LIQUID-CRYSTALLINE POLYMER MATERIAL

Abstract: The invention relates to an organic polymer having a fixed polar structure which is characterized in that it consists of a densely cross-linked polymerization product of monomers, for which monomers it holds that a) at least a part of the monomers exhibit a tilted smectic phase, b) at least a part of the monomers have one or more chiral centres, c) at least a part of the monomers are provided with one or more electron-donating and/or electron-accepting groups so that a polar axis exists transversely to the longitudinal direction of the monomers, and d) the monomers are provided with polymerizable groups, intended for cross-linking and chosen among acrylate, methacrylate, styrene or other polymerizable groups intended for cross-linking. The invention also concerns a process for producing the polymeric material and use thereof in optical components.

Description: Liquid-crystalline polymer material The present invention relates to a material in the form of a polymer having a chiral tilted smectic structure which can be used, for example, for optical components on printed-circuit boards. State of the art A series of application areas exist where solid organic materials having non-linear optical (NLO) properties can be included to fulfil various functions. The most important area is in optical communication, and it is this area, in particular, which is forcing the pace of research on NLO materials. Many demands are made on the materials for ensuring that they are of practical use. The ideal material should primarily have the following properties. Large non-linear response - Small optical losses Short response time Thermal stability up to 250°C Good mechanical properties High optical damage threshold - Chemical stability Ability to be shaped into thin films Processability While it has proved difficult to manufacture a material which meets all these requirements, certain properties become more important than others depending on the specific applications which may be under consideration. The electronics industry demands components which operate in the wavelength range of 600-1550 nm so that they are suitable for fibre optics. The components should withstand temperatures from -40 to 200°C, and they should be stable for at least 10 years. According to the American military standard, the components should withstand continuous use at 125°C. The main reason why organic materials have attracted increasing interest in the non-linear optics field in recent years has been because of their structures, which can afford non-linear optical coefficients at the molecular level (molecular hyperpolariz- ability) which far exceed the coefficients of the inorganic crystals, such as, for example, LiNb0 3 , which are commercially available today. It is the combination of an aligned structure and a strong dipole which provides the nonlinear optical effects. The processability of the polymers, and their good mechanical properties, have, in turn, increased the interest in these materials still further. For a material to exhibit optical non-linearity of the socalled second order, it must be non-centrosymmetric, which implies that it is macroscopically oriented in a polar manner, at least in the sense that the polarizability does not exhibit mirror symmetry. Obtaining a high degree of polar orientation in organic materials is a major problem. Attempts to achieve polar alignment have been made by orienting different types of organic or polymeric materials in electric fields. This has resulted either in materials which have been poorly oriented or in materials in which the dipoles have relaxed with time. Hitherto, the mechanical and thermal stability of polymeric liquid- crystalline materials has been well below the desired performance characteristics. Consequently, the liquid-crystalline polymer materials which have hitherto been proposed have been poled electrets, i.e. materials which are non-polar per se and which exhibit a certain degree °f artificial, thermo.dynamically unstable, polar alignment. WO 92/20058 describes surface-stabilized ferro- electric liquid crystals which are used to obtain a monomer whose polymerization in sufficiently thin layers (approximately 2 μm) between electrode-coated glass plates can be reversed in an electri field. These monomers suffer from the disadvantage that they depend on the glass plates, with their surface conditioning, and on the electric field, for maintenance of the polar alignment. It is thus desirable to produce a polymer material which exhibits permanent polar alignment and nonlinear optic effects, and which is mechanically and thermally stable, without being dependent upon the glass plates or the electric field, and where the layer can be made to be thicker than 2 μm. Such a material has a great potential for producing cheap optical components for the electronics industry. Applications can be to control light on optical printed-circuit boards, to control the refractive index with electric fields, to control the wavelength of light, etc. See J. Lindstrόm, (1991) Icke-linjara optiska material (Non-linear optical materials), FOA Report C 20843-2.4, ISSN 0347- 3694 with regard to non-linear optics and second order effects. Object of the present invention The object of the present invention is to supply a novel type of polymer material which permanently exhibits non-linear optical activity, and to supply a process for producing this material. This material is to be mechanically and thermally stable over wide temperature ranges and easy to machine and handle. Summary of the invention It has now been found, surprisingly, that this object can be achieved with an organic polymer having a fixed polar structure, which is characterized in that it consists of a densely cross-linked polymerization product of monomers, for which monomers it holds that a) at least a part of the starting monomers exhibit a tilted smectic phase, b) at least a part of the starting monomers have one or more chiral centres, c) at least a part of the starting monomers are provided with one or more electron-donating and/or electron- accepting groups so that an electric dipole moment or a non-nύrror-symmetrical polarizability exists transversely to the longitudinal direction of the monomers, and d) the monomers are provided with polymerizable groups which are intended for cross-linking and which are in the form of acrylate, methacrylate, styrene or other polymerizable groups which are intended for cross-linking, with these polymerizable groups intended for cross-linking being present in the monomers at one or both ends of the monomers, and at both ends of the monomers in at least some of the starting monomers, with the cross- linked monomers being fixed, in the polymer, in their position and direction with regard to the electron-donating and/or electron-accepting groups, i.e. the polar axis, so that the polymer is macroscopically aligned in a polar manner and forms a thermally and mechanically stable material having non-linear optical properties, which material is easy to shape and machine for manufacturing components. Manufacturing this polymer is a delicate procedure. One requirement is that the surface conditions must be very strictly controlled if the tilted smectic phase is to become a perfect monocrystal. The polymerization must be extremely well controlled and must not be allowed to affect the optically active parts of the molecule. The phase prop¬ erties must not be destroyed by the polymerization. It is important that the cross-linking is complete in order to ensure the stability of the macroscopic polar alignment. As a result of all this, manufacture of the polymer material according to the invention is far from being trivial. A preferred embodiment of the invention is an organic polymer having a fixed polar alignment which is characterized in that the monomers exhibit