WO2013156053A1

WO2013156053A1 - Polymer for use in alignment layer

Info

Publication number: WO2013156053A1
Application number: PCT/EP2012/056922
Authority: WO
Inventors: Lachezar Komitov; Bertil Helgee; Nils Olsson
Original assignee: Lachezar Komitov; Bertil Helgee; Nils Olsson
Priority date: 2012-04-16
Filing date: 2012-04-16
Publication date: 2013-10-24
Also published as: TWI598406B; TW201348335A; CN104380187B; JP6192710B2; KR20150001759A; JP2015514237A; KR101951267B1; CN104380187A

Abstract

A polymer compound for use in a surface-director alignment layer is provided, said polymer compound comprising: a polymer backbone comprising repeating units; a first side group attached to at least some of said repeating units and comprising a photo-functiona! moiety comprising at least one benzophenone moiety or derivative thereof; and a second side group attached to at least some of said repeating units; said second side group having a pronounced shape anisotropy capable of inducing vertical alignment of a liquid crystal material. A method of forming a surface-director alignment layer using the polymer compound, and a method of forming a liquid crystal cell using the polymer compound are also provided. By using a benzophenone moiety as the photo-functional moiety in a polymer compound for use in a surface-director alignment layer a desired pre- tilt angle of liquid crystal molecules in a liquid crystal cell can be accurately controlled by photo-irradiation of the polymer.

Description

POLYMER FOR USE IN ALIGNMENT LAYER

Field of the invention

The present invention relates to a polymer compound for use in surface director alignment layers, and liquid crystal devices utilizing such surface director alignment layer.

Background of the invention

Liquid crystal devices generally comprise a liquid crystal material layer arranged on a substrate, or sandwiched between a pair of substrates.

Liquid crystal molecules are typically relatively rigid molecules exhibiting shape anisotropy which have the ability to self-assemble along their long axis in a certain preferred direction. The average direction of the molecules is specified by a vector quantity and is called director.

In liquid crystal displays (LCDs), the desired initial alignment of the liquid crystal molecules in the absence of an external field, such as an electric field, is generally achieved by appropriate surface treatment of the confining solid substrate, typically by applying a so-called alignment layer on the surface of the confining substrate facing the liquid crystal bulk. The initial liquid crystal alignment is defined by solid surface/liquid crystal interactions at the interface between the liquid crystal layer and the alignment layer.

The orientation of the liquid crystal molecules adjacent to the confining surface is transferred to the liquid crystal molecules in the bulk via elastic forces, thus imposing essentially the same alignment to all liquid crystal bulk molecules.

The director of the liquid crystal molecules near the interface between the liquid crystal layer and the alignment layer (herein also called surface director) is constrained to point in a certain direction, such as perpendicular to the confining substrate surfaces, also referred to as homeotropic or vertical alignment (VA), or in parallel with the confining substrate surfaces, also referred to as homogeneous or planar alignment (PA), or at a predefined tilt angle, also referred to as a pre-tilt angle with respect to the confining substrate surfaces, somewhere between vertical and planar alignment, referred as tilted alignment (TA). The type of alignment desired in a liquid crystal display depends on the intended application of the device.

Known methods for establishing alignment layers are, for instance, the organic film rubbing method and the inorganic film vapor deposition method.

According to the organic film rubbing method, an organic coating of for instance polyimide is formed on a substrate surface. The organic coating is thereafter rubbed in a predetermined direction using a cloth of e.g. cotton, nylon or polyester. As a result, the liquid crystal molecules in contact with the organic layer will be oriented along the rubbing direction. However, the rubbing method has problems in that it may create scratches on the surface of the alignment film due to the mechanical rubbing, and it generates dust and static electrical charges which may result in damage to the thin film transistors in a liquid crystal display device.

In the inorganic film vapor deposition method, an inorganic film is formed on a substrate surface by vapor deposition of an inorganic substance, such as silicon oxide, obliquely to the confining substrate so that the liquid crystal molecules are oriented by the inorganic film in a certain direction depending on the inorganic material and evaporation conditions. Since the production cost is high, the method is not suitable for large-scale production, and therefore, this method is not used in practice.

A more recent technique for establishing alignment layer is photo- alignment which involves exposure of an alignment layer to light and thereby generating anisotropy of the physical properties of the alignment layer surface which in turn induces a particular alignment direction of the liquid crystal. One advantage of the photo-alignment method is that it is a non-contact process and thereby the above-mentioned problems associated with the organic film rubbing method are avoided.

Vertical (homeotropic) alignment (VA) and planar alignment (PA) are the two major kinds of liquid crystal alignment employed in LCDs. Vertical alignment is particularly advantageous in LCD TVs as the very low

transmission dark state results in an excellent contrast ratio. In many cases it is advantageous to direct the liquid crystal molecules in a predefined tilt angle (TA) which may for example shorten the response time of the liquid crystal material upon the application of an electric field and/or promote a more homogeneous reorientation of the liquid crystal molecules when the electrical field is applied. By inducing a nearly vertical alignment with only a small pre- tilt of the liquid crystal molecules with respect to the substrate surface normal (e.g. 85-88° as counted with respect to the substrate surface) a fast switching of the liquid crystal molecules of an LCD may be achieved without

significantly degradation of the contrast of the LCD.

EP 2 131 233 discloses a polymer for an aligning film material for use in a liquid crystal display device, wherein the aligning film may be adapted by photo-irradiation thereof, to control the alignment of liquid crystal molecules such that the average p re-tilt angle of the liquid crystal molecules is 87 to 89.5°. The polymer comprises a photo-functional group selected from the group of a cinnamate group, an azobenzene group, a stillbene group, cinnamoyl group, and a coumarin group. However, these photo-functional groups are likely to react unspecifically in many conventional polymerization methods such as radical polymerization, and consequently, the preparation of the polymer according to EP2 131 233 is restricted to a time-consuming polymerization method, for example the preparation of polyimide, involving a first step of a condensation reaction followed by a curing step. Thereby, the choice of suitable monomers for use in the polymer backbone according to EP 2 131 233 is also limited.

Summary of the invention

In view of the above-mentioned and other drawbacks of the prior art, a general object of the present invention is to provide a polymer for surface- director alignment layer which can easily be configured such that a desirable p re-tilt angle of a liquid crystal material is achieved.

The present inventors have found that this and other objects can be achieved by utilizing a polymer compound according to the present invention. The present invention is based on the realization that a benzophenone moiety or derivatives thereof can advantageously be used as a photo-functional moiety in a polymer compound in a surface-director alignment layer for very accurate control of a desired pre-tilt angle of liquid crystal molecules in a liquid crystal device by photo-irradiation of the polymer. In particular, the present inventors have found that a benzophenone moiety or derivative thereof exhibits excellent photo-functional properties that promote high photo stability and thermal stability, and in addition, that a polymer compound comprising a benzophenone moiety according to the invention may easily be prepared using a radical polymerization method. According to the invention, an alignment layer inducing a desirable pre-tilt angle of a liquid crystal material with uniform distribution over the whole liquid crystal device area can be obtained.

According to a first aspect, the invention provides a polymer compound for use in a surface-director alignment layer. The polymer compound comprises: a polymer backbone comprising repeating units; a first side group attached to at least some of the repeating units, wherein the first side group comprises a photo-functional moiety comprising at least one benzophenone moiety or derivative thereof; and a second side group attached to at least some of the repeating units; the second side group having a pronounced shape anisotropy capable of inducing vertical alignment of a liquid crystal material.

The polymer compound may optionally also comprise other functional side groups, e.g. anchoring side groups, alkyl side-chains or ion movement inhibiting side groups.

