CN1223665A - Process for preparing cellulose acetoacetate alkanoates - Google Patents

Abstract

The present invention relates to a process for preparing a substituted cellulose acetoacetate alkanoate without using a carboxamide/lithium chloride solvent system. The process involves contacting cellulose in a carboxylic acid diluent with an acetylating compound selected from the group consisting of a carboxylic acid anhydride and an acyl chloride, an acetoacetylating compound selected from the group consisting of diketene, an alkyl acetoacetate and 2,2,6-trimethyl-4H-1,3-dioxin-4-ketone, and a mineral acid catalyst under conditions and in a molar ratio sufficient to cause the cellulose, acetylating compound and acetoacetylating compound to react to produce a substituted cellulose acetoacetate alkanoate.

Description

Preparation method of cellulose acetoacetate alkanoate

This is an original application based on provisional serial number 60/016278, filed April 24, 1996.

field of invention

The present invention relates to a process for the preparation of substituted cellulose acetoacetate alkanoates without the use of carboxamide/lithium chloride solvent systems.

Background of the invention

A number of methods have been described for the synthesis of cellulose esters containing acetoacetyl groups. U.S. Patent Nos. 5,292,877, 5,360,843, 5,521,304, and 5,420,267 describe various methods for the preparation of cellulose acetoacetate, which include: solubilizing cellulose in a carboxamide/lithium chloride solvent, adding compounds such as diketene or acetyl Acetoacetylated compound of tert-butyl acetate, and optimally further addition of carboxylic anhydride or acid chloride. The carboxamide is either 1-methyl-2-pyrrolidone or N,N-dimethylacetamide.

A disadvantage of the carboxamide/lithium chloride solvent system is that both lithium chloride and carboxamide are expensive materials that require recovery and recycling on an industrial scale. Also, when using a carboxamide/lithium chloride solvent system, the concentration of cellulose must be kept below about 8% by weight, otherwise the viscosity of the solution is too high from a practical point of view.

Hagemeyer (US Patent 2,500,029) and Caldwell (US Patent 2,521,897) describe the preparation of cellulose acetoacetate alkanoates. Both patents describe the reaction of cellulose acetate and other cellulose esters with diketene in organic solvents with or without catalysis by pyridine, sodium acetate. This method requires two acetylations, two isolations and possibly two hydrolysis steps to convert cellulose to cellulose acetoacetate alkanoate. Staudinger and Eicher [Makromol. Chem. 1953, 10, 261-279] describe the direct conversion of cellulose to cellulose acetoacetate (DS=3.0). The one-step nature of their method is attractive but misleading. Their process requires regenerated cellulose; so must include: preparation of cellulose diacetate, hydrolysis from start to finish back to cellulose, and then, reacetylation with diketene (in this process using sodium acetate in acetic acid Carry out), just obtain required cellulose acetoacetate. Staudinger and Eicher do not describe how to obtain partially substituted cellulose acetoacetate, nor how to obtain cellulose alkanoate acetoacetate directly from cellulose. Kirillova and Padchenko [Journal of Applied Chemistry (Zh. Prikladnoi Khimii) 1964, 37, 925-927] describe the reaction of cellulose with diketene in acetic acid using sulfuric acid catalysis to give cellulose acetoacetate. They varied solvent mixtures, catalysts, and reagent ratios, but failed to achieve high degrees of substitution. They make no mention of attempts to prepare cellulose acetoacetate alkanoates, but their work suggests that attempts to react cellulose with diketenes and carboxylic anhydrides catalyzed by mineral acids were unsuccessful due to incomplete reactions.

Summary of the invention

It is therefore an object of the present invention to provide an economical process for the preparation of substituted cellulose acetoacetate alkanoates.

Another object of the present invention is to provide a method for preparing substituted cellulose acetoacetate alkanoates without using a carboxamide/lithium chloride solvent system.

Still another object of the present invention is to provide a process for preparing partially substituted cellulose acetoacetate alkanoate in which the degree of substitution of alkanoyl group and the degree of substitution of acetoacetyl group can be independently controlled.