a structure selected from among the following: A) compounds of the formula I, in which Rι-Rι can be H, Z, OZ, OH, F or Cl, where Z is methyl or ethyl; k, 1, p, q and r are 0 or 1; Q and T are CO, C0 2 , OCO, COS, SCO, CH 2 0, OCH 2 , N=CH, CH=N, CH 2 - CH 2 , CH=CH, C≡C N=N or NON; with X being an electron donor, electron acceptor or hydrogen, and Y being an electron donor or hydrogen if X is an electron acceptor or hydrogen, and Y being an electron acceptor or hydrogen if X is an electron donor or hydrogen; A and D are identical or different and are OR', SR', NRTt", COOR', OCOR', COSR', SCOR', NR'COR" or NCOR'COR", where R* and/or R" represent a straight or branched alkyl chain having 5-12 carbon atoms, i.e. primary, secondary or tertiary pentyl hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl, which can be chiral or non chiral, with or without the said polymerizable group at the end, and completely, partially or not at all perfluorinated, with it being possible to replace methylene groups in the chain with oxygen atoms or ester units, with it being possible in those cases where chirality is present, the chiral centres can be substituted by Z, F, Cl, OH, OZ, NH 2 , NZ 2 or CF 3 with Z being defined as above, where R' can be H if R" is as above, and R" can be H if R' is as above, with, if chirality is present, D being chiral, B) compounds of the formula I, but in which one or more of the aromatic rings contains one or more heteroatoms selected from among N, O, S and B, C) compounds of the formula I, but in which one or more of the aromatic rings is/are replaced with 5- or 7-membered heteroaromatic rings, with the heteroatoms being selected from among N, O, S and B, D) compounds of the formula I, but in which one or more of the aromatic rings is/are replaced with cycloaliphatic rings having 5-7 carbon atoms in the ring, and E) compounds of the formula I, but in which one or more of the aromatic rings is/are replaced with 5-, 6- or 7-membered aliphatic heterocyclic rings having N, O, S or B in the ring. Another embodiment of the invention is an organic polymer having a fixed polar structure which is characterized in that it includes a monomer which is in tilted smectic phase and which has, at both ends, polymerizable groups intended for cross- linking, together with a monomer which has a polymerizable group at one end, and which has one or more chiral centres, with at least one of the monomers being provided with one or more electron-donating and/or electron-accepting groups. Still another embodiment of the invention is an organic polymer having a fixed polar structure which is characterized in that only one type of monomer which fulfils points a)-d) is included in the polymer. It is particularly preferable for the electron-donating and/or electron- accepting groups to be attached to the monomer which has one or more chiral centres. The invention also relates to a process for producing an organic polymer having a fixed polar structure, wherein the monomers in the tilted smectic phase are aligned in a polar order by an external electrical field, and subsequently cross-linked at the selected polymerizable groups by photopolymerization to fix the polar alignment permanently. The invention also relates to the use of the polymer material in optical components. Definitions A smectic liquid-crystalline phase is understood to mean a liquid-crystalline phase having a layered structure. In certain smectic phases, the longitudinal axis of the molecules which are aligned in parallel forms an angle with the normal of the layer, the so-called tilt angle. This angle should be as large as possible in order to achieve the best non-linear optical properties of the material. A pyroelectric material is understood to mean a material which has a macroscopic polar order, which material consequently exhibits a permanent macroscopic polarization different from zero in its thermodynamic equilibrium state. The electric polarization of the material is a function of temperature. A ferroelectric material is understood to mean a material which has a macroscopic polar order and whose polarization can be reversed using an external electric field, when the external electric field reverses direction. A special case of such a material where the molecular polarization alternates from layer to layer, together with the tilt angle of the molecules having opposite direction in two adjacent layers in the absence of an external field, is called antiferroelectric material. Antiferroelectric materials thus form a subclass of ferroelectric materials. Antiferroelectric and ferroelectric liquid crystals can both be made to change the molecular orientation and thus the direction of polarisation according to the direction of an applied external electrical field, while for pyroelectric liquid crystals the orientation is fixed. Both pyroelectric, ferroelectric and antiferroelectric liquid crystals belong to the family of tilted smectic liquid crystals, which among themselves display several different variants. With regard to ferroelectric, antiferroelectric and pyroelectric materials, see also Rόmpp Chemie Lexikon, ninth edition, pages 1331 and 3702, respectively. This literature citation is hereby incorporated by reference. Molecular hyperpolarizability is understood to mean a molecular parameter which appears in a material composed of molecules having non-linear optical properties. See also WO 92/20058. A strong hyperpolarizability implies a capacity for strong polari- zation, which can be achieved by the monomers being provided with electron-donating and/or electron-accepting groups. An electron-donating or, respectively, an electron-accepting group is a group which has the capacity to donate electron density or, respectively, positive charge density to, preferably, an aromatic ring. Dense cross-linking is understood to mean a high degree of cross-linking. The expression "at least a part of for describing the monomers is understood to mean a sufficient quantity for achieving the property which is sought by means of adding that particular monomer. The expression is also understood to mean a part of one and the same monomer. All the sought-after proper-ties can be present in a single monomer. That the polymer material according to the invention is macroscopically polar means that the material as a whole has a polar axis, i.e. that either a polarization is present which is different from zero or the polarizability is different in two opposite directions, i.e. that the polarizability does not exhibit mirror symmetry. This implies that the material is helix-free and that the polarization is uniform with regard to direction and size. Furthermore, the polarization is permanent and does not alter time. That the polymer material according to the invention is processable means that it can be machined and shaped for manufacturing components. Optical components are, according to the invention, understood to mean, in particular, components which are intended to be used on printed-circuit boards, in optical communication, for telecommunication, for optoelectronics, for controlling the refractive index using an electric field, for producing frequency doubling, for controlling and guiding optical waves, for regulating the colour of light, for acting as a circuit breaker, and the like. Short description of the figures So that the present invention can be readily understood and implemented, it will be described in more detail below with reference to the attached figures, of which: - Fig. 1 shows the reactions for synthesizing a bifunctional monomer according to Example 1 below, Fig. 2 shows the reactions for synthesizing a monofunctional chiral monomer having an electron-accepting group according to Example 3, Fig. 3 shows a phase diagram for different mixtures of the monomers ϋ according to Example 1 and K) according to Example 3, in which i denotes