The term "side group having pronounced shape anisotropy" as used herein refers to a molecule having pronounced shape anisotropy in its actual environment. A side group having pronounced shape anisotropy exhibits a distinct difference between its short axis (axes) and its long axis (axes), and is relatively rigid in its structure.

When the polymer compound of the invention is used in a surface- director alignment layer, the second side groups of the polymer are typically oriented substantially vertical with respect to the plane of the alignment layer (and of the substrate), and thus promotes a vertical alignment of an adjacent liquid crystal material. In order to achieve the desirable pre-tilt of the liquid crystal material, the polymer compound of the invention further comprises first side groups comprising at least one photo-functional benzophenone moiety or derivatives thereof, the orientation of which may be controlled by photo- irradiation. Photo-irradiation of the polymer compound causes the first side groups to adopt a tilted orientation. However, depending on for example the molecular structure of the first and second side groups and/or the photo- reactive property of the photo-functional moiety (described further below), the photo-irradiation may result in re-orientation of the second side group in addition to, or instead of, a re-orientation of the first side groups. In any case, the photo-irradiation is performed to achieve an overall orientation of the first and the second side groups which, through steric and polar interactions between the liquid crystal molecules and the first and second side groups, promotes a desirable pre-tilt angle of the liquid crystal molecules.

Typically, the photo-functional moiety of the invention is photo-reactive. By "photo-reactive" is meant that it may undergo a chemical reaction in response to illumination. Such chemical reaction(s) may include, for example, dimerization, polymerization and isomerization reactions. Said reactions may involve reactions within the first side group, between two or more of the first side groups, between a first side group and a second side group, and/or between a first side group and the polymer backbone. Thus, when the polymer compound according to the invention is used as or in a surface- director alignment layer, the orientation of a first side group comprising a photo-reactive moiety and/or the orientation of other side groups can be controlled to provide a desirable pre-tilt angle of liquid crystal molecules in contact the surface-director alignment layer. Via elastic forces also the liquid crystal bulk adopts the same pre-tilt angle.

Advantageously, in embodiments of the invention, the first side group may have the following general formula (I):

wherein

l_i is a linking group attached to said repeating unit, U comprising 3 to 30 linking atoms, such as 5 to 15 linking atoms;

Ri is hydrogen, halogen, Ci to C₂o alkyl, substituted Ci to C₂o alkyl, Ci to C₂o alkoxy, substituted Ci to C₂Q alkoxy, Ci to C₂o alkenyl, substituted Ci to C₂₀ alkenyl, d to C₂₀ alkynyl, substituted Ci to C₂₀ alkynyl, Ci to C₂₀

aminoalkyl, substituted Ci to C₂o aminoalkyl, typical examples include hydrogen, or C Cn alkyl or Ci-C alkoxy;

n is 0 to 4;

R₂ and R₃ are each independently hydrogen, halogen, Ci to C₃ alkyl, substituted Ci to C₃ alkyl, Ci to C₃ alkoxy, substituted Ci to C₃ alkoxy, Ci to C₃ aminoalkyl, substituted Ci to C₃ aminoalkyl.

In embodiments of the invention, the second-side group has a linear shape anisotropy with a long axis extending along the main extension of the second side group and a short axis perpendicular to the long axis, and is attached end-on to the repeating units.

Advantageously, in embodiments of the invention, the second-side group may have the following general formula (II):

wherein

L-2 is a linking group attached to said repeating unit, said L₂ comprising 3 to 30 linking atoms, such as 5 to 15 linking atoms;

m is 0 or 1

X is -COO-, -CH=CH-, or -C≡C-;

R₄ is hydrogen, halogen, Ci to C20 alkyl, substituted Ci to C20 alkyl, Ci to C20 alkoxy, substituted Ci to C₂o alkoxy, Ci to C₂o alkenyl, substituted Ci to C₂o alkenyl, Ci to C₂₀ alkynyl, substituted Ci to C₂₀ alkynyl, Ci to C₂o

aminoalkyl, substituted Ci to C₂o aminoalkyl, typical examples include hydrogen, or C-I-C-M alkyl or C Cn alkoxy,

n is 0 to 4;

R5 and R₆ are each independently hydrogen, halogen, Ci to C₃ alkyl, substituted Ci to C₃ alkyl, Ci to C₃ alkoxy, substituted Ci to C₃ alkoxy, Ci to C₃ aminoalkyl, substituted Ci to C₃ aminoalkyl.

When the polymer compound is used as a surface-director alignment layer it is desirable that the liquid crystal molecules of a liquid crystal material should be affected by the orientation of both the first and second side groups. To achieve this, advantageously, the first side group and a second side group may be of a similar length. Hence, in embodiments of the invention, the linking group Li may comprise up to 10 more linking atoms than the linking group L-2, for example up to 6 more linking atoms.

For example, in embodiments of the invention, l_i may comprise up to 6 more linking atoms than L₂, and wherein Ri may be hydrogen or halogen, and R may be C₃ to Ce alkyl or C₃ to CQ alkoxy, such as a hexyloxy. In such embodiments, the first and the second side groups have a similar extension from the polymer backbone.

The linking groups l_i and L₂ may each comprise an optionally substituted saturated or unsaturated hydrocarbon chain, such as an alkyl, alkenyl, aryl, alkylaryl alkoxy or polyether, aryloxy group, siloxane chain. For example, L₁ and L₂ may each independently be Ci to C30 alkyl, substituted Ci to C₃₀ alkyl, Ci to C₃₀ alkoxy, substituted Ci to C₃₀ alkoxy, Ci to C₃o alkenyl, substituted Ci to C₃₀ alkenyl, Ci to C₃₀ alkynyl, substituted Ci to C₃o alkynyl, Ci to C₃₀ aminoalkyl, or substituted Ci to C₃₀ aminoalkyl. Typical examples include C1-C15 alkyl or C1-C15 alkoxy, such as C₃-C alkyl or C₃-Cn alkoxy.

In an exemplary embodiment of the invention, the repeating unit of the polymer backbone is a maleimide, U is a Cn alkoxy; Ri , R2 and R₃ are hydrogen; L₂ and R₄ are C₆ alkoxy; R₅ is H or N-alkylamide, R₆ is H or N- alkylamide, m is 1 ; and X is -COO-.

In another exemplary embodiment of the invention, the repeating unit of the polymer backbone is a hexylacrylate, l_i is a Cn alkoxy; Ri , R₂ and R₃ are hydrogen; L₂ and R₄ are C₆ alkoxy; R₅ is H or N-alkylamide, R₆ is H or N- alkylamide, m is 1 ; and X is -COO-.

In embodiments of the invention, the ratio between the number of the first side group and the number of the second side group in the polymer compound may be in the range of from 10:1 to 1 :100, such as from 2:1 to 1 :10, for example 1 :1. Using these ratios a desirable degree of re-orientation of the first and/or the second side group may be achieved upon photo- irradiation of the polymer.

In embodiments of the invention, the ratio between the number of the first side group and the total number of the repeating units in the polymer compound is in the range from 1 :1 to 1 :100, for example 1 :10.

The number of first and second side groups, with respect to the total number of repeating units, may typically be adapted to give a desirable distribution of the side groups along the length of the polymer backbone such that, when the polymer is used as an alignment layer, there are enough side groups along the polymer backbone to achieve appropriate solid

surface/liquid crystal interactions at the interface between the liquid crystal layer and the alignment layer comprising the polymer, to cause the liquid crystal molecules of a liquid crystal material to become aligned with a desirable p re-tilt angle.

