WO2019190756A1

WO2019190756A1 - Regioselectively substituted cellulose esters

Info

Publication number: WO2019190756A1
Application number: PCT/US2019/022173
Authority: WO
Inventors: Robert Jacks SHARPE; Bin Wang
Original assignee: Eastman Chemical Co
Current assignee: Eastman Chemical Co
Priority date: 2018-03-28
Filing date: 2019-03-14
Publication date: 2019-10-03
Anticipated expiration: 2020-09-28
Also published as: TW201942233A

Abstract

The present application discloses regioselectively substituted cellulose esters comprising aryl substituted acryloyl substituents, and films made from the regioselectively substituted cellulose esters.

Description

REGIOSELECTIVELY SUBSTITUTED CELLULOSE ESTERS

FIELD OF THE INVENTION

This invention relates to the field of cellulose chemistry, cellulose ester compositions, methods of making cellulose ester, and films made from the cellulose esters.

BACKGROUND OF THE INVENTION

Cellulose is a /3-1 ,4-linked polymer of anhydroglucose. Cellulose is typically a high molecular weight, polydisperse polymer that is insoluble in water and virtually all common organic solvents. The use of unmodified cellulose in wood or cotton products such as housing or fabric is well known. Unmodified cellulose is also utilized in a variety of other applications usually as a film, such as cellophane, as a fiber, such as viscose rayon, or as a powder, such as microcrystalline cellulose used in pharmaceutical

applications. Modified cellulose such as cellulose esters are also widely utilized in a wide variety of commercial applications. Prog. Polym. Sci. 2001 , 26, 1605-1688. Cellulose esters are generally prepared by first converting cellulose to a cellulose triester before hydrolyzing the cellulose triester in acidic aqueous media to the desired degree of substitution. Hydrolysis of cellulose triacetate under these conditions yields a random copolymer that can consist of 8 different monomers depending upon the final degree of substitution. Macromolecules 1991 , 24, 3050.

This application describes new regioselectively substituted cellulose esters prepared by first treating cellulose with trifluoroacetic anhydride in trifluoroacetic acid, followed by the addition of acyl donors and/or acyl donor precursors. The regioselectively substituted cellulose esters can be formed into films having C- optical activity.

SUMMARY OF THE INVENTION

The present invention discloses a regioselectively substituted cellulose ester comprising: (i) a plurality of R¹-CO- substituents;

(ii) a plurality of R⁴-CO- substituents;

(iii) a plurality of pivaloyl substituents; and

(iv) a plurality of hydroxyl substituents,

wherein the degree of substitution of R¹-CO- at the C2 position

(“C2DSRI -CO-”) is in the range of from about 0.7 to about 1.0;

wherein the degree of substitution of R¹-CO- at the C3 position

(“C3DSRI -CO-”) is in the range of from about 0.2 to about 0.9;

wherein the degree of substitution of R¹-CO- at the C6 position

(“C6DSRI -CO-”) is in the range of from about 0 to about 0.1 ; wherein the degree of substitution of R⁴-CO- at the C2 position

(“C2DSR4-CO-”) is in the range of from about 0 to about 0.15;

wherein the degree of substation of R⁴-CO- at the C3 position

(“C3DSR4-CO-”) is in the range of from about 0 to about 0.15;

wherein the degree of substitution of R⁴-CO- at the C6 position

(“C6DSR4-CO-”) is in the range of from about 0.1 to about 0.9;

wherein the degree of substitution of the pivaloyl (“DSPV”) is in the range of from about 0 to about 0.7;

wherein the degree of substitution of hydroxyl is in the range of from about 0.1 to about 0.8;

wherein R¹ is chosen from (Ci-2o)alkyl; halo(Ci-2o)alkyl; (C2-2o)alkenyl, or (C3-7)cycloalkyl;

wherein R⁴ is -(C2-2o)alkenyl-(C6-2o)aryl, wherein the aryl is

unsubstituted or substituted by 1 to 6 R⁵ groups, and wherein the alkenyl is unsubstituted or substituted cyano; and

wherein R⁵ is chosen from (Ci-e)alkyl, halo(Ci-6)alkyl, (Ci-6)alkoxy, halo(Ci-6)alkoxy, halo, (C3-7)cycloalkyl, (C6-io)aryl, nitro, (C6-2o)aryl, or (C6-2o)aryl-C02-.

The present invention also discloses films made from the

regioselectively substituted cellulose esters disclosed herein. DETAILED DESCRIPTION

In this specification and in the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings.

The singular forms“a,”“an,” and“the” include plural referents unless the context clearly dictates otherwise.

Values may be expressed as“about” or“approximately” a given number. Similarly, ranges may be expressed herein as from“about” one particular value and/or to“about” or another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent“about,” it will be understood that the particular value forms another aspect.

A“NRZ film” is a film that satisfies the following conditions: Using the Nz value, which is n_z = (n_x-nz)/(n_x-n_y) = 0.5. Alternatively, using the Rth value, which Rth=[n_z-(n_x+n_y)/2]^*d = 0. Here, n_x, n_y, and n_z are refractive indexes of the film in the x, y, and z directions, respectively, and d is the film thickness.

Optical films are commonly quantified in terms of birefringence which is, in turn, related to the refractive index n. The refractive index can typically be in the range of 1 .4 to 1 .8 for polymers in general, and can be

approximately 1 .46 to 1 .50 for cellulose esters. The higher the refractive index, the slower a light wave propagates through that given material.

For an unoriented isotropic material, the refractive index will be the same regardless of the polarization state of the entering light wave. As the material becomes oriented, or otherwise anisotropic, the refractive index becomes dependent on material direction. For purposes of the present invention, there are three refractive indices of importance, denoted n_x, n_y, and n_z, which correspond to the machine direction (“MD”), the transverse direction (“TD”) and the thickness direction respectively. As the material becomes more anisotropic (e.g., by stretching), the difference between any two refractive indices will increase. This difference is referred to as the "birefringence." Because there are many combinations of material directions to choose from, there are correspondingly different values of birefringence. The two that are the most common, namely the planar birefringence (or“in-plane”

birefringence) A_e and the thickness birefringence (or“out-of-plane”

birefringence) Ath, are defined as:

(1 a) A_e= n_x - n_y

(1 b) Ath= n_z - (n_x + n_y)/2

The birefringence A_e is a measure of the relative in-plane orientation between the MD and TD directions and is dimensionless. In contrast Ath gives a measure of the orientation of the thickness direction, relative to the average planar orientation.

Another term often used with regards to optical films is the optical retardation R. R is simply the birefringence times the thickness d, of the film in question. Thus,

(2a) Re = A_ed = (n_x - n_y)d

(2b) Rth = Athd = [n_z - (n_x + n_y)/2]d

Retardation is a direct measure of the relative phase shift between the two orthogonal optical waves and is typically reporte d in units of nanometers (nm). Note that the definition of Rth varies among some authors, particularly with regards to the sign (+/-), depending on how Rth is calculated.

Materials are also known to vary with regards to their

birefringence/retardation behavior. For example, most materials when stretched will exhibit a higher refractive index along the stretch direction and a lower refractive index perpendicular to the stretch. This follows because, on a molecular level, the refractive index is typically higher along the polymer chain's axis and lower perpendicular to the chain. These materials are commonly termed "positively birefringent" and represent most standard polymers, including current commercial cellulose esters. Note that, as we will describe later, a positively birefringent material can be used to make either positive or negative birefringent films or waveplates. To avoid confusion, the birefringence behavior of the polymer molecule itself will be referred to as the "intrinsic birefringence" and is a property of the polymer. From a material optics standpoint, intrinsic birefringence is a measure of the birefringence that would occur if the material was fully stretched with all chains perfectly aligned in one direction (for most polymers this is a theoretical limit since they can never be fully aligned). For purposes of the present invention, it also provides a measure of the sensitivity of a given polymer to a given amount of chain orientation. For example, a sample with high intrinsic birefringence is going to exhibit more birefringence during film formation than a sample with low intrinsic birefringence, even though the relative stress levels in the film are approximately the same.