isotropic phase, sA*, sC* and sE*, respectively, denote chiral smectic A phase, C phase and E phase, respectively, and c denotes crystalline phase, Fig. 4 shows how LI/I depends on the angle of rotation a and the external electrical field which is applied to the polymer material. The monomers and their preparation The polymer material according to the invention places a number of specific demands on the monomer system employed, i.e. the mixture of monomers. The system must be chiral and have a tilted smectic phase (in order to make the system ferroelectric) so that it can be aligned in a polar manner, be cross-linkable so that a stabilized material can be formed, and at the same time be designed for non-linear optics, i.e. be hyperpolarizable. While all these properties are desirable, they are difficult to achieve in one monomer. For this reason, the system is designed as a mixture of two or more monomers, with a copolymer being obtained on polymerization. However, it is theoretically possible to meet all the demands using one and the same monomer. A substantial amount of synthesis work, with regard to finding suitable electron-donating and/or electron-accepting groups which are compatible with a monomer in tilted smectic phase and which also permit cross-linking, has been required in order to produce monomers which meet these demands. If one of the miscible monomers has one or more chiral centres and the other exhibits a tilted smectic phase, the resulting mixture then acquires a chiral tilted smectic phase. It is also possible to conceive of having four monomers which fulfil the four requirements individually. It is easier to work with mixtures of monomers. It is possible to conceive of all combinations of the four requirements, apart from the fact that the chiral monomer should be provided with one or more electron-donating and/or electron- accepting groups in order to achieve the best result. A great advantage of using organic materials in accordance with the invention is provided by the possibilities of modifying the molecular structure. The flexibility of the molecular structure makes it possible to maximize the properties which are of interest. The properties of the different monomers are selected on the basis of those properties which it is desired to reinforce in the final polymer. For example, three of the properties can be introduced into one monomer, and four or five other monomers can then be added in order to obtain a strong fourth property. It is also possible to conceive of up to 20 or 30 monomers in the mixture. For example, a chiral tilted smectic phase may be desired which exists over a wider temperature range. If each individual monomer has a chiral tilted smectic phase which exists over a fairly narrow temperature range, a mixture which has a phase over a wider range can be obtained if many different monomers are mixed together. The temperature interval over which the tilted smectic phase exists should be at least approximately 10°C. See Figure 3. It will be evident to the person skilled in the art that other liquid-crystalline phases having titled molecules with respect to the layers can be used in place of smectic C, i.e. smectic F, smectic I, smectic G, smectic H, smectic J, smectic K, or combinations of these phases, and with the C phase. These phases differ from each other as a result of the molecular packing within the smectic layers differing. The smectic C phase is that which is most used due to the fact that it has the lowest viscosity and is the easiest to predict before carrying out the synthesis. The monomer syntheses for the purpose of the invention are unique. However, it is possible to conceive of a large number of molecular elements which can be combined so as to meet the four demands which are placed on the monomers: that they exhibit a tilted smectic phase, are chiral, are polar and are cross-linkable, with the different elements being responsible for one or more properties. Consequently, the choice of monomer is not crucial as long as the four demands are met. All known and conceivable monomers and monomeric elements can be used. In order to increase the hyperpolarizability, the monomers can be provided with electron-donating and/or electron-accepting groups. The aim is to have as strong dipole as possible, for example -N0 2 in combination with -NH 2 . Examples of electron- donating groups are -CN, -N0 2 , -S0 2 R, -CH(CN) 2 and -CHO and examples of electron- donating groups which can be used are -OH, -SH, -NH 2 , -NR 2 , -OR or -SR, with R representing an alkyl, aryl, alkylaryl or arylalkyl group or a fluorinated variant of any one of these. It is conceivable and desirable to have polarizing groups on all the monomers in the mixture. The more and the better groups, the better are the non-linear properties. However, each change in the structure of the monomers can result in that the correct liquid-crystalline phase not will be obtained. Monomers which have a polymerizable group intended for cross-linking in the form of an acrylate, meth-acrylate, styrene or other suitable polymerizable group intended for cross-linking, at one end or at both ends of the monomers, are here termed mono-functional and bifunctional monomers, respectively. In polymerized form, the monofunctional monomers will have a free end while bifunctional monomers are polymerized at both ends and therefor act as cross-linkers. The crosslinks may also connect the molecules in such a way that the hyperpolarizable groups will be extended over several monomers transversely or longitudinally. The following are examples of monomer combinations which should be possible to use in accordance with the invention: . ° ? with chirality being indicated by a dot under the formula The aim of the monomer synthesis was first to produce bifunctional liquid- crystalline compounds exhibiting the sc phase. The intention of the bifimctionality of the monomers is to provide the possibility of cross-linking of the material and thermally stabilize the structure. In the second place, the aim was to produce chiral liquid- crystalline monomers which behave in a ferroelectric manner when they are mixed with the first-mentioned type of monomer. Two examples of monomer syntheses in accordance with the invention are given in Examples 1 and 3 below. In Example 1, two cross-linkable compounds were prepared which exhibited a smectic C phase and which differed from each other in that one possessed acrylate groups and the other methacrylate groups as polymerizable groups: In Example 3, two chiral monomers were prepared which were provided with a dipole group. They differed from each other in that the polymerizable group was an acrylate group in the one case and a methacrylate group in the other: These examples are only illustrative and are not limiting as regards the choice and combinations of groups in the monomers or the process for synthesizing the monomers. The underlined numerals relate to the compounds in Figures 1 and 2, in which the reaction series are reproduced schematically. In the synthesis of the monomers, and in the poly-merization, the following chemicals are used: 4'-hydroxy-4-biphenylcarboxylic acid (J_), 8-bromo-l-octene, 11- bromo-1-undecene, 3,4-dihydro-2H-pyran, dicyclohexylcarbodiimide (DCC), 4- dimethylaminopyridine (DMAP), 9-borabicyclo[3.3.1]nonane (9-BBN) (0.5M in THF, i.e. tetrahydrofuran), hydrogen peroxide (35% by weight in water), triethylamine, acryloyl chloride, meth-acryloyl chloride, 4,4'-dihydroxybiphenyl (97%), bromoundecanol, p-toluenesulphonic acid (p-TSA), 4-hydroxy-3-nitrobenzoic acid (98%), (S)-(+)-2-octanol (99%), diethylazodicarboxylate (DEAD), triphenylphosphine (TPP), dioxane and dimethylformamide (DMF) purchased from Aldrich. Hydroquinone (4) was purchased from BDH Chemicals Ltd. 2,4,6-Trimethylbenzoyldiphenylphosphine oxide (Lucirin™), which was purchased from BASF, was used as a photo-initiator. All the substances were used without further purification. The compounds were chemically characterized by means of 1H NMR on a 250 MHz Bruker, and, if necessary, by means of FTIR on a Perkin-Elmer 1760X. The purity was measured by means of HPLC, Varian. All the literature citations which are referred to in this description are hereby incorporated in their entirety by reference. Example 1 Two monomers according to the invention were prepared in steps 1 -9 as described below, see Figure 1. 