In terms of the foregoing and other purposes, the present invention provides a method for preparing substituted cellulose acetoacetate alkanoate, comprising: making cellulose in a carboxylic acid diluent with a mixture selected from carboxylic anhydrides and acid chlorides (conditions is an acetylated compound of an acid chloride in combination with an acid acceptor) selected from diketene, alkyl acetoacetate and 2,2,6-trimethyl-4H-1,3-dioxin-4-one The acetoacetylation compound of (dioxin-4-one) and the inorganic acid catalyst are contacted under conditions and molar ratios sufficient to react cellulose, acetylation compound and acetoacetylation compound to produce substituted cellulose acetoacetate alkanoic acid ester.

According to one embodiment of the invention, the process is carried out until a substituted cellulose acetoacetate alkanoate having a degree of substitution of 2.7 to 3.0 is obtained. The substituted cellulose acetoacetate alkanoate is then hydrolyzed.

The substituted cellulose acetoacetate alkanoates prepared by the process of the invention are dispersible in water by means of the added organic co-solvents without the use of other dispersing aids, even if the cellulose ester concentration is higher than 15% by weight Low viscosity dispersions are also formed. Substituted cellulose acetoacetate alkanoates are crosslinkable and can be formulated into coatings.

Detailed description of the invention

The invention relates to a method for preparing substituted cellulose acetoacetate alkanoate. The method comprises: contacting cellulose with an acetylating compound, an acetoacetylating compound, and a mineral acid catalyst in a carboxylic acid diluent under conditions and molar ratios sufficient to react the cellulose, the acetylating compound, and the acetoacetylating compound to form Substituted cellulose acetoacetate alkanoate. After formation of the substituted cellulose acetoacetate alkanoate, the by-products present can be removed by isolating the product by adding a non-solvent. In another embodiment of the present invention, the substituted cellulose acetoacetate alkanoate is hydrolyzed to a lower degree of substitution prior to isolation.

Various sources of cellulose can be used in the process of the invention. The cellulose is preferably first mixed with water in order to activate the cellulose. The mixture of water and cellulose is then contacted with the carboxylic acid to associate the cellulose with the carboxylic acid by solvent exchange to provide a mixture of cellulose and carboxylic acid for reaction. Suitable cellulose sources include hardwood wood pulp, softwood wood pulp, cotton linters, regenerated cellulose, and bacterial cellulose that has been treated to substantially remove impurities such as lignin.

Preferred carboxylic acids are carboxyl-terminated aliphatic carboxylic acids containing 1 to 26 carbon atoms, which may be saturated or unsaturated. Examples of carboxylic acids include valeric acid, acetic acid, butyric acid, propionic acid, capric acid, caproic acid, and nonanoic acid. Acetic acid is particularly preferred as diluent in the practice of the present invention.

The acetylating compound is selected from carboxylic acid anhydrides and acid chlorides, with the proviso that in the case of acid chlorides an acid acceptor is also used. Combinations of carboxylic anhydrides and acid chlorides, or combinations of carboxylic anhydrides or acid chlorides can also be used as acetylated compounds.

The carboxylic anhydrides contain 4 to 26 carbon atoms, preferably 4 to 20 carbon atoms, and even more preferably 4 to 8 carbon atoms. Carboxylic anhydrides may contain more than one carboxylic acid group, such as mixed anhydrides. Examples of carboxylic acid anhydrides include acetic anhydride, propionic anhydride, butyric anhydride, nonanoic anhydride, caproic anhydride, undecanoic anhydride, lauric anhydride, palmitic anhydride, as well as stearic anhydride, oleic anhydride, and linoleic anhydride. Acetic anhydride is particularly preferred in the practice of the present invention.

Examples of acid chlorides include acetyl chloride, propionyl chloride, butyryl chloride, hexanoyl chloride, lauroyl chloride and stearyl chloride. Acid chlorides are used in combination with acid acceptors, examples of which include pyridine, sodium bicarbonate and sodium acetate.

The acetoacetylating compound is selected from the group consisting of diketene, 2,2,6-trimethyl-4H-1,3-dioxin-4-one and alkyl acetoacetate, wherein the alkyl group is linear or branched, Contains 1 to 18 carbon atoms. The preferred alkyl acetoacetate is tert-butyl acetoacetate because of its high rate of formation to the reactive intermediate acetoketene.