Polymers can have positive, negative, or zero intrinsic birefringence. Negative intrinsic birefringent polymers exhibit a higher refractive index perpendicular to the stretch direction (relative to the parallel direction). Certain styrenics and acrylics can have negative intrinsic birefringent behavior due to their rather bulky side groups. Depending on composition, some cellulose esters having aromatic ring structures can exhibit negative intrinsic

birefringence as well. Zero intrinsic birefringence, in contrast, is a special case and represents materials that show no birefringence with stretching and thus have a zero intrinsic birefringence. Such materials can be ideal for certain optical applications as they can be molded, stretched, or otherwise stressed during processing without showing any optical retardation or distortion.

The actual compensation film(s) that is used in an LCD can take on a variety of forms including biaxial films where all three refractive indices differ and two optical axes exist, and uniaxial films having only one optical axis where two of the three refractive indices are the same. There are also other classes of compensation films where the optical axes twist or tilt through the thickness of the film (e.g., discotic films), but these are generally of lesser importance. Generally, the type of compensation film that can be made is limited by the birefringence characteristics of the polymer (i.e., positive, negative or zero birefringence). The sign can be placed before or after the type of film (e.g., +A or A+). A few examples are described below.

In the case of uniaxial films, a film having refractive indices such that

(3a) n_x > n_y = n_z "+A" optical film is denoted as a "+A" optical film. In such films, the x-direction (machine direction) of the film has a high refractive index, whereas the y and thickness directions are approximately equal in magnitude (and lower than n_x). This type of film is also referred to as a positive uniaxial crystal structure with the optic axis along the x-direction. Such films can be made by uniaxially stretching a positive intrinsic birefringent material using, for example, a film stretcher.

In contrast, a "-A" uniaxial film is defined as

(3b) n_x < n_y = n_z "-A" optical film

where the x-axis refractive index is lower than the other directions (which are approximately equal). One method for making a -A optical film is to stretch a negative intrinsic birefringent polymer or, alternately, by coating a negatively (intrinsic) birefringent liquid crystal polymer onto a surface such that the molecules are lined up in a preferred direction (for example, by using an underlying etched orientation layer).

In terms of retardation,“±A” optical films have the following relationship between R_e and Rth, shown in (3c):

(3c) Rth = -Re/2 "±A" optical films

Another class of uniaxial optical films is the C optical film which can also be "+C" or "-C". The difference between a C and an A optical film is that, in C optical films, the unique refractive index (or optical axis) is in the thickness direction as opposed to in the plane of the film. Thus,

(4a) n_z > n_y = n_x "+C" optical film

(4b) n_z < n_y = n_x "-C" optical film

C optical films can be produced by taking advantage of the stresses that form during solvent casting of a film. Tensile stresses are generally created in the plane of the film due to the restraint imposed by the casting belt, which are also equi-biaxial stretched in nature. These tend to align the chains in the plane of the film resulting in -C or +C films for positive and negative intrinsic birefringent materials respectively. As many cellulose ester films used in displays are solvent cast, and many are essentially positive birefringent, then it is apparent that solvent cast cellulose esters normally only produce -C optical films. These films can also be uniaxially stretched to produce +A optical films (assuming the initial as-cast retardation is very low).

Besides uniaxial optical films, it is also possible to use biaxial oriented films. Biaxial films are quantified in a variety of ways including simply listing the 3 refractive indices n_x, n_y and n_z in the principal directions (along with the direction of these principal axes). Generally, n_x¹ n_y ¹n_z.

One specific biaxial oriented film has unique optical properties to compensate light leakage of a pair of crossed polarizer or in-plane switching (“IPS”) mode liquid crystal displays. The optical film has a parameter Nz in the range of from about 0.4 to about 0.9, or equals about 0.5, where Nz is defined as

(5) Nz = (n_x-n_z)/(n_x-n_y)

This parameter gives the effective out-of-plane birefringence relative to the in-plane birefringence. Nz can be chosen to be about 0.5 when used as a compensation film for a pair of crossed polarizers. When Nz is about 0.5, the corresponding out-of-plane retardation, Rth, equals about 0.0 nm.

To show the optical film’s compensation effect, the following light transmission or leakage of a pair of crossed polarizers with and without compensation films is calculated by computer simulation.

“Degree of substitution” means the average number of substituents per anhydroglucose monomer of the cellulose ester. Degree of substitution can refer to a substituent attached to the anhydroglucose monomer, for example an acyl group. Degree of substitution can also refer to the number of free hydroxyl (i.e, DSOH) groups on the anhydroglucose monomer. The degree of substitution can specify the position on the anhydroglucose monomer. For example, the degree of substitution can apply to the C2, C3, or C6 position of the anhydroglucose monomer(e.g., C2DS, C3DS, C6DS):

“Degree of polymerization” means the number of glucose units that make up one polymer molecule.

Regioselectively substituted cellulose esters suitable for use in making optical films can comprise a plurality of alkyl-acyl substituents and a plurality of aryl-acyl substituents. As used herein, the term“acyl substituent” shall denote a substituent having the structure:

o

A or R-CO-.

Such acyl groups in cellulose esters are generally bound to the pyranose ring of the cellulose via an ester linkage (i.e., through an oxygen atom).

As used herein, the term“alkyl-acyl” shall denote an acyl substituent where“R” is an alkyl group. Often the carbon units of the alkyl groups are included; for example, (Ci-6)alkyl-acyl. Examples of alkyl-acyl groups include acetyl, propionyl, butyryl, and the like.

As used herein, the term“alkyl” shall denote a hydrocarbon substituent. Alkyl groups suitable for use herein can be straight, branched, or cyclic, and can be saturated or unsaturated. The carbon units in the alkyl group is often included; for example (Ci-6)alkyl. Alkyl groups suitable for use herein include any (C1 -20), (C1 -12), (C1 -5), or (C1 -3) alkyl groups. In various embodiments, the alkyl can be a C1 -5 straight chain alkyl group. In still other embodiments, the alkyl can be a C1 -3 straight chain alkyl group. Specific examples of suitable alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, octyl, decyl, dodecyl, cyclopentyl, and cyclohexyl groups. The acylating agents can be any known in the art for acylating cellulose to produce cellulose esters. In one embodiment of the invention, the acylating reagent is one or more C1 -C20 straight- or branched-chain alkyl or aryl carboxylic anhydrides, carboxylic acid halides, diketene, or acetoacetic acid esters. Examples of carboxylic anhydrides include, but are not limited to, acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, hexanoic anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauric anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, substituted benzoic anhydrides, phthalic anhydride, and isophthalic anhydride. Examples of carboxylic acid halides include, but are not limited to, acetyl, propionyl, butyryl, hexanoyl, 2-ethylhexanoyl, lauroyl, palmitoyl, benzoyl, substituted benzoyl, and stearoyl halides. Examples of acetoacetic acid esters include, but are not limited to, methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate, and tert-butyl acetoacetate. In one embodiment of the invention, the acylating reagent is at least one C2-C9 straight- or branched-chain alkyl carboxylic anhydrides selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, and stearic anhydride. The acylating reagents can be added after the cellulose has been dissolved in the tetraalkylammonium alkylphosphate. If so desired, the acylating reagent can be added to the tetraalkylammonium alkylphosphate prior to dissolving the cellulose in the tetraalkylammonium alkylphosphate. In another embodiment, the tetraalkylammonium alkylphosphate and the acylating reagent can be added simultaneously to the cellulose to produce the cellulose solution.

“Haloalkyl” means an alkyl substituent where at least one hydrogen is replaced with a halogen group. The carbon units in the haloalkyl group is often included; for example halo(Ci-6)alkyl. The haloalkyl group can be straight or branched. Nonlimiting examples of haloalkyl include chloromethyl, trifluoromethyl, dibromoethyl and the like. “Alkenyl” means an alkyl group of at least two carbon units containing at least one double bond. The carbon units in the alkenyl group is often included; for example (C2-6)alkenyl. The alkenyl group can be straight or branched. Nonlimiting examples of alkenyl include ethenyl, allyl, 1 -butenyl, and the like.

“Cycloalkyl” means a cyclic alkyl group having at least three carbon units. The carbon units in the cycloalkyl group is often included; for example (C3-8)cycloalkyl. Nonlimiting examples of cycloalkyl include cyclopropyl, cyclobutyl, cyclohexyl, cycloheptyl, and the like.

“Aryl” means an aromatic carbocyclic group. The aryl group can be monocyclic or polycyclic. If one of the rings in the polycyclic ring system is aryl, then the polycyclic ring system is considered aryl. In other words, all of the carbocyclic rings in a polycyclic aryl group do not have to be aromatic.

The carbon units in the aryl group is often included; for example (C6-2o)aryl. Nonlimiting examples of aryl include phenyl, naphthalenyl, 1 , 2,3,4- tetrahydronaphthalenyl, and the like.

“Heteroaryl” means an aryl where at least one of the carbon units in the aryl ring is replaced with a heteroatom such as O, N, and S. The heteroaryl is ring can be monocyclic or polycyclic. Often the units making up the heteroaryl ring system is include; for example a 5- to 20-membered ring system. A 5- membered heteroaryl means a ring system having five atoms forming the heteroaryl ring. Nonlimiting examples of heteroaryl include pyridinyl, quinolinyl, pyrimidinyl, thiophenyl and the like.

“Alkoxy” means alkyl-O- or an alkyl group terminally attached to an oxygen group. Often the carbon units are included; for example (Ci-6)alkoxy. Nonlimiting examples of alkoxy include methoxy, ethoxy, propoxy and the like.

“Haloalkoxy” means alkoxy where at least one of the hydrogens is replace with a halogent. Often the carbon units are included; for example halo(Ci-6)alkoxy. Nonlimiting examples of haloalkoxy include trifluoromethoxy, bromomethoxy, 1 -bromo-ethoxy and the like.

“Halo” means halogen such as fluoro, chloro, bromo, or iodo. A“Reverse A film” is a film that satisfies the following conditions: The in-plane retardation is in the range of from about 100 nm to about 300 nm as measured at 589 nm, R_e450/R_e550 is less than 1 , and R_e650/R_e550 is greater than 1 , wherein R_e450, R_e550, and R_e650 are the in-plan retardation values of the film as measured at a wavelength of 450 nm, 550 nm and 650 nm, respectively.

As used herein the term“chosen from” when used with“and” or“or” have the following meanings: A variable chosen from A, B and C means that the variable can be A alone, B alone, or C alone. A variable A, B, or C means that the variable can be A alone, B alone, C alone, A and B in combination, B and C in combination, A and C in combination, or A, B, and C in combination.

The cellulose esters prepared by the methods of this invention are useful in a variety of applications. Those skilled in the art will understand that the specific application will depend upon the specific type of cellulose ester as factors such as the type of acyl substituent, DS, MW, and type of cellulose ester copolymer significantly impact cellulose ester physical properties. Prog. Polvm. Sci. 2001 , 26, 1605-1688.

In yet another embodiment of the invention, the cellulose esters are used in coating applications. Examples of coating applications include but, are not limited to, automotive, wood, plastic, or metal coatings. Examples of preferred cellulose esters for use in coating applications include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, or a mixture thereof.

In still another embodiment of the invention, the cellulose esters are used as thermoplastics.

In still another embodiment of the invention, the cellulose esters are used in applications involving solvent casting of film. Examples of these applications include photographic film and protective and compensation films for liquid crystalline displays. Examples of preferred cellulose ester for use in solvent cast film applications include cellulose triacetate, cellulose acetate, cellulose propionate, and cellulose acetate propionate. In still another embodiment of the invention, the cellulose esters of the present invention can be used in applications involving solvent casting of film. Examples of such applications include photographic film, protective film, and compensation film for LCDs. Examples of cellulose esters suitable for use in solvent cast film applications include, but are not limited to, cellulose triacetate, cellulose acetate, cellulose propionate, and cellulose acetate propionate.

In an embodiment of the invention, films are produced comprising cellulose esters of the present invention and are used as protective and compensation films for LCD. These films can be prepared by solvent casting as described in US 2009/0096962 or by melt extrusion as described in US 8,344,134, both of which are incorporated in their entirety in this invention to the extent they do not contradict the statements herein.

When used as a protective film, the film is typically laminated to either side of an oriented, iodinated PVOH polarizing film to protect the PVOH layer from scratching and moisture, while also increasing structural rigidity. When used as compensation films (or plates), they can be laminated with the polarizer stack or otherwise included between the polarizer and liquid crystal layers. These compensation films can improve the contrast ratio, wide viewing angle, and color shift performance of the LCD. The reason for this important function is that for a typical set of crossed polarizers used in an LCD, there is significant light leakage along the diagonals (leading to poor contrast ratio), particularly as the viewing angle is increased. It is known that various combinations of optical films can be used to correct or "compensate" for this light leakage. These compensation films must have certain well-defined retardation (or birefringence) values, which vary depending on the type of liquid crystal cell or mode used because the liquid crystal cell itself will also impart a certain degree of undesirable optical retardation that must be corrected.

Compensation films are commonly quantified in terms of birefringence, which is, in turn, related to the refractive index n. For cellulose esters, the refractive index is approximately 1.46 to 1.50. For an unoriented isotropic material, the refractive index will be the same regardless of the polarization state of the entering light wave. As the material becomes oriented, or otherwise anisotropic, the refractive index becomes dependent on material direction. For purposes of the present invention, there are three refractive indices of importance denoted n_x, n_y, and n_z, which correspond to the MD, the TD, and the thickness direction, respectively. As the material becomes more anisotropic ( e.g . by stretching), the difference between any two refractive indices will increase. This difference in refractive index is referred to as the birefringence of the material for that particular combination of refractive indices. Because there are many combinations of material directions to choose from, there are correspondingly different values of birefringence. The two most common birefringence parameters are the planar birefringence defined as A_e = n_x-n_y, and the thickness birefringence (Ath) defined as: Ath = n_z-(n_x+n_y)/2. The birefringence A_e is a measure of the relative in-plane orientation between the MD and TD and is dimensionless. In contrast, Ath gives a measure of the orientation of the thickness direction, relative to the average planar orientation.

Optical retardation (R) is related the birefringence by the thickness (d) of the film: R_e = A_ed = (n_x-n_y)d; Rth = Athd = [n_z-(n_x+n_y)/2]. Retardation is a direct measure of the relative phase shift between the two orthogonal optical waves and is typically reported in units of nanometers (nm). Note that the definition of Rth varies with some authors, particularly with regards to the sign (±)

Materials are also known to vary with regards to their

birefringence/retardation behavior. For example, most materials when stretched will exhibit a higher refractive index along the stretch direction and a lower refractive index perpendicular to the stretch. This follows because, on a molecular level, the refractive index is typically higher along the polymer chain's axis and lower perpendicular to the chain. These materials are commonly termed "positively birefringent" and represent most standard polymers including all current conventional cellulose esters.

To avoid confusion, the birefringence behavior of the polymer molecule itself will be referred to as the "intrinsic birefringence" and is a property of the polymer. From a material optics standpoint, intrinsic birefringence is a measure of the birefringence that would occur if the material was fully stretched with all chains perfectly aligned in one direction (for most polymers this is a theoretical limit since they can never be fully aligned). For purposes of the present invention, it also provides a measure of the sensitivity of a given polymer to a given amount of chain orientation. For example, a sample with high intrinsic birefringence is going to exhibit more birefringence during film formation than a sample with low intrinsic birefringence, even though the relative stress levels in the film are approximately the same.

Polymers can have positive, negative, or zero intrinsic birefringence. Negative (intrinsic) birefringent polymers exhibit a higher refractive index perpendicular to the stretch direction (relative to the parallel direction), and consequently also have a negative intrinsic birefringence. Certain styrenics and acrylics are known to have negative intrinsic birefringent behavior due to their rather bulky side groups. Depending on composition, some cellulose esters with aromatic ring structure exhibit negative intrinsic birefringence as well. Zero intrinsic birefringence, in contrast, is a special case and represents materials that show no birefringence with stretching and thus have a zero intrinsic birefringence. Such materials are ideal for optical applications as they can be molded, stretched, or otherwise stressed during processing without showing any optical retardation or distortion.

The actual compensation film(s) that is used in an LCD can take on a variety of forms including biaxial films where all three refractive indices differ and two optical axes exist, and uniaxial films having only one optical axis where two of the three refractive indices are the same. There are also other classes of compensation films where the optical axes twist or tilt through the thickness of the film (e.g. discotic films), but these are of lesser importance to understanding the present invention. The important point is that the type of compensation film that can be made is limited by the birefringence

characteristics of the polymer (i.e. positive, negative or zero intrinsic birefringence).

Compensation films or plates can take many forms depending upon the mode in which the LCD display device operates. For example, a C-plate compensation film is isotropic in the x-y plane, and the plate can be positive (+C) or negative (-C). In the case of +C plates, n_x=n_y<n_z. In the case of -C plates, n_x=n_y>n_z. Another example is A-plate compensation film which is isotropic in the y-z direction, and again, the plate can be positive (+A) or negative (-A). In the case of +A plates, n_x>n_y=n_z. In the case of -A plates, n_x<n_y=n_z.

In general, aliphatic cellulose esters provide values of Rth ranging from about 0 to about -350 nm at a film thickness of 60 pm. The most important factors that influence the observed Rth is type of substituent and the DSOH.

Film produced using cellulose mixed esters with very low DSOH had Rth values ranging from about 0 to about -50 nm. US Patent No. 8,344,134. By significantly increasing DSOH of the cellulose mixed ester demonstrated that larger absolute values of Rth ranging from about -100 to about -350 nm could be obtained. US Appln. No. 2009/0096962. Cellulose acetates typically provide Rth values ranging from about -40 to about -90 nm depending upon DSOH.

In order to obtain the desired R_e values using the cellulose esters of the present invention, the films must be stretched. By adjusting the stretch conditions such as stretch temperature, stretch type (uniaxial or biaxial), stretch ratio, pre-heat time and temperature, and post-stretch annealing time and temperature the desired R_e, and Rth, can be achieved. The precise stretching conditions depend upon the specific composition of the cellulose esters, the amount and type of plasticizer, and the glass transition

temperature of that specific composition. Flence, the specific stretching conditions can vary widely. The stretching temperature can range from 140°C to 190 °C. The stretch ratio can range from 1.0 to 1.3 in the machine direction (MD) and can range from 1.1 to 1.8 in the TD. The pre-heat time can range from 10 to 300 s, and the pre-heat temperature can be the same as the stretch temperature. The post-annealing time can range from 0 to 300 s, and the post-annealing temperature can range from 10°C to 40°C below the stretching temperature. Film thickness is depends upon the film thickness before stretching and upon the stretching conditions. After stretching, the preferred film thickness is from about 10 pm to about 200 pm. More preferred is when the film thickness is from about 20 pm to about 100 pm. Even more preferred is when the film thickness is from about 25 pm to about 70 pm.

Regioselectively Substituted Cellulose Esters

The present invention discloses a regioselectively substituted cellulose ester comprising: (i) a plurality of R¹-CO- substituents; (ii) a plurality of R²- CO- substituents; (iii) a plurality of R⁴-CO- substituents; and (iv) a plurality of hydroxyl substituents, wherein the degree of substitution of R¹-CO- at the C2 position (“C2DSRI -CO-”) is in the range of from about 0.7 to about 1.0; wherein the degree of substitution of R¹-CO- at the C3 position (“C3DSRI -CO-”) is in the range of from about 0.2 to about 0.9; wherein the degree of substitution of R¹- CO- at the C6 position (“C6DSRI -CO-”) is in the range of from about 0 to about 0.1 ; wherein the degree of substitution of R⁴-CO- at the C2 position (“C2DSR4- co-”) is in the range of from about 0 to about 0.15; wherein the degree of substation of R⁴-CO- at the C3 position (“C3DSR4-CO-”) is in the range of from about 0 to about 0.15; wherein the degree of substitution of R⁴-CO- at the C6 position (“C6DSR4-CO-”) is in the range of from about 0.1 to about 0.9; wherein the degree of substitution of the R²-CO- (“DSR2-CO-”) is in the range of from about 0 to about 0.7; wherein the degree of substitution of hydroxyl is in the range of from about 0.1 to about 0.8; wherein R¹ is chosen from (Ci-2o)alkyl; halo(Ci-2o)alkyl; (C2-2o)alkenyl, or (C3-7)cycloalkyl; wherein R² is chosen from ethyl or t-butyl; wherein R⁴ is -(C2-2o)alkenyl-(C6-2o)aryl, wherein the aryl is unsubstituted or substituted by 1 to 6 R⁵ groups, and wherein the alkenyl is unsubstituted or substituted cyano; and wherein R⁵ is chosen from (Ci-e)alkyl, halo(Ci-6)alkyl, (Ci-6)alkoxy, halo(Ci-6)alkoxy, halo, (C3-7)cycloalkyl, (C6-io)aryl, nitro, (C6-2o)aryl, or (C6-2o)aryl-C02-.

In one embodiment of the regioselectively substituted cellulose ester, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 25,000 Da to about 500,000 Da.

In one embodiment of the regioselectively substituted cellulose ester, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 5,000 Da to about 500,000 Da. In one embodiment of the regioselectively substituted cellulose ester, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 250,000 Da to about 500,000 Da. In one embodiment of the regioselectively substituted cellulose ester, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 5,000 Da to about 250,000 Da. In one embodiment of the regioselectively substituted cellulose ester, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 25,000 Da to about 250,000 Da. In one embodiment of the regioselectively substituted cellulose ester, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 50,000 Da to about 250,000 Da. In one embodiment of the regioselectively substituted cellulose ester, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 80,000 Da to about 250,000 Da. In one embodiment of the regioselectively substituted cellulose ester, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 80,000 Da to about 150,000 Da. In one embodiment of the regioselectively substituted cellulose ester, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 100,000 Da to about 150,000 Da. In one embodiment, R¹-CO- is propionyl. In one embodiment, R¹-CO- is butyryl. In one embodiment, R¹-CO- is a combination of propionyl and butyryl.

In one embodiment, R¹ is chosen from a (Ci-2o)alkyl.

In one embodiment, R¹ is chosen from methyl, ethyl, propyl, isopropyl, n-butyl, or t-butyl. In one embodiment, R¹ is chosen from methyl, ethyl, or propyl.

In one embodiment, the C6DSRI-CO- is less than 0.3. In one

embodiment, the C6DSRI-CO- is less than 0.1.In one embodiment, C6DSRI -CO- is less than 0.08. In one embodiment, C6DSRI-CO- is less 0.06.

In one embodiment, C2DSRI-CO- is in the range of from 0.6 to 0.9, and C3DSRI-CO- is in the range of from 0.3 to 0.8. In one embodiment, C2DSRI -CO- is in the range of from 0.7 to 0.9, and C3DSRI-CO- is in the range of from 0.4 to 0.8.

In one embodiment, the sum of C2DSRI-CO- and C3DSRI-CO- is in the range of from 1 .1 to 1 .9. In one embodiment, the sum of C2DSRI-CO- and C3DSRI-CO- is in the range of from 0.9 to 1 .9. In one embodiment, the sum of C2DSRI-CO- and C3DSRI-CO- is in the range of from 0.7 to 1 .9.

In one embodiment,

one class of this

embodiment, R⁴ is chosen from

, or

. In one class of this embodiment, R⁴ is

In one class of this embodiment, R⁴ is

. In one class of

this embodiment,

In one embodiment, C2DSR4-CO- is in the range of from about 0 to about 0.1 , and C3DSR4-CO- is in the range of from about 0 to about 0.1. In one embodiment, C2DSR4-CO- is in the range of from about 0 to about 0.08, and C3DSR4-CO- is in the range of from about 0 to about 0.08.

In one embodiment, C2DSR4-CO- is in the range of from about 0 to about 0.05, and C3DSR4-CO- is in the range of from about 0 to about 0.05.

Film

The present application discloses a film comprising a regioselectively substituted cellulose ester comprising: (i) a plurality of R¹-CO- substituents; (ii) a plurality of R²-CO- substituents; (iii) a plurality of R⁴-CO- substituents; and (iv) a plurality of hydroxyl substituents, wherein the degree of substitution of R¹-CO- at the C2 position (“C2DSRI -CO-”) is in the range of from about 0.7 to about 1.0; wherein the degree of substitution of R¹-CO- at the C3 position (“C3DSRI -CO-”) is in the range of from about 0.2 to about 0.9; wherein the degree of substitution of R¹-CO- at the C6 position (“C6DSRI -CO-”) is in the range of from about 0 to about 0.1 ; wherein the degree of substitution of R⁴- CO- at the C2 position (“C2DSR4-CO-”) is in the range of from about 0 to about 0.15; wherein the degree of substation of R⁴-CO- at the C3 position (“C3DSR4- co-”) is in the range of from about 0 to about 0.15; wherein the degree of substitution of R⁴-CO- at the C6 position (“C6DSR4-CO-”) is in the range of from about 0.1 to about 0.9; wherein the degree of substitution of the R²-CO- (“DSR2-CO-”) is in the range of from about 0 to about 0.7; wherein the degree of substitution of hydroxyl is in the range of from about 0.1 to about 0.8; wherein R¹ is chosen from (Ci-2o)alkyl; halo(Ci-2o)alkyl; (C2-2o)alkenyl, or (C3- 7)cycloalkyl; wherein R² is chosen from ethyl or t-butyl; wherein R⁴ is -(C2- 2o)alkenyl-(C6-2o)aryl, wherein the aryl is unsubstituted or substituted by 1 to 6 R⁵ groups, and wherein the alkenyl is unsubstituted or substituted cyano; and wherein R⁵ is chosen from (Ci-6)alkyl, halo(Ci-6)alkyl, (Ci-6)alkoxy, halo(Ci- 6)alkoxy, halo, (C3-7)cycloalkyl, (C6-io)aryl, nitro, (C6-2o)aryl, or (C6-2o)aryl-C02-.

In one embodiment of the film, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 25,000 Da to about 500,000 Da. In one embodiment of the film, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 5,000 Da to about 500,000 Da. In one embodiment of the film, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 250,000 Da to about 500,000 Da. In one embodiment of the film, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 5,000 Da to about 250,000 Da. In one embodiment of the film, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 25,000 Da to about 250,000 Da. In one embodiment of the film, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 50,000 Da to about 250,000 Da. In one embodiment of the film, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 80,000 Da to about 250,000 Da. In one embodiment of the film, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 80,000 Da to about 150,000 Da. In one embodiment of the film, the weight average molecular weight (“Mw”) of the regioselectively substituted cellulose ester is in the range of from about 100,000 Da to about 150,000 Da.

In one embodiment, R¹-CO- is propionyl. In one embodiment, R¹-CO- is butyryl. In one embodiment, R¹-CO- is a combination of propionyl and butyryl.

In one embodiment, R¹ is chosen from a (Ci-2o)alkyl. In one embodiment, R¹ is chosen from methyl, ethyl, propyl, isopropyl, n-butyl, or t-butyl. In one embodiment, R¹ is chosen from methyl, ethyl, or propyl.

In one embodiment, the C6DSRI-CO- is less than 0.3. In one

In one embodiment,

one class of this

embodiment, R⁴ is chosen from

, or

. In one class of this embodiment, R⁴ is

. in one class of

this embodiment,

In one embodiment, C2DSR4-CO- is in the range of from about 0 to about

0.1 , and C3DSR4-CO- is in the range of from about 0 to about 0.1. In one embodiment, C2DSR4-CO- is in the range of from about 0 to about 0.08, and C3DSR4-CO- is in the range of from about 0 to about 0.08.

In one embodiment, the film is a uniaxial or biaxial optical film. In one class of this embodiment, the film is a uniaxial optical film. In one class of this embodiment, the film is a biaxial optical film.

In one embodiment, the film has a birefringence (“Dh”) between about 0.007 to about 0.010 as measured at a wavelength of 589 nm. In one embodiment, the film has a Dh between about 0.008 to about 0.010 as measured at a wavelength of 589 nm. In one embodiment, the film has a Dh between about 0.009 to about 0.010 as measured at a wavelength of 589 nm.

In one embodiment, the film has a percent haze of less than about 0.9. In one embodiment, the film has a percent haze of less than about 0.8. In one embodiment, the film has a percent haze of less than about 0.7. In one embodiment, the film has a percent haze of less than about 0.6. In one embodiment, the film has a percent haze of less than about 0.5. In one embodiment, the film has a percent haze of less than 0.4. In one embodiment, the film has a percent haze of less than about 0.3. In one embodiment, the film has a percent haze of less than about 0.2.

In one embodiment, the film is a C+ film, C- film, an A+ film, or a A- film. In one class of this embodiment, the film is a C+ film. In one class of this embodiment, the film is a C- film. In one class of this embodiment, the film is an A+ film. In one class of this embodiment, the film is an A- film. In one class of this embodiment, the film is an A- film.

In one embodiment, the film is a C+ film, a C- film, a reverse A film, or a NRZ film.

In one class of this embodiment, is a C+ film. In one subclass of this class, the film has an out-of-plane retardation (“Rth”) as measured at a wavelength of 589 nm is in the range of from 0 nm to about 20 nm. In one sub-subclass of this subclass, the film is uniaxially, biaxially, or 45 degree stretched.

In one class of this embodiment, the film is a C- film. In one subclass of this class, the film has an of the out-of-plane retardation (“Rth”) as measured at a wavelength of 589 nm is in the range of from 0 nm to about -18 nm. In one sub-subclass of this subclass, the film is uniaxially, biaxially, or 45 degree stretched.

In one class of this embodiment, the film is a C- film. In one subclass of this class, the film has an of the out-of-plane retardation (“Rth”) as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from 0 to about -12. In one sub-subclass of this subclass, the film is uniaxially, biaxially, or 45 degree stretched.

In one class of this embodiment, the film is a C- film. In one subclass of this class, the film has an of the out-of-plane retardation (“Rth”) as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -2 to about -17. In one sub-subclass of this subclass, the film is uniaxially, biaxially, or 45 degree stretched.

In one class of this embodiment, the film is a C- film. In one subclass of this class, the film has an of the out-of-plane retardation (“Rth”) as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -2 to about -15. In one sub-subclass of this subclass, the film is uniaxially, biaxially, or 45 degree stretched.

In one sub-subclass of this subclass, the film has a Rth450/Rth550 > 1 and a Rth650/Rth550 >0.9, wherein Rth450, Rth550, and Rth650 are out-of- plane retardations as measured at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.

In one class of this embodiment, the film is a reverse A film. In one subclass of this class, the film satisfies the relations of R_e450/R_e550 < 1 and Re650/R_e550 > 1 , wherein R_e450, R_e550, and R_e650 are the in-plane retardations as measured at the wavelengths of 450 nm, 550 nm, and 650 nm, respectively. In one sub-subclass of this subclass, the film the in-plane retardation (“R_e”) of the film as measured at the wavelength of 589 nm is in the range of from about 100 nm to about 300 nm. In one sub-sub-subclass of this sub-subclass, the film is uniaxially, biaxially, or 45 degree stretched.

Any of the above-described films can have a thickness in the range of from about 40 to about 120 miti, in the range of from about 40 to about 70 miti, or in the range of from about 5 to about 20 miti. Thickness and average thickness are used interchangeably in this application. As used herein, “average thickness” shall denote an average of at least three evenly-spaced measurements of the optical film’s thickness.

In various embodiments, additives such as plasticizers, stabilizers, UV absorbers, antiblocks, slip agents, lubricants, dyes, pigments, retardation modifiers, etc. may be mixed with the regioselectively substituted cellulose esters used in preparing the above-described optical films. Examples of these additives can be found, for example, in U.S. Patent Application

Publication Nos. US 2009/0050842, US 2009/0054638, and US

2009/0096962, the contents of which are incorporated herein by reference.

In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -50 to 50. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -50 to 0. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from 0 to 50. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -20 to 20. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -20 to 0. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from 0 to 20. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -15 to 15. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -15 to 0. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from Oto 15. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -10 to 10. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -10 to 0. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from 0 to 10. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -5 to 0. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -5 to 0. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from 0 to 5. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) in the range of from -3 to 3. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -3 to 0. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from 0 to 3. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -1 to 1. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -1 to 0. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from 0 to 1. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -0.5 to 0.5. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -0.5 to 0. In one embodiment, the previously disclosed films have an Rth as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from 0 to 0.5.

Any of the above-described optical films can be made by solvent casting, melt extrusion, lamination, or a coating process. These procedures are generally known in the art. Examples of solvent casting, melt extrusion, lamination, and coating methods can be found, for example, in U.S. Patent Application Publication Nos. US 2009/0050842, US 2009/0054638, and US 2009/0096962, the contents of which are incorporated herein by reference. Further examples of solvent casting, melt extrusion, lamination, and coating methods to form films can be found, for example, in U.S. Patent Nos.

4,592,885 and 7,172,713, and U.S. Patent Application Publication Nos.

US 2005/0133953 and US 2010/0055356, the contents of which are incorporated herein by reference.

In order to assist in obtaining the desired Re and Rth values using the regioselectively substituted cellulose esters described herein, the films can be stretched. By adjusting the stretch conditions, such as stretch temperature, stretch type (uniaxial or biaxial), stretch ratio, pre-heat time and temperature, and post-stretch annealing time and temperature, the desired R_e, and Rth, can be achieved. The precise stretching conditions may depend upon the specific composition of the regioselectively substituted cellulose ester, the amount and type of plasticizer, and the glass transition temperature of that specific composition. Hence, the specific stretching conditions can vary widely. In various embodiments, the stretching temperature can be in the range of from about 160 to about 200°C. Additionally, the stretch ratio based on 1.0 in the machine direction (“MD”) can range from about 1.3 to about 2.0 in the transverse direction (“TD”). The pre-heat time can be in the range of from about 10 to about 300 seconds, and the pre-heat temperature can be the same as the stretch temperature. The post-annealing time can range from about 0 to about 300 seconds, and the post-annealing temperature can range from about 10 to about 40°C below the stretching temperature. Film thickness may depend upon the film thickness before stretching and upon the stretching conditions. After stretching, the film thickness can be from about 1 pm to about 500 pm, from about 5 pm to about 200 pm, or from about 10 pm to about 120 pm.

In addition to the optical properties, the films prepared from the regioselectively substituted cellulose esters described herein have other valuable features. Many conventional cellulose esters used in LCD displays have relatively high moisture uptake which affects dimensional stability and results in changing optical values of the film. Films prepared from the regioselectively substituted cellulose esters described herein have low moisture uptake, and the optical values of the film change very little at high humidity and temperature. Thus, in various embodiments, the regioselectively substituted cellulose esters can contain less than 2 weight percent moisture, less than 1 weight percent moisture, or less than 0.5 weight percent moisture. In other various embodiments, the change in R_e for the cellulose ester film can be less than 4 percent, less than 1 percent, or less than 0.5 percent when stored at 60 °C, 100 percent relative humidity for 240 hours.

The regioselectively substituted cellulose esters described herein are surprisingly thermally stable which makes them very useful in melt extrusion of film. Thus, one aspect of the present invention relates to regioselectively substituted cellulose esters that have less than 10 percent weight loss by thermogravimetric analysis at 330 °C, 340 °C, or 350 °C.

As noted above, the optical films described herein can be employed in LCDs. Particularly, the above-described optical films can be employed as part or all of a compensation film in the polarizer stack of an LCD. As described above, polarizer stacks generally include two crossed polarizers disposed on either side of a liquid crystal layer. Compensation films can be disposed between the liquid crystal layer and one of the polarizers. In one or more embodiments, the above-described single layer optical film can be employed by itself as a compensation film (i.e., a waveplate) in an LCD. In such an embodiment, the single layer optical film can be disposed between the liquid crystal layer and one of the polarizing filters of the LCD. In other embodiments, the above-described A- optical film can be employed in a compensation film (i.e., a waveplate) in an LCD. In such embodiments, the A- optical film can be disposed adjacent to at least one additional optical film, where such additional optical film can be a C- optical film. In still other embodiments, the above-described C+ optical film can be employed in a compensation film (i.e., a waveplate) in an LCD. In such embodiments, the +C optical film can be disposed adjacent to at least one additional optical film, where such additional optical film can be a A+ optical film. In any of the foregoing embodiments, LCDs prepared comprising the optical films described herein can operate in in-plane-switching (“IPS”) mode.

The optical compensation film described herein can also be employed in OLED. For example, a QWP combined with a linear polarizer to form a circular polarizer. When the circular polarizer is put in front of an OLED device, it can reduce the ambient light reflected from OLED metal electrodes to improved viewing quality, such as high contrast ratio and less color shift, especially when the QWP has a reverse dispersion close to ideal.

The optical films described herein can also be employed in circular polarizers. Particularly, a single quarter waveplate can be prepared

comprising one or more of the above-described optical films of the present invention, which can be used to convert linear polarized light to circular polarized light. This aspect may be particularly valuable for use in circular- polarized 3-dimensional (“3-D”) glasses and/or 3-D media displays, such as televisions (“3-D TV”). Accordingly, in one or more embodiments, a single quarter waveplate can be prepared comprising the above-described single layer optical film. In other various embodiments, a single quarter waveplate can be prepared comprising the above-described A- optical film. Such quarter waveplates can be applied to the glass of a 3-D TV, such as above the polarizing stack. Additionally, such quarter waveplates can be applied to the glass of 3-D glasses. In the case of 3-D glasses, the optical film can be applied so that the optical axis in one lens is perpendicular or substantially perpendicular to the optical axis of the other lens. The result in 3-D glasses is that certain observed polarization is blocked in one lens but will pass through the other lens leading to the observed 3-D optical effect. In various

embodiments, a quarter waveplate comprising one or more of the above- described optical films can be employed in conjunction with at least one additional polarizer, which can be a linear polarizer.

Any of the disclosed films can be incorporated into a multilayer film.

The present application also relates to a multilayer film comprising any of the disclosed films of the present application.

Experimental

Abbreviations

Ak is alkanoyl; aq. is aqueous; BU2O is butanoic anhydride or butyric anhydride; Bu is butyryl, butanoate or butyrate; BuOH is butyric acid or butanoic acid; BzOH is benzoic acid; BZ2O is benzoic anhydride; °C is degree Celsius; TCA is 2-cyano-4-methylcinnamyl; C2DS is degree of substitution of the 2 position of the anydroglucose residue; C3DS is degree of substitution of the 3 position of the anhydroglucose residue; C6DS is the degree of substitution of the 6 position of the anydroglucose residue; CIC is combustion ion chromatography; d is deuterated or deuterium; Da is dalton; DCE is dichloroethane; DCM is dichloromethane; DEP is diethyl phthalate; DMAc is N,N-dimethylacetamide; DMAP is 4-dimethylaminopyridine; DMSO-d6 is hexadeuterated dimethyl sulfoxide; min is minute; equiv or eq. is equivalent; g is gram; h is hour; KOAc is potassium acetate; M_w is weight average molecular weight; M is molar; 4MC is 4-methoxycinnamyl; MEK is methyl ethyl ketone; MeOH is methanol; mg is milligram; MHz is megahertz; MIPK is methyl isopropyl ketone; ml_ or ml is milliliter; mI_ is microliter; mm is

millimeter; mmHg is millimeters mercury; N2 is nitrogen; NMR is nuclear magnetic resonance; Np is naphthoyl; 2-NpOH is 2-naphthoic acid; 2 NpOH is naphthoic acid; Np20 is naphthoic anhydride; 2-Np20 is 2-naphthoic anhydride; ppm is parts per million; Pr is propionyl; 'PrOH is isopropyl alcohol; PrOH is propionic acid; Pr20 is propionic anhydride; RDS is relative degree of substitution; rt is room temperature; TFA is trifluoroacetic acid; TFAA is trifluoroacetic anhydride; TPP is triphenyl phosphate; wt % is weight percent;

Materials and Methods

NMR Characterization

NMR Characterization: Proton NMR data were obtained on a JEOL Model Eclipse-600 NMR spectrometer operating at 600 MHz. The sample tube size was 5 mm, and the sample concentrations were ca. 20 mg/mL DMSO-d6. Each spectrum was recorded at 80 °C using 64 scans and a 15 second pulse delay. One to two drops of trifluoroacetic acid-d were added to each sample to shift residual water from the spectral region of interest.

Chemical shifts are reported in ppm from tetramethylsilane with the center peak of DMSO-d6 as an internal reference (2.49 ppm).

Quantitative ¹³C NMR data were obtained on a JEOL Model GX-400 NMR spectrometer operating at 100 MHz. The sample tube size was 10 mm, and the sample concentrations were ca. 100 mg/mL DMSO-d6. Chromium(lll) acetylacetonate was added to each sample at 5 mg/100 mg cellulose ester as a relaxation agent. Each spectrum was typically recorded at 80 °C using 10000 scans and a 1 second pulse delay. Chemical shifts are reported in ppm from tetramethylsilane with the center peak of DMSO-d6 as an internal reference (39.5 ppm).

The proton and carbon NMR assignments, the degree of substitution and the RDS of the various acyl groups of the cellulose esters were determined by adapting the procedures disclosed in US 2012/0262650. The C2, C3, and C6 DS were determined by ¹³C NMR. The total DS for any substituent is determined by ¹H NMR.

Molecular Weight Determination

For cellulose esters described in this report, Gel permeation

chromatography analysis was performed in N-Methylpyrrolidinone containing 1 % glacial acetic acid by weight. The instrumentation consisted of an Agilent series 1 100 liquid chromatography system. The system components comprised a degasser, an isocratic pump with a flow rate set at 0.8 ml/min, an auto-sampler with an injection volume of 50 microliters, and a column oven set at 40 °C and a refractive index detector set at 40 °C. The column set consisted of an Agilent PLgel 10 micron guard (7.5 x 50 mm) and a Mixed-B (7.5 x 300 mm) column in series. Samples were prepared prepared by weighing 25 mg into a 2 dram screw cap vial and dissolving in 10 ml of the solvent. 10 microliters of toluene were added as a flow rate marker. The instrument was calibrated with a series of 14 narrow molecular weight polystyrene standards ranging from 580 to 3,750,000 in molecular weight. Instrument control and data collection/processing were carried out using Agilent GPC software version 1.2 build 3182.29519. For cellulose samples described in this report, Gel permeation chromatography analysis was performed in 70:30 N-methylpyrrolidinone/ tributylmethylammonium

dimethylphosphate by weight. The instrumentation consisted of an Agilent series 1 100 liquid chromatography system. The system components comprised a degasser, an isocratic pump with a flow rate set at 0.5 ml/min, an auto-sampler with an injection volume of 50 microliters, and a column oven set at 60 °C and a refractive index detector set at 40 °C. The column set consisted of an Agilent PLgel 10 micron guard (7.5 x 50 mm) and a Mixed-B (7.5 x 300 mm) column in series. Samples were prepared prepared by weighing 12.5 mg into a 2 dram screw cap vial and dissolving in 10 ml of the solvent. 10 pL of toluene were added as a flow rate marker. The instrument was calibrated with a series of 14 narrow molecular weight polystyrene standards ranging from 580 to 3,750,000 in molecular weight. Instrument control and data collection/processing were carried out using Agilent GPC software version 1.2 build 3182.29519.

Dope Preparations

The solutions of the cellulose esters for preparation of the films and the film preparation were made by adapting the procedures disclosed in US 2012/0262650.

General Procedure for Film Casting and Optical Film Analysis

A solvent (DCM, 10% MeOH in DCM, 10 % Acetone in DCM, 10%

DCE in DCM, MEK, or MIPK) and the regioselective cellulose ester (8 to 12 wt %) and optionally a plasticizer (10 wt %, DEP or TPP) were mixed to make a dope. Then, films were cast onto glass using a knife applicator and dried either at room temperature, in the case of a DCM based dope or at 85°C in a forced air oven for 10 min. for dopes made from MEK and MIPK based dopes. The cast films were annealed at 100°C and 120°C in a forced air oven for 10 min each to remove the residual solvents. The thickness of the films was measured using a Metricon Prism Coupler 2010 (Metricon Corp.) or

PosiTector 6000. The birefringence, optical dispersion and retardations were measured using a M-2000V Ellipsometer (J. A. Woollam Co.).

Examples

General Procedure A for Synthesis of 2,3-Substituted Cellulose Esters.

Preparation of Intermediate 1. A 2000 ml_ jacketed reaction kettle was fitted with a 4-neck removable top. To the top was affixed an overhead stirring shaft, a temperature probe, a reflux condenser, and a ground glass stopper. The reaction was connected via a rubber tubing to a Thermo Neslab RTE-7 temperature controller, and the setpoint was set to 25 °C. The reactor was charged with Placetate F cellulose pulp (70 g, 5 wt. %). To a separate 500 ml_ graduated cylinder was added TFA (1 180 g) followed by TFAA (151 g). The resulting solution was then slowly poured into the reactor. The temperature controller was set to 60 °C, and the material was mixed via overhead stirring. After ~75 minutes, the mixture had formed a dark orange solution, at which point the temperature controller was set to 50 °C. While this process was taking place, a separate oven-dried 250 ml_ round bottomed flask was charged with propionic acid (41.5 g, 1.3 equiv) and TFA (10 ml_) with magnetic stirring under an atmosphere of nitrogen. To this solution was slowly added TFAA (1 18 g, 1.3 equiv), and the solution was allowed to stir for 45 minutes. The reaction kettle was then fitted with a liquids addition funnel. The funnel was then charged with the previously prepared mixed anhydride.

The funnel was opened, and the anhydride solution was added to the cellulose dope such that the addition was complete within 10 minutes. The resulting mixture was allowed to stir for 12 hours. The dope was then precipitated by pouring into 6000 ml_ deionized water to afford the product as a white solid. The solids were broken down to a uniform particle size via homogenization. The solids were collected by filtration on a frit. The solids were then suspended in 2000 ml_ of 5 M KOAc(aq.) and slurried for 36 hours. The solids were collected by filtration on a frit and washed continuously with denionized water for 8 hours. The solids were then dried in a ceramic dish in vacuo at 60 °C for 12 hours. The product was analyzed by ¹FI NMR, ¹³C

NMR, CIC, and GPC. DS = 1.31 , DS C2 = 0.76, DS C3 = 0.43, DS C6 = 0.01.

By adapting General Procedure A, the following intermediate cellulose esters in Table 1were prepared.

Table 1

General Procedure for Synthesis of Cellulose Esters for Negative C Compensation Films. Preparation of Example 1 : An oven-dried 500-mL jacketed 3-neck round- bottomed flask was transferred to the fume hood and affixed to the hood scaffolding. The flask was then allowed to purge under an atmosphere of nitrogen while cooling. The flask was then fitted with a mechanical stirrer and adapter along with a positive pressure of nitrogen. The flask was then charged with EX 2 (20 grams) using a solids addition funnel. DMAc (50 ml_) was added to the flask followed by pyridine (150 ml_). The reaction

temperature was adjusted to 50 °C, and the mixture was allowed to stir until complete dissolution of the cellulose ester was observed. The reaction temperature was adjusted to 25 °C, and 2-benzothiophene carbony chloride (10.3 g, 0.6 equiv) was added over the course of about 2 minutes. The reaction mixture was then allowed to hold for 3 hours, whereupon pivaloyl chloride (8.1 g, 0.77 equiv) was added dropwise over the course of 2 minutes. The reaction mixture was then warmed to 40 °C and allowed to stir for at least 12 hours. The resulting mixture was then diluted with 100 ml_ acetone and poured into a beaker containing 2000 ml_ deionized water, causing a white solid to precipitate. The solids were broken down to a uniform size via homogenization, and the solids were collected via vacuum filtration on a coarse frit. The solids were washed on the filter twice with 200 ml_ 'PrOH.

The solids were then washed continuously with room temperature deionized water for 8 hours. The solids were then dried in vacuo in a ceramic dish (22.5 mm Hg, 60 °C) for 12 hours. The product was analyzed by ¹H NMR, ¹³C NMR, GPC, and CIC. DSBz = 0.29, DSC2 = 0.83, DSC3=0.52, DSC6=0.96.

By adapting general procedure B, the following cellulose esters were prepared

Table 2

¹ Propionic anhydride used instead of pivaloyl chloride.

Represents the degree of substitution of propionyl instead of pivaloyl

CLAIMS NOT LIMITED TO DISCLOSED EMBODIMENTS

The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention.

The inventors hereby state their intent to rely on the Doctrine of

Equivalents to determine and assess the reasonably fair scope of the present invention as it pertains to any apparatus not materially departing from but outside the literal scope of the invention as set forth in the following claims.

Claims

We Claim:

1. A regioselectively substituted cellulose ester comprising:

(i) a plurality of R¹-CO- substituents;

(ii) a plurality of R²-CO- substituents;

(iii) a plurality of R⁴-CO- substituents; and

(iv) a plurality of hydroxyl substituents,

wherein the degree of substitution of R¹-CO- at the C2 position

(“C2DSRI -CO-”) is in the range of from about 0.5 to about 1.0;

wherein the degree of substitution of R¹-CO- at the C3 position

(“C3DSRI -CO-”) is in the range of from about 0.2 to about 0.9;

wherein the degree of substitution of R¹-CO- at the C6 position

(“C6DSRI -CO-”) is in the range of from about 0 to about 0.1 ;

wherein the degree of substitution of R⁴-CO- at the C2 position

(“C2DSR4-CO-”) is in the range of from about 0 to about 0.15;

wherein the degree of substation of R⁴-CO- at the C3 position

(“C3DSR4-CO-”) is in the range of from about 0 to about 0.15;

wherein the degree of substitution of R⁴-CO- at the C6 position

(“C6DSR4-CO-”) is in the range of from about 0.1 to about 0.9;

wherein the degree of substitution of the R²-CO- (“DSR2-CO-”) is in the range of from about 0 to about 0.7;

wherein R² is chosen from ethyl or t-butyl;

wherein R⁴ is -(C2-2o)alkenyl-(C6-2o)aryl, wherein the aryl is

wherein R⁵ is chosen from (Ci-6)alkyl, halo(Ci-6)alkyl, (Ci-6)alkoxy, halo(Ci-6)alkoxy, halo, (C3-7)cycloalkyl, (C6-io)aryl, nitro, (C6-2o)aryl, or (C6-2o)aryl-C02-.

2. The regioselectively substituted cellulose ester of claim 1 , wherein R¹- is chosen from methyl, ethyl, propyl, isopropyl, n-butyl, or t-butyl.

3. The regioselectively substituted cellulose ester of any one of claims 1 -2,

wherein

4. The regioselectively substituted cellulose ester of claim 3, R⁴-CO- is chosen

from

5. The regioselectively substituted cellulose ester of claim 4, wherein R⁴-CO-

7. The regioselectively substituted cellulose ester of claim 4, wherein R⁴-CO-

8. The regioselectively substituted cellulose ester of any one of claims 1 -7, wherein R¹-CO- is propionyl.

9. The regioselectively substituted cellulose ester of any one of claims 1 -7, wherein R¹-CO- is butanoyl.

10. The regioselectively substituted cellulose ester of any one of claims 8 or 9, DSR2-CO- is in the range of from 0.1 to 0.6.

1 1 . The regioselectively substituted cellulose ester of any one of claims 8 or 9, DSR2-CO- is from 0 to 0.1 .

12. The regioselectively substituted cellulose ester of any one of claims 1 -1 1 , C6DSRI -CO- is less than 0.08.

13. The regioselectively substituted cellulose ester of any one of claims 1 ,-12 wherein the weight average molecular weight (“M_w”) is in the range from about 25,000 Da to about 500,000 Da.

14. A film comprising a regioselectively substituted cellulose ester of any one of claims 1 -14.

15. The film of claim 14, wherein the film is a C- film.

16. The film of any one of claims 14-15, wherein the film has an of the out-of- plane retardation (“Rth”) as measured at a wavelength of 589 nm divided by the thickness of the film (“d”) is in the range of from -17 to about -2.

17. The film of any one of claims 14-16, wherein the film satisfies the relations of Rth450/Rth550 is in the range of from about 1 .0 to 1 .3 and

Rth650/Rth550 is in the range of from about 0.9 to 1 .0, wherein Rth450, Rth550, and Rth650 are the out-plane retardations as measured at the wavelengths of 450 nm, 550 nm, and 650 nm, respectively.

18. The film of any one of claims 14-17, wherein the film is a uniaxially, biaxially, or 45 degree stretched film.

19. A multilayer film comprising the film any one of claims 14-18.