1. Preparation of ethyl 4-(4-hydroxy)phenylbenzoate (2) Compound 1 (5.27 g, 24.60 mmol) was dissolved in a solution of 17 ml of ethanol (99.5% by volume) and 10 ml of benzene. Sulphuric acid was added in catalytic quantity and the mixture was refluxed at 100°C for 24 hours. The reaction mixture was poured into water and the whole was extracted three times with dichloromethane. The organic phase was separated off and washed three times with water, dried using magnesium sulphate and evaporated. The yellow-white powder was dissolved in trichloromethane, where unreacted compound i precipitated. The trichloromethane solution was filtered and evaporated, resulting in a white crystalline powder. Yield: 4.79 g (89%). Η NMR (CDC1 3 ): L=1.42 (t, 3H, -CH.-CH,. 4.40 (q, 2H, -CH 7 CHA 6.95 (d,2H, 3'-H and 5 * -H), 7.53 (d, 2H, 2'-H and 6'-H), 7.61 (d, 2H, 2-H and 6-H), 8.10(d,2H,3-H and 5-H). 2. Preparation of 4'-( 11 -undecenyloxy)-4-biphenylcarboxylic acid (3) Compound 2 (6.0 g, 24.77 mmol) was dissolved in 30 ml of ethanol. Potassium hydroxide (85% by weight) (1.88 g, 28.41 mmol), dissolved in 10 ml of ethanol, was then added dropwise to the solution. This turned the solution yellow, with the colour being due to the phenolate ion which had been formed. Potassium iodide (1.08 g, 6.44 mmol) and 11-bromo-l-undecene (5.76 g, 24.77 mmol) were added. The solution was decolorized during 24 hours of boiling to reflux. Potassium hydroxide (4.90 g, 74.31 mmol) was then added in order to effect alkaline hydrolysis of the ester. The potassium salt which formed precipitated and was filtered from the solution. In order to form the carboxylic acid, the salt was dissolved in a mixture of 30 ml of acetic acid and 30 ml of ethanol and the whole was stirred at 120°C for one hour. The final product, a white crystalline powder, pre-cipitated when the solution was cooled, and was filtered off. The reaction was monitored by FTIR, with the carbonyl peak of the salt at 1628 cm "1 shifting to 1669 cm "1 for the acid. Yield: 6.00 g (66%) of 3. Η NMR (CDC1 3 ): L=1.34 (m,12H, -OCH 2 CH 2 (CH2) 6 -), 1.80 (p, 2H, -OCH,CH 7 - , 2.05 (q, 2H, CHK-HCH ), 4.01 (t,2H, -OCHj-), 4.93 (d, IH, CH 2 =CH-cis), 4.98 (d.lH.CH 7 =CH- trans), 5.79 (m,lH,CH 2 =CH-), 6.98(d,2H,3'-H and 5'-H), 7.55 (d, 2H, 2'-H and 6'-H), 7.65 (d, 2H, 2-H and 6-H), 8.11 (d, 2H, 3-H and 5-H). 3. Preparation of 4-(2-tetrahydropyranyloxy)phenol (5) Compound 4 (15.0 g, 136.23 mmol) was dissolved in diethyl ether, together with a catalytic quantity of p-TSA, at room temperature. 3,4-Dihydro-2H-pyτan was added dropwise and the solution was stirred at room temperature for one hour. A mixture of ethanol and ammonia (1/1) (volume/volume) was added until the solution became alkaline. The reaction mixture was poured into water and the whole was extracted three times with dichloromethane. The organic phase was separated off and washed three times with water, dried with magnesium sulphate and evaporated. The product was purified by column chromatography (silica gel, hexane EtOAc as eluent), which gave a white crystalline powder. Yield: 7.40 g (56%). 1H NMR (CDCL 3 ): L=1.65 (m, 4H, 1.87 (m 2H, -CH?CH- ,3.62(m, IH, -CHjOCHO-), 3.94 (m, IH, -CH^OCHO-), 4.64 (s, IH, HOAr-), 5.27(t, IH, -CH-), 6.73(d, 2H, 2-H and 6-H), 6.95 (d, 2H, 3-H and 5-H). 4. Preparation of 4-(2-tetrahydropyτanyloxy)-l-(l 1- undecenyloxy)benzene (6) Compound 5 (5.0 g, 25.74 mmol) and potassium carbonate (10.67 g, 77.22 mmol) were dissolved in DMF and the solution was then stirred at room temperature for one hour. 8-Bromo-l-octene (4.92 g, 25.74 mmol) or 11-bromo-l -undecene (6.00 g, 25.74 mmol) was added at room temperature. The temperature was raised to 100°C and the solution was stirred for 24 hours. The DMF was then removed by distillation under vacuum (30°C, 10 mm Hg). The reaction mixture was poured into water and the whole was extracted three times with dichloromethane. The organic phase was separated off an washed three times with water, dried using magnesium sulphate and evaporated. The product was purified by column chromatography (silica gel, hexane/EtOAc as eluent). The final product 6 was in the form of white crystals. Yield: 5.60 g (65%) for 6. l H NMR (CDC1 3 ): L=1.30 (m, 4H+12H, -CH 7 CH 7 CH 7 OCHO- + CH 2 =CHCH 2 -(CH 2 ) 6 -), 1.66 (m, 2H, CH 2 CHOO-), 1.86 (m, 2H, OCH 7 CH 7 -). 2.07 (m, 2H, CH2=CHCH 2 -), 3.60 (m, IH, -CH ? OCHO-), 3.91 (t, 2H, -OCH,(CH 7 W), 3.94 (m, IH, -CH 2 0CHO-), 4.94 (d, IH, CH 7 =CH-, cis), 5.00 (d, IH, CH 7 =CH-, trans), 5.28 (t, IH, -OCHO-), 5.81 (m, IH, CH 2 =CH-), 6.81 (d, 2H, 2-H and 6-H), 6.98 (d, 2H, 3-H and 5-H). 5. Preparation of 4-(l l-undecenyloxy)phenol (7) Compound 6 (5.60 g, 16.74 mmol) was dissolved in 20 ml of ethanol at room temperature. Hydrochloric acid was added in catalytic quantity at room temperature while stirring the solution thoroughly. The solution was stirred for one hour and was then poured into water and the whole was extracted three times with dichloromethane. The organic phase was separated off and washed three times with water, dried using magnesium sulphate and evaporated. The remaining product consisted of white crystals. Yield: 4.23 g (90%) for 7. Η NMR (CDC1 3 ): L=1.28 (m, 12H, CHr=CHCH,(CH,)Λ 1.74 (p, 2H, OCHjCϋr), 2.04 (q, 2H, CH2=CHCH 2 -), 3.80 (t, 2H, -OCH 7 CH 7 -), 4.92 (d, IH, CH,=CH-. cis), 4.98 (d, IH, CH,=CH-. trans), 5.50 (m, IH, CH 2 =CH-), 6.76 (s, 4H, 2-H, 3-H, 5-H and 6-H). 6. Preparation of 4-( 11 -undecenyloxy)phenyl 4-(4-( 11 -un- decenyloxy)phenyl)benzoate (8) Compound 3 (0.50 g, 1.36 mmol), compound 7 (0.48 g, 1.36 mmol), DCC (0.37 g, 1.77 mmol) and DMAP (0.025 g, 0.20 mmol) were dissolved in 15 ml of dichloromethane and the solution refluxed for 24 hours. The reaction mixture was then cooled to -5°C for 30 minutes in a freezer. The carb-amide which had formed from DCC and unreacted compound 3 were precipitated and filtered off from the solution. The solvent was evaporated off and the resulting solid was recrystallized twice from ethanol in order to give white crystals. Yield: 0.69 g (85%). Thermal characterization is shown in Table 1. Η NMR (CDC1 3 ):L=1.31 (m, 24H, CH 2 =CHCH 2 (CH 2 ) 6 -, 1.79 (m, 4H, -OCH ? CH,-), 2.05 (m, 4H,CH2=CHCU 2 -), 3.95 (t, 2H, -ArArOCH,CH,- . 4.01 (t, 2H, -ArOCH,CH,-). 4.93 (d, 2H, CH 2 =CH-, cis), 5.00 (d, 2H, CH,=CH-. trans), 5.82 (m, 2H, CH 2 =CH-), 6.94 (d, 2H, 3"-H and 5"-H), 7.01 (d, 2H, 3Η and 5'-H), 7.12 (d, 2H, 2"-H and 6"-H), 7.59 (d, 2H, 2'-H and 6'-H), 7.69 (d, 2H, 3-H and 5-H), 8.23 (d, 2H, 2-H and 6-H). 7. Preparation of 4-( 11 -hydroxyundecyloxy)phenyl 4-(4-( 11 - hydroxyundecyloxy)phenyl)benzoate (9) All the glass equipment was dried overnight in an oven at 150°C in order to avoid destroying the hygroscopic 9-borabicyclo[3.3.1]nonane (9-BBN). Compound 8 (1.00 g, 1.67 mmol) was added to a 100 ml flask, which was flushed with argon for 30 minutes 40 ml dry. THF was added through a septum and the solution was stirred at room temperature for 30 minutes in the argon atmosphere. 9-BBN (0.5 M in THF) (10 ml, 5 mmol) was then added through a septum and the solution was stirred at room temperature for a further 20 hours in the argon atmosphere. 