8 46.2 45.6 9 64.5 38.9 44 10 68.5 54.2 < -40 55 TABLE 2 : Liquid crystal data for the 4-methoxylphenyl 4-[x-(2-nitrophenoxy)alkoxy] benzoates.

C-I/N# Sc#-N S1-Sc# I/N#-C Compounds N-I C-S# SA#-N S1-SA# S1-C*/S2** 40 94.5 - - - 82.4 50 115.5 - - - 85.9 51 95.3 55.3 60 157.3t 227.3 214.0≈ 175.7≈ 146.0** 70 136.0t 190.1 - 65.0t 80 134.6# 181.4 115.21 72.51 36.8* 100 125# 199.8 - - 66.3# Compound [90]: (K1, K2, K3 are crystalline phases or high-order smectic LC phases).

C- > K1 K1- > K2 K2- > K3 K3- > I 133.7 C 147.1 C 179 C 223.5 C

I- > K3 K3- > K2 K2- > K1 222.0 C 177.3 C 143.1 C TABLE 3 : The transition temperatures ( C) of compounds [40], [50], [51], [60], [70], [80], [90] and [100].

Claims (9)

1. Conjugated polymers, oligomers and co-polymers having repeating units based on aniline monomers, some or all of which are substituted by one or more spacer groups terminated by mesogenic moieties.

2. The preparation of materials in accordance with claim 1, via the synthesis of suitably substituted nitrobenzenes and subsequent reduction to the aniline monomers, followed by oxidative polymerisation in a Bronsted acid medium.

3. Materials in accordance with claim 1, possessing liquid crystalline self-organisation and properties.

4. Materials in accordance with claims 1 and 3, which are processed by exploiting the effects of applied electric or magnetic fields on their molecular organisation.

5. The use of materials in accordance with claims 1 and 3, in switchable electronic or optical devices which exploit the reversible electronic effects of applied electric or magnetic fields on their molecular organisation.

6. Materials in accordance with claims 1 and 3, which are processed by exploiting the effects of focused laser radiation on their molecular organisation.

7. Materials in accordance with any of the above claims, synthesised substantially as shown in Schemes 1 or 2 of the invention.

8. Materials in accordance with any of the above claims, which possess semiconductive or highly conductive electronic properties when doped by chemical oxidation, reduction and/or protonation.

9. Materials in accordance with claim 8, in which the electronic conductivity is enhanced by the application of external electric or magnetic fields or by the use of laser radiation.