The ratio of the number of first side groups to second side groups in the polymer, and the ratio of the number of first and/or second side groups to the total number of repeating units, may advantageously be adapted to give a desirable p re-tilt upon photo-irradiation of the polymer. The optimal ratio(s) will typically depend on the method used for photo-irradiation, for example depending on the direction of the linearly polarized electromagnetic radiation and/or the wavelength thereof, and/or the exposure time, the temperature, and the surrounding atmosphere. However, the optimal ratio to achieve a desirable p re-tilt may also depend on the respective structure of the first and second side groups.

In embodiments of the invention, the repeating units may be derived from at least one of maleimide, acrylate, methacrylate, vinyl, styrene, and N- vinyllactam monomer, and derivatives thereof, and mixtures thereof.

In embodiments of the invention, the polymer backbone may comprise a first type of repeating unit, also referred to as "first repeating unit(s)", and additionally a second type of repeating unit, herein also referred to as "second repeating units". Each of said first and second repeating units may be selected from maleimide, acrylate, methacrylate, vinyl, styrene, and N- vinyllactam monomer, and derivatives thereof, and mixtures thereof. The first repeating units are typically different from the second repeating units.

In some embodiments, at least some of the first repeating units may be functionalized with the first side group or the second side group, and at least some of the second repeating units may optionally also be functionalized with said first or second side groups. In other embodiments, at least some of the second repeating units are functionalized with the first side group and/or at least some of the second repeating units are functionalized with the second side group, and the first repeating units may optionally lack said first and second side groups. In yet other embodiments, at least some of the first repeating units may be functionalized with the first side group, and at least some of the second repeating units may be functionalized with the second side groups, or vice versa.

In embodiments of the invention at least some of the repeating units, e.g. some of the first and/or the second repeating units, may be functionalized with a third side group, which may typically be a C2 to C₂o alkyl or substituted C₂ to C20 alkyl, for example a C₂ to Cn alkyl, such as a C₈ alkyl. For example, a third side group may comprise N-a!kylmaleimide.

Furthermore, in a second aspect, the invention relates to a surface- director alignment layer, comprising a polymer compound as described above deposited onto a surface.

In a third aspect, the invention relates to a method for photo-orientation of a surface-director alignment layer comprising the steps of: providing a substrate; applying the above-described polymer compound onto a surface of the substrate to provide a surface director alignment layer; and irradiating the surface-director alignment layer with electromagnetic radiation at an angle of incidence in the range of from 1° to 89° with respect to the substrate normal, said electromagnetic radiation being linearly polarized in the plane of incidence and having a wavelength in the range of from 200 nm to 400 nm, for example from 250 to 320 nm. The plane of incidence is defined as a plane containing the incident light and the substrate normal.

In a fourth aspect, the present invention relates to a liquid crystal device, comprising at least one confining substrate; a liquid crystal bulk material; and a surface-director alignment layer arranged between the at least one confining substrate and the liquid crystal bulk material, the surface- director alignment layer being in contact with the liquid crystal bulk material causing liquid crystal molecules comprised in the liquid crystal bulk material to form a desired pre-tilt angle with respect to the surface of the surface-director alignment layer in the absence of an applied electric field, wherein the surface-director alignment layer comprises the polymer compound as descriped above.

In embodiments of the invention, the pre-tilt angle is controllable by photo-irradiating the surface-director alignment layer. In embodiments of the invention, the p re-tilt angle may be in the range of 85-89.5°, for example 87-89.5°, such as 87.5-88.5°. Such small deviation from the vertical alignment (pre-tilt) reduces the response time of the liquid crystal material and/or promotes a more homogeneous reorientation of the liquid crystal molecules upon the application of an electric field.

In a fifth aspect, the invention relates to a method for the manufacture of the liquid crystal device described above. The method comprises the steps of: providing a substrate; providing a first electrode layer on the substrate; applying a polymer compound as described herein onto the surface of the first electrode layer to provide a surface director alignment layer; irradiating the surface-director alignment layer with electromagnetic radiation at an angle of incidence in the range of from 1° to 89° with respect to the substrate normal, said electromagnetic radiation being linearly polarized in the plane of incidence and having a wavelength in the range of from 200 to 400 nm, for example from 250 to 320 nm; and arranging a liquid crystal material in contact with the alignment layer.

In a sixth aspect, the invention relates to the use of the above- described polymer compound in an alignment layer for a liquid crystal device.

In a seventh aspect, the invention relates to a display comprising the above-described liquid crystal device or produced by the above-described method for the manufacture of the liquid crystal device.

Brief description of the drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing example embodiments of the invention, wherein:

Fig. 1 is a flow chart schematically illustrating a method for

manufacturing a surface-director alignment layer of the present invention.

Fig. 2a-c schematically illustrate the surface-director alignment layer manufactured according to the method of Fig. 1 in states following the corresponding method steps; and Fig. 3 illustrates the direction of the incident electro-magnetic radiation during photo-irradiation according to the present method, and shows the plane of incidence P and the surface normal N.

Fig. 4 illustrates an embodiment a liquid crystal device according to embodiments of the present invention.

Description of example embodiments of the present invention

In the following description, the present invention is described with reference to a polymer compound suitable for use in a surface-director alignment layer, to the synthesis of such polymer compound and to liquid crystal devices, such as a liquid crystal display, utilizing such a polymer compound as, or in, a surface-director alignment layer.

The present inventors have surprisingly found that a benzophenone moiety or derivatives thereof can advantageously be used as a photo- functional moiety in a pendant group of a polymer compound for use in a surface-director alignment layer. Due to the photo-functional properties of the benzophenone or benzophenone derivative, the polymer compound can easily be controlled to promote, when used in a surface-director alignment layer, a desirable pre-tilt angle of liquid crystal molecules. Such control is carried out by irradiating the polymer compound comprising the

benzophenone moiety with electro-magnetic radiation.

An embodiment of a surface-director alignment layer according to the invention and a method for photo-orientation of such a surface-director alignment layer will now be described with reference to Fig. 1 , which is a flow chart schematically illustrating such a method, and Fig. 2a-c which

schematically illustrate the surface-director alignment layer in states following the corresponding method steps of Fig. 1.

In a first step, a substrate 201 is provided. For example, the substrate may be a glass substrate. Typically an electrode layer is already provided on the surface of the substrate; if not, a conventional electrode layer may be applied on the substrate 201 before applying the alignment layer.

In the second step, a polymer compound according to embodiments of the invention is applied onto the substrate 201. The polymer is typically first prepared by polymerization of a monomeric mixture in solution before being dissolved, dispersed or dispended in a liquid medium, such as a volatile solvent, which solution/dispersion/suspension is then coated on the substrate surface, followed by removal of the liquid medium. Suitable coating methods include, but are not limited to, conventional deposition methods such as spin- coating, spray-coating, doctorblade coating, roll-coating, flexprinting, ink-jet printing, dipping, etc. Alternatively, in another embodiment of the invention, a reaction mixture comprising a mixture of monomers and/or pre-polymers may be coated on the substrate surface, followed by in situ polymerization of the reaction mixture directly on the substrate surface.

As shown in Fig. 2b, the polymer compound comprises a polymer backbone 209 comprising repeating units 204, 205 of which some repeating units 204 have a first side group 206 attached thereto and other repeating units 205 have a second side group 207 attached thereto. The first side group 206 comprises at least one photo-functional moiety 208 comprising a benzophenone moiety or a derivative thereof.

In Fig. 2b, both the first side groups 206 and second side groups 207 have a pronounced shape anisotropy, that is, the first and second side groups have a linear anisotropy with a long axis extending along the main extension of the second side group and a short axis perpendicular to the long axis. Both the first and second side groups are attached end-on to said repeating units. Thus, as illustrated in Fig. 2a, both the first side groups and the second side groups have an orientation which is in a substantially vertical direction with respect to the plane of the surface-director alignment layer when no electric field is applied and without exposure of the alignment layer to electromagnetic irradiation.