10 ml of ethanol were added and oxidation was carried out by adding hydrogen peroxide (35% by volume) (3 ml, 30 mmol). The solution was stirred for one hour and then poured into water. White crystals were precipitated and filtered off from the solution. Yield: 1.05 g (99%). Thermal characterization is presented in Table 1. The product was not soluble in deuterated chloroform, acetone or DMSO; as a consequence, there was no Η NMR charac- terization. FTIR (KBr): 3334 cm "1 (O-H stretching); 2928-2851 cm "1 (aliphatic C-H stretching); 1744 cm '1 (C=0 stretching); 1618 cm "1 (aromatic C=C stretching); 1517 cm "1 (aromatic carbon-to-carbonyl carbon stretching); 1299-1217 cm "1 (several C-0 stretching frequencies). 8. Preparation of 4-( 11 -acryloy loxyundecyloxy )pheny 1 4-(4-(l l-acryloyloxyundecyloxy)phenyl)benzoate (\0) Compound 9 (0.50 g, 0.79 mmol) was dissolved in 40 ml of THF at 60°C and the solution was stirred for one hour. Triet-hylamine (0.24 g, 2.37 mmol) was added. Acryloyl chloride (0.22 g, 2.05 mmol), dissolved in 10 ml of THF, was then slowly added dropwise while stirring the solution thoroughly. The chloride salt of triethylamine precipitated over 20 hours at 60°C while the reaction mixture was being stirred. The reaction mixture was poured into water (10% by weight ammonium chloride) and the whole was extracted three times with dichloromethane. The organic phase was separated off and washed three times with water, dried using magnesium sulphate and evaporated. The pro-duct was purified by column chromatography (silica gel, he-xane EtOAc as eluent). The solvent was evaporated off and the resulting solid substance was recrystallized twice from ethanol in order to afford white crystals. Yield: 0.30 g (50%). Purity (HPLC) 99%. Thermal characterization is shown in Table 1. Η NMR (CDC1 3 ): L = 1.32 (m, 28H, CH 2 =CHCH 2 (CH 2 ) 7 -), 1.66 (m, 4H, -COOCH 7 CH 7 -), 1.80 (m, 4H, - ArOCHzCHjr), 3.95 (t, 2H, -ArArOCH,CH,-). 4.01 (t, 2H, -ArOCH 7 CH 7 -), 4.16 (t, 4H, -COOCHA 5.82 (d, 2H, CH?=CH-. cis), 6.11 (m, 2H, CH 2 -CH-), 6.40 (d, 2H, CH 7 =CH-, trans), 6.93 (d, 2H, 3"-H and 5"-H), 7.00 (d, 2H, 3'-H and 5'-H), 7.13 (d, 2H, 2"-H and 6"-H), 7.59 (d, 2H, 2'-H and 6'-H), 7.64 (d, 2H, 3-H and 5-H), 8.22 (d, 2H, 2-H and 6-H). 9. Preparation of 4-(l l -methacryloyloxyundecyloxy)phenyl 4-(4-(l l-methacryloyloxyundecyloxy)phenyl)benzoate (11) Compound 9 (0.54 g, 0.85 mmol) was dissolved in 40 ml of THF at 60°C and the solution was stirred for one hour. Tri-ethylamine (0.34 g, 3.40 mmol) was added. Acryloyl chloride (0.23 g, 2.55 mmol), dissolved in 10 ml of THF, was then added slowly dropwise while stirring the solution thoroughly. The chloride salt of triethylamine precipitated out over 20 hours at 60°C while the reaction mixture was stirred. The reaction mix-ture was poured into water (10% by weight ammonium chloride) and the whole was extracted three times with dichloromethane. The organic phase was separated off and washed three times with water, dried using magnesium sulphate and evaporated. The product was purified by column chromatography (silica gel, hexane-ZEtOAc as eluent). The solvent was evaporated off and the re-sulting solid substance was recrystallized twice from ethanol in order to yield white crystals. Yield: 0.30 g (48%). It was not possible to measure the purity by HPLC since the compound was not soluble in acetonitrile. Thermal characterization is pre-sented in Table 1. ! H NMR (CDC1 3 ): L = 1.30 (m, 28H, CH 7 =CHCH 7 (CH ? ) 7 - , 1.65 (m, 4H, -COOCH 2 CHr), 1.77 (m, 4H, -ArOCH 7 CH 7 - , 1.93 (s, 6H, (CH 7 =CCH 3 QO-K 3.95 (t, 2H, -ArArOCH^CH ), 4.01 (t, 2H, -ArOCH ? CH 7 - , 4.12 (t, 4H, -COOCH,- - 5.51 (s, 2H CU 2 =CH-, cis), 6.08 (s, 2H, CHr=CH-, trans), 6.93 (d, 2H, 3"-H and 5"-H), 7.00 (d, 2H, 3'-H and 5'-H), 7.13 (d, 2H, 2"-H and 6"-H), 7.59 (d, 2H, 2'-H and 6'-H), 7.64 (d, 2H, 3-H and 5-H), 8.22 (d, 2H, 2-H and 6-H). Example 2 Compounds in Example 1 were subjected to thermal cha-racterization on a Perlάn-Elmer DSC-7 using a heating cooling speed of 10°C/min. DSC denotes differen- tial scanning calo-rimetry. Hot-stage microscopy using polarized light (Leitz Ortholux POL BKII equipped with a Mettlel FP82 Hot Stage and an FP80 central processor) was employed for the thermal and mor-phological characterizations. Patterns from small-angl X-ray scattering (SAXS) of the different liquid-crystalline phases were registered with a Statton camera, which was equipped with a resistive oven, using Cu KI radiation from a Philips PW 1830 generator. Table 1. Liquid-crystalline phases and phase transitions for compounds 8 and 9-11 from Example 1 , according to optical microscopy, DSC 1 and SAXS measurements. Compound Phase transitions (0C) during heating. cooling: 8 c84S B 117S c 160S A 181i il76S A 154S c 112S B 72c 9 c86S E 143S c 160S A 170i il65 A 160S c 127S E 70c 1t c42S E 89S c 118S A 128i i25S A 1 15S c 81S E 58c ui c84S E 90S c 123S A 130i il27S A 122S c 74S E 53c 1. The data refer to the second heating and the first cooling 2. c: cystalline; S E : smectic E; Sβ." smectic B; S c : smectic C; S A : smectic A; i: isotropic 3. Compounds mixed with inhibitor (hydroquinone) (0.1 % by weight) in order to prevent spontaneous thermal polymerization The Sc phases in Table 1 are in a thermodynamically stable state since they occur both during heating and cooling. Example 3 A further two monomers according to the invention were prepared in steps 1 -9 described below. See Figure 2. 1. Preparation of 4-hydroxy-4'-(2-tetrahydropyranyloxy)biphenyl (1) Dihydropyran ( 1.82 g, 21.7 mmol) was added dropwise to a mixture of 4,4'-dihydroxybiphenyl (7.92 g, 43.0 mmol) and p-TSA (0.34 g, 1.7 mmol) in dioxane (50 ml) and THF (10 ml) at room temperature. The reaction mixture was stirred for 15 minutes. The reaction was then stopped by adding an EtOH/NH 3 mixture (1/1 volume/volume) until the solution was somewhat alkaline. It was then diluted with dichloromethane (100 ml) and mixed with an aqueous solution of NaHC0 3 (15% by weight). The precipitate was filtered off and washed once with dichloromethane. The filtrates were collected and the organic phase was filtered off. The aqueous phase was extracted once again with dichloromethane. All the organic solvents were collected, dried using magnesium sulphate and evaporated. The remaining solid substance was purified by column chromatography (silica gel, hexane/EtOAc as eluent), giving white crystals. Yield: 2.67 g (48%), Η NMR (CDC1 3 ): L = 1.65 (m, 4H, 1.87 (m, 2H, -CH 2 CH-), 3.62 (m, IH, -QLOCHO-), 3.94 (m, IH, -CH^OCHO-), 5.21 (s, IH, HOAr-), 5.47 (t, IH, -CH-), 6.85 (d, 2H, 3-H and 5-H), 7.10 (d, 2H, 3'-H and 5'-H), 7.42 (m, 4H, 2-H, 6-H, 2'-H and 6'-H). 2. Preparation of 4-( 11 -hydroxyundecyloxy)-4 , -(2-tetrahydropyranyloxy)biphenyl (2) Compound I (2.80 g, 10.3 mmol), potassium hydroxide (0.70 g, 14.4 mmol) and ethanol (40 ml) were mixed and stirred at 60°C for one hour before 1 1-bromo-l-undecanol (2.86 g, 11.4 mmol) was added. The mixture was boiled at reflux for 16 hours and then poured into water. The aqueous phase was extrac-ted three times with dichloromethane and the organic layer was then dried using magnesium sulphate an evaporated. The result-ing solid substance was recrystallized from hexane/EtOAc (95/5) (volume/volume) in order to give white crystals. Yield: 3.65 g (80%), Η NMR (CDC1 3 ); L = 1.31 (m, 14H, -(CH 2 ) 7 CH 2 CH 2 OH), 1.54-1.68 (m, 6H, CH ? CH 7 CH 7 OCHO- and -CH 2 CH 2 OH), 1.80-1.90 (m, 4H, -CH ? CH- and -CHjCHzOAr), 3.62 (m, 3H, -CH^OCHO- and -CH 2 CU 2 0H), 3.94 (m, 3H, -CHjOCHO- and -CH ? CH,OArl 5.47 (t, IH, -CH-), 6.96 (d, 2H, 3-H and 5-H), 7.10 (d, 2H, 3'-H and 5'-H), 7.46 (m, 4H, 2-H, 6-H, 2'-H and 6'-H). 