WO2010118755A1

WO2010118755A1 - Maleimide-n-vinyllactam based sidechain polymers for lcd alignment layers

Info

Publication number: WO2010118755A1
Application number: PCT/EP2009/002724
Authority: WO
Inventors: Lachezar Komitov; Bertil Helgee; Nils Olsson
Original assignee: Lachezar Komitov; Bertil Helgee; Nils Olsson
Priority date: 2009-04-14
Filing date: 2009-04-14
Publication date: 2010-10-21
Also published as: TWI501985B; KR20120050926A; JP2012523486A; KR101612725B1; TW201041912A; CN102439065A; CN102439065B; JP5701289B2

Abstract

A polymer for use in a surface-director alignment layer is provided, said polymer being a co-polymer comprising maleimide and/or derivatives thereof and N-vinyllactam and/or derivatives thereof, wherein at least some of said repeating units are functionalized with a pendant side-chain. The polymer of the invention is suitable for use in or as alignment layer material in a liquid crystal device.

Description

MALEIMIDE-N-VINYLLACTAM BASED SIDECHAIN POLYMERS FOR LCD

ALIGNMENT LAYERS

Technical Field

The present invention relates to a polymer for use in a surface-director alignment layer, a surface-director alignment layer material comprising such a polymer and a liquid crystal device comprising an alignment layer comprising such a polymer.

Technical Background

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

Liquid crystal molecules are typically relatively rigid molecules having pronounced shape anisotropy, which have the ability to align 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, the desired initial alignment of the liquid crystal layer in the absence of an external field, such as an electric field, is generally achieved by appropriate surface treatment of the confining solid substrate surfaces, such as by applying a so-called alignment layer (orientation layer) on the confining substrate surfaces facing said liquid crystal bulk. The initial liquid crystal alignment is defined by solid surface/liquid crystal interactions in 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 to the confining substrate surfaces, also referred to as homeotropic or vertical alignment (VA) in parallel with the confining substrate surfaces, also referred to as homogeneous or planar alignment (PA), or at a certain tilt angle, also referred to as tilted alignment (TA), with respect to the confining substrate surfaces. The type of alignment employed in a liquid crystal display depends on the desired application of the device.

Known methods for establishing alignment layers are, for instance, the inorganic film vapor deposition method and the organic film rubbing method. 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, and the method thus is not suitable for large-scale production, this method is practically not used.

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, so that the liquid crystal molecules in contact with the layer will be oriented in the rubbing direction.

Polyimides are in most cases used as organic surface coating due to their comparatively advantageous characteristics, such as chemical stability, thermal stability, etc. The application of a polyimide layer generally includes a baking step at 200-300 ⁰C as described below.

Polyimides may be prepared according to, for instance, Scheme I or Scheme Il below: ^!

Polyamic acid

Polyimide

Scheme I

Polyamic acid

Polyimide

Scheme Il

In the first step, equimolar amounts of a tetracarboxylic acid anhydride and a diamine are mixed in an amide solvent, such as N-methylpyrrolidone (NMP). A spontaneous reaction occurs and a polyamic acid, which is a pre- polymer of polyimide, is formed. In this state, the pre-polymer is distributed to its users, such as LCD manufacturers. However, since the pre-polymer solution is unstable at room temperature, the solution is generally cooled upon transportation and storage to avoid degradation, or any other unwanted chemical reaction, of the pre-polymer.

Generally, the polyamic acid is diluted by the liquid crystal device manufacturer to about 5 %, often with a mixture of NMP and Butyl Cellosolve 4:1 (w/w).

cV⁰

VJ

NMP Butyl Cellosolve

The polyamic acid is generally applied using, for instance, spin coating or some type of printing technique on a glass substrate coated with a transparent, patterned indium tin oxide (ITO) electrode layer. The layer of polyamic acid is then dried in an oven at around 100⁰C, and thereafter heated to about 200⁰C for 1-2 h. During this heating cycle polyamic acid is converted to polyimide. This step is also referred to as curing or baking of the polyimide. The resulting polyimide is thermally very stabile and insoluble in all solvents. The polymer can only be removed by degrading it, for instance, using an alkaline medium.

A drawback of this organic film application process is the baking step, resulting in both a long production time and high production costs. Furthermore, high temperatures, such as about 200 ⁰C, are undesirable in the manufacturing of, for instance, liquid-crystal-on-silicon (LCOS) and thin film transistors (TFT) since high temperatures may result in decreased yields and thus film defects. The required baking temperature is also too high for use on plastic substrates. It is also difficult to control the anchoring strength between the organic film applied using said organic film application process and a liquid crystal bulk layer.

Further, one drawback of the polyimide approach is that the polyamic acid is very unstable and need to be stored at low temperature, such as in a freezer.

It would be a great advantage if some or all of the above disadvantages could be avoided.

Summary of the invention One object of the present invention is to at least partly overcome the problems of the prior art and to provide a material that advantageously can be utilized in or as an alignment layer material, such as for a liquid crystal device.

The present inventors have found that the above object at least partly can be met by providing a polymer based on maleimide and N-vinyllactam repeating units according to the present claims.

Hence, in a first aspect, the invention relates to a polymer for use in a surface-director alignment layer, said polymer being a copolymer comprising repeating units of maleimide and/or derivatives thereof and N-vinyllactam and/or derivatives thereof, wherein at least some of said repeating units are functionalized with a pendant side-group S^x.

Polymers of the present invention have a high photo and thermal stability. Copolymers of ethylmaleimide with vinylpyrrolidone has been shown to promote temperature stable and high quality alignment layers, the properties of which are comparable to those of commercial polyimides. As long as the side-chains are appropriately chosen so as not to decrease the stability properties by being unstable in themselves, the copolymers are very stable. The solubility of the copolymers with a wide variety of different side- chains is very good in standard solvents, such as NMP and PGMEA.

Compared to conventional polyimides the polymers of the present invention are much more stable in solution, and do not require low temperature storage. Further, the polymers of the present invention are easier and faster to process than polyimides since they form polymer films on glass or plastic substrates well without baking at elevated temperatures, without requiring curing.

The side-groups S^x may be attached to said repeating units via a spacer group L.

The maleimide and N-vinyllactam repeating units may amount to at least 50 %, such as at least 75 %, for example at least 90 %, of the repeating units of the polymer backbone. Furthermore, the ratio between maleimide and N-vinyllactam units in the polymer backbone may be in the range of from 1 :10 to 10:1 , such as 1 :2 to 2:1 , for example about 1 :1.