As used herein, the term "end-on attached" refers to an attachment of the side group to the polymer backbone at or near an end of a long axis of the side group molecule. For example, in a rod-like side group, such as a calamitic mesogenic group, the point of attachment is at or near one of the terminal ends of the side group.

The third step of the method, also illustrated in Fig. 2c, involves irradiating the polymer compound with linearly polarized electromagnetic radiation 210 having a wavelength in the range of from 200 to 400 nm, for example from 250 to 320 nm. The polymer compound may be irradiated at an angle of incidence in the range of from 1° to 89°, such as from 20° to 70°, for example from 30° to 60° from the substrate normal N. The light polarization direction is in the plane of incidence P, see Fig. 3. The substrate normal N, the angle of light incidence a and the plane of incidence P are illustrated in Fig. 3.

The irradiation may be performed for at least 30 seconds, for example at least 40 seconds, such as for at least 1 minute. Irradiation may be performed up to 5 and up to 10 minutes, for example up to 3 minutes, or up to 2 minutes.

As a result of the photo-irradiation, a tilted orientation of at least the first side groups 206, and optionally also of the second side groups 207, is typically achieved, as shown in Fig. 2c. By exposure to photo-irradiation the benzophenone-derived photo-functional moiety is initiated to undergo chemical reaction (s). The chemical reaction(s) may involve any type of cross- linking reactions resulting in the formation of irreversible covalent bonds (not shown) between, for example, a first side group and an adjacent first side group and/or a second side group and/or one or more repeating units of the polymer backbone. It should be noted that such reaction may cause a change of orientation also of the second side group, as shown in Fig. 2c. However in alternative embodiments of the invention (not shown in Fig. 2c) there may be a mixture of first and second side groups of which not all have a tilted orientation, which imposes an inhomogeneous distribution of the pre-tilt of the liquid crystal molecules at the interface between the alignment layer and the liquid crystal layer. However, due to elastic properties of the liquid crystal, such inhomogeneous surface distribution of the pre-tilt of the liquid crystal molecules becomes homogeneous in the liquid crystal bulk at certain distance from the alignment layer, typically less than 100 nm, resulting in orientation of the liquid crystal layer with a desired pre-tilt.

It is typically desirable to achieve a surface-director alignment layer which can cause liquid crystal molecules of a liquid crystal material to align in a pre-tilt angle in the range from 85° to 89.5°, for example 87.5° to 89.5°, with respect to a surface of the surface-director alignment layer. Accordingly, in case that the irradiation of the polymer results in a tilted orientation of all or most of the first and second side groups, the overall orientation should, in order to achieve the desired pre-tilt angle of the liquid crystal molecules, also be in the range from 85° to 89.5° with respect to a surface of the surface- director alignment layer. However, in case that only the first side groups are re-oriented during the photo-irradiation of the polymer compound, the ultimate orientation of the individual first side group would typically be less than 85°, e.g. 80-85°, in order to achieve the desired pre-tilt (in the range from 85° to 89.5°) of a liquid crystal material, as the orientation of the first side group must compensate for the fact that the second side groups may still be oriented to promote vertical alignment. Consequently, in such cases, the ultimate desired orientation of the first side group will depend on, for example, the number of first side groups with respect to the number of second side groups. The final pre-tilt angle may also be influenced by the illumination conditions (including light incidence angle a), the temperature, the

surrounding atmosphere etc.The extent of the re-orientation of the side groups may be adapted by, for example, adapting the direction of the linearly polarized electromagnetic radiation and/or the wavelength thereof, and the exposure time of the photo-irradiation. However, the result from the photo- irradiation step, may also depend on, for example, the number of first side groups comprising the photo-functional moiety, the chemical structure of the first and second side groups and the chemical structure the photo-functional moiety (i.e. different derivatives of benzophenone) as well as the structure of the polymer backbone.

The polymer compound of the invention may be a random co-polymer comprising repeating units having a first side group attached thereto, repeating units having a second side group attached thereto, and repeating units which lack said first and second side groups. The repeating units may be of the same type, except with respect to said side groups.

By "random co-polymer" is meant a polymer comprising at least two different monomeric units which are randomly distributed along the length of the polymer backbone. An example is a a co-polymer comprising a first type of repeating unit having a first side group attached thereto and other repeating units of the same type but having a second side group attached thereto instead of the first side group. Another example is a co-polymer comprising first repeating units having a first side group attached thereto and second repeating units having a second side group attached thereto.

A random co-polymer may be obtained by polymerizing a mixture of at least two different monomeric units, typically by a radical addition

polymerization, a method which is well known in the art.

The radical polymerization method is particularly advantageous for the preparation of polymers for use in an alignment material, as the polymer product from the radical polymerization does not need to be cured, and the alignment layer can easily be formed by merely evaporating the solvent after deposition onto a substrate. This enables the use of temperature sensitive substrates, such as plastic substrates, since no excessive heating is needed to produce the alignment layer. Furthermore, as the polymer does not require curing after deposition, the total time for forming the alignment layer on the substrate is short - it only involves deposition of a very thin alignment film from a solution containing the polymer compound of the present invention, followed by evaporation the solvent. Moreover, due to the small amount of solvent used, the process is both less costly and, more environmentally friendly. In addition, using a radical polymerization method a blend of many different monomers can easily be polymerized to give a desirable co-polymer composition.

In embodiments of the invention, the polymer compound may be a random co-polymer comprising a first type of repeating units (also referred to as "first repeating units") and a second type of repeating units (Also referred to as "second repeating units"), wherein the first repeating units is different from the second repeating units. For example, in embodiments of the invention, the polymer compound may be a random co-polymer comprising first repeating units of which at least some may be functionalized with the first side group, and further comprising second repeating units of which at least some may be functionalized with the second side group. Alternatively, both the first and second repeating units may be functionalized with the first and second side groups. In another embodiment of the invention only one of the first and the second repeating units may be functionalized with the first side group and/or the second side group.

Typically, the first repeating units and/or the second repeating units may independently be derived from at least one of maleimide, acrylate, methacrylate, vinyl, styrene, and N-viny!lactam monomer, and derivatives thereof, and mixtures thereof.

For example, in an embodiment of the invention, the polymer compound is a random copolymer comprising first repeating units of a maleimide functionalized with either the first side group, or the second side group, or a third or further side group, and second repeating units of a N-vinyl pyrrolidone.

For example, in an embodiment of the invention, the polymer compound is a random copolymer comprising a first repeating unit of an acrylate functionalized with either the first side group, or the second side group, or a third or further side group.

According to embodiments of the invention, the first side group, also denoted S¹, may advantageously have the following general formula (I):

(I)

wherein

Li is a linking group attached to said first repeating unit, said Li comprising 3 to 30 linking atoms, such as 5 to 15 linking atoms;

Ri is hydrogen, halogen, Ci to C₂o alkyl, substituted Ci to C₂o alkyl, Ci to C₂o alkoxy, substituted Ci to C₂₀ alkoxy, Ci to C₂o alkenyl, substituted Ci to C20 alkenyl, Ci to C₂₀ alkynyl, substituted C-i to C₂o alkynyl, Ci to C₂o aminoalkyl, substituted Ci to C20 aminoalkyl, typical examples include hydrogen, or Ci-Cn alkyl or Ci-C alkoxy;

n is 0 to 4;

R₂ and R3 are each independently hydrogen, halogen, Ci to C₃ alkyl, substituted Ci to C3 alkyl, Ci to C₃ alkoxy, substituted Ci to C3 alkoxy, Ci to C₃ aminoalkyl, substituted Ci to C₃ aminoalkyl.

According to embodiments of the invention, the second side group, also denoted S², may advantageously have the following general formula (II):

(ID

wherein

L₂ is a linking group attached to said first repeating unit, said L₂ comprising 3 to 30 linking atoms, such as 5 to 15 linking atoms;

m is 0 or 1 ;

X is -COO-, -CH=CH-, or -C≡C-;

R₄ is hydrogen, halogen, Ci to C20 alkyl, substituted Ci to C₂o alkyl, Ci to C₂₀ alkoxy, substituted Ci to C₂₀ alkoxy, Ci to C20 alkenyl, substituted Ci to C₂₀ alkenyl, Ci to C₂₀ alkynyl, substituted Ci to C₂₀ alkynyl, Ci to C₂o aminoalkyl, substituted Ci to C₂o aminoalkyl, typical examples include hydrogen, or C C alkyl or C1-C11 alkoxy,

n is 0 to 4;

R₅ and R₆ are each independently hydrogen, halogen, Ci to C₃ alkyl, substituted Ci to C3 alkyl, Ci to C₃ alkoxy, substituted Ci to C3 alkoxy, Ci to C₃ aminoalkyl, substituted Ci to C₃ aminoalkyl.

In embodiments of the invention, Li may comprise up to 10 more linking atoms than L2, for example, up to 6 more linking atoms. The linking groups Li and L₂ may comprise an optionally substituted saturated or unsaturated hydrocarbon chain, such as an alkyl, alkenyl, aryl, alkylaryl alkoxy or polyether, aryloxy group, siloxane chain. For example, Li and L₂ may each independently be Ci to C₃₀ alkyl, substituted Ci to C30 alkyl, Ci to C₃o alkoxy, substituted Ci to C₃₀ alkoxy, Ci to C30 alkenyl, substituted Ci to C₃o alkenyl, Ci to C₃₀ alkynyl, substituted Ci to C₃₀ alkynyl, Ci to C30

aminoalkyl, or substituted Ci to C₃₀ aminoalkyl. Typical examples include Ci- C15 alkyl or Ci-C₁₅ alkoxy, such as C₃-C alkyl or C₃-Cn alkoxy.

In embodiments of the invention, the ratio between the number of the first side group and the number of the second side group in the polymer compound may advantageously be in the range of from 10:1 to 1 :100, such as from 2:1 to 1 :10, for example 1 :1.

In embodiments of the invention, the ratio between the number of the first side group and the total number of the first repeating units in the polymer compound may advantageously be in the range from 1 :1 to 1 :100, for example 1 :10.

The ratio between the number of first and second side groups in the polymer, and the ratio between the number of first and/or second side groups with respect to the total number of first repeating units, may advantageously be adapted such that the overall (tilted) orientation of the side groups, upon photo-irradiation of the polymer, can, when used as an alignment layer, cause the liquid crystal molecules of a liquid crystal material to align in a desirable p re-tilt angle. The optimal ratio will typically depend on the method used for photo-irradiation, for example depending on the direction of the linearly polarized electromagnetic radiation and/or the wavelength thereof,

temperature and/or the exposure dose of the photo-irradiation. However, the optimal ratio to achieve a desirable p re-tilt may also depend on the respective structure of the first and second side groups.

In embodiments of the invention the first and/or the second repeating units may be functionalized with a third type of side group, which may typically be a C₂ to C₂₀ alkyl or substituted C₂ to C₂₀ alkyl, for example a C₂ to C11 alkyl, such as a C₈ alkyl. For example, a third side group may comprise N- alkylmaleimide. In embodiments of the invention, in addition to the first side groups and the second side group, optionally the polymer compound may additionally comprise one or more of the following types of side groups:

- a third type of side group S³ selected from an aliphatic and an aromatic group;

- a fourth type of side group S⁴ forming a pendant side-chain capable of anchoring the polymer compound to a substrate (herein referred to as an anchoring side group);

- a fifth type of side group S⁵ forming an ion movement inhibitor side group.

The side groups S³ and S⁴ may, if needed, each be attached to the polymer backbone by means of a linking group L as described above.

It is noted that the polymer compound may comprise repeating units which do not comprise any side group. The inclusion of repeating units of the polymer backbone where no side group is attached to the backbone may result in regular or irregular spaces in between the side groups described above.

The physicochemical properties of the polymer compound according to embodiments of the invention, such as glass transition temperature T_g, elastic modulus, coherence of deposited films, film smoothness, wetting properties, surface energy, etc may be adjusted to desired values by incorporating, in the polymer backbone repeating units comprising side groups S³ selected from optionally substituted, such as heteroatom substituted, halogenated, such as fluorinated, branched or straight chained aliphatic and aromatic groups, such as alkyls, aryls or alkylaryls, polyethers, siloxanes or alcohols.

Typical examples of S³ side groups include optionally fluorinated, such as perfluorated, C-i-Ci₈-alkyls, such as C₄-Ci2-alkyls or -alcohols, and those groups defined above as spacers L. For example, S³ groups being an alkyl chain generally decreases T_g of the polymer while S³ groups being an any I generally increases T_g of the polymer. The side groups S³ are preferably linear. In embodiments of the invention, the side groups S may contribute to vertical alignment of a liquid crystal material. In embodiments of the invention, the anchoring side groups S⁴ may preferably be used to anchor the polymer to the underlying substrate. An anchoring side group S⁴ is typically an optionally substituted C₂ to C₂o, for example C₂ to C₈, hydrocarbon chain with a functionalizing group in or at the end distant from the polymer backbone, which functionalizing group is capable of forming a bond, such as a covalent bond, an ion-bond or a hydrogen bond to chemical groups on the surface of a substrate, for example, but not limited to, free hydroxyl groups on a glass surface or e.g. epoxy, amino, thiol or isocyano groups introduced by preliminary activation of the substrate surface.

Non-limiting examples of such functionalizing groups suitable in an anchoring side group includes amino, hydroxy, isocyano, and glycidyl groups. Those skilled in the art will be able to select the suitable functionalization on the anchoring side group dependent on the substrate material.

Non-limiting examples of an anchoring side-chain group S⁴ are disclosed in the structural formulas (III) to (VI) below, where Z represents a portion of the polymer backbone and L is a spacer group, preferably having the length of 1 to 10, such as 1 to 5 spacer atoms, such as an alkyl spacer:

Ion movement inhibiting S⁵ groups may be utilized in the polymer compound to reduce the concentration of mobile ions in the liquid crystal bulk material when the polymer compound is used as an alignment layer, and thus to reduce the conductivity of the liquid crystal bulk material. Ion movement inhibiting groups are typically strongly polar, non-ionic groups that attract ions. Examples of ion movement inhibiting groups are hydroxyl groups and other, including materials conventionally known as ion traps, such as coronands. In embodiments of the invention, the polymer compound has a glass transition temperature (T_g) of at least 180°C. . A polymer with a high T_g results in a more temperature stable liquid crystal alignment.

Fig. 4 illustrates a double-sided liquid crystal device according to embodiments of the invention. The liquid crystal device 300 comprises a first confining substrate 301 and a second confining substrate 302, which are mutually spaced apart. In the space between the substrates 301 , 302, a liquid crystal material 303 is disposed, sandwiched between the substrates 301 and 302.

On the first substrate 301 a surface-director alignment layer 304 is arranged in contact with the liquid crystal material 303. Depending on the presence of anchoring side groups on the polymer of the present invention, the surface-director alignment layer 304 may be chemically bonded to the substrate 301.

The surface-director alignment layer 304 comprises at least one polymer according to embodiments of the present invention. Hence, the surface-director alignment layer 304 promotes a homeotropic alignment with a small pre-tilt of the liquid crystal material 303 at least at or near the interface towards the surface-director alignment layer 304.

The skilled person will recognize that a liquid crystal device 300 of the present invention may comprise means for generating an electrical field in the liquid crystal material 303. Changes in the electrical field typically re-orient the liquid crystal material, i.e. cause switching of the liquid crystal director. For example such means may be represented by a pair of electrodes. In the embodiment described in Fig. 4, a first electrode 305 is arranged between the alignment layer 304 and the substrate 301 , and a second electrode 307 is arranged on the second substrate 302.

The surface-director alignment layer 304 will, in the absence of an applied electric field, induce a desirable pre-tilt alignment of the surface- director of the liquid crystal material 303.

A second alignment layer 306 is arranged between the second substrate 302 and the liquid crystal material 303. This second alignment layer may also comprise a polymer of embodiments of the present invention, or may alternatively be of another kind of alignment layer material.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Examples

The present invention will now be described with reference to the following examples, illustrating further the invention. It is to be noted that the experimental examples are provided to illustrate the present invention and are not intended to limit the scope of the invention. The scope of the invention is solely defined by the appended claims.

All examples were performed at room temperature and under normal atmospheric conditions, except where indicated otherwise.

Commercially available chemical compounds are used as received with the following exceptions: i) N-vinyl-pyrrolidone (NVP) and N-vinyl- caprolactame are passed through aluminium oxide prior to use in order to remove added stabilizer, ii) when dry THF is required ordinary THF is dried by passing it through aluminium oxide prior to use. Aluminium oxide activated neutral Brockmann 1 , 58 A, (CAS 1344-28-1 ) was used for drying of THF and purification of NVP.

In all examples below, standard reactions well known to a person skilled in the art were used for the preparation of the polymers. The polymeric alignment materials can for example be made by copolymerization of functionalized maleimides and N-vinyl pyrrolidone . The preparations of these materials and the used side groups are given below.

Scheme I. Sample mesogenic and alkyl monomer synthesis.

N-Octvllmaleimide (VIII): Octylamine is dissolved in chloroform and an equivalent amount of maleic anhydride is added. After two hours of stirring at room temperature the solvent is drawn off. The formed amic acid is used without purification and dissolved in acetic anhydride and an equivalent amount of sodium acetate is added. The mixture is refluxed for six to eight hours and then the solvent is drawn off under vacuum. The residue is passed through a short silica gel column using petrol ether /ethyl acetate 2/1 or 4/1 as eluent. The maleimide is then re-crystallised from ethanol or methanol. This procedure works well for amines octyl to at least hexadecyl. Imides from hexyl and shorter are liquids and must be more carefully chromatographed using the same conditions as above.

Maleimide (XI): 4.2 g (9.55 mmol) II, 0.93 g (9.55 mmol) maleimide, and 2.5 g (9.55 mmol) triphenylphosphine was dissolved in 40 ml of dried tetrahydrofuran. 9.55 mmol diethylazodicarboxylate (DEAD) (4.4 ml 40 % solution in toluene) was added drop wise to the reaction mixture. The mixture was stirred at room temperature for three hours and the evaporated till dryness. The residue was taken up in petrol ether/ethyl acetate 2/1 and purified by chromatography on silica gel. Yield: 2.8 g 56 %. ¹H NMR (CDCI₃, δ, pattern, number of protons; 1.0, t, 3; 1 .1 - 1.6 three m, around 20; 1.8, m, 4; 3.5, t, 2; 4, t, 2; 4.4, t, 2; 6.7, s, 2; 7.0, d, 2; 7.6, 2d, 4; 8.1 , d, 2.

Maleimide (XIII): 6.5 g (13 mmol) IX, 1.26 g (13 mmol) maleimide, and 3.4 g (13 mmol) triphenylphosphine was dissolved in 100 ml of dried tetrahydrofuran. 13 mmol diethylazodicarboxylate (5.9 ml 40 % solution in toluene) was added drop wise to the reaction mixture. The mixture was stirred at room temperature for three hours and then evaporated till dryness. The residue was taken up in toluene/ethyl acetate 4/1 and purified by

chromatography on silica gel. Yield: 4.0 g 53 %. ¹H NMR (CDCI₃, δ, pattern, number of protons; 0.9, t, 3; 1.1 - 1.6, 3m; 1.8, m, 4; 3.5, t, 2; 3.9, t, 2; 4.1 , t, 2; 6.7, s, 2; 6.9, 2d, 4; 7.1 , d, 2; 8.1 , d, 2.

Maleimide (XV): 1.5 g (4 mmol) XIV, 0.40 g (4.1 mmol) maleimide and

1.13 g (4.1 mmol) triphenylphosphine were dissolved in 20 ml dry THF and 0.72 g (4.1 mmol) diethylaxodicarboxylate was added as a 2.19 M solution. The reaction mixture was stirred at room temperature for 5 hours. The solvent was drawn off and the residue was refluxed in petrol ether/ethyl acetate 2/1 and hot filtered. The solvent was removed under vacuum and the residue was re-crystallized from methanol yielding a contaminated product.

Chromatography using petrol ether/ethyl acetate 2/1 as eluent gave a low yield of pure product due to losses during re-crystallization experiments. Yield: 0.3 g 0.6 mmol, 17 %. ¹H NMR (CDCI_3l δ, pattern, number of protons; 0.9, t, 3; 1.3, - 1.7, 3m, 12; 1.8, m, 4; 3.6, t, 2; 4, t, 4; 6. 7, s, 2; 6.93, m, 4; 7.45, m, 4.

Scheme II. Synthesis of benzophenone side-chain monomer. 4-(1 1-hydroxyundecyloxy)-benzophenon (XX): 20 mmol (4 g) 4- hydroxybenzophenon, 20 mmol (5 g) 11-bromo-1-undecanol and 25 mmol (3.4 g) anhydrous potassium carbonate was added to 00 ml butanone and heated to 80 °C for 6 days. The mixture was hot filtered, the solvent was drawn off and the residue was re-crystallized from methanol. Yield 4.8 g (64 %).¹ H NMR (CDCI₃, δ, pattern, number of protons; 1 .3 bs, 12; 1.4 - 1.6, 2m, 4; 1.8, m ,2; 3.65, t, 2; 4.05, t, 2; 6. 95, d, 2; 7.47, m, 2; 7.58, m, 1 ; 7.75, d 2; 7.82, d, 2.

4-( -maleimidoundecyloxy)-benzophenon (XVI).· 1.5 g (4.0 mmol) XX, 0.40 g (4.1 mmol) maleimide and 1.13 g (4.1 mmol) triphenylphosphine were dissolved in 20 ml dry THF and 0.72 g (4.1 mmol) d iethylaxod icarboxy late was added as a 2.19 M toluene solution. The reaction mixture was stirred at room temperature over night. The solvent was drawn off and the residue was taken up in petrol ether/ethyl acetate 2/1 heated and filtered. The solvent was removed under vacuum to a suitable volume and subjected to column chromatography using petrol ether/ethyl acetate 2/1 as eluent. Yield: 1.2 g, 67 %. ¹H NMR (CDC ): δ, pattern, number of protons : 1.2- 1.65, 3m, 16; 1.8, m ,2; 3.5, t, 2; 4.05, t, 2; 6. 7, s, 2; 7, d, 2; 7.47, m, 2; 7.58, m, 1 ; 7.75, d 2; 7.82, d, 2.

Scheme III. Synthesis of maleimide polymer.

XVIII: 0.3 mmol (150 mg) maleimide XVII, 0.2mmol (90 mg) XVI, 1.5 mmol (313mg) N-octylmaleimide, 2.0 mmol (222 mg) N-vinyl pyrrolidone and 15mg 2,2'-azobis(2-methylpropionitrile) (AIBN) were dissolved in 15 ml of benzene. The polymerization was performed 18 hours in 60 degrees oil bath. Purification by reprecipitation three times into methanol from a few ml chloroform. 66% yield. Relative side group ratios in fair accordance with the ratios added according to NMR. The ratio of first side groups (benzophenone) to second side groups was 2:3.

Scheme IV. Synthesis ofacrylate polymer.

11-(4-benzovlphenoxv)undecyl prop-2-enoate) (XIX): 1.84 g (5 mmol) ([4-(11-hydroxyundecoxy)benzophenone) (XX) was dissolved in 25 ml of chloroform and 2 g (28 mmol) triehtyl amine was added. The mixture was cooled in an ice-bath and 0.5 g (5.1 mmol) acryloyi chloride was added with a syringe. The mixture was stirred for 2 h while cooling and for 2 h at room temperature. The reaction mixture was poured into water, acidified with hydrochloric acid and then the two phases were separated. The aqueous phase was extracted with chloroform and the combined organic layers were washed with water and brine. After being dried and evaporated to dryness the product was chromatographed on silica gel using petrol ether /ethyl acetate 2/1 as eluent. Yield 1.0 g 47 %. The ¹H-NMR spectrum was in accordance with the structure. 4-hexoxyphenyl) 4-(6-prop-2-enov!oxyhexoxy)benzoate (XXI): 1 .6 g (3.9 mmol) (4-hexoxyphenyl) 4-(6-hydroxyhexoxy)benzoate, 0.9 g (12.7 mmol) triethylamine and 0.36 g (4 mmol) acryloyi chloride was reacted in 25 ml chloroform. The mixture was stirred over night. The same work-up procedure as for XIX was used with the exception that petrol ether/ethyl acetate 4/1 was used as eluent. Yield: 1.14 g 62 %. The H-NMR spectrum was in accordance with the structure.

Acrvlate Polymer (XXII): 140 mg (0.3 mmol) XXI, 127 mg (0.3 mmol) XIX, 218 mg (1.4 mmol) hexyl acrylate and 9 mg (0.06 mmol) AIBN were dissolved in 10 ml of benzene The stabilizer in hexyl acrylate had been removed by passing it through aluminium oxide. The reaction mixture was degassed 10 repeated cycles of applied vacuum and nitrogen inlet. The stirred mixture was polymerized for 18 h at 80 °C. Then most of the solvent was drawn off and the residue was precipitated in methanol. The polymer was reprecipitated 3 times from chloroform into methanol.. Yield 0.20 g 41 %. The H-N R spectrum showed that the polymer composition was in accordance with the ratios of the added components. The ratio of first side groups

(benzophenone) to second side groups was 1 :1. High T_a photo aligning materials that gives tilt

Scheme V. Synthesis of vinylpyrrolidone maleimide polymer. XXIII: 0.1 mmol (45 mg) VA maleimide XV, O.l mmol (45 mg) benzophenone XVI, 0.3 mmol (52mg) phenylmaleimide, 0.5 mmol (56 mg) N- vinyl pyrrolidone and 4 mg 2,2'-azobis(2-methylpropionitrile) (AIBN) were dissolved in 4 ml of benzene. The polymerization was performed 47 hours in 60 degrees oil bath. Purification by reprecipitation two times into methanol from a few ml chloroform. 55% yield. 110 mg. The ratio of first side groups (benzophenone) to second side groups was 2:3.

XXIV: 0.1 mmol (45 mg) VA maleimide XV, 0.05mmol (23 mg) benzophenone XVI, 0.35 mmol (60mg) phenylmaleimide, 0.5 mmol (56 mg) N-vinyl pyrrolidone and 4 mg 2,2'-azobis(2-methylpropionitrile) (AIBN) were dissolved in 4 ml of benzene. The polymerization was performed 48 hours in 60 degrees oil bath. Purification by reprecipitation two times into methanol from a few ml chloroform. 22% yield. 40 mg. The ratio of first side groups (benzophenone) to second side groups was 1 :1.

General method of preparing a liquid crystal cell

a) Preparation of the polymer solution: Alignment layers made from the copolymers of the present invention are deposited from 0.2-5 % solution of the copolymers in solvents such as NMP and PGMEA. The copolymer solution is first filtrated through 0.2 μηι filter.

b) Deposition of the copolymer: The copolymer solution is spread onto the surface of clean glass substrates bearing a prefabricated transparent conductive electrode made from ITO, for instance, by means of spinner (at speed 3000 rps). The substrates are kept for some time at room temperature in order to allow the solvent to evaporate. This process can be shortened if the substrates are kept at elevated temperature (e.g. 80-120°C).

c) Photo-orientation of the copolymer: UV illumination of the

experimental substrates coated with photo-sensitive copolymer is performed in standard USHIO equipment (typically UV System USHIO DEEP, type: UIS- S2511 KK-AKB01), giving 5 mW/cm² linearly polarised light from a high pressure mercury UV lamp without UV filters. The lamp used by the present inventors has efficient light wavelengths of 250 nm to 320 nm and 365 nm respectively. The sample is illuminated through an UV filter cutting all wavelengths below 290 nm. The light polarization direction is in the plane of incidence.

d) Cell preparation: The experimental liquid crystal cells consist of two substrates assembled parallel to each other and separated at several μιη distance. The distance between the substrates is fixed usually by glass or polymer spacers. The substrates are facing to each other with their surfaces covered with alignment layer. The cell gap which they form is filled with liquid crystal by means of capillary forces.

e) Evaluation of the alignment characteristics of the copolymers: the evaluation of the alignment of the liquid crystal in the experimental cells, promoted by the alignment layers made from the copolymers of the present invention, is carried out by means of: optical polarizing microscopy and/or Muller matrix spectrometer (I. Dahl, Meas. Sci. Technol. 12, 1938, 2001 ). Preparation of cells and tiit-anqle studies using compounds XVIII and

XXIII as alignment layers

Using 1 % XVIII in PGMEA: 1 wt% of XVIII in PGMEA was spincoated onto a substrate (2000 rpm for 30 seconds) and maintained at100°C for 15 minutes. The substrate was irradiated at 45° (oblique incidence) with linearly polarized UV light (290 nm filter was used to remove UV light below 290 nm). The light polarization was in the plane of incidence. Two substrates produced this way were assembled in a conventional sandwich cell parallel to each other with the alignment film deposited onto the surfaces facing each other. The substrates were arranged to form a gap of about 4 pm filled with a liquid crystal. The substrates were oriented in such way that the illumination directions of the substrates were anti-parallel, forming a so-called anti-parallel liquid crystal cell. A liquid crystal material, MLC 6608 (Merck) (Δε<0), filled in the cell gap at isotropic temperature.

It was found that the p re-tilt of the liquid crystal molecules increased with the exposure time, see Table . Table 1. Usin XVIII

Above, "VA" refers to vertical alignment and "PA" refers to planar alignment. In this context also PA with a small tilt is considered planar alignment.

Using 1 % XXIII in PGMEA: 1wt % XXIII in PMGEA was spincoated onto a substrate (2000 rpm for 30 seconds) and maintained at 00°C for 15 minutes. The substrate was irradiated at 45 degrees (oblique incidence) with linearly polarized UV light (290 nm filter was used to remove UV light below 290 nm). The light polarization was in the plane of incidence. Two substrates produced this way were assembled in a conventional sandwich cell parallel to each other with the alignment film deposited onto the surfaces facing each other. The substrates were arranged to form a gap of about 4 m filled with a liquid crystal. The substrates were oriented in such way that the illumination directions of the substrates were anti-parallel, forming a so-called anti-parallel liquid crystal cell. A liquid crystal material, MLC 6608 (Merck) (Δε<0), filled in the cell gap at isotropic temperature.

Again, it was found that the tilt of the LC molecules increased with the exposure time, see Table 2. Table 2. Usin XXIII

The skilled person realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

1. A polymer compound for use in a surface-director alignment layer, said polymer compound comprising:

a polymer backbone (209) comprising repeating units (24, 205);

a first side group (206) attached to at least some of said repeating units, said first side group comprising a photo-functional moiety (208) comprising at least one benzophenone moiety or derivative thereof; and

a second side group (207) attached to at least some of said repeating units; said second side group having a pronounced shape anisotropy capable of inducing vertical alignment of a liquid crystal material.

2. The polymer compound according to claim 1 , wherein said photo- functional moiety is photo-reactive.

3. The polymer compound according to claim 1 or 2, wherein said second-side group has a linear anisotropy with a long axis extending along the main extension of said second side group and a short axis perpendicular to said long axis, and wherein said second side group is attached end-on to said repeating units.

4. The polymer compound according to any one of claims 1 to 3, wherein the first side group has the following general formula (I):

(I)

wherein Li is a linking group attached to said repeating unit, said S_i comprising 3 to 30 linking atoms;

Ri is hydrogen, halogen, Ci to C20 alkyl, substituted Ci to C₂o alkyl, Ci to C₂o alkoxy, substituted C-i to C₂o alkoxy, Ci to C₂o alkenyl, substituted Ci to C₂o alkenyl, Ci to C20 alkynyl, substituted Ci to C20 alkynyl, Ci to C₂o

aminoalkyl, or substituted Ci to C₂₀ aminoalkyl;

n is 0 to 4;

R₂ and R₃ are each independently hydrogen, halogen, Ci to C3 alkyl, substituted Ci to C₃ alkyl, Ci to C₃ alkoxy, substituted C to C₃ alkoxy, Ci to C₃ aminoalkyl, substituted Ci to C₃ aminoalkyl;

and wherein said second-side rou has the following general formula

(ID

wherein

L₂ is a linking group attached to said repeating unit, said L₂ comprising

3 to 30 linking atoms;

m is 0 or 1

X is -COO-, -CH=CH-, or -C≡C-;

R₄ is hydrogen, halogen, Ci to C₂₀ alkyl, substituted Ci to C₂₀ alkyl, Ci to C₂₀ alkoxy, substituted Ci to C₂₀ alkoxy, Ci to C₂₀ alkenyl, substituted Ci to C₂₀ alkenyl, Ci to C₂o alkynyl, substituted Ci to C₂₀ alkynyl, d to C₂o

aminoalkyl, substituted Ci to C₂₀ aminoalkyl;

n is 0 to 4;

R5 and R₆ are each independently hydrogen, halogen, C-i to C₃ alkyl, substituted Ci to C₃ alkyl, Ci to C₃ alkoxy, substituted Ci to C₃ alkoxy, Ci to C₃ aminoalkyl, substituted Ci to C₃ aminoalkyl.

5. The polymer compound according to claim 4, wherein l_i comprises up to 10 more linking atoms than L₂.

6. The polymer compound according to claim 4, wherein Li comprise up to 6 more linking atoms than L_2l and wherein Ri is hydrogen or halogen, and R₄ is C₃ to C₆ alkyl or C₃ to C₆ alkoxy.

7. The polymer compound according to claim 4 or 5, wherein Li and L₂ are each independently Ci to C30 alkyl, substituted Ci to C₃o alkyl, Ci to C₃₀ alkoxy, substituted Ci to C₃o alkoxy, Ci to C₃₀ alkenyl, substituted Ci to C₃₀ alkenyl, Ci to C₃₀ alkynyl, substituted Ci to C₃₀ alkynyl, Ci to C₃o aminoalkyl, or substituted Ci to C₃o aminoalkyl.

8. The polymer compound according to any one of the claims 1 to 7, wherein the ratio between the number of said first side group and the number of said second side group in said polymer compound is in the range of from 10:1 to 1 :100, such as from 2:1 to 1 :10.

9. The polymer compound according to any one of the claims 1 to 8, wherein the ratio between the number of said first side group and the total number of said repeating units in said polymer compound is in the range from 1 :1 to 1 :100.

10. The polymer compound according to any one of the claims 1 to 9, wherein said repeating units comprise a first repeating unit selected from maleimide, acrylate, methacrylate, vinyl, styrene, N-vinyllactam monomer, and derivatives thereof, and mixtures thereof.

11. The polymer compound according to any one of claims 4 to 10, wherein said first repeating unit is a maleimide, l_i is a C-n alkoxy; Ri, R₂ and R₃ are hydrogen; L₂ and R₄ are C₆ alkoxy; R₅ is H or N-alkylamide; R₆ is H or N-alkylamide; m is 1 ; and X is -COO-.

12. The polymer compound according to any one of claims 4 to 10, wherein said first repeating unit is an acrylate, l_i is a C-n alkoxy; R-i , R₂ and R₃ are hydrogen; L₂ and R₄ are C6 alkoxy; R₅ is H or N-alkylamide; R₆ is H or N-alkylamide; m is 1 ; and X is -COO-.

13. The polymer compound according to claim 10, wherein said repeating units further comprise a second type of repeating units selected from at least one of maleimide, acrylate, methacrylate, vinyl, styrene, N- vinyllactam monomer or mixtures thereof, and derivatives thereof, and mixtures thereof, wherein said second type of repeating units are different from said first type of repeating units, and wherein at least some of said second repeating units are functionalized with said first side group and/or at least some of said second repeating units are functionalized with said second side group.

14. A surface-director alignment layer, comprising at least one polymer compound according to any one of the claims 1 to 13.

15. A liquid crystal device (300), comprising

at least one confining substrate (301 , 302);

a liquid crystal bulk material (303); and

a surface-director alignment layer (304) arranged between said at least one confining substrate and said liquid crystal bulk material, said surface- director alignment layer being in contact with a surface of said liquid crystal bulk material causing liquid crystal molecules comprised in said liquid crystal bulk material to form a desired p re-tilt angle with respect to a surface of said surface-director alignment layer in the absence of an applied electric field, wherein said surface-director alignment layer comprises a polymer compound according to any one of claims 1 to 13.

16. The liquid crystal device according to claim 15, wherein said p re-tilt angle is controllable by photo-irradiating said surface-director alignment layer.

17. The liquid crystal device according to claim 15, wherein said pre-tilt angle is in the range of from 85° to 89.5° with respect to the plane of the surface-director alignment layer.

18. A method of photo-orientation of a surface-director alignment layer comprising the steps of:

providing a substrate;

applying a polymer compound according to claim 1 on a surface of said substrate to provide a surface director alignment layer; and

irradiating said surface-director alignment layer with electromagnetic radiation at an angle of incidence in the range of from 1° to 89° with respect to the substrate normal, said electromagnetic radiation being linearly polarized in the plane of incidence and having a wavelength in the range of from 200 to 400 nm.

19. A method of manufacture of a liquid crystal device according to claim 15, comprising the steps of:

providing a substrate;

providing a first electrode layer on the substrate;

applying a polymer compound according to claim 1 on a surface of said first electrode layer to provide a surface director alignment layer;

irradiating said surface-director alignment layer with a electromagnetic radiation, at an angle of incidence in the range of from 1° to 89° with respect to the substrate normal, said electromagnetic radiation being linearly polarized in the plane of incidence and having a wavelength in the range of from 200 to 400 nm; and.

arranging a liquid crystal material in contact with said alignment layer.

20. Use of a polymer compound according to any one of the claims 1 to 13 in an alignment layer for a liquid crystal device.

21. A display comprising a liquid crystal device according to claim 15 or produced by the method according to claim 19.