3. Preparation of 4- [( 11 -acryloyloxy)undecyloxy ]-4'-(2- tetrahydropyranyloxy)biphenyl (3) and 4-[(l l-methacryloyloxy)undecyloxy]-4'-(2- tetrahydropyranyloxy)biphenyl (4) Acryloyl chloride or methacryloyl chloride was dis-solved in dry THF (10 ml) and this solution was added dropwise to a stirred solution of compound 2 (4.08 g, 9.25 mmol) and triethylamine (1.40 g, 13.88 mmol) in dry THF (25 ml) at 0°C. After six hours, the reaction mixture was poured into a 15% by weight solution of ammonium chloride and the whole was extracted three times with dichloromethane. The organic phases were col-lected, dried using magnesium sulphate and evaporated. The re-maining solid substance was purified by column chromatography (silica gel, hexane/EtOAc as eluent), giving white crystals. Yield: 2.74 g (58%), Η NMR (CDC1 3 ): L = 1.31 (m, 14H, and -CH 2 CH 2 OCO-), 1.80-1.90 (m, 4H, -CH?CH- and CI^CH^Ar), 3.62 (m, IH, -CH 2 0CHO-), 3.94 (m, 3H, -CH -OCHO- and -CH 2 CH 2 OAr), 4.15 (t, 2H, CH 7 CH 7 OCO- ), 5.47 (t, IH, -CH-), 5.84 (d, IH, CH^CH-, cis), 6.14 (d, IH, CH 2 =CH-), 6.37 (d, IH, CH 2 =CH-, trans), 6.96 (d, 2H, 3-H and 5-H), 7.10 (d, 2H, 3'-H and 5'-H), 7.46 (m, 4H, 2-H, 6-H, 2'-H and 6'-H). 4. Preparation of 4-hydroxy-4'-[(l 1 -acryloyloxy)undecyloxy]biphenyl (5) and 4- hy droxy-4'- [( 11 -methacryloyloxy)undecyloxy]biphenyl (6) Compound 3 or 4 (2.74 g, 5.37 mmol) was dissolved in a mixture of ethanol (25 ml) and THF (5 ml) at room temperature. Hydrochloric acid (5 ml) was added and the solution became milky and then clear after a while. After 1 hour, the reaction was stopped and the reaction mixture was poured into water. The mixture was extracted three times with dichloromethane. The or-ganic layers were then collected, dried using magnesium sulphate and evaporated in order to give white crystals after recrys-tallization from ethanol. Yield: 1.42 g (63%), Η NMR (CDC1 3 ): L = 1.31 (m, 14H, -(CH^C^OCO-), 1.63 (m, 2H, -CHjCHsOCO-), 1.78 (m, 2H, -CH 2 CH 2 OAr), 3.98 (m, 2H, -CH ? CH 7 OAr), 4.15 (t, 2H, CH 7 CH 7 OCO-). 4.78 (2, IH, HOAr-), 5.84 (d, IH, CH^CH, cis), 6.14 (d, IH, CH 2 =CH-), 6.37 (d, IH, CH CH-, trans), 6.89 (d, 2H, 3-H and 5-H), 6.96 (d, 2H, 3'-H and 5'-H), 7.46 (m, 4H, 2-H, 6-H, 2'-H and 6'-H). 5. Preparation of ethyl 4-hydroxy-3-nitrobenzoate (7) 4-Hydroxy-3-nitrobenzoic acid (10.0 g, 54.6 mmol), sulphuric acid (1 ml), ethanol (>99%), (15.1 ml, 327.9 mmol) and benzene (10 ml) were added to a single- necked 100 ml round-bottomed flask which was fitted with a benzene-filled Dean-Stark trap and a condenser. The temperature was raised to 105°C and the reaction mixture was stirred for 24 hours. The solvents were then evaporated off and the crude product was dissolved in dichloromethane (200 ml), which solution was extracted twice with an aqueous solution of NaHC0 3 (15% by weight) and twice with water. The organic phase was separated off, dried using magnesium sulphate and evaporated. Pale yellow crystals were obtained. Yield: 10.6 g (92%), Η NMR (CDC1 3 ): L = 1.40 (t, 3H, CH 3 ), 4.40 (q, 2H, -CH 2 CH 3 ), 7.21 (m, IH, 5-H), 8.23 (d, IH, 6-H), 8.81 (s, IH, 2-H), 10.17 (s, IH, -OH). 6. Preparation of ethyl 4-[(R)-(+)-2-octyloxy]-3-nitrobenzoate (8) A mixture of (S)-(+)-2-octanol (3.00 g, 20.8 mmol) and DEAD (3.50 g, 20.8 mmol), dissolved in diethyl ether (10 ml), was added dropwise to a solution of compound 7 (4.40 g, 20.8 mmol) and TPP (5.40 g, 20.8 mmol), and the whole was stirred at room temperature for three days. The precipitated triphenylphosphine oxide was filtered off and the solvent was evaporated off. The resulting, untreated, product was purified by column chromatography (silica gel, hexane/EtOAc as eluent), giving a yellow oil. Yield: 5.93 g (85%), 1H NMR (CDC1 3 ): L = 0.87 (m, 3H, 1.27 (m, 8H, -(CH 2 ) 4 CH 3 ), 1.40 (t, 6H, -CHCH 3 and -OCH 2 CH 3 ), 1.67 (m, IH, -CHCH 2 -), 1.81 (m, IH, -CHCH 2 -), 4.38 (q, 2H, -OCHjCH-,), 4.60 (m, IH, -CH-), 7.09 (m, IH, 5-H), 8.15 (d, IH, 6-H), 8.43 (s, IH, 2-H). 7. Preparation of 4-[(R)-(+)-2-octyloxy]-3-nitrobenzoic acid (9) Compound 8 (1.20 g, 3.72 mmol) and potassium hydroxide (0.62 g, 11.2 mmol) were mixed in ethanol (30 ml) and this reaction mixture was stirred at 50°C for three hours. It was then acidified with hydrochloric acid and poured into water. The reaction mixture was then extracted three times with dichloro-methane. The organic phases were collected and washed twice with water, dried using magnesium sulphate and evaporated to afford a yellow oil which solidified when it was allowed to stand. Yield: 1.02 g (93%), Η NMR (CDC1 3 ): L = 0.87 (m, 3H, -(CH 2 ) 5 CH 3 ), 1.27 (m, 8H, -(CH 2 ) 4 CH 3 ), 1.40 (d, 3H, -CHCH 3 ), 1.67 (m, IH, -CHCH 2 -), 1.81 (m, IH, -CHCH 2 -), 4.62 (m, IH, -CH-), 7.11 (m, IH, 5-H), 8.21 (d, IH, 6-H), 8.50 (s, IH, 2-H). 8. Preparation of 4"-[(l l-acryloyloxy)undecyloxy]-4'-biphenyl 4-[(R)-(+)-2- octyloxy]-3-nitrobenzoate Q0) Compound 5 (1.25 g, 3.03 mmol), compound 9 (0.89, 3.03 mmol), DCC (0.81 g, 3.94 mmol) and DMAP (55 mg, 0.46 mmol) were dissolved in dichloromethane (15 ml) and the solution was stirred at room temperature for two days. The reaction mixture was then diluted with dichloromethane (100 ml) and extracted three times with water, dried using magnesium sulphate and evaporated. The product was purified by column chromatography (silica gel, hexane/EtOAc as eluent), which give white crystals after recrystallization from ethanol/hexane (90/10) (volume/volume). Yield: 1.56 g (75%), thermal characterization: c56S A 62i, i61S A l lc, Η NMR (CDC1 3 ): L = 0.87 (m, 3H, -(CH 2 ) 5 CH 3 ), 1.31 (m, 22H, -(CH 2 ) 7 CH 2 CH 2 OCO- and -(CH^CHa), 1.40 (d, 3H, CHCH 3 ), 1.63 (m, 3H, -CHjCHsOCO- and -CHCH 2 -), 1.78 (m, 3H, -CH^C^OAr and -CHCH 2 -), 3.98 (m, 2H, -CH 7 CH ? OAr). 4.15 (t, 2H, -CH ? CH ? OCO-), 4.62 (m, IH, -CH-), 5.84 (d, IH, Cϋ €H-, cis), 6.14 (d, IH, CH 2 =CH-), 6.37 (d, IH, CH^CH-, trans), 6.99 (d, 2H, 3"-H and 5"-H), 7.17 (m, IH, 5-H), 7.26 (d, 2H, 3'-H and 5'-H), 7.49 (d, 2H, 2"-H, 6"-H), 7.58 (d, 2H, 2'-H and 6'-H), 8.30 (d, IH, 6-H), 8.50 (s, IH, 2-H). 9. Preparation of 4"-[(l l-methacryloyloxy)undecyloxy]-4'-biphenyl 4-[(R)-(+)-2- octyloxy]-3-nitrobenzoate (11) Compound 6 (1.42 g, 3.35 mmol), compound 9 (0.99 g, 3.35 mmol), DCC (0.91 g, 4.41 mmol) and DMAP (60 mg, 0.51 mmol) were dissolved in dichloromethane (15 ml) and the solution was stirred at room temperature for two days. The reaction mixture was then diluted with dichloromethane (100 ml) and the whole was extracted three times with water, dried using magnesium sulphate and evaporated. The product was purified by column chromato-graphy (silica gel, hexane/EtOAc as eluent), which afforded white crystals after recrystallization from ethanol hexane (90/10). Yield: 1.78 g (75%), thermal characterization: c43S A 60i, i57S A 17c, Η NMR (CDC1 3 ): L = 0.87 (m, 3H, -(CH sCHj), 1.31 (m, 22H, -(CH 2 ) 7 CH 2 CH 2 OCO- and -(CH 2 ) 4 CH 3 ), 1.40 (d, 3H, -CHCH 3 ), 1.63 (m, 3H, -CH^CH^CO- and -CHCH 2 -), 1.78 ( , 3H, -CH 2 H 2 OAT and -CHCH 2 -), 1.94 (s, 3H, 3.98 (m, 2H, -CH,CH,OAr). 4.15 (t, 2H, -CH 7 CH 7 OCO-.. 4.62 (m, IH, -CH-), 5.54 (s, IH, CH 2 =CCH 3 -, cis), 6.09 (s, IH, CH 2 =CCH 3 -, trans), 6.99 (d, 2H, 3"-H and 5"-H), 7.17 ( IH, 5-H), 7.26 (d, 2H, 3'-H and 5'-H), 7.49 (d, 2H, 2"-H, 6"-H), 7.58 (d, 2H, 2'-H and 6'-H), 8.30 (d, IH, 6-H), 8.50 (s, IH, 2-H). Example 4 A polymer according to the invention was prepared from the monomers from Examples 1 and 3 in the following manner. 