The N-vinyllactam of the polymer of the present invention may be selected from the group consisting of N-vinylpyrrolidone, N-vinylpiperidine and N-vinylcaprolactame. Further, the polymer may comprise repeating units selected from among: repeating units functionalized with an anchoring side- group S⁴; repeating units functionalized with a pendant side-groups S⁵ selected from optionally substituted, halogenated, branched or straight chained aliphatic and aromatic groups, such as alkyls, aryls or alkylaryls, polyethers, siloxanes or alcohols; repeating units functionalized with an ion movement inhibiting side-group S⁶; repeating units functionalized with reactive, preferably photo-reactive, side-groups S⁷; and repeating units functionalized with photo-responsive side-groups S⁸. The polymer optionally comprises a crosslinking group.

In embodiments of the invention, the polymer comprises repeating units functionalized by a pendant side-group S¹ having pronounced shape anisotropy. Said side-group S¹ having a pronounced shape anisotropy may be selected from among side-groups S1^a inducing planar alignment of a liquid crystal material and side-groups S1^b inducing vertical alignment of a liquid crystal material.

At least part of the above side-groups may be attached to said repeating units via the maleimide-nitrogen. In another aspect, the invention relates to a surface-director alignment layer, comprising at least one polymer according to the invention deposited onto a solid substrate.

In yet another aspect, the invention relates to a liquid crystal device, comprising at least one confining substrate, a liquid crystal bulk and an surface-director alignment layer arranged between said at least one confining substrate and said liquid crystal bulk, in contact with a surface of said liquid crystal bulk, wherein said surface-director alignment layer comprises a polymer according to the invention. For example, the liquid crystal device may comprise: a first and a second confining substrate sandwiching said liquid crystal bulk layer; a first surface-director alignment layer is arranged between said first confining substrate and said liquid crystal bulk, in contact with a surface of said liquid crystal bulk; and a second surface-director alignment layer is arranged between said first confining substrate and said liquid crystal bulk, in contact with a surface of said liquid crystal bulk; wherein at least one of, preferably both, said first and said second surface-director alignment layer comprises a polymer according to the invention.

In a further aspect, the invention relates to a method for photo- orientation of a surface-director alignment layer material, comprising: providing an alignment layer material according to the invention; and illuminating said alignment layer material with linearly polarized electromagnetic radiation having a wavelength in the range of from 200 to 300 nm. In particular, the linearly polarized electromagnetic radiation may have a wavelength in the range of 230 to 270 nm, for example about 250 nm.

Brief Description of the Drawings

Figure 1 is a block diagram illustrating a method for photo-orientation of an alignment layer material of the present invention.

Figure 2 illustrates¹ a liquid crystal device utilizing an alignment layer of the present invention.

Detailed Description of the Invention

The present invention relates to a polymer which is suitable for use in or as an alignment layer material for a liquid crystal device. The polymer of the invention is a co-polymer comprising repeating units of maleimide, N-vinyllactames, such as vinylpyrrolidone, N- vinylpipehdine and N-vinylcaprolactame, and derivatives thereof, wherein at least a part of said repeating units are functionalized with a pendant side- group.

As used herein, a "co-polymer comprising repeating units of maleimide and N-vinyllactam" and analogue expressions, refer to a co-polymer obtainable by polymerization from a mixture of maleimide monomers and N- vinyllactam monomers.

N-vinyllactam is a compound of the following chemical formula I:

where x in (CHb)_x refer to an integer between 2 and 10, typically 3-5.

As used herein, a maleimide is a compound of the following chemical formula II: /

\\- L-S^x (II)

wherein S^x is selected from among H, methyl, ethyl or from a group of side- groups S¹, S⁴, S⁵, S⁶, S⁷ and S⁸ described herein, and L is an optionally present spacer group, connecting the side-group S^x to the maleimide ring nitrogen. In cases where the spacer L is not present, the side-group S^x is directly attached to the maleimide ring nitrogen.

A mixture of N-vinyllactam and maleimide can be polymerized by methods well known in the art, typically radical addition copolymerization, forming a copolymer of maleimide and N-vinyllactam.

In such a mixture of N-vinyllactam and maleimide, it is possible to use a blend of different maleimides, i.e. a blend of at least two different maleimides with different side-groups S^x and/or spacer L. This will lead to a co-polymer with more than one type of side-groups and/or linkers attached to the polymer backbone.

Such a blend of different maleimides may be utilized to tailor the properties of the resulting polymer. Non-limiting examples of such blends of maleimides will be further described below in the present specification. Examples of suitable polymerization reactions will be described below in the Examples.

The result from the polymerization is a copolymer according to the invention, comprising repeating units of maleimide and N-vinyllactam having the following general formula:

In the resulting copolymer, the maleimide and N-vinyllactam units are not regularly distributed, and hence, the exact structural formula of the polymer is impossible to produce as the polymers are not perfect alternating copolymers as the figure would imply.

However, at a 1 :1 molar ratio of maleimide and N-vinyllactam monomers in the reaction mixture, the arrangement in the resulting polymer tends to be an essentially alternating maleimide-N-vinyllactam-maleimide-N- vinyllactam structure.

As will be apparent to those skilled in the art, the polymer of the present invention may also comprise additional repeating units, other than maleimide and N-vinyllactam repeating units. Examples of such repeating units include monomers or pre-polymers that can be incorporated in a polymer chain by means of radical addition polymerization, typically any polymehzable ethylenically unsaturated compound known to those skilled in the art. Examples of such polymerizable, ethylenically unsaturated compounds include, but are not limited to styrenes and (meth)acrylates. In embodiments of the present invention, the maleimide and the N- vinyllactam repeating units together amounts to a significant portion of the repeating units in the polymer. Typically, they constitute at least about 50 %, such as at least about 75 %, for example at least about 90 % based on the number of repeating units of a polymer chain. 100 % maleimide and N- vinyllactam is also contemplated. In polymers of the invention, the number ratio between maleimide repeating units and N-vinyllactam repeating units may for example be in the range of between 1 :10 and 10:1 , preferably in the range between 1 :2 to 2:1 , for example at ratio of about 1 :1. Being close to a 1 :1 ratio results in a more stable polymer composition during polymerization and less need to control the feed composition closely to keep the same polymer composition during the polymerization time, as this copolymerization is close to alternating. A high ratio (excess of maleimide) will result in a rather short polymer.

A low ratio (excess of N-vinyllactam) will result in a polymer with a low degree of side-group (S^x) content, as it is normally the maleimides that carry the side- groups S^x.

The co-polymers of the present invention are soluble in standard solvents, such as NMP and PGMEA, and a solution of the polymer can thus be deposited on a substrate by means of conventional deposition methods, such as, but not limited to spin-coating, spray-coating, doctorblade coating, roll-coating, flexprinting, ink-jet printing, dipping, etc.

As the polymer can be prepared and dissolved in its polymerized state, an alignment layer may easily be obtained by merely evaporating the solvent after deposition onto a substrate. This enables the use of temperature sensitive substrates as no excessive heating is needed to obtain the alignment layer.

Further, as the polymer does not need curing after deposition the total time for forming the alignment layer on the substrate is fast as it only involves deposition and then evaporation of a very thin solvent film.

The pendant side-group S^x attached to maleimide monomers, typically via the maleimide ring nitrogen, may for example include side-groups selected from among: optionally substituted, such as fluorinated, straight or branched chained alkyl groups, aryl groups and alkylaryl groups, anchoring side-groups, crosslinking side-groups, ion movement inhibiting side-group, reactive, preferably photo-reactive, side-groups, photo-responsive side- groups and side-groups having a pronounced shape anisotropy. However, also other side-groups may be contemplated for use in the present invention. The side-groups S^x may, if needed, each be attached to the polymer backbone by means of a spacer group L, typically comprising between 0 and 30 linking atoms, such as 0 or between 5 and 15, where 0 linking atoms represents the case where the side-group is attached directly on the polymer backbone via a direct bond. However, spacer groups longer than 30 linking atoms are also contemplated for use in the present invention. A spacer group L may for example be utilized to facilitate the attachment of a side-group S^x to the maleimide ring nitrogen and may also be utilized to increase the mobility of the attached side-groups.

The spacer group L is typically an optionally substituted saturated or unsaturated hydrocarbon chain, such as an alkyl, alkenyl, aryl, alkylaryl alkoxy or polyether, aryloxy group, siloxane chain. Typical examples include C₅-C₁₅ alkyl or alkyloxy chains.

In embodiments of the invention, side-groups S¹ having a pronounced shape anisotropy may be attached to the polymer of the invention. For example, the molecules of a liquid crystal material (mesogens) are typically molecules exhibiting such pronounced shape anisotropy.

As used herein the term "side-group having pronounced shape anisotropy" 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.

In embodiments of the present invention, the side-groups having pronounced shape anisotropy are mesogenic side-groups

As defined in Handbook of Liquid Crystals, vol 1 Fundamentals, pub. John Wiley & Sons Inc, 1998, the term "mesogenic" relates to a structure that is generally compatible with mesophase formation". This definition is used throughout the present specification.

Hence, a mesogenic side-group is a side-group having a mesogenic structure. In "Handbook of Liquid Crystals, (supra)" a mesogen is equalled with a

"mesomorphic compound", i.e. a compound that under suitable conditions of temperature, pressure and concentration can exist as a mesophase, i.e. a liquid crystal phase.

Mesogens are typical examples of molecules having pronounced shape anisotropy. Hence, side-groups comprising mesogens falls under this definition. On the other hand, the side-group does not have to be mesogens in order to be a mesogenic side-group, and also mesogenic side-groups not being mesogens are contemplated for use in the present invention.

Side-groups S¹ in accordance with the present invention having pronounced shape anisotropy may have the shape of a linear, calamitic, such as rod- or lath-like, discotic, sanidic,. pyramidal, bent (also referred to as banana), chevron, or other shape exhibiting a pronounced shape anisotropy. The surface properties of a substrate influences the orientation of the mesogens of a liquid crystal layer in contact with said substrate surface, at least in the interface between the substrate surface and the liquid crystal layer. Typically, the interface conditions propagate through the liquid crystal layer, so that the whole liquid crystal layer orientation is influenced by the orientation at the interface.

Two main routes are used to influence the orientation of the liquid crystal layer. One route (surface energy route) is to use the general surface properties to increase compatibility with the tails of the liquid crystal materials which promotes vertical alignment (low surface energy) as in Example 10 below, or increase compatibility with the mesogenic cores which promotes planar alignment (high surface energy) as in Example 12 below. Another route is to use steric interactions to align the liquid crystals. Such steric interactions are especially pronounced when a liquid crystal layer is in contact with a substrate surface which presents groups with pronounced shape anisotropy, such as linear-, lath- and disc-like, and as a result the mesogens of the interface between the liquid crystal layer and the substrate surface tend to align to the orientation of the groups with defined shape anisotropy presented on the substrate surface.

For example, a substrate surface presenting groups, with shape anisotropy, such as linear-, lath- and disc-like, being aligned essentially planar to the substrate surface, the mesogens in the interface towards the substrate surface also tends to align planar to the substrate surface. On the other hand, utilizing a substrate surface that presents groups with shape anisotropy being aligned essentially vertical to the substrate surface, the mesogens in the interface towards the substrate surface also tends to align vertical to the substrate surface.

Alternatively, the side-groups with pronounced shape anisotropy align to the orientation of the mesogens of the liquid crystal layer at said interface. By utilizing side-groups having defined shape anisotropy in a polymer of the invention, a liquid crystal material, such as the LC-layer in a liquid crystal device, tends to align to the orientation of the side-groups attached to the polymer backbone. A polymer of the present invention having side-groups with pronounced shape anisotropy can thus advantageously be used as or in an alignment layer in a liquid crystal device, since it influences the orientation of the mesogens in at least the interface between such an alignment layer and a liquid crystal layer in contact with the alignment layer.

In one embodiment, side-groups S^1a with pronounced shape anisotropy, such as linear-, lath- and disc-like, that induces planar alignment of the mesogens in the interface, i.e. essentially parallel to the substrate surface, may be attached to the polymer of the invention. An alignment layer based on such a polymer can be used to promote planar alignment of a liquid crystal layer. An illustrative, non-limiting example of such a polymer is described below in Example 6. In another embodiment, side-groups S^1b with pronounced shape anisotropy, such as linear-, lath- and disc-like, that induces vertical alignment of the mesogens in the interface, i.e. essentially perpendicular to the substrate surface, may be attached to the polymer of the invention. An alignment layer based on such a polymer can be used to promote vertical alignment of liquid crystal molecules. An illustrative, non-limiting example of such a polymer is described below in Examples 1-3.

For example, for linear side-groups having pronounced shape anisotropy, side-on attachment of side-groups may promote horizontal (planar) alignment, with the long axis along the polymer surface. On the other hand, end-on attachment of linear side-groups may promote vertical (homeotropic) alignment, with its long axis perpendicular to the polymer surface. However, in the case of a side-group having a bent shape (so-called banana shape), side-on attachment to the polymer backbone may promote tilted alignment of liquid crystal molecules, and end-on attachment may promote planar alignment of liquid crystal molecules.

"Linear" side-groups having pronounced shape anisotropy are also known under different terms, such as calamitic, lath-like and rod-shaped side- groups. A linear side-group has a well defined long axis extending along the main extension of the molecule, and a short axis perpendicular to the long axis.

As used herein, the term "end-on attached" refers to a linear side- group having pronounced shape anisotropy that is attached to the polymer backbone by means of an spacer that is attached to the side-group at or near an end of a long axis of the side-group molecule, so that the spacer is essentially parallel to the long axis of the side-group. 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. As used herein, the term "side-on attached" refers to a linear side- group having pronounced shape anisotropy that is attached to the polymer backbone by means of spacer that is attached to the side-group so that the spacer is essentially perpendicular to the long axis of the side-group molecule.

For further definitions of terms relating to liquid crystals and related terms, reference is made to "Definitions of basic terms relating to low-molar- mass and polymer liquid crystals" (IUPAC Recommendations 2001 , Pure Appl Chem, VoI 73, No 5, pp 845-895, 2001), hereby incorporated by reference in its entirety.

In embodiments of the invention, 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 include 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-group S⁴ are disclosed in the following structural formulas (III) to (Vl) where Z, as above, 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:

The physicochemical properties of the polymer of the invention, such as glass transition temperature T₉, 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 S⁵ 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. These properties, in particular surface energy, are known to strongly influence the orientation direction of the liquid crystals and the anchoring strength.

Typical examples of S⁵ side-groups include optionally fluorinated, such as perfluorated, Ci-Ci₈-alkyls, such as C₄-Ci₂-alkyls or -alcohols, and those groups defined above as spacers L. For example, when S⁵ side-groups are alkyl chains, T₉ of the polymer generally decreases in proportion to the length of the alkyl chain. On the other hand, when S⁵ side-groups are aryl groups, T₉ of the polymer generally increases.

In polymers of the invention where part of the repeating units are functionalized with side-groups S¹ having pronounced shape anisotropy, as is described above, it is preferred that the polymer also comprises repeating units functionalized with side-groups S⁵. In such a polymer, the ratio of S¹ to S⁵ are in the range of 1 : 100 to 100: 1 , typically from about 1 : 1 to 1 :20. However it shall be noted that polymers of the invention having only S¹ or S⁵ side-groups also work well for some applications.

In embodiments of the invention ion movement inhibiting S⁶ groups may utilized in the alignment layer to reduce the concentration of mobile ions in the LC bulk material, and thus to reduce the conductivity of the LC 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 polymers in the composition of the present invention may be crosslinked by a crosslinking group connecting two separate repeating units, such as by internal crosslinking, connecting two repeating units within the same polymer backbone or external crosslinking, connecting two separate polymer backbones, where at least one of the two represents a polymer of the present invention. It is also possible to use a crosslinking group to connect one polymer of the present invention with another polymer. In this invention crpsslinking is preferably done with photo-reactive groups such as those described below, but can be performed with thermally induced reactions as well using any reactive groups attached to the polymer.

The copolymer of the present invention may comprise reactive, preferably photo-reactive side-groups S⁷. Reactive side-groups can be used to fix the obtained arrangement of the alignment layer, so as to make it less susceptible to temperature induced changes.

Photo-reactive side-groups with shape anisotropy, can be aligned in a desired orientation by illumination with e.g. linearly-polarized light, ie. light can be used to dimerize/polymerize only those groups that have a particular orientation compared to the polarized light, thus gaining a prefered orientation of those groups in the polymer.

This can have the advantage that photo-orientation can often be a one step process that can both align the, material and crosslink it so the alignment orientation gets higher thermal stability at the same time. Photo-orientation also has the benefit that it does not introduce dirt, scratches or static discharges as rubbing methods used today can do. It is also easier to control accurately, resulting in high yield. Dimerization/polymerization of reactive side-groups may be achieved between two reactive side-groups attached to one and the same polymer backbone or between two reactive side-groups attached to separate polymer backbones.

Possible photo-reactive groups with shape anisotropy include, but are not limited to, chalcones, coumarins, cinnamoics.

The copolymers of the present invention may comprise photo- responsive side-groups S⁸.

Photo-responsive side-groups with shape anisotropy can be aligned in a desired orientation by illumination with e.g. linearly polarized light. For example, and in combination with reactive groups, light can be used to orient the side-groups, and thereafter, a dimerization/polymerization as described above, can be used to irreversibly fixate the obtained orientation with the same benefits as the photo-reactive groups above to the liquid crystal alignment. In this case the photo reactive group does not have to have shape anisotropy as the orientation can be performed by a photo responsive group with shape anisotropy. Alternatively, the photo-responsive groups could be oriented by light at an elevated temperature,_! and thereafter the temperature is lowered, whereby a reversible fixation of the orientation is achieved. Photo-responsive groups suitable for use in the present invention include, but are not limited to, azo- containing groups, stilbenes, etc.

Furthermore, photo-orientation of a polymer according to the present invention may be achieved by photo-orientation of the polymer backbone using UV light, independent of the presence of any photo-responsive and/or photo-reactive side-groups S⁷. Such photo-orientation of the polymer backbone is schematically illustrated in Fig. 1. Firstly, an alignment layer material comprising at least one polymer according to the present invention is provided. The alignment layer material may be coated onto a substrate as described hereinafter. Secondly, in order to achieve photo-orientation of the polymer backbone, the alignment layer material is illuminated with linearly polarized UV light having a wavelength in the range of 200 to 300 nm. For example, the UV light may have a wavelength in the range of from 230 to 270nm, such as about 250nm. <

Maleimide monomers functionalized with linkers and/or side-groups as defined in the context of this invention may be synthesized according to methods well known in the art.

Exemplary synthesis processes are described below in the Examples section of the present specification.

For example maleic anhydride may be reacted with an amine to form a functionalized maleimide monomer. Alternatively, maleimide (with a hydrogen connected to the maleimide ring nitrogen) can be reacted with an alcohol to form a functionalized maleimide.

A double-sided liquid crystal device 100 is illustrated in Fig. 2 and comprises a first confining substrate 101 and a second confining substrate 102 being mutually spaced apart. In the space between the substrates 101 , 102, a liquid crystal material 103 is disposed, sandwiched between the substrates 101 and 102.'

On the first substrate 101 is arranged a surface-director alignment layer of the present invention 104 in contact with the liquid crystal material 103. Depending on the presence of anchoring side-groups on the polymer of the present invention, the surface-director alignment layer 104 may be chemically bonded to the substrate 101. The surface-director alignment layer 104 comprises at least one polymer of the present invention as is described above and hence, this surface-director alignment layer 104 promotes a homeotropic alignment of the liquid crystal material 103 at least at or near the interface towards the surface- director alignment layer 104.

Those skilled in the art will recognize that a liquid crystal device 100 of the present invention may comprise means for obtaining an electrical field in the liquid crystal material 103. Changes in the electrical field typically effects switching of the liquid crystal material. For example such means may be represented by a pair of electrodes. In the embodiment described in figure 1 , a first electrode 105 is arranged between the alignment layer 104 and the substrate 101 , and a second electrode 107 is arranged on the second substrate 102.

The surface-director alignment layer 104 will induce a homeotropic alignment of the surface-director of the liquid crystal material 103.

A second alignment layer 106 is arranged between the second substrate 102 and the liquid crystal material 103. This second alignment layer may also comprise a polymer of the present invention, or may alternatively be of another kind of alignment layer material.

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.

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, H) 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 IV. Sample mesogenic and alkyl monomer synthesis.

N-dodecylmaleimide (VIII): Dodecylamine 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. lmides from hexyl and shorter are liquids and must be more carefully chromatographed using the same conditions as above. Yield: 41 %. NMR (CDCI₃): δ, pattern, number of protons; 0.85, t, 3; 1.25, m; 2.6, m, 2; 3.5, t, 2; 6.7, s, 2.

Maleimide Xl: 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 %. 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 %. 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 %. NMR (CDCI₃): 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 V. Mesogenic monomers used for planar alignment (PA) and photo-alignment.

In general, for the monomers one of the two methods described in scheme IV is used. Other ways to make maleimides known in the art may also be used. S

XXII

Scheme Vl: Ethylphenyl maleimide A third way to make maleimides is shown in scheme Vl above. All materials were used as is from the supplier. All steps were performed under nitrogen atmosphere.

To a stirred solution of maleic anhydride(10 mmol, 980 mg) in 30 ml toluene ethylaniline(10 mmol, 1220 mg) was added dropwise. Solution was stirred for an hour while a precipitate came. ZnBr2 (10 mmol, 2250 mg) was added and the solution warmed to 80 ⁰C. At high temperature hexamethyldisilazane (HMDS) (14 mmol, 2250 mg) was added dropwise with syringe during 15 minutes, too fast addition will cause formation of char. After heating for one hour the reaction mixture was poured into 180 ml 0.5% HCI and the aqueous phase extracted twice with 150 ml EtAc. The organic phases was then washed with 150 ml saturated NaHCO₃ and brine in succession. The solution was dried and purified with chromatography using toluene/EtAc 19/1 as eluant. Yield was 66 %.

Polymer synthesis

Example 1: Copolymer promoting vertical alignment (VA)

Scheme VII: VA copolymer preparation

0.4 mmol (225 mg) maleimide XIII, 1.6 mmol (424 mg) N- dodecylmaleimide VIII, 2.0 mmol (222 mg) NVP purified by passing through aluminium oxide and 0.12 mmol (19 mg) 2,2'-Azobis(2-methylpropionitrile) (AIBN) were dissolved in 10 ml of benzene in a round bottomed flask and the flask was sealed with a rubber septum. Through the septum via a syringe needle vacuum followed by nitrogen inlet was applied. Ten repeated vacuum - nitrogen inlet cycles was used to get rid of oxygen in the flask. The flask was heated in an oil bath thermo-stated to 60 ⁰C. After 15 h the solution was poured into methanol and the formed polymer precipitated. The polymer was re-precipitated twice from chloroform into methanol and at last once from chloroform into an acetone/methanol 1/3 mixture. The solvent was decanted and pure methanol was added. Finally the polymer was placed in a vial and heated on a hot plate to drive off residual solvent. The last traces of solvent were removed by heating the polymer to 60 ⁰C for 2 hours in a vacuum oven. Yield: 0.7 g, 80 %. NMR (CDCI₃): δ, pattern; 0.9, t; 1 - 5 side-group signals on top of broad main-chain signals; 6.9, 2d; 7.1 , d; 8.1 , d. The polymer composition with respect to mesogen/alkyl ratio was determined using methyl and aromatic signals in¹H NMR and found to be 1/4.2. This means that 19.2 % of the side-groups, pyrrolidone groups ignored, are mesogens.

This material was deposited as an alignment layer onto the inner surfaces of glass substrates of a sandwich cell prepared according the described procedures. The cell is filled with the nematic liquid crystal MLC 6608 with negative dielectric anisotropy (Δε<0) and is first examined under polarizing microscope for defining the kind of alignment of the liquid crystal promoted by the alignment layer. The observed alignment in this cell was homeotropic, i.e. along the substrate normal. The pre-tilt angle of the preferred direction of liquid crystal alignment from the substrate normal was subsequently measured by means of the Muller matrix spectrometer. If the alignment layer is mechanically rubbed, a small pre-tilt, less 1 degree, is obtained.

The alignment layer also showed a good thermal stability.

Example 2: Copolymer XXVI

Scheme VIII. VA copolymer preparation with fluorinated alkane VA copolymer: 0.5 mmol (331 mg) mesogenic maleimide XIII, 0.5 mmol (228 mg) perfluorohexyl propyl maleimide XXV , 1.5 mmol (400 mg) dodecylmaleimide,2.5 mmol (277mg) NVP purified by passing through aluminium oxide and 0.15 mmol (25 mg) 2,2'-Azobis(2-methylpropionitrile) (AIBN) were dissolved in 25 ml of benzene. The polymerization was performed 40 hours in oil bath at 60⁰C. Purification by reprecipitation three times into methanol from a few ml chloroform and once into methanol/acetone 2/1 to get the final polymer XXVI.

The material was tested in the same way as in example one with similar yields and properties. The material gives vertical alignment with slow filling speed due to the low surface energy that the fluorinated groups have.

Example 3: High Tg VA polymer

Scheme IX: High T₉ VA copolymer

0.40 mmol (180 mg) maleimide XIII₁ 1.6 mmol (277 mg) N- phenylmaleimide, 2.0 mmol (222 mg) N-vinyl pyrrolidone and 0.12 mmol (19 mg) 2,2'-azobis(2-methylpropionitrile) (AIBN) were dissolved in 10 ml of benzene. The mixture was polymerized and worked up according to the description in example 1. Yield: 0.26 g 38 %. NMR (CDCI₃) δ, pattern; 0.9, bs; 1.1 - 5 side-group signals on top of broad main-chain signals; 6.9, bs; 7.0 - 7.6, bs. With stiff side-groups and mesogens the glass temperature can be increased compared to the case with soft alkane chains. This material shows a Tg of about 200 ⁰C. This material was deposited as an alignment layer onto the inner surfaces of glass substrates of a sandwich cell prepared according the described procedures. The cell is filled with the nematic liquid crystal MLC 6608 with negative dielectric anisotropy (Δε<0) and is first examined under polarizing microscope for defining the kind of alignment of the liquid crystal promoted by the alignment layer. The observed alignment in this cell was homeotropic, i.e. along the substrate normal. Next, the pre-tilt angle of the preferred direction of liquid crystal alignment from the substrate normal was measured by means of the Muller matrix spectrometer. If the alignment layer is mechanically rubbed, a pre-tilt is obtained.

The alignment layer also showed a good thermal stability.

Scheme X: VA copolymer with caprolactam

VA copolymer with N-vinyl ε-caprolactam XXX : 0.4 mmol (225 mg) maleimide XIII. 1.6 mmol (424 mg) N-dodecylmaleimide, 2.0 mmol (278 mg) N-vinyl ε-caprolactam and 0.12 mmol (19 mg) 2,2'-Azobis(2- methylpropionitrile) (AIBN) dissolved in 10 ml of benzene in a round bottom flask and the flask was sealed with a rubber septum. Through the septum via a syringe needle vacuum followed by nitrogen inlet was applied. Ten repeated vacuum - nitrogen inlet cycles was used to get rid of oxygen in the flask. The flask was heated in an oil bath thermo-stated to 60 ⁰C. After 15 h the solution was poured into methanol and the formed polymer precipitated. The polymer was re-precipitated twice from chloroform into methanol and at last once from chloroform into an acetone/methanol 1/3 mixture. The solvent was decanted and pure methanol was added. Finally the polymer was placed in a vial and heated on a hot plate to drive off residual solvent. The last traces of solvent were removed by heating the polymer to 70 ⁰C for 4 hours in a vacuum oven. Yield: 0.75 g, 81 %.

Example 5: Copolymer promoting planar alignment (PA)

Scheme Xl. Copolymerization

0.4 mmol (265 mg) maleimide XVI, 1.6 mmol (334 mg) N- octylmaleimide, 2.0 mmol (222 mg) NVP purified by passing through aluminium oxide and 0.12 mmol (19 mg) 2,2'-Azobis(2-methylpropionitrile) (AIBN) were dissolved in 10 ml of benzene. The polymerization and work-up were carried out in accordance with the preparation in Example 1. Yield: 0.66 g, 80 %. NMR (CDCI₃): δ, pattern; 0.9, t; 1 - 5 side-group signals on top of broad main-chain signals; 6.5, d; 6.9, d; 7.1 , d; 8.0, d. The polymer composition with respect to mesogen/alkyl ratio was determined using methyl and aromatic signals in¹H NMR and found to be 1/1.8. This means that 36 % of the side-groups, pyrrolidone groups ignored, are mesogens.

This material was deposited as an alignment layer onto the inner surfaces of glass substrates of a sandwich cell prepared according the described procedures. The cell is filled with the nematic liquid crystal MLC 6873-100 with positive dielectric anisotropy (Δε>0) and is first examined under polarizing microscope for defining the kind of alignment of the liquid crystal promoted by the alignment layer. The observed alignment in this cell was homogenous, i.e. essentially parallel to the substrate. The alignment layer also showed a good thermal stability.

Example 6

Scheme XII. Photo-reactive PA copolymer

0.1 mmol (67 mg) maleimide XVII, 0.4 mmol (106 mg) N- hexylmaleimide, 0.5 mmol (54 mg) NVP purified by passing through aluminium oxide and 0.03 mmol (5 mg) 2,2'-Azobis(2-methylpropionitrile) (AIBN) were dissolved in 20 ml of benzene in a round bottomed flask and the flask was sealed with a rubber septum. Through the septum via a syringe needle vacuum followed by nitrogen inlet was applied. Ten repeated vacuum- nitrogen inlet cycles was used to get rid of oxygen in the flask. The flask was heated in an oil bath thermo-stated to 60 ⁰C. After 17 h the majority of the benzene was evaporated in a rotavapor and the solution was poured into methanol and the formed polymer precipitated. The polymer was re- precipitated twice from chloroform into methanol. Finally the polymer XXXIV was placed in a vial and residual solvent removed at room temperature. Yield: 0.10 g, 44 %.

This material was deposited as an alignment layer onto the inner surfaces of glass substrates of a sandwich cell prepared according the described procedures. However instead of rubbing the sample it was put under linearly polarized light, 15 minutes with 5mW/cm² to orient the sample. The cell is filled with the nematic liquid crystal MLC 6873-100 with positive dielectric anisotropy (Δε>0) and is first examined under polarizing microscope for defining the kind of alignment of the liquid crystal promoted by the alignment layer. The observed alignment in this cell was homogenous, i.e. paralell to the substrate .

Example 7: VA copolymer run according to the procedure of Example 6 above using XVIII as the monomer.

Scheme XIII. Photo-reactive VA copolymer 0.2 mmol (118 mg) maleimide XVIII, 1.8 mmol (477 mg) N- octylmaleimide, 2.0 mmol (222 mg) NVP purified by passing through aluminium oxide and 0.12 mmol (19 mg) 2,2'-Azobis(2-methylpropionitrile) (AIBN) were dissolved in 10 ml of benzene. The polymerization and work-up were carried out in accordance with the preparation of Example 1.

Yield: 0.66 g, 81 %, cinnamic ester 5 % dodecyl group 95 %. NMR (CDCI₃): δ, pattern; 0.9, t; 1 - 5 broad signals, 6.5, d; 6.9, d; 7.08, d; 7.5, d; 7.8, d. This material was deposited as an alignment layer onto the inner surfaces of glass substrates of a sandwich cell prepared according the described procedures. The cell is filled with the nematic liquid crystal MLC 6608 with negative dielectric anisotropy (Δε<0) and is first examined under polarizing microscope for defining the kind of alignment of the liquid crystal promoted by the alignment layer. The observed alignment in this cell was homeotropic, i.e. along the substrate normal. The alignment layer also showed a good thermal stability.

Example 8: Alkyl chains

Scheme XIV Copolymer with only alkyl side-groups.

209 mg (1.0 mmol) N-octylmaleimide, 111 mg (1.0 mmol) NVP purified by passing through aluminium oxide and 9.8 mg (0.12 mmol) 2,2'-Azobis(2- methylpropionitrile) (AIBN) were dissolved in 5 ml of benzene. The polymerization and work-up were carried out in accordance with the preparation of VA copolymer above. Yield: 0.23 g, 72 %. NMR (CDCI₃) pattern; 0. 85, s; 1.2, s; 1.5, s; 1.6 - 4.5 broad signals.

This material was deposited as an alignment layer onto the inner surfaces of glass substrates of a sandwich cell prepared according the described procedures. The cell is filled with the nematic liquid crystal MLC 6873-100 with positive dielectric anisotropy (Δε>0) and is first examined under polarizing microscope for defining the kind of alignment of the liquid crystal promoted by the alignment layer. The observed alignment in this cell was varying depending on rubbing and thermal conditions. With only alkyl chains the material has low anchoring strength and sensitive alignment.

Example 9

Scheme XV: Low surface energy material

Without mesogens the material has generally lower anchoring strength and more sensitive alignment.

200 mg fluorinated chain (0.44 mmol) 184 mg alkyl chain (0.88 mmol), 146 mg N-Vinyl pyrrolidone (1.32 mmol) purifie by passing through activated aluminum oxide and 13 mg AIBN were dissolved in 13 ml benzene. The polymerization and work-up were carried out in accordance with the example 1. Yield 180mg. 34%.

The material was used to make cells in the same way as in example 8. It gives very poor wetting properties compared to polymer XXXVI due to the very low surface energy due to the fluorinated chains.

Example 10

Scheme XVI: Copolymers with varying lengths of the alkyl groups.

Copolymer with varying alkane chain length. 8+12 alkane chains. 1 mmol(209mg) N-octylmaleimide, 1 mmol(265mg) N- dodecylmaleimide, 2 mmol(222 mg) NVP purified by passing through aluminium oxide and 0.12 mmol (19 mg) 2,2'-Azobis(2-methylpropionitrile) (AIBN) were dissolved in 10 ml Benzene. The polymerization and work-up were carried out in accordance with the preparation in Example 1. Yield: 0.55 g, 79 %.

The material was used to make cells in the same way as in Example 1. It gives homeotropic alignment. By incorporating an extra longer alkane compared to Example 8 the VA stability of the material is increased and this material shows a homeotropic alignment when tested using the method described in Example 8. The alignment is more rubbing and temperature dependant than when mesogens are used, as in Example 1.

Example 11

Scheme XVII: Copolymer with a short alkane chain

1 mmol(153 mg) N-butylmaleimide, 1 mmol(111 mg) NVP purified by passing through aluminium oxide and 0.06 mmol (9.7 mg) 2,2'-Azobis(2- methylpropionitrile) (AIBN) were dissolved in 5 ml Benzene. The polymerization and work-up were carried out in accordance with the preparation in Example 1. Yield: 0.1 g, 38 %.

When in contrast to the previous example a shorter alkyl chain is used the PA promoting properties increase and the butylmaleimide based copolymer gives PA alignment and higher glass temperature. The material was used to make cells in the same way as in Example 8. It gives planar alignment with rubbing-induced pre-tilt.

When oriented by UV light as described in general method c2 below it also gives good, uniform planar alignment. Example 12

Scheme XVIII. Ethylphenyl based PA copolymer

PA copolymer: 1mmol (201 mg) ethyl-phenyl-maleimide XXII , 1 mmol (111 mg) NVP purified by passing through aluminium oxide and 0.06 mmol (10 mg) 2,2'-Azobis(2-methylpropionitrile) (AIBN) were dissolved in 10 ml of benzene. The polymerization was performed overnight in 60 degrees oil bath. Purification by reprecipitation three times into methanol from a few ml chloroform Yield: 0.180 g, NMR (CDCI₃) δ, pattern; number of protons; 1.1- 1.2 broad triplet from terminal ethyl carbon; 3, 1 - 5 side-group signals on top of broad main-chain signals; 6.9-7.35; broad peak from aromatic protons (broad due to near the polymer backbone), 4.

This material was deposited as an alignment layer onto the inner surfaces of glass substrates of a sandwich cell prepared according the described procedures. The cell is filled with the nematic liquid crystal MLC 6873-100 with positive dielectric anisotropy (Δε>0) and is first examined under polarizing microscope for defining the kind of alignment of the liquid crystal promoted by the alignment layer. The observed alignment in this cell was homogenous, i.e. essentially parallel to the substrate. The alignment layer also showed a good thermal stability. This material is soluble in PGMEA and NMP. As a general "extended" backbone with high glass temperature and planar alignment this seems a good choice for adding other groups to as an alternative to alkane chains.

When oriented by UV light as described in general method c2 below it also gives good uniform planar alignment. i i

Example 13

Scheme XIX

PA copolymer: 1'mmol (201 mg) ethylphenyl maleimide, 0.5 mmol (175mg) 2-hexyloxybiphenyl maleimide, 1.5 mmol (166 mg) NVP purified by passing through aluminium oxide and 0.09 mmol (15 mg) 2,2'-Azobis(2- methylpropionitrile) (AIBN) were dissolved in 15 ml of benzene. The polymerisation was performed 22 hours in 60 degrees oil bath. Purification by re-precipitation three times into methanol from a few ml chloroform. It is soluble in NMP and PGMEA. This material was deposited as an alignment layer onto the inner surfaces of glass substrates of a sandwich cell prepared according the described procedures. The cell is filled with the nematic liquid crystal MLC 6873-100 with positive dielectric anisotropy (Δε>0) and is first examined under polarizing microscope for defining the kind of alignment of the liquid crystal promoted by the alignment layer. The observed alignment in this cell was homogenous, i.e. essentially parallel to the substrate normal but with tilt highly sensitive to the rubbing conditions. When oriented by UV light as described in general method c2 below it gives good uniform planar alignment. xample 14

XLIV

Scheme XX

Maleimidecopolymerfunctionalized with hydroxy group. 1.0 mmol (197 mg) 6-hydroxyhexylmaleimide (1.0 mmol (207 mg) N-octylmaleimide , 2.0 mmol (222 mg) N-vinyl pyrrolidone and 0.12 mmol (19 mg) 2,2'-Azobis(2- methylpropionitrile) (AIBN) were dissolved in a mixture of 5 ml benzene and 5 ml ethanol. The mixture was polymerized at 60⁰C for 15 h. The polymer was precipitated in diethyl ether and re-precipitated once from benzene/ethanol into ether. Yield: 0.29 g. NMR (CDCI₃) δ pattern, number of protons; 0.75, bs; 1.35 - 1.75, 2 broad singlets and a shoulder; 1.8 - 4.5 broad signals including not separated signals from methylene protons adjacent to imide nitrogen and alcohol at 3.4 and 3,6 respectively. Photo copolymer from functionalizationi 00 mg corresponding to about

0.16 mmol -OH groups of the resulting copolymer XLIII, 50 mg (0.20 mmol) 4-hexyloxycinnamic acid(XLIV), 10 ml of methylene chloride, and a catalytic amount of 4-methylaminopyridine was stirred until everything was dissolved. The mixture was cooled on an ice bath and 50 mg (0.24 mmol) DCC (dicyclohexylcarbamide) was dissolved in a small amount of methylene chloride and added. The reaction mixture was stirred at room temperature over night. The formed urea precipitate was filtered off and most of the solvent was removed under vacuum. Attempts to precipitate the polymer in methanol failed. The solvents were removed under vacuum and methanol was added to the residue and heated to reflux. The solvent was decanted while hot and the procedure was repeated twice. This workup method needs refining but a low yield 40 mg, of polymer XLV was obtained. NMR (CDCI₃): δ, pattern; 0.85, t; 1.1 - 5 side group signals on top of broad main-chain signals, remaining -CH₂-OH shown as a shoulder on N-CH₂ ; 6.25, d; 6.85, d; 7.45, d; 7.6, d. The cinnamic ester/alkyl group ratio was found to be 1/1.5 and the conversion of hydroxyl groups to ester was about 66 %.. This material was deposited as an alignment layer onto the inner surfaces of glass substrates of a sandwich cell prepared according the described procedures. The cell is filled with the nematic liquid crystal MLC 6873-100 with positive dielectric anisotropy (Δε>0) and is first examined under polarizing microscope for defining the kind of alignment of the liquid crystal promoted by the alignment layer. The observed alignment in this cell was homogenous, i.e. along the substrate. The alignment layer also showed a good thermal stability and could be photo-oriented with UV light. The example shows just one of very many alternative ways to make side chain maleimide/vincaprolactame copolymers by functionalization.

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 μm 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). Then the substrates are kept for some time at room temperature in order to get rid of the solvent. This process can be shorter if the substrates are kept at elevated temperature (80° - 120⁰C).

c1. Mechanical treatment

The substrates covered with alignment layer comprising the copolymer of the present invention,, e.g. promoting planar alignment, may be rubbed mechanically along a certain direction. Rubbing might not be necessary in the case of alignment layer made from the copolymer promoting vertical alignment. c2. Photo-orientation of the copolymer

UV illumination of the experimental substrates covered with photosensitive copolymer was performed in standard USHIO equipment giving 5 mW/cm² linearly polarised light from high pressure mercury UV lamp without UV filters. The photosensitive polymer was deposited onto the glass substrate by spin coating from 1% wt solution of the polymer in PGMEA. Then the substrate was exposed on UV illumination at normal incidence. The illumination time was chosen to be 15 minutes.

d. Cell preparation

The experimental cells consist of two substrates assembled parallel to each other and separated on several μm 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

• Muller matrix spectrometer (I. Dahl, Meas. Sci. Technol. 12, 1938, 2001)

To summarize, it is shown herein that polymers of the present invention are suitable to use in or as alignment layers for liquid crystal devices.

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.

Claims

1. Polymer for use in a surface-director alignment layer, said polymer being a copolymer comprising repeating units of maleimide and/or derivatives thereof and N-vinyllactam and/or derivatives thereof, wherein at least some of said repeating units are functionalized with a pendant side-group S^x.

2. Polymer according to claim 1 , wherein maleimide and N-vinyllactam repeating units amount to at least 50 %, such as at least 75 %, for example at least 90 %, of the repeating units of the polymer backbone.

3. Polymer according to any of the preceding claims, wherein the ratio between maleimide and N-vinyllactam units in the polymer backbone is in the range of from 1 :10 to 10:1 , such as 1 :2 to 2: 1 , for example about 1 :1.

4. Polymer according to any of the preceding claims, wherein said N- vinyllactam is selected from the group consisting of N-vinylpyrrolidone, N- vinylpiperidine and N-vinylcaprolactame.

5. Polymer according to any of the preceding claims, wherein said polymer comprises repeating units selected from among: repeating units functionalized with an anchoring side-group S⁴; repeating units fώhctionalized with a pendant side-groups S⁵ selected from optionally substituted, halogenated, branched or straight chained aliphatic and aromatic groups, such as alkyls, aryls or alkylaryls, polyethers, siloxanes or alcohols; repeating units functionalized with an ion movement inhibiting side- group S⁶; repeating units functionalized with reactive, preferably photo-reactive, side-groups S⁷; and repeating units functionalized with photo-responsive side-groups S⁸.

6. Polymer according to any of the preceding claims, comprising a crosslinking group.

7. Polymer according to any of the preceding claims, comprising repeating units functionalized by a pendant side-group S¹ having pronounced shape anisotropy.

8. Polymer according to any of the preceding claims, wherein at least part of said side-groups are attached to said repeating units via the maleimide-nitrogen.

9. Polymer according to any of the preceding claims wherein said side- groups S are attached to said repeating units via a spacer group L.

10. Polymer according to any one of the claims 7 to 9, wherein said side-group S¹ having a pronounced shape anisotropy is selected from among side-groups S1^a inducing planar alignment of a liquid crystal material, and side-groups S1^b inducing vertical alignment of a liquid crystal material.

11. Surface-director alignment layer, comprising at least one polymer according to any of the claims 1 to 10 deposited onto a solid substrate.

12. Liquid crystal device, comprising at least one confining substrate, a liquid crystal bulk and an surface-director alignment layer arranged between said at least one confining substrate and said liquid crystal bulk, in contact with a surface of said liquid crystal bulk, wherein said surface-director alignment layer comprises a polymer according to any of the claims 1 to 10.

13. Liquid crystal device according to claim 12, comprising: a first and a second confining substrate sandwiching said liquid crystal bulk layer; a first surface-director alignment layer is arranged between said first confining substrate and said liquid crystal bulk, in contact with a surface of said liquid crystal bulk; and a second surface-director alignment layer is arranged between said first confining substrate and said liquid crystal bulk, in contact with a surface of said liquid crystal bulk; wherein at least one of, preferably both, said first and said second surface-director alignment layer comprises a polymer according to any of the claims 1 to 10.

14. Method for photo-orientation of a surface-director alignment layer material, comprising providing a surface-director alignment layer material according to claim 11 ; and illuminating said surface-director alignment layer material with linearly polarized electromagnetic radiation having a wavelength in the range of from 200 nm to 300 nm.

15. Method according to claim 14, wherein said linearly polarized electromagnetic radiation has a wavelength in the range of from 230 to

270 nm, for example about 250 nm.