Examples of inorganic acid catalysts include sulfuric acid, methanesulfonic acid and perchloric acid, and the preferred inorganic acid catalyst is sulfuric acid. The mineral acid catalyst can be added in the form of a solution with a carboxylic acid.

The structure of the substituted cellulose acetoacetate alkanoate prepared according to the inventive method is as follows:

In the above structure, R ² , R ³ and R ⁶ are independently selected from hydrogen, acetoacetyl and R ¹ C=O, provided that at least one of R ₂ , R ₃ and R ₆ is acetoacetyl, and R ₂ , at least one of R ₃ and R ₆ is an acyl group. Examples of the alkyl group include methyl, ethyl, propyl, pentyl, nonyl, dodecyl, 2-propyl, 2-methyl-2-propyl and 2-butyl. Preferably the alkyl group is methyl.

As mentioned above, ^R1 is selected from alkyl or branched chain alkyl containing 1 to 20 carbon atoms, phenyl, naphthyl and alkenyl or branched chain alkenyl containing 1 to 20 carbon atoms.

The total substitution degree of the substituted cellulose acetoacetate alkanoate [the total substitution degree is the sum of the substitution degrees of acetoacetyl group and acetyl group of each anhydroglucose unit (DS/AGU)] is 0.1-3.0. Preferably, the degree of substitution of the substituted cellulose acetoacetate alkanoate is 2.0-3.0, more preferably 2.1-2.8. The weight average molecular weight (Mw) of the substituted cellulose acetoacetate alkanoate is about 20,000 to about 1,000,000, and the intrinsic viscosity (I.V.) is 0.1 to 1.5 dL/g (deciliter/gram), preferably 0.2 to 0.6 dL /g.

The purification method of the substituted cellulose acetoacetate alkanoate comprises contacting the substituted cellulose acetoacetate alkanoate solution coexisting with by-products with a non-solvent to separate the substituted cellulose acetoacetate alkanoate esters. The non-solvent can be any solvent in which the starting materials (other than cellulose) and by-products are miscible but the substituted cellulose acetoacetate alkanoate product is not. Examples of non-solvents include water, methanol, ethanol, and 2-propanol. A preferred non-solvent is water. The amount of non-solvent is generally at least about 900%, based on weight units of non-solvent per weight unit of cellulosic starting material.

The substituted cellulose acetoacetate alkanoate product can be isolated from the non-solvent by methods known in the art, such as filtration, drying, decanting and washing, to obtain substantially pure substituted cellulose acetoacetate alkanoate esters. Isolation steps can be repeated until the desired purity is obtained.

The order of addition of the acetylating compound, the acetoacetylating compound and the mineral acid catalyst can be changed. Either of these compounds can be added first to the combination of cellulose and carboxylic acid diluent, or they can be added simultaneously, or as a pre-blend. However, it should be noted that changing the order of addition will change the substitution position of the acetoacetyl and acetyl groups.

The molar ratio of cellulose to anhydride is, preferably, 1:1 to 1:6, more preferably 1:2 to 1:4.

The molar ratio of cellulose to diketene is, preferably, 1.0:0.1 to 1.0:5.0, more preferably 1:1 to 1.0:3.0.

The weight ratio of the catalyst is preferably 0.05-0.5 part, more preferably 0.1-0.3 part of catalyst per part of cellulose.

The weight ratio of carboxylic acid is preferably 3-10 parts, more preferably 4-6 parts of catalyst per part of cellulose.

Preferably, the cellulose is contacted with the acetylating compound in a carboxylic acid diluent to form a mixture, cooled if necessary to 0°C to 25°C. The acetoacetylating compound and mineral acid catalyst are then added to the mixture. Raise the temperature to 50°C to 160°C to react cellulose, acetylated compound and acetoacetylated compound to generate substituted cellulose acetoacetate alkanoate.

The duration of the process should be sufficient to produce the desired substituted cellulose acetoacetate alkanoate in sufficient yield. The reaction time is largely influenced by the reactants, the reaction temperature, the concentration and choice of reactants, the choice and concentration of solvent for the reactants, and other factors known to those skilled in the art.

In another embodiment of the present invention, the cellulose acetoacetate alkanoate product having a higher degree of substitution ranging from about 2.7 to about 3.0 can be hydrolyzed to cellulose acetyl alkanoate having a lower degree of substitution by adding water. Acetate alkanoate. A catalyst may optionally be used to increase the rate of hydrolysis, or to neutralize the catalyst remaining from the acetylation to aid in the hydrolysis of the acetoacetate.

The ratio of acetoacetate and alkanoate in the product can be effectively controlled during the hydrolysis process, for example: high temperature hydrolysis in the absence of a catalyst contributes to a low acetoacetyl group content while retaining the alkanoate group. Low temperature hydrolysis in the presence of mineral acid catalysts favors low alkanoic acyl content and high acetoacetyl content. This choice was followed because loss of acetoacetyl groups is a unimolecular process accelerated by higher temperatures. In contrast, cellulose alkanoate hydrolysis is a bimolecular process in which water is the nucleophile and mineral acid catalysis accelerates the process.

The substituted cellulose acetoacetate alkanoate prepared by the inventive method can be dispersed in water by means of the added organic co-solvent, without other dispersing aids, forming a low-viscosity dispersion, even if the cellulose concentration is 15% (weight ) above as well. Substituted cellulose acetoacetate alkanoates are crosslinkable and can be formulated into coatings.

The following non-limiting examples further illustrate the practice of the invention.

example

In the following examples, the method of activating cellulose consists of soaking hardwood cellulose pulp NATCHEZ HVX from International Paper or SULFATATE HJ from Rayonier in distilled water, followed by carboxylic acid The diluent was subjected to three solvent exchanges. The cellulose and carboxylic acid diluent were slurried and the resulting slurry was added to a 500 mL (milliliter) three-necked round bottom flask equipped with mechanical stirring, a thermometer, and a nitrogen inlet. The slurry was cooled to 5°C and the carboxylic anhydride and diketene were added to form a mixture. As used herein, "equivalents" means the number of reagent equivalents per cellulose anhydroglucose unit.

The mineral acid catalyst was added to the mixture in the form of a solution of its carboxylic acid diluent and maintained at a temperature of from about 5°C to about 10°C for 30 minutes. The mixture was first warmed to about 23°C, then heated to the specified reaction temperature, and kept at this temperature until a clear solution was obtained. The resulting solution was cooled to about 20°C to 40°C.

When hydrolysis is not desired, or when selective hydrolysis of the acetoacetate groups is desired, magnesium acetate is added to the clear solution in an amount sufficient to neutralize the catalyst. Magnesium acetate is dissolved in a mixture of water and carboxylic acid.

When the substituted cellulose acetoacetate alkanoate is to be hydrolyzed, the water content of the solution is adjusted to about 6 to about 16% (by weight) by adding a specified amount of a mixture of water and carboxylic acid diluent, and at In some cases, sulfuric acid catalyst is also added to the mixture. The hydrolysis is carried out at a temperature of from about 40°C to about 90°C with the aid of 0 to about 1.0% by weight sulfuric acid catalyst over a specified period of time to form a reaction mixture.

The substituted cellulose acetoacetate alkanoate product was isolated by adding the reaction mixture dropwise to water with vigorous stirring. The product is washed with a non-solvent, and dried in a vacuum oven at about 40°C to about 60°C under a nitrogen atmosphere.

The test steps used for the results shown in this paper are as follows:

The degree of substitution of anhydroglucose units (DS/AGU) of cellulose was determined by H ¹ NMR in d-6 dimethyl sulfoxide (DMSD). Dimethyl sulfoxide contains a few drops of trifluoroacetic acid to move any hydroxyl protons downfield.

Intrinsic viscosity (I.V.) is measured at 25°C using a solution containing 0.25 g of polymer per 100 mL of a solvent consisting of 60% by weight phenol and 40% by weight tetrachloroethane. Intrinsic viscosity is given in units of dL/g.

Infrared spectroscopy was used to further confirm that the product was a substituted cellulose acetoacetate alkanoate. Example 1 The following reagents were subjected to the above procedure. The results are summarized in Table 1.

Cellulose Natchez HVX

Servings 1

Carboxylic Acid Diluent Acetic Acid

Servings 8

Carboxylic anhydride Acetic anhydride

Equivalent 3.0～5.0

Diketene equivalent 1.0～3.5

Sulfuric acid (parts) 0.185

Reaction temperature 60℃

Non-solvent Water

Washing 4×100 parts of water

Hydrolysis Not performed

Table 1

Diketene/Anhydride Acetoacetyl Acetyl I.V.

(equivalent/equivalent) (DS) (DS)

1.0/5.5 0.39 2.45 0.33

2.0/4.5 0.61 2.30 0.31

2.5/4.0 0.71 2.11 0.30

3.5/3.0 0.97 1.54 0.45 The results in Table 1 demonstrate that substituted cellulose acetate acetoacetate products with the desired degree of substitution can be directly synthesized from cellulose.

Example 2

The following reagents were subjected to the above procedure. The results are summarized in Table 2.

Cellulose Sulfatate HJ

serving 1

Carboxylic acid diluent Butyric acid

Servings 10

Carboxylic anhydride Butyric anhydride

Equivalent 4.0

Diketene equivalent 0.75～2.3

Sulfuric acid (parts) 0.10

Reaction temperature 60℃

non-solvent water

Washing 4×100 parts of water

Hydrolysis Not performed

Table 2

Diketene/Anhydride Acetoacetyl Butyryl I.V.

(equivalent/equivalent) (DS) (DS)

2.3/4.0 1.36 1.60 0.29

1.5/4.0 1.01 1.64 0.30

0.75/4.0 0.67 2.07 0.40

The results in Table 2 demonstrate that substituted cellulose acetoacetate butyrate products with desired degrees of substitution can be directly synthesized from cellulose.

Example 3

The following reagents were subjected to the above procedure. The results are summarized in Table 3.

Cellulose Natchez HVX

serving 1

Carboxylic Acid Diluent Acetic Acid

Servings 5

Carboxylic anhydride Acetic anhydride

Equivalent 4.0

Diketene equivalent 3.5

Sulfuric acid (parts) 0.20

Reaction temperature 60℃

hydrolysis:

Temperature 55℃

  Hydrolysis medium

  Contains 12% (weight) water in acetic acid

Servings 13

    Catalyst         0.3% (weight) sulfuric acid

Non-solvent Water

Washing 4×100 parts of water

table 3

Hydrolysis time Acetoacetyl Butyryl I.V.

(hour) (DS) (DS) (dL/g)

0 0.84 1.83 0.45

2 0.78 1.77 0.34

4 0.75 1.71 0.32

6 0.72 1.68 0.31

8 0.73 1.50 0.32

The results in Table 3 demonstrate that the ratio of acetate and acetoacetate in the product is controlled by hydrolysis, and acid-catalyzed low-temperature hydrolysis helps to remove acetate from the product, and hardly removes acetoacetate.

Example 4

The following reagents were subjected to the above procedure. The results are summarized in Table 4.

Cellulose Natchez HVX

serving 1

Carboxylic Acid Diluent Acetic Acid

Servings 5

Carboxylic anhydride Acetic anhydride

Equivalent 4.0

Diketene equivalent 3.5

Sulfuric acid (parts) 0.20

Reaction temperature 60℃

hydrolysis:

Temperature 85°C

Hydrolysis medium

Contains 12% in acetic acid

(weight) water

Servings 13

Catalyst None ( _{neutralization} of acetylation with Mg(OAc)

Act on the remaining sulfuric acid)

non-solvent water

Washing 4×100 parts of water

Table 4

Hydrolysis time Acetoacetyl Butyryl I.V.

(hour) (DS) (DS)

0 0.84 1.83 0.45

2 0.65 1.82 0.47

4 0.57 1.79 0.47

6 0.47 1.77 0.46

8 0.42 1.76 0.41

The results in Table 4 demonstrate that controlling the ratio of acetate to acetoacetate in the product by hydrolysis at high temperature without the use of mineral acid catalysts facilitates the removal of acetoacetate from the product with little removal of acetoacetate. esters.

Example 5

Preparation of Cellulose Acetate Acetoacetate Aqueous Dispersion

10 g of cellulose acetate acetoacetate prepared in Example 3 with an acetyl DS of 1.83, an acetoacetyl DS of 0.84 and an I.V. of 0.45 were dissolved in 10 g of cyclohexanone in a vessel equipped with mechanical stirring. , forming a mixture. 35 g of distilled water were slowly added to the mixture with vigorous stirring. The resulting mixture is a stable liquid film-forming aqueous dispersion of cellulose acetate acetoacetate.

The results of Example 5 demonstrate that cellulose acetoacetate can be used as an additive or film former in volatile organic compound modified (reduced-voc) waterborne coatings, its types include aqueous dispersion type and emulsion type.

The invention has been described in detail with particular reference to the preferred embodiments of the invention, but it should be understood that changes and modifications can be made within the spirit and scope of the invention. Also, all patents, patent applications (published and unpublished, foreign or domestic), literature or other publications noted above incorporated herein are incorporated by reference for any disclosure relevant to the practice of the invention .

Claims (25)

1. A process for the preparation of substituted cellulose acetoacetate alkanoates comprising: allowing cellulose in a carboxylic acid diluent with an acetylated compound selected from the group consisting of carboxylic anhydrides and acid chlorides, provided that the acid chloride is combined with an acid acceptor Using, an acetoacetylated compound selected from diketene, alkyl acetoacetate and 2,2,6-trimethyl-4H-1,3-dioxin-4-one (dioxin-4-one) and The inorganic acid catalyst is contacted under conditions and molar ratios sufficient to react cellulose, acetylated compound and acetoacetylated compound to produce substituted cellulose acetoacetate alkanoate. 2. 2. The method of claim 1, wherein the degree of substitution of the acetoacetyl and acetyl groups of the substituted cellulose acetoacetate alkanoate is from about 0.1 to about 3.0 per anhydroglucose unit. 3. The method of claim 1, wherein the reaction is carried out at 20°C to 160°C. 4. The method of claim 3, wherein the reaction is carried out at 50°C to 90°C. 5. The method of claim 1, wherein the cellulose is derived from a cellulose source selected from the group consisting of hardwood wood pulp, softwood wood pulp, cotton linters, regenerated cellulose, and bacterial cellulose. 6. The method of claim 5, wherein the cellulose is derived from hardwood wood pulp. 7. The method of claim 1, wherein the carboxylic acid diluent is selected from the group consisting of valeric acid, acetic acid, butyric acid, propionic acid, capric acid, caproic acid, and nonanoic acid, and combinations thereof. 8. The method of claim 7, wherein the carboxylic acid diluent is acetic acid. 9. The method of claim 1, wherein the carboxylic anhydride contains 8 to 20 carbon atoms. 10. The method of claim 1, wherein the carboxylic anhydride is selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, nonanoic anhydride, caproic anhydride, undecanoic anhydride, lauric anhydride, palmitic anhydride, stearic anhydride, oleic anhydride and linoleic anhydride, and its combination. 11. The method of claim 10, wherein the carboxylic anhydride is acetic anhydride. 12. The method of claim 1, wherein the acetoacetylated compound is tert-butyl acetoacetate. 13. The method of claim 1, wherein the inorganic acid catalyst is selected from the group consisting of sulfuric acid, methanesulfonic acid, perchloric acid, and combinations thereof. 14. The method of claim 13, wherein the mineral acid catalyst is sulfuric acid. 15. The method of claim 1, wherein the mineral acid catalyst is neutralized after the reaction. 16. The method of claim 15, wherein the neutralizing agent is selected from the group consisting of magnesium acetate, sodium acetate, magnesium carbonate, sodium carbonate, sodium bicarbonate, sodium hydroxide, and magnesium hydroxide. 17. 15. The method of claim 15, further comprising hydrolyzing the substituted cellulose acetoacetate alkanoate in the absence of a mineral acid catalyst to effect selective hydrolysis of the acetoacetate groups. 18. The method of claim 1, further comprising, hydrolyzing the cellulose acetoacetate alkanoate in the presence of a mineral acid to effect selective hydrolysis of the alkanoate groups. 19. 17. The method of claim 17, wherein the substituted cellulose acetoacetate alkanoate is hydrolyzed by adding water to the solution and maintaining the specified time and temperature. 20. The method of claim 18, wherein the hydrolysis is carried out at 40°C to 90°C. twenty one. The method of claim 1, wherein when generating substituted cellulose acetoacetate alkanoate, residual unreacted starting materials and by-products should be removed by filtration before adding the non-solvent, said method further comprising a purification step The step includes contacting the substituted cellulose acetoacetate alