Source: https://patents.justia.com/patent/9926384
Timestamp: 2019-12-13 03:25:07
Document Index: 695824170

Matched Legal Cases: ['Application No. 61', 'art 2', 'art 1', 'art 2', 'art 1', 'Application No. 17169625']

US Patent for Regioselectively substituted cellulose esters produced in a tetraalkylammonium alkylphosphate ionic liquid process and products produced therefrom Patent (Patent # 9,926,384 issued March 27, 2018) - Justia Patents Search
Justia Patents ProcessesUS Patent for Regioselectively substituted cellulose esters produced in a tetraalkylammonium alkylphosphate ionic liquid process and products produced therefrom Patent (Patent # 9,926,384)
Jul 31, 2014 - EASTMAN CHEMICAL COMPANY
This application is a continuation application of U.S. Non-Provisional application Ser. No. 13/357,635 filed on Jan. 25, 2012, now U.S. Publication Number 2012-0121830; which is a continuation application of U.S. Non-Provisional application Ser. No. 12/539,817 filed on Aug. 12, 2009, now U.S. Pat. No. 8,524,887; which claims the benefit of U.S. Provisional Application No. 61/169,560 filed on Apr. 15, 2009, which are all hereby incorporated by reference.
This invention is relates to the field of cellulose chemistry, specifically to cellulose solutions, the production of cellulose esters, and products produced therefrom.
Cellulose is a β-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 an acidic aqueous media to the desired degree of substitution (DS, the number of substituents per anhydroglucose monomer). Hydrolysis of cellulose triacetate under these conditions yields a random copolymer that can consist of 8 different monomers depending upon the final DS [Macromolecules 1991, 24, 3050].
In the broadest sense, an ionic liquid (IL) is simply any liquid containing only ions. Hence, molten salts such as NaCl which melts at temperatures greater than 800° C. could be classified as ionic liquids. From a practical point of view, the term ionic liquid is now used for organic salts that melt below approximately 100° C.
One embodiment of this invention relates to the dissolution of cellulose in one or more tetraalkylammonium alkylphosphates. The invention further relates to the dissolution of cellulose in a mixture comprising one or more tetraalkylammonium alkylphosphates and one or more aprotic solvents at a contact time and temperature sufficient to dissolve cellulose. The invention yet further relates to the dissolution of cellulose in a mixture comprising one or more tetraalkylammonium alkylphosphates and one or more ionic liquids wherein the cation is imidazolium. The invention still further relates to the dissolution of cellulose in a mixture comprising one or more tetraalkylammonium alkylphosphates and one or more acids wherein the acids do not combine with the cellulose at a contact time and temperature sufficient to dissolve cellulose. Another embodiment of this invention relates to shaped articles prepared from a cellulose solution comprising at least one tetraalkylammonium alkylphosphate or mixtures thereof. Another embodiment of this invention relates to compositions comprising derivatives of cellulose prepared from a cellulose solution comprising at least one tetraalkylammonium alkylphosphate or mixtures thereof. Another embodiment of this invention relates to compositions comprising regioselectively substituted cellulose esters prepared from a cellulose solution comprising at least one tetraalkylammonium alkylphosphate or mixtures thereof. In yet another embodiment of the invention, the cellulose esters of the present invention are used as protective and compensation films for liquid crystalline displays.
FIG. 1 shows the dissolution of 12.5 wt % cellulose in tributylmethylammonium dimethyl phosphate ([TBMA]DMP). Cellulose absorbance was measured at 1000 cm−1.
FIG. 2 shows modeled wt % cellulose and the experimental absorbance values for 10 wt % cellulose dissolved in [TBMA]DMP.
FIG. 7 shows the contact period involving the addition of 0.5 eq Ac2O at 100° C. The x axis has been shifted so that each reaction begins at the same point of anhydride addition (15 min).
FIG. 8 shows the contact period involving the addition of 2.5 eq Ac2O at 80° C. The x axis has been shifted so that each reaction begins at the same point of anhydride addition (72 min).
FIG. 9 shows a plot of DS versus time for the time period involving addition of 2.5 eq Ac2O in the absence and presence of acid at 80° C.
FIG. 10 shows a plot of absorbance for infrared bands at 1815 cm-1 (anhydride), 1732 cm-1 (acid), and 1226 cm-1 (ester+acid) versus contact time during esterification of cellulose dissolved in [TBMA]DMP.
FIG. 11 compares a plot of absorbance for infrared bands at 1815 cm−1 and 1732 cm−1 versus contact time during the esterification of cellulose dissolved in [TBMA]DMP when Ac2O/Pr2O or Ac2O/Pr2O+MSA are added at 100° C.
FIG. 12 compares a plot of absorbance for infrared bands at 1815 cm-1 and 1732 cm−1 versus contact time during the esterification of cellulose dissolved in [TBMA]DMP when Ac2O/Pr2O or Ac2O/Pr2O+MSA are added at 60° C.
FIG. 13 shows a plot of DS versus time for the time period involving addition of 1.0 eq Ac2O and 1.0 eq Pr2O in the absence and presence of MSA at 60° C.
FIG. 14 shows a plot of absorbance for infrared bands at 1825 cm-1 (acetic anhydride and 1724 cm-1 (acetic acid) versus contact time during esterification of cellulose dissolved in 75/25 wt/wt [TBMA]DMP/DMF mixture.
The cellulose can have an α-cellulose content of at least 90%, and more preferably, an α-cellulose content of at least 95%. The cellulose can have a degree of polymerization (DP) of at least 10, at least 250, at least 1000 or at least 5,000. As used herein, the term “degree of polymerization,” when referring to cellulose and/or cellulose esters, shall denote the average number of anhydroglucose monomer units per cellulose polymer chain. Furthermore, the cellulose can have a weight average molecular weight in the range of from about 1,500 to about 850,000, in the range of from about 40,000 to about 200,000, or in the range of from 55,000 to about 160,000. Additionally, the cellulose suitable for use in the present invention can be in the form of a sheet, a hammer milled sheet, fiber, or powder. In one embodiment, the cellulose can be a powder having an average particle size of less than about 500 micrometers (“μm”), less than about 400 μm, or less than 300 μm.
One or more cosolvents mixed with tetraalkylammonium alkylphosphates can be useful in preparing solutions of cellulose. Cosolvents include, but are not limited to, aprotic solvents, protic solvents, acids, and ionic liquids other than tetraalkylammonium alkylphosphates. For example, aprotic solvents are useful in the present invention. In the present invention, aprotic solvents are those which do not contain hydrogen attached to oxygen, nitrogen, or sulfur that can dissociate and have a dielectric constant greater than about 30. Further, the suitable aprotic solvents do not have an acidic proton that can be removed by base during cellulose dissolution or esterification. When aprotic solvents are utilized with tetraalkylammonium alkylphosphates, higher cellulose concentrations with lower cellulose solution viscosities can be achieved allowing for reduced contact temperatures. Further, the cellulose ester products often have better solubility when utilizing aprotic solvents than they do in tetraalkylammonium alkylphosphates alone, which is often important when making selected cellulose ester compositions. Examples of suitable aprotic solvents include hexamethylphosphoramide, N-methylpyrrol idone, nitromethane, dimethylformamide, dimethylacetamide, acetonitrile, sulfolane, dimethyl sulfoxide, and the like. In one embodiment, aprotic solvents include, but are not limited to, N-methylpyrrolidone (NMP) and dimethylformamide (DMF). The aprotic solvents may be present in an amount from about 0.1 to about 99 wt % based on total weight of the cosolvents and tetraalkylammonium alkylphosphates. In another embodiment of the invention, the amount of cosolvents is from about 5 to about 90 wt % or from about 10 to about 25 wt % based on total weight of the cosolvents and tetraalkylammonium alkylphosphates.
In another embodiment of the invention, ionic liquids, other than tetraalkylammonium alkylphosphates, can be utilized as a cosolvent. The ionic liquid can be any known in the art capable of assisting in dissolving the cellulose in the tetraalkylammonium alkylphosphate. Suitable examples of such ionic liquids are disclosed in U.S. patent application entitled “Cellulose Esters and Their Production In Carboxylated Ionic Liquids” filed on Feb. 13, 2008 and having Ser. No. 12/030,387 and in U.S. patent application entitled “Cellulose Esters and Their Production in Halogenated Ionic Liquids filed on Aug. 11, 2008 and having Ser. No. 12/189,415; both of which are herein incorporated by reference to the extent they do not contradict the statements herein.
When dissolving cellulose in the present invention to produce a cellulose solution, the contact temperature and time is that which is sufficient to obtain a homogeneous mixture of the cellulose in the tetraalkylammonium alkylphosphate. In one embodiment of the invention, the contact temperature is from about 20° C. to about 150° C. or from about 50° C. to about 120° C. In one embodiment of the invention, the contact time is from about 5 min to about 24 hours or from about 30 min to about 3 hours. Those skilled in the art will understand that the rate of dissolution is dependent upon temperature and how well the cellulose is dispersed in the tetraalkylammonium alkylphosphate. The amount of cellulose that can be dissolved in the tetraalkylammonium alkylphosphate of the present invention depends upon the particular tetraalkylammonium alkylphosphate used to dissolve the cellulose and the DP of the cellulose. In one embodiment, the concentration of cellulose in the cellulose solution is from about 1 wt % to about 40 wt % based on the total weight of the cellulose solution or from about 7 wt % to about 20 wt %.
In the esterification of cellulose dissolved in tetraalkylammonium alkylphosphates, the contact temperature is that which is sufficient to produce the desired cellulose ester. In one embodiment, the contact temperature is from about 20° C. to about 140° C. In another embodiment, the contact temperature is from about 50° C. to about 100° C. or from about 60° C. to about 80° C.
It is important to understand that in the present invention, little or no cellulose phosphate ester is formed during the cellulose esterification. That is, the tetraalkylammonium alkylphosphate is not acting as a phosphate donor. This is in contrast to ionic liquids, such as, 1,3-dialkylimidazolium carboxylates wherein at least one of the acyl groups of the cellulose ester is donated by the ionic liquid, which is described in U.S. patent application entitled “Cellulose Esters and Their Production In Carboxylated Ionic Liquids” filed on Feb. 13, 2008 and having Ser. No. 12/030,387, which has previously been incorporated by reference to the extent it does not contradict the statements herein. That is, the ionic liquid acts as an acylating reagent. The cellulose esters of the present invention can be prepared by a process comprising:
a) contacting cellulose with at least one tetraalkylammonium alkylphosphate to form a cellulose solution;
b) contacting the cellulose solution with at least one acylating reagent at a contact temperature and contact time sufficient to produce an acylated cellulose solution comprising at least one cellulose ester;
c) contacting the acylated cellulose solution with at least one non-solvent to cause the cellulose ester to precipitate to produce a cellulose ester slurry comprising precipitated cellulose ester and the tetraalkylammonium alkylphosphate;
d) separating at least a portion of the precipitated cellulose ester from the cellulose ester slurry to produce a recovered cellulose ester and precipitation liquids comprising the tetraalkylammonium alkylphosphate.
In another embodiment of this invention, the process of producing cellulose esters further comprises washing the recovered cellulose ester with a wash liquid to produce a washed cellulose ester.
In the present invention, we found that when adding one or more acylating reagents, the C6 position of cellulose was acylated much faster than C2 and C3. Consequentially, the C6/C3 and C6/C2 RDS ratios are greater than 1 which is characteristic of a regioselectively substituted cellulose ester. The degree of regioselectivity depends upon at least one of the following factors: type of acyl substituent, contact temperature, ionic liquid interaction, equivalents of acyl reagent, order of additions, and the like. Typically, the larger the number of carbon atoms in the acyl substituent, the C6 position of the cellulose is acylated preferentially over the C2 and C3 position. In addition, as the contact temperature is lowered in the esterification, the C6 position of the cellulose can be acylated preferentially over the C2 or C3 position. As mentioned previously, the type of ionic liquid and its interaction with cellulose in the process can affect the regioselectivity of the cellulose ester. For example, when carboxylated ionic liquids are utilized, a regioselectively substituted cellulose ester is produced where the RDS is C6>C2>C3. When the tretraalkylammonium dialkylphosphates of the present invention are utilized, a regioselectively substituted cellulose ester is produced where the RDS is C6>C3>C2. This is significant in that regioselective placement of substituents in a cellulose ester leads to regioselectively substituted cellulose esters with different physical properties relative to conventional cellulose esters.
The cellulose esters prepared by the process of the present invention are precipitated by contacting the cellulose ester solution with a non-solvent to precipitate at least a portion of the cellulose ester, and thereby produce a slurry comprising precipitated cellulose ester and precipitation liquids. Examples of non-solvents include, but are not limited to, C1-C8 alcohols, water, or a mixture thereof. In one embodiment, the methanol is utilized for precipitation of the cellulose esters. The amount of non-solvent can be any amount sufficient to cause at least a portion of the cellulose ester to precipitate. In one embodiment, the amount of non-solvent can be at least about 10 volumes, at least 5 volumes, or at least 0.5 volumes, based on the total volume of the acylated cellulose solution. The contact time and temperature required for precipitation of the cellulose ester can be any time or temperature required to achieve the desired level of precipitation. In embodiments of this invention, the contact time for precipitation is from about 1 to about 300 min, from about 10 to about 200 min, or from 20 to 100 min. The contact temperature for precipitation can range from about 0 to about 120° C., from about 20 to about 100° C., or from 25 to about 50° C.
In one embodiment, washing of the recovered cellulose ester can be performed in such a manner that at least a portion of any undesired by-products and/or color bodies are removed from the recovered cellulose ester to produce a washed cellulose ester. In one embodiment, the non-solvent utilized as a wash liquid can contain a bleaching agent in the range of from about 0.001 to about 50 weight percent, or in the range of from 0.01 to 5 weight percent based on the total weight of the wash liquid. Examples of bleaching agents suitable for use in the present invention include, but are not limited to, chlorites, such as sodium chlorite (NaClO2); hypohalites, such as NaOCl, NaOBr, and the like; peroxides, such as hydrogen peroxide and the like; peracids, such as peracetic acid and the like; metals, such as Fe, Mn, Cu, Cr and the like; sodium sulfites, such as sodium sulfite (Na2SO3), sodium metabisulfite (Na2S2O5), sodium bisulfite (NaHSO3) and the like; perborates, such as sodium perborate (NaBO3.nH2O where n=1 or 4); chlorine dioxide (ClOC2); oxygen; and ozone. In one embodiment, the bleaching agent employed in the present invention can include hydrogen peroxide, NaOCl, sodium chlorite and/or sodium sulfite. In one embodiment, at least 70 percent, or at least 90 percent of the total amount of byproducts and/or color bodies are removed from the recovered cellulose ester.
In another embodiment, when the cellulose ester non-solvent is a C1-C8 alcohol or a mixture thereof, such as, MeOH, only a portion of alcohol is removed from the precipitation liquids by a liquid/liquid separation process to produce a fractionated precipitation liquid. After partial separation, the total amount of alcohols in the fractionated precipitation liquid is in the range of from about 0.1 to about 60 weight percent, in the range of from about 5 to about 55 weight percent, or in the range of from 15 to 50 weight percent. The fractionated precipitation liquid can then be treated at a temperature, pressure, and time sufficient to convert the at least a portion of the carboxylic acid contained in the precipitation liquids to alkyl esters, such as, methyl esters, by reacting the carboxylic acids with the alcohol present in the fractionated precipitation liquids. The esterification can be conducted at a temperature in the range of from 100° C. to 180° C., or in the range of from 130° C. to 160° C. Additionally, the pressure during esterification can be in the range of from about 10 to about 1,000 pounds per square inch gauge (“psig”), or in the range of from 100 to 300 psig. The fractionated precipitation liquids can have a residence time during esterification in the range of from about 10 to about 1,000 minutes, or in the range of from 120 to 600 minutes. In one embodiment, at least 5, at least 20, or at least 50 mole percent of the carboxylic acids in the precipitation liquids can be esterified during the above-described esterification to produce a reformed fractionated precipitation liquids. Following the above-described esterification, the carboxylate esters, one or more alcohols, and water produced during the esterification can be substantially removed by treating the reformed fractionated precipitation liquids with at least one liquid/liquid separation process. It has been found that conversion of the carboxylic acid to an alkyl ester facilitates its removal from the precipitation liquids. In this embodiment, at least 80, at least 90, or at least 95 weight percent of the one or more alcohols, carboxylate esters, water, and/or residual carboxylic acids and optionally cosolvents can be removed from the precipitation mixture, thereby producing a recycled tetraalkylammonium alkylphosphate stream. At least a portion of the carboxylate esters removed in this process can be converted to anhydrides by CO insertion.
When used as a protective film, the film is typically laminated to either side of an oriented, iodinated polyvinyl alcohol (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.
Optical retardation (R) is related the birefringence by the thickness (d) of the film: Re=Δed=(nx−ny)d; Rth=Δthd=[nz−(nx+ny)/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 (±).
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, nx=ny<nz. In the case of —C plates, nx=ny>nz. 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, nx>ny=nz. In the case of −A plates, nx<ny=nz.
One aspect of the present invention relates to compensation film comprising regioselectively substituted cellulose esters wherein the compensation film has an Rth range from about −400 to about +100 nm. In another embodiment of the invention, compensation films are provided comprising regioselectively substituted cellulose esters having a total DS from about 1.5 to about 2.95 of a single acyl substituent (DS 0.2 of a second acyl substituent) and wherein the compensation film has an Rth value from about −400 to about +100 nm.
Further information concerning ionic liquids, their use in the production of cellulose esters and cellulose derivatives, the use of cosolvents with ionic liquids in processes to produce cellulose esters and cellulose derivatives, and treatment of cellulose esters are disclosed in U.S. patent application entitled “Cellulose Esters and Their Production In Carboxylated Ionic Liquids” filed on Feb. 13, 2008 and having Ser. No. 12/030,387 and its Continuation-In-Part Application entitled “Regioselectively Substituted Cellulose Esters Produced In A Carboxylated Ionic Liquid Process and Products Produced Therefrom” filed on Sep. 12, 2009; U.S. patent application entitled “Cellulose Esters and Their Production in Halogenated Ionic Liquids filed on Aug. 11, 2008 and having Ser. No. 12/189,415 and its Continuation-In-Part Application entitled “Regioselectively Substituted Cellulose Esters Produced In A Halogenated Ionic Liquid Process and Products Produced Therefrom” filed on Sep. 12, 2009; U.S. patent application “Production of Ionic Liquids” filed on Feb. 13, 2008 having Ser. No. 12/030,425; and U.S. patent application entitled “Reformation of Ionic Liquids” filed on Feb. 13, 2008 having Ser. No. 12/030,424; U.S. patent application entitled “Treatment of Cellulose Esters” filed on Aug. 11, 2008, having Ser. No. 12/189,421; U.S. patent application entitled “Production of Cellulose Esters In the Presence of A Cosolvent” filed on Aug. 11, 2008 having Ser. No. 12/189,753; and U.S. Provisional Application entitled “Regioselectively Substituted Cellulose Esters and Their Production in Ionic Liquids” filed on Aug. 13, 2008 having Ser. No. 61/088,423; all of which are incorporated by reference to the extent they do not contradict the statements herein.
Experimental tetraalkylammonium alkyl phosphates were prepared as described in the examples. The degree of polymerization of the cellulose was determined by capillary viscometry using copper ethylenediamine (Cuen) as the solvent. Prior to dissolution, the cellulose was typically dried for 14-18 h at 50° C. and 5 mm Hg.
The relative degree of substitution (RDS) at C6, C3, and C2 in the cellulose ester of the present invention was determined by carbon 13 NMR following the general methods described in “Cellulose Derivatives”, ACS Symposium Series 688, 1998, T. J. Heinze and W. G. Glasser, Editors, herein incorporated by reference to the extent it does not contradict the statements herein. Briefly, the carbon 13 NMR data was obtained using a JEOL NMR spectrometer operating at 100 MHz or a Bruker NMR spectrometer operating at 125 MHz. The sample concentration was 100 mg/mL of DMSO-d6. Five mg of Cr(OAcAc)3 per 100 mg of sample were added as a relaxation agent. The spectra were collected at 80° C. using a pulse delay of 1 second. Normally, 15,000 scans were collected in each experiment. Conversion of a hydroxyl to an ester results in a downfield shift of the carbon bearing the hydroxyl and an upfield shift of a carbon gamma to the carbonyl functionality. Hence, the RDS of the C2 and C6 ring carbons were determined by direct integration of the substituted and unsubstituted C1 and C6 carbons. The RDS at C3 was determined by subtraction of the sum of the C6 and C2 RDS from the total DS. The carbonyl RDS was determined by integration of the carbonyl carbons using the general assignments described in Macromolecules, 1991, 24, 3050-3059, herein incorporated by reference to the extent it does not contradict the statements herein. In the case of cellulose mixed esters containing a plurality of acyl groups, the cellulose ester was first converted to a fully substituted cellulose mixed p-nitrobenzoate ester. The position of the p-nitrobenzoate esters indicate the location of the hydroxyls in the cellulose mixed ester.
Color measurements were made following the general protocol of ASTM D1925. Samples for color measurements were prepared by dissolving 1.7 g of cellulose ester in 41.1 g of n-methylpyrrolidone (NMP). A HunterLab Color Quest XE colorimeter with a 20 mm path length cell operating in transmittance mode was used for the measurements. The colorimeter was interfaced to a standard computer running Easy Match QC Software (HunterLab). Values (L*; white to black, a*; +red to −green, b*; +yellow to −blue) were obtained for NMP (no cellulose ester) and for the cellulose ester/NMP solutions. Color difference (E*) between the NMP solvent and the sample solutions were then calculated (E*=[(Δa*)2+[(Δb*)2+[(ΔL*)2]0.5 where Δ is the value for the sample solutions minus the value for the solvent. As the value for E*approaches zero, the better the color.
Sulfur and phosphorus concentration in cellulose esters were determined by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP). The samples were prepared by digestion in concentrated HNO3 followed by dilution with ultra-pure water after addition of an internal standard. The final matrix was 5% by weight HNO3 in water. The samples were then analyzed for phosphorus (177.434 nm) and sulfur (180.669 nm) content using a Perkin Elmer 2100DV Inductively Coupled Plasma-Optical Emission Spectrometer that was calibrated using NIST traceable standards.
Solvent casting of film was performed according to the following general procedure. Dried cellulose ester and 10 wt % plasticizer were added to a 90/10 wt % solvent mixture of CH2Cl2/methanol (or ethanol) to give a final concentration of 5-30 wt % based on cellulose ester+plasticizer to produce a cellulose ester/solvent mixture. The cellulose ester/solvent mixture was sealed, placed on a roller, and mixed for 24 hours to create a uniform cellulose ester solution. After mixing, the cellulose ester solution was cast onto a glass plate using a doctor blade to obtain a film with the desired thickness. Casting was conducted in a fume hood with relative humidity controlled at 50%. After casting, the film and glass were allowed to dry for one hour under a cover pan (to minimize rate of solvent evaporation). After this initial drying, the film was peeled from the glass and annealed in a forced air oven for 10 minutes at 100° C. After annealing at 100° C., the film was annealed at a higher temperature (120° C.) for another 10 minutes.
Film optical retardation measurements were made using a J. A. Woollam M-2000V Spectroscopic Ellipsometer having a spectral range of 370 to 1000 nm. RetMeas (Retardation Measurement) program from J. A. Woollam Co., Inc. was used to obtain optical film in-plane (Re) and out-of-plane (Rth) retardations. Values are reported at 589 or 633 nm at a film thickness of 60 μm.
Example 1 Preparation of Tributylmethylammonium Dimethylphosphate [TBMA]DMP
To a 1 L 3-neck round bottom flask equipped for mechanical stirring 400 g of freshly distilled tributylamine and 302 g trimethylphosphate (1 eq) were added. This resulted in two clear phases with the top phase being tributylamine. The flask was then placed in an oil bath, and the reaction mixture was blanked with N2. The oil bath was heated to 120° C. and the contact mixture was stirred for 49 h resulting in a pale, yellow, homogeneous mixture. After cooling to ambient temperature, the sample solidified giving a white solid (Yield>99%).
Analysis by proton NMR indicated >99% conversion of the starting materials to tributylmethylammonium dimethylphosphate. Thermogravimetric analysis (TGA) indicated the onset of thermal decomposition of the [TBMA]DMP at ca. 240° C. Analysis by differential scanning calorimetry (DSC) showed a melt (Tm) centered at 55° C. during the first heating scan to 100° C. at 20° C./min. After cooling from the melt at 20° C./min to −100° C. and heating again to 100° C. at 20° C./min, a Tg (glass transition temperature) was observed at −52° C., two Tc (crystallization temperature) were observed at 14 and 23° C., and two Tm were observed at 54 and 66° C.
This example illustrates the preparation of a tetraalkylammonium alkylphosphate having a melting point less than 100° C.
Example 2 Dissolution of Cellulose in Tributylmethylammonium Dimethylphosphate ([TMBA]DMP)
Prior to cellulose dissolution, 52.26 g tributylmethylammonium dimethylphosphate ([TBMA]DMP) was added to a 3-neck 100 mL round bottom flask equipped for mechanical stirring and with a N2/vacuum inlet. The flask was placed in an 80° C. oil bath, and the [TBMA]DMP was stirred for 17 hours at ca. 0.9 mm Hg. The [TBMA]DMP was cooled to 70° C., and an iC10 diamond tipped infrared probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) was inserted to measure absorbance.
To the [TBMA]DMP was added 7.46 g (12.5 wt %) of cellulose (DP ca. 335) while stirring vigorously (5 min addition). The cellulose easily and quickly dispersed in the [TBMA]DMP to produce a cellulose solution. Vacuum was applied with the aid of a bleed valve (ca. 1 mm Hg), and the oil bath was heated to 100° C. By the time the cellulose and [TBMA]DMP reached 100° C. (ca. 60 min), the mixture was a viscous, translucent cellulose solution with no visible particles. The cellulose solution was stirred for an additional 65 min at 100° C. at which point it was a clear cellulose solution.
FIG. 1 shows the dissolution of 12.5 wt % cellulose in [TBMA]DMP. Cellulose absorbance was measured at 1000 cm−1. The cellulose was added to the [TBMA]DMP while heated to 70° C. in order to insure dispersion of the cellulose and to avoid clumping. By the time all of the cellulose was added, the cellulose was beginning to dissolve. The contact temperature was then increased to 100° C. As the contact temperature increased, the rate of cellulose dissolution increased significantly and by the time the cellulose and [TBMA]DMP reached 100° C., the cellulose was essentially dissolved in the [TBMA]DMP to produce a homogeneous cellulose solution.
Example 3 Development of Models for Analysis of the Amount of Cellulose Dissolved in Tetraalkylammonium Alkyl Phosphates
Following the general procedure of Example 2, different concentrations of cellulose (2.5, 5.0, 7.5, 10.0, 12.5 wt %) were dissolved in tributylmethylammonium dimethylphosphate. Using initial and final concentrations, absorbances at the different concentrations were fit using a partial least-squares method over the spectral region of 860-1320 cm−1. Additionally, a linear least squares fit was made to the second derivative of a cellulose absorbance band at 1157 cm−1. This band was selected on the basis that there is little or no interference from tetraalkylammonium alkylphosphates in this spectral region. FIG. 2 shows modeled wt % cellulose, and the experimental absorbance values for 10 wt % cellulose dissolved in tributylmethylammonium dimethylphosphate. As can be seen, the modeled wt % cellulose and the experimental absorbance were in excellent agreement.
Example 4 Comparison of the Dissolution of Cellulose in Different Tetraalkylammonium Alkylphosphates
The following additional tetraalkylammonium alkylphosphates were prepared by the general method of Example 1: tributylmethylammonium dimethylphosphate [TBMA]DMP, tripentylmethylammonium dimethylphosphate [TPMA]DMP, trioctylmethylammonium dimethylphosphate [TOMA]DMP, trimethylethanolammonium dimethylphosphate [TMEA]DMP, trimethylethoxyethanolammonium dimethylphosphate [TMEEA]DMP, and trimethylethylacetateammonium dimethylphosphate [TMEAA]DMP. Following the general method of Example 2 using a fixed concentration of cellulose (7.5 wt %, DP 335), the solubility of cellulose in each of these tetraalkylammonium alkylphosphates were evaluated. The total amount of cellulose dissolved was determined using the linear model described in Example 3. The results are summarized in Table 1.
The amount of cellulose dissolved in selected tetraalkylammonium alkylphosphates.
tetraalkylammonium wt % cellulose alkylphosphates cellulose dissolved dissolved
[TBMA]DMP 7.5 100 [TMEA]DMP 6.5 87 [TMEEA]DMP 5.9 79 [TPMA]DMP 2.1 28 [TMEAA]DMP 1.0 13 [TOMA]DMP 0.0 0
Example 5 Dissolution of Cellulose in a Mixture of Tributylmethylammonium Dimethylphosphate and Dimethylsulfoxide
To a 3-neck 100 mL round bottom flask equipped for mechanical stirring and having a N2/vacuum inlet and an iC10 diamond tipped infrared probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) was added a mixture of 51.31 g of [TBMA]DMP and 17.10 g of dimethyl sulfoxide (DMSO) (25 wt %). While stirring rapidly at room temperature, 7.60 g of cellulose (10 wt %, DP ca. 335) was added to the [TBMA]DMP and DMSO solution (6 min addition). The cellulose/[TBMA]DMP/DMSO mixture was stirred for an additional 4 min to insure that the cellulose was well dispersed before raising a preheated 80° C. oil bath to the flask. Ten minutes after raising the oil bath, all of the cellulose was dissolved giving a pale yellow, low viscosity, cellulose solution.
Example 6 Esterification of Cellulose Dissolved in Tributylmethylammonium Dimethylphosphate in the Absence of a Catalyst
A 7.5 wt % cellulose solution was prepared according to the general method of Example 2. The temperature of the cellulose solution was adjusted to 80° C. prior to adding 3 equivalents of acetic anhydride (Ac2O) drop wise (6 min) to produce an acylated cellulose solution. Samples of the acylated cellulose solution were removed during the course of the reaction, and the cellulose ester was isolated by precipitation in methanol to produce a cellulose ester slurry. The cellulose ester slurry was filtered to produce a recovered cellulose ester. Each recovered cellulose ester sample was washed with four 200 mL portions of methanol to produce a washed cellulose, then dried at 50° C., 10 mm Hg, to yield a dried cellulose ester product.
Example 7 Esterification of Cellulose Dissolved in 1-Butyl-3-Methylimidazolium Dimethylphosphate (Comparative)
A 3-neck 100 mL round bottom flask was equipped for mechanical stirring, with an iC10 diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA), and with an N2/vacuum inlet. To the flask were added 50.65 g of 1-butyl-3-methylimidazolium dimethylphosphate ([BMIm]DMP). While stirring at room temperature 4.11 g (7.5 wt %) of cellulose (DP ca. 335, 6 min addition) were added. Vacuum (2 mm Hg) was then applied with the aid of a bleed valve and a preheated 80° C. oil bath was raised to the flask. Six minutes after raising the oil bath, a clear cellulose solution was produced. The cellulose solution was stirred for an additional 11 min before the oil bath was dropped, and the cellulose solution was allowed to cool to room temperature.
9.57 g (3.7 eq) of acetic anhydride was added dropwise over the course of 10 minutes to produce a reaction mixture. After the addition was complete, the reaction mixture was stirred for 33 min before a sample was removed, and the cellulose ester precipitated in methanol (Sample 1). At this point, no color had formed in the reaction mixture. A preheated 50° C. oil bath was raised to the flask. The reaction mixture was stirred for 34 min before a sample was removed, and cellulose ester precipitated in methanol (Sample 2). There was little change in the reaction mixture color. The oil bath temperature setting was increased to 80° C. Within 13 minutes, the reaction mixture color was deep amber, and the viscosity started to increase. After an additional 8 minutes, the reaction mixture gelled. Stirring was continued for an additional 30 minutes before dropping the oil bath. The reaction mixture was a black gel. To solidify the gel, methanol was added directly to the flask (Sample 3). After filtration, each sample was washed with four 200 mL portions of methanol, and the cellulose ester solids were dried overnight at 50° C., 5 mm Hg. Sample 1 (white solid) and Sample 2 (tan solid) were soluble in solvents like DMSO and NMP. Sample 3 (black solid) was insoluble in all solvents evaluated. It is important to note that sample 2 (DS=2.48) was not soluble in acetone at 100 mg/mL; a gel was formed. In this invention, we have found that cellulose acetates prepared from cellulose dissolved in tetraalkylammonium alkylphosphates are fully soluble in acetone at 100 mg/mL when they have a DS from about 2.45 to about 2.55.
Another reaction was conducted in an identical manner to prior reaction except that 0.1 eq MSA was used as a catalyst. As shown in FIG. 5, inclusion of methyl sulfonic acid (MSA) did not change the reaction rate relative to when no MSA was present. As in the case of the reaction involving no MSA, after raising the reaction temperature to 80° C., the reaction mixture viscosity was observed to increase. A sample was quickly removed and precipitated in MeOH. Within a few minutes of sampling, the reaction mixture also gelled. That is, the presence of MSA did not inhibit gelation.
These examples illustrate a number of important points. Dissolution of cellulose in [BMIm]DMP is known (Green Chemistry 2008, 10, 44-46; Green Chemistry 2007, 9, 233-242). However, this example shows that esterification of cellulose dissolved in [BMIm]DMP is not successful. Esterification of cellulose dissolved in [TBMA]DMP at 80° C. does not lead to gelation (Example 6). The cellulose ester product obtained is typically a white solid having a DS range of 2.45-2.55 and is completely soluble in acetone. In contrast, esterification of cellulose dissolved in [BMIm]DMP at 80° C. leads to rapid gelation. The cellulose ester product is always highly colored and is insoluble in all solvents. Inclusion of MSA does not change the reaction rates nor does it prevent gelation. This is in contrast to what is observed in the esterification of cellulose dissolved in [BMIm]Cl where inclusion of MSA both accelerates the rates of reaction and prevents gelation as disclosed in U.S. patent application entitled “Cellulose Esters and Their Production in Halogenated Ionic Liquids filed on Aug. 11, 2008 and having Ser. No. 12/189,415.
Example 8 Esterification of Cellulose Dissolved in Tetraalkylammonium Alkylphosphates-Strong Acid Mixtures
Prior to cellulose dissolution, to a 3-neck 100 mL round bottom flask equipped for mechanical stirring and with a N2/vacuum inlet, 53.46 g of tributylmethylammonium dimethylphosphate ([TBMA]DMP) were added. The flask was placed in an 80° C. oil bath, and the solution was stirred overnight under vacuum (16.5 h at ca. 0.5 mm Hg). The [TBMA]DMP was cooled to 70° C., and an IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) was inserted to obtain absorbance data.
To the [TBMA]DMP was added 5.94 g (10 wt %) of microcrystalline cellulose while stirring vigorously (5 min addition). The cellulose easily and quickly dispersed in the [TBMA]DMP. Vacuum was applied with the aid of a bleed valve (ca. 1 mm Hg), and the oil bath was heated to 100° C. By the time the cellulose and [TBMA]DMP reached 98° C. (ca. 20 min), nearly all of the cellulose was dissolved. The cellulose and [TMBA]DMP were stirred for an additional 100 min at 100° C. at which point the mixture was a clear, pale yellow, cellulose solution.
To the cellulose solution was added 1.87 g (0.5 eq) of acetic anhydride (Ac2O) drop wise over the course of 3 min. The cellulose solution viscosity dropped significantly, and the cellulose solution color became slightly darker. At this point, the cellulose solution was cooled to 80° C. before adding 9.35 g (2.5 eq) Ac2O drop wise over the course of 9 min to produce an acylated cellulose solution. Samples of the acylated cellulose solution were removed at different time intervals, and the cellulose ester was isolated by precipitation in 200 mL methanol to produce a cellulose ester slurry. Precipitated cellulose ester was isolated by filtration to produce a recovered cellulose ester. Each recovered cellulose ester sample was washed with four 200 mL portions of methanol to produce a washed cellulose ester then dried invacuo (50° C., ca. 10 mm Hg). Based on in situ IR, the reaction was nearly complete 11 min after the end of the 2nd anhydride addition. The contact period was extended further in order to see how the acylated cellulose solution color changed. As the reaction progressed, the acylated cellulose solution became darker amber, nearly brown at the end of the reaction.
FIG. 6 shows a plot of absorbance for infrared bands at 1825 cm−1 (acetic anhydride) and 1724 cm−1 (acetic acid shifted to a higher wave number due to interaction with the [TBMA]DMP) versus contact time during esterification of cellulose dissolved in [TBMA]DMP. The DS values shown in FIG. 6 were determined by proton NMR spectroscopy and correspond to the samples removed during the course of the contact period. As FIG. 6 illustrates, the rate of reaction at 100° C. was extremely fast. The Ac2O was consumed so rapidly that Ac2O was not observed during the addition. At 80° C., the rate of reaction slowed slightly but was still very rapid. After the start of 2nd anhydride addition, only 21 minutes were required to reach a DS of 2.48.
Two additional reactions were conducted following the exact same protocol described above except that 1 wt % perchloric acid (HClO4) (based on [TBMA]DMP) or 1 wt % methane sulfonic acid (MSA) (based on [TBMA]DMP) was added with the 0.5 eq Ac2O as a mixture. FIGS. 7 and 8 compares a plot of absorbance for infrared bands at 1724 cm−1 versus contact time during the esterification of cellulose dissolved in [TBMA]DMP when Ac2O, Ac2O+HClO4, or Ac2O+MSA are added. The DS values shown in FIG. 8 were determined by proton NMR spectroscopy and correspond to the samples removed during the course of the contact period. FIG. 7 shows the contact period involving the addition of 0.5 eq Ac2O at 100° C. The x axis has been shifted so that each reaction begins at the same point of anhydride addition (15 min). In all 3 cases, the rate of reaction at 100° C. was extremely fast. The Ac2O was consumed so rapidly that Ac2O was not observed during the addition. FIG. 8 shows the contact period involving the addition of 2.5 eq Ac2O at 80° C. The x axis has been shifted so that each reaction begins at the same point of anhydride addition (72 min). In all 3 cases, the rate of reaction slowed slightly due to a decrease in temperature but was still very rapid. That is, inclusion of these acids did not accelerate the reaction rates. In fact, comparing the initial slopes (72-90 min) of the plots and the DS values obtained for each reaction showed that inclusion of MSA slowed the reaction rates significantly. This is more easily seen by FIG. 9 which shows a plot of DS versus time for the time period involving addition of 2.5 eq Ac2O in the absence and presence of acid at 80° C. Furthermore, analysis of these samples by gel permeation chromatography (GPC, Table 2) showed that inclusion of these strong acids at high concentrations had a negligible impact on the molecular weights of the cellulose ester products. Typically, inclusion of these acids at these concentrations would significantly reduce the molecular weights of the cellulose ester products.
Molecular weights and sample colors for each sample removed from the contact mixture during esterification of cellulose dissolved in [TBMA]DMP in the presence and absence of 1 wt % acid.
Mn Mw Mz Mw/Mn Sample Color
Sample 1 35171 118384 313653 3.37 white Sample 2 32990 119285 304868 3.62 white Sample 3 30601 119971 328116 3.92 off-white Sample 4 29996 125338 334972 4.18 tan
Ac2O + HClO4
Sample 1 33266 120082 317027 3.61 white Sample 2 31528 124730 325057 3.96 white Sample 3 31788 129486 337277 4.07 off-white Sample 4 30956 137136 365184 4.43 tan
Sample 1 34895 114799 291538 3.29 white Sample 2 32423 114750 288847 3.54 white Sample 3 31805 117425 300574 3.69 white Sample 4 29832 121941 320374 4.09 white
Example 9 Preparation of Cellulose Mixed Esters from Cellulose Dissolved in Tetraalkylammonium Alkylphosphates-Strong Acid Mixtures
Prior to cellulose dissolution, 61.11 g tributylmethylammonium dimethylphosphate ([TBMA]DMP) was added to a 3-neck 100 mL round bottom flask equipped for mechanical stirring and with a N2/vacuum inlet. The flask was placed in an 80° C. oil bath, and the [TBMA]DMP was stirred overnight under vacuum (ca. 16.5 h at ca. 0.5 mm Hg). The liquid was cooled to 70° C., and an IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md., USA) was inserted.
To the [TBMA]DMP was added 6.79 g (10 wt %) of microcrystalline cellulose while stirring vigorously (5 min addition). The cellulose easily and quickly dispersed in the [TBMA]DMP. The oil bath was then heated to 100° C. By the time the cellulose and [TBMA]DMP reached 97° C. (ca. 35 min), nearly all of the cellulose was dissolved. The cellulose and [TBMA]DMP was stirred for an additional 75 min at 100° C. at which point the mixture was a clear, pale yellow, cellulose solution.
To the cellulose solution was added a chilled mixture of 2.14 g (0.5 eq) of acetic anhydride (Ac2O) and 2.73 g propionic anhydride (Pr2O) drop wise over the course of 3 minutes to produce an acylated cellulose solution. The acylated cellulose solution viscosity dropped significantly, and the acylated cellulose solution color became slightly darker. At this point, the acylated cellulose solution was cooled to 60° C. before adding a chilled mixture of 4.28 g (1 eq) of Ac2O and 5.45 g Pr2O drop wise over the course of 7 minutes. Samples of the acylated cellulose solution were removed at different time intervals, and the cellulose ester was isolated by precipitation in 200 mL of 75/25 MeOH/H2O to produce a cellulose ester slurry. The cellulose ester slurry was filtered to produce a recovered cellulose ester and precipitation liquids. Each recovered cellulose ester sample was washed with four 200 mL portions of 75/25 MeOH/H2O to produce a washed cellulose ester then dried invacuo (50° C., ca. 10 mm Hg) to produce a dried cellulose ester product.
FIG. 10 shows a plot of absorbance for infrared bands at 1815 cm−1 (anhydride), 1732 cm−1 (acid shifted to a higher wave number due to interaction with the [TBMA]DMP), and 1226 cm−1 (ester+acid) versus contact time during esterification of cellulose dissolved in [TBMA]DMP. The DS values shown in FIG. 10 were determined by proton NMR spectroscopy and correspond to the samples removed during the course of the contact period. As FIG. 10 illustrates, the rate of reaction at 100° C. was sufficiently fast that anhydride was not observed during the addition. At 60° C., the rate of reaction slowed. After the start of the 2nd anhydride addition, 142 minutes were required to reach a DS of 2.42. Relative to Example 8, the reaction rate after the 2nd addition was slower primarily due to the difference in contact temperature.
An additional reaction was conducted following the exact same protocol described above except 1 wt % methane sulfonic acid (MSA) was added with the 0.5 eq Ac2O+0.5 eq Pr2O as a mixture. FIGS. 11 and 12 compares a plot of absorbance for infrared bands at 1815 cm−1 and 1732 cm−1 versus contact time during the esterification of cellulose dissolved in [TBMA]DMP when Ac2O/Pr2O or Ac2O/Pr2O+MSA was added. FIG. 11 shows the contact period involving the addition of 0.5 eq Ac2O and 0.5 eq Pr2O at 100° C. The x axis has been shifted so that each reaction begins at the same point of anhydride addition (30 min). In both cases, the rate of reaction at 100° C. was fast. In the case of Ac2O/Pr2O (no MSA), anhydride was consumed so rapidly that none was observed during the addition. However, with Ac2O/Pr2O+MSA, a small concentration of anhydride was observed during the addition period. FIG. 12 shows the contact period involving the addition of 1 eq Ac2O and 1 eq Pr2O with and without MSA at 60° C. The x axis has been shifted so that each reaction begins at the same point of anhydride addition (113 min). In both cases, the rate of reaction slowed due to the lower contact temperature. Based on FIG. 12, it is evident that the rate of anhydride consumption was slower when MSA was present in the contact mixture. Moreover, comparing the initial slopes (115-175 min) of the 1732 cm−1 absorbances also indicates that inclusion of MSA slowed the reaction rate. This is easily seen in FIG. 14 which shows a plot of DS versus time for the time period involving addition of 1.0 eq Ac2O and 1.0 eq Pr2O in the absence and presence of acid at 60° C. Furthermore, analysis of these samples by gel permeation chromatography (Table 3) showed that inclusion of these strong acids at high concentrations had a negligible impact on the molecular weights of the products. In esterification of cellulose using typical solvents, inclusion of these acids at these concentrations would significantly reduce the molecular weights of the cellulose ester products.
Molecular weights and sample colors for each sample removed from the contact mixture during esterification of cellulose dissolved in [TBMA]DMP in the presence and absence of 1 wt % MSA. Reaction times were measured from the point of 2nd anhydride addition at 60° C.
reaction time Sample (min) Mn Mw Mz Mw/Mn Color
Sample 1 14 51153 151020 412998 2.95 white Sample 2 28 52243 143508 387475 2.75 white Sample 3 51 43906 134878 378363 3.07 white Sample 4 142 34520 131462 390056 3.81 pale yellow
Ac2O/Pr2O + MSA
Sample 1 9 53846 140171 365799 2.6 white Sample 2 29 49959 132034 353502 2.64 white Sample 3 56 46795 129352 344249 2.76 white Sample 4 150 37879 129378 375018 3.42 white Sample 5 277 33913 129788 390131 3.83 white
Example 10 Preparation of Cellulose Esters from Cellulose Dissolved in Tetraalkylammonium Alkylphosphates-Aprotic Solvent Mixtures
Cellulose (10 wt %, DP ca. 335) was dissolved in a 75/25 mixture by weight of [TBMA]DMP/dimethylformamide according to the general procedure of Example 5 which gave a light yellow solution. The temperature of the cellulose solution was adjusted to 50° C. prior to adding 3 equivalents of Ac2O drop wise over the course of 16 minutes to produce an acylated cellulose solution. After adding the Ac2O, the acylated cellulose solution was stirred for 64 min at 50° C. before raising the contact temperature to 80° C. The color of the acylated cellulose solution was light yellow throughout the contact period. Samples of the acylated cellulose solution were removed during the course of the reaction, and the cellulose ester was isolated by precipitation in methanol to produce a cellulose ester slurry. The cellulose ester slurry was filtered to produce a white, recovered cellulose ester and precipitation liquids. Each sample of the recovered cellulose ester was washed with three 200 mL portions of to produce a washed cellulose ester then dried at 50° C., 10 mm Hg to produce a dried cellulose ester product.
FIG. 14 shows a plot of absorbance for infrared bands at 1825 cm−1 (acetic anhydride and 1724 cm−1 (acetic acid) versus contact time during esterification of cellulose dissolved in [TBMA]DMP/DMF. The DS values shown in FIG. 14 were determined by proton NMR spectroscopy and correspond to the acylated cellulose solution samples removed during the course of the contact period. As FIG. 14 illustrates, even at 50° C. the rate of reaction was adequate. After the start of anhydride addition, only 23 minutes were required to reach a DS of 0.85. When the contact temperature was increased to 80° C., reaction rates increased leading to a DS of 2.48 when the reaction was terminated. It is important to note that the acylated cellulose solution color was maintained throughout the contact period and that the cellulose esters obtained by sampling the acylated cellulose solution were white.
A second reaction was conducted in an identical manner using the cellulose solution prepared in Example 5 (10 wt % cellulose in 75/25 [TBMA]DMP/DMSO). In this case, even at 50° C., the acylated cellulose solution color rapidly darkened, and the acylated cellulose solution viscosity decreased significantly. When the contact temperature was increased to 80° C., the acylated cellulose solution color turned black, and the solution viscosity became extremely low. The cellulose esters were isolated by precipitating with methanol to produce a cellulose ester slurry followed by filtration to produce a recovered cellulose ester. The cellulose esters of Samples 1 and 2 were white; Sample 3 was deep brown; and Sample 4 was gray-black in appearance. Table 4 compares the molecular weights of the cellulose ester products obtained from the [TBMA]DMP/DMSO acylated cellulose solution to the cellulose ester products from the [TBMA]DMP/DMF acylated cellulose solution (Table 4). In the case of the [TBMA]DMP/DMSO acylated cellulose solution, both Mn and Mw for the cellulose acetates were significantly lower relative to the cellulose acetates from the [TBMA]DMP/DMF acylated cellulose solution. Without wishing to be bound by theory, the discoloration and cellulose ester product degradation is believed to be arise from the relatively acidic proton alpha to the SO double bond which is absent in the case of DMF.
Molecular weights for each sample removed from the acylated cellulose solution during esterification of cellulose dissolved in [TBMA]DMP/DMSO or [TBMA]DMP/DMF. Reaction times are from the end of anhydride addition.
reaction time (min) DS Mn Mw Mz Mw/Mn
[TBMA]DMP/DMSO
Sample 1 6 0.73 19441 75483 272860 3.88 Sample 2 60 1.68 8531 28050 146489 3.29 Sample 3 86 2.12 8413 41964 383794 4.99 Sample 4 113 2.23 7717 43316 389919 5.61
[TBMA]DMP/DMF
Sample 1 7 0.85 25365 120596 499556 4.75 Sample 2 60 1.80 23833 126008 502791 5.29 Sample 3 91 2.24 21452 128833 513726 6.01 Sample 4 128 2.48 18857 134760 553723 7.15
Example 11 Preparation of Cellulose Acetate Propionate from Cellulose Dissolved in 75/25 Tributylmethylammonium Dimethylphosphate/N-Methylpyrrolidone
Cellulose (10 wt %, DP ca. 335) was dissolved in a 75/25 mixture by weight of [TBMA]DMP/NMP at 100° C. in 10 minutes according to the general procedure of Example 5 which gave a light yellow cellulose solution. To the cellulose solution at 100° C. was added 3.3 eq Pr2O (contained trace amount of Ac2O) drop wise over the course of 13 minutes to produce an acylated cellulose solution. Fifteen minutes from the end of addition, the IR absorbance values begin to plateau, and the absorbance values indicated that the DS was near the desired value. The IR probe was removed from the acylated cellulose solution, and the acylated cellulose solution was immediately poured into 300 mL of 75/25 Methanol/H2O while mixing with a Heidolph homogenizer to produce a cellulose ester slurry comprising precipitated cellulose ester and precipitation liquids. The precipitated cellulose ester was isolated by filtration than washed 3× with 200 mL portions of 75/25 MeOH/H2O to produce a washed cellulose ester before drying overnight at 10 mm Hg, 50° C. which provided 11.9 g of a snow white, dried cellulose ester solid. Analysis by 1H NMR revealed that the cellulose ester had a DS of 2.34 (DSPr=2.30, DSAc=0.04). Analysis by quantitative carbon 13 NMR showed that the dried cellulose ester product was regioselectively substituted having a ring RDS of: RDS C6=0.97, RDS C3=0.64, RDS C2=0.73. The cellulose ester product was fully soluble in a variety of solvents including DMSO, NMP, acetone, and 90/10 CH2Cl2/MeOH at 100 mg/l mL.
Example 12 Casting of Film and Film Optical Measurements
A series of essentially 6,3- and 6,2-regioselectively substituted cellulose esters (1-3) were prepared according to the general procedure of Example 11 (high C6 RDS). Commercial (Comparative Examples 4 and 6) cellulose esters available from Eastman Chemical Company, were produced by the general procedures described in U.S. Patent Publication 2009/0096962 and U.S. Patent Publication 2009/0050842. Comparative Example 5 was prepared as described in U.S. Patent Publication 2005/0192434. The cellulose ester in Example 5 is essentially 2,3-regioselectively substituted and differed from the examples of the present invention in that it has a low RDS at C6 while the cellulose esters of the present invention have a high RDS at C6. The ring RDS was determined for each sample before film was cast, and the film optical properties determined. The results are summarized in Table 5.
The degree of substitution, relative degree of substitution, and out- of-plane retardation (nm) for compensation film for cellulose esters of the present invention versus comparative (C) cellulose esters.
Example DS DSPr DSAc RDS C6 RDS C3 RDS C2 Rth (589)
1 2.49 2.44 0.05 1.00 0.70 0.78 −118.7 2 2.45 2.44 0.01 1.00 0.68 0.76 −140.4 3 2.10 2.08 0.02 0.95 0.60 0.55 −381.9 4 (C) 2.73 2.69 0.04 0.83 0.98 0.90 −29.2 5 (C) 1.99 1.94 0.05 0.36 0.80 0.83 −80.2 6 (C) 1.93 1.77 0.16 0.56 0.71 0.66 −209.9
Example 13 Preparation of Cellulose Acetate Propionate Benzoate from a Regioselectively Substituted Cellulose Acetate Propionate
The cellulose acetate propionate prepared in Example 11 (5 g) and pyridine (50 g) was charged to a 300 mL, round-bottom flask equipped with a mechanical stirrer and water condenser. The mixture was stirred at room temperature under nitrogen atmosphere to yield a clear solution. Benzoyl chloride (12.8 g) was then added drop wise through an addition funnel. After the completion of addition (ca. 1 h), the temperature was raised to 70° C. The mixture was stirred for additional 5 h and then allowed to cool to room temperature. The resulting solution was precipitated into methanol (800 g) with vigorous stirring, filtered, washed repeatedly with methanol, and dried under vacuum to yield a fibrous product (4.7 g). Analysis by 1H NMR revealed a DSPr=2.29, DSAc=0.04, DSBz=0.70. Analysis by 13C NMR revealed that the regioselectivity of the initial sample was preserved under the reaction conditions.
Example 14 Preparation of Cellulose Benzoate Propionate from Cellulose Dissolved in 70/30 Tributylmethylammonium Dimethylphosphate/N-Methylpyrrolidone Using a Staged Anhydride Addition
Cellulose (10 wt %, DP ca. 335) was dissolved in a 70/30 mixture by weight of [TBMA]DMP/NMP at 100° C. according to the general procedure of Example 5 which gave a light yellow cellulose solution. To the cellulose solution at 100° C. was added 2.5 eq Pr2O drop wise over the course of 3 minutes. to produce an acylated cellulose solution. Ten minutes after the end of Pr2O addition, benzoic anhydride (4 eq) was added in one portion as a melt (melted at 85° C.). The acylated cellulose solution was stirred for an additional 35 minutes at which time the IR absorbance values indicated that the DS was near the desired value. The IR probe was removed from the acylated cellulose solution, and the acylated cellulose solution was immediately poured into 300 mL of methanol while mixing with a Heidolph homogenizer to produce a cellulose benzoate propionate slurry. The cellulose benzoate propionate was isolated by filtration then washed 8× with 200 mL portions of methanol before drying overnight at 10 mm Hg, 50° C. Analysis by 1H NMR revealed that the cellulose benzoate propionate had a DS of 2.91 (DSPr=2.58, DSBz=0.33). Analysis by quantitative carbon 13 NMR showed that the product was regioselectively substituted having a ring RDS of: RDS C6=1.00, RDS C3=0.91, RDS C2=1.00 and a benzoate carbonyl RDS of: RDS C6=0.04, RDS C3=0.12, RDS C2=0.17. The product was soluble in a variety of solvents including DMSO, NMP, and CH2Cl2.
1. A cellulose ester comprising:
(a) at least one aliphatic acyl substituent;
4. The cellulose ester of claim 1, wherein said at least one aliphatic acyl substituent comprises acetate, propionate, or a combination thereof.
5. The cellulose ester of claim 1, wherein said at least one aromatic acyl substituent comprises a benzoate.
6. The cellulose ester of claim 1, wherein said cellulose ester has a degree of polymerization in the range of 5 to 1,000.
7. A film comprising a regioselectively substituted cellulose ester, wherein said regioselectively substituted cellulose ester comprises:
(c) a degree of substitution from 1.8 to 2.9,
wherein the ring RDS ratio of said aliphatic acyl substituent for C6/C3 or C6/C2 is at least 1.05 and the carbonyl RDS at C2 and C3 for said aromatic acyl substituent is greater than at C6.
8. The film of claim 7, wherein said cellulose ester has a RDS ratio of C6>C3>C2.
9. The film of claim 7, wherein said cellulose ester has a RDS ratio of C6>C2>C3.
10. The film of claim 7, wherein said at least one aliphatic acyl substituent comprises acetate, propionate, or a combination thereof.
11. The film of claim 7, wherein said at least one aromatic acyl substituent comprises a benzoate.
12. The film of claim 7, wherein said film comprises a compensation film.
13. The film of claim 12, wherein said compensation film comprises a +C plate, a −C plate, a +A plate, or −A plate.
14. The film of claim 7, wherein said film has an Rth in the range of −400 to +100 nm.
15. The film of claim 7, wherein said film has an Rth in the range of −160 to +270 nm.
16. The film of claim 7, wherein said film has an Rth in the range of −60 to +100 nm.
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European Search Report—Application No. 17169625.5-1302 dated Aug. 7, 2017.
Patent number: 9926384
Patent Publication Number: 20140343271
Inventors: Charles Buchanan (Kingsport, TN), Norma Buchanan (Bluff City, TN), Elizabeth Guzman-Morales (Kingsport, TN)
Primary Examiner: Everett White
Application Number: 14/447,704
International Classification: C08B 1/00 (20060101); C08B 3/00 (20060101); G02B 1/10 (20150101); G02B 5/32 (20060101); C08B 3/06 (20060101); C08B 3/16 (20060101); G02B 1/14 (20150101); C08B 3/04 (20060101); C08B 3/08 (20060101); C08B 3/10 (20060101);