70 mole% of the bifunctional monomer ϋ from Example 1 and 30 mole% of monomer JO from Example 3, together with 1 part of initiator to 250 parts of monom mixture calculated on the number of mole, were mixed. The mixture was first heated to iso-tropization and then cooled to smectic A* phase. Cells were produced from two glass plates having electrodes of indium tin oxide (ITO) coated with a 1000 A layer of SiO. The inner side of the glass plates was covered with a aligning layer of spun-on and longitudinally brushed polyimide, which orientes the liquid-crystal molecules along the glass surface. The cell, having a distance of 2 μm between the plates and the d mensions of approximately 1x2 cm, was supplied with the monomer mixture by means of capillary filling at a temperature corresponding t smectic A* phase. Isotropic phase can also be used. The aligning layer ensured that a book-shelf structure in smectic A* phase was automatically obtained, which structure w then retained after transition to smectic C* phase. With the aid of an electric field, which was generated between the electrodes on the glass plates, using 15-30 V (typically 20 V) DC the spontaneous polarization was rendered uniform in smectic C* phase, in the direction of the field and in the whole sample, because the transverse polarization of the monomers is rotated into the same direction. When the original C material possesses helical alignment, the latter will be straightened out in the electric field and the material will remain permanently helix-free after the polymerization. A ferroelectric monodomain is achieved in this manner. Due to the fact that the optic axis in such an aligned sample possesses a unique direction parallel to the cell surfaces, the degree of orientation can be monitored in a pola-rization microscope since total extinction is obtained when the optic axis is parallel or perpendicular to the polarizer. It is also possible to orient the sample by means of shearing in smectic A* phase prior to illumination with UV light. The electric field was maintained and, once good orientation of the monomer mixture had been achieved, the cell was illuminated with UV light from an OSRAM Ultra- Vitalux lamp, for instance during 20 minutes with a 300 W lamp, as a result of which the polar alignment was fixed permanently by means of photo-induced poly-merization of the structure. Consequently, the alignment remains after the voltage has been switched off and it is not possible, either, to reverse the orientation in the material by reversing the field. It is also not possible, after the polymerization, to see any phase transitions when the temperature is raised or lo-wered (20-150°C). Thus, the uniform book-shelf structure was locked in place by the polymerization. The direction of the macroscopic polar alignment of the sample, i.e. the resultant direction in which the electron-accepting groups of the monomers were pointing, was perpendi-cular to the plane of the film. In-situ photopolymerization of liquid-crystalline acrylates and diacrylates has been described by D.J. Broer et al, Macromol. Che . 1988, 189, 185; 1989, 190, 19 and 2255. The photopolymerization allows the mesophase of the monomer prior to polymerization to be selected appropriately, since the temperature can be chosen at will. Another great ad-vantage is that tailor-made components can be produced using a light mask which screens off the UV light during photo-lithography of the monomer mixture such that the polymerized area assumes a certain desired form. Other polymerization pro¬ cedures can also be used provided that the polymerization can be carried out at a temperature at which an appropriate mesophase exists. The layer can also be made to be thicker than 2 μm, for example 5 μm, which is an important advance in relation to previously known materials. Example 5 The properties of the novel polymer material from Example 4 were investigated with regard to liquid-crystalline phases, thermal stability and processability, as follows. Studies of thermal decomposition were carried out on a Perkin-Elmer TGA7. Dichroic infrared measurements, when in vesti -gating the thermal stability of aligned samples, were carried out on an FTIR Perkin-Elmer 1760X. Dichroic denotes exhibiting dichroism. Polymer networks of the S A *, S c * and S E * types were formed by both polyp 0) and poly(ϋ), depending on the poly-merization temperature. The structures of the liquid-crystal-line-like polymer networks of poly(lθ) were confirmed by X-ray investigations. The thermal stability of the alignment was investi-gated by infrared dichroism in accordance with the procedure of F. Sahlen et al., Polymer, in press 1996. The dichroic ratio was calculated and the normalized dichroic ratio was plotted against the temperature. It was observed that the alignment de-creased somewhat with increasing temperature but was restored again completely on cooling. The final thermal stability of the polymer network was approximately 360°C; the polymer decomposes above this tempe-rature. The electronics industry requires that, for soldering onto printed-circuit boards, the material which is employed should withstand at least 250°C; previously known non-linear optical materials do not meet this criterion. The polymeric film which is formed is a thermoset plastic which is one single network exhibiting dense cross-linking. Components can potentially be mass- produced from the po-lymer which has been prepared. They can be manufactured both as machinable thin films and as bulk material. An alternative to machining is to use a light mask to screen off the UV light du-ring photolithography of the monomer mixture so that the poly-merized area assumes a certain desired form. Example 6 The Pockels effect was measured in order to determine the non-linear optical properties of the material. The Pockels effect, or the linear electrooptical effect, signifies that the refractive index is altered by the influence of an applied external electri- cal field. The procedure using crossed polari-zers was used. The method and the apparatus are described in the article by C.P.J.M. van der Vorst and C. J.M. van Weerdenburg, Nonlinear Optical Properties of Organic Materials III, 1990, SPIE Vol. 1337, 246-257. The apparatus principally consisted of the following components. A 10 mW, 632.8 nm HeNe laser (Melles Griot) was used to generate a laser beam which was passed through a polarizing prism which was rotated 45° to the left, seen from the laser. After that, the polarized laser beam was passed through the sample at an angle ω, the so-called angle of rotation, with 90° corresponding to the laser beam impinging perpendicularly to the surface of the sample. The sample was located between the same glass plates which were used during the polymerization in Example 4. The beam was then passed through a Soleil-Babinet compensator (wavelength range 250-3500 nm, phase retardation 0-2S±l% at 546 nm and 0-lS±0.5% at 1000 nm) and after that through a polarizing prism which was rotated 45° to the right, seen from the laser. The polarizing prisms had an extinction of <10 "5 (Melles Griot). After this polarizing prism, the intensity I of the beam was measured with a detector having a Si photo-diode (Melles Griot). In front of the detector, a filter was located which transmitted 632.8 nm, FWHM 3±0.6 nm (Melles Griot). In addition, a function generator (Stanford Research Systems DS 355) and a lock-in amplifier (Stanford Research Systems SR 850 DSP) were used. An electrical field was applied perpendicularly straight across the sample. The voltage which generates the field was a direct-current voltage having an overlaid alternating voltage whose amplitude was less than the direct-current voltage. Figure 4 shows a graph in which δl/I is plotted against the angle of rotation ω for different strengths of the electric field which is applied over the material. δl/I is given as a normalized value, i.e. the highest value is set at 1 and remaining values are calculated relative to this value. At its highest, the absolute value of the signal was approximately 10 "5 . It is evident from the graph that δl/I is proportional to the strength of the electric field and that δl/I varies with the angle of rotation. This is explained by the external electric field modulating the refractive index of the material, as a result of which the intensity I is modulated due to the non-linear optical properties of the material. Figure 4 consequently demonstrates that a non-linear response can be obtained in accordance with the invention. The material has been stable as regards the measured values shown in Figure 4 for more than two months, i.e. up until today. The measured results showed that the material from Example 4 exhibited non-linear optical activity.

Claims: Claims 1. Polar organic polymer having a tilted liquid-crystalline structure, characterized in that it consists of a densely cross-linked polymerization product of monomers, for which monomers it holds that a) at least a part of the monomers exhibit a tilted smectic phase, b) at least a part of the monomers have one or more non- racemicchiral centres, c) at least a part of the monomers are provided with one or more electron-donating and/or electron-accepting groups so that a polar axis exists transversely to the longitudinal direction of the monomers, and d) the monomers are provided with polymerizable groups which are intended for cross-linking and which are in the form of acrylate, methacrylate, styrene or other polymerizable groups which are intended for cross-linking, with these polymerizable groups which are intended for cross-linking being present in the monomers at one or both ends of the monomers, and at both ends of the monomers in at least some of the monomers, with the cross-linked monomers being fixed, in the polymer, in their position and direction with regard to the electron-donating and/or electron-accepting groups, i.e. the polar axis, so that the polymer is macroscopically aligned in a polar manner and forms a thermally and mechanically stable material having non-linear optical properties. 2. Polar organic polymer having a tilted liquid-crystalline structure according to Claim 1 , characterized in that the monomers exhibit a structure selected from among the following: A) compounds of the formula I, in which R Rι 4 can be H, Z, OZ, OH, F or Cl, where Z is methyl or ethyl; k, 1, p, q and r are 0 or 1 ; Q and T are CO, C0 2 , OCO, COS, SCO, CH 2 0, OCH 2 , N=CH, CH=N, CH=CH, C≡C, N=N or NON; with X being an electron donor, electron acceptor or hydrogen, and Y being an electron donor or hydrogen if X is an electron acceptor or hydrogen, and Y being an electron acceptor or hydrogen if X is an electron donor or hydrogen; A and D are identical or different and are OR', SR', NR'R", COOR', OCOR', COSR', SCOR*, NR'COR" or NCOR'COR", where R' and/or R" represent a straight or branched alkyl chain having 5-12 carbon atoms, i.e. primary, secondary or tertiary penty hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl, which can be chiral or non-achira with or without the said polymerizable group at the end, and completely, partially or not at all perfluorinated, with it being possible to replace methylene groups in the chain with oxygen atoms or ester units, with it being possible, in those cases where chirality is present, for the chiral centres to be substituted by Z, F, Cl, OH, OZ, NH 2 , NZ 2 or CF 3 , with Z being defined as above, where R' can be H if R" is as above, and R" can be H if is as above, with, if chirality is present, D being chiral, B) compounds of the formula I, but in which one or more of the aromatic rings contains one or more heteroatoms selected from among N, O, S and B, C) compounds of the formula I, but in which one or more of the aromatic rings is/are replaced with 5- or 7-membered hetero-aromatic rjngs, with the heteroatoms being selected from among N, O, S and B, D) compounds of the formula I, but in which one or more of the aromatic rings is/are replaced with cycloaliphatic rings having 5-7 carbon atoms in the ring, and E) compounds of the formula I, but in which one or more of the aromatic rings is/are replaced with 5-, 6- or 7-membered ali-phatic heterocyclic rings having N, O, S or B in the ring. 3. Polar organic polymer having a tilted liquid-crystalline structure accordin to Claim 1 or 2, characterized in that it includes a monomer which is in a tilted smectic phase and which has, at both ends, polymerizable groups intended for cross-linking, together with a monomer which has a polymerizable group at one end, one or more chir centres and one or more electron-donating and or electron-accepting groups. 4. Polar organic polymer having a tilted liquid-crystalline structure according to any one of the preceding claims, characterized in that the polymer includes only one type of monomer which fulfils points a)-d). 5. Polar organic polymer having a tilted liquid-crystalline structure according to Claim 3, characterized in that the cross-linkable monomer is also provided with one or more electron-donating and/or electron-accepting groups. 6. Polar organic polymer having a tilted liquid-crystalline structure according to any one of the preceding claims, characterized in that the electron-donating and or electron-accepting groups are attached to the monomer which has one or more chiral centres. 7. Process for producing a polar organic polymer having a tilted liquid- crystalline structure, characterized in that monomers, for which monomers it holds that a) at least a part of the monomers exhibit a tilted smectic phase, b) at least a part of the monomers have one or more chiral centres, c) at least a part of the monomers are provided with one or more electron-donating and/or electron-accepting groups so that a polar axis exists transversely to the longitudinal direction of the monomers, and d) the monomers are provided with polymerizable groups which are intended for cross-linking and which are in the form of acrylate, methacrylate, styrene or other polymerizable groups which are intended for cross-linking, with these polymerizable groups which are intended for cross-linking being present in the monomers at one or both ends of the monomers, and at both ends of the monomers in at least some of the monomers, which exhibit a tilted smectic phase are aligned in a polar order by an external electric field, and subsequently crosslinked at the selected polymerizable groups by photopolymerization to fix the polar alignment permanently. 8. Use of a polar organic polymer having a tilted liquid-crystalline structure, characterized in that the polymeric mate-rial is produced by means of monomers, for which monomers it holds that a) at least a part of the monomers exhibit a tilted smectic phase, b) at least a part of the monomers have one or more chiral centres, c) at least a part of the monomers are provided with one or more electron-donating and or electron- accepting groups so that a polar axis exists transversely to the longitudinal direction of the monomers, and d) the monomers are provided with polymerizable groups which are intended for cross-linking and which are in the form of acrylate, methacrylate, styrene or other polymerizable groups which are intended for cross-linking, with these polymerizable groups which are inten-ded for cross-linking being present in the monomers at one or both ends of the monomers, and at both ends of the monomers in at least some of the monomers, which exhibit a tilted smectic phase when mixed, being orientated in an external electric field, so that a macroscopic polar alignment is produced by means of the transverse polar axes of the monomers being rotated in the same direction, after which crosslinking of the monomers which have been aligned in this way is brought about by photopo-lymerization, and the polar alignment is fixed permanently in this manner.

Inventors: HERMANN DAVID, HULT BO ANDERS, KOMITOV LACHEZAR, LAGERWALL SVEN TORBJOERN, RUDQUIST PER, SAHLEN CARL FREDRIK, STEBLER BENGT, TROLLSAAS OLOF MIKAEL, HERMANN, DAVID, HULT, BO, ANDERS, KOMITOV, LACHEZAR, LAGERWALL, SVEN, TORBJOERN, RUDQUIST, PER, SAHLEN, CARL, FREDRIK, STEBLER, BENGT, TROLLSAAS, OLOF, MIKAEL
Applicants: HERMANN DAVID, HULT BO ANDERS, KOMITOV LACHEZAR, LAGERWALL SVEN TORBJOERN, RUDQUIST PER, SAHLEN CARL FREDRIK, STEBLER BENGT, TROLLSAAS OLOF MIKAEL, HERMANN, DAVID, HULT, BO, ANDERS, KOMITOV, LACHEZAR, LAGERWALL, SVEN, TORBJOERN, RUDQUIST, PER, SAHLEN, CARL, FREDRIK, STEBLER, BENGT, TROLLSAAS, OLOF, MIKAEL
Application year: 1996
Main classification: C09K19
IPC codes: C08F20, C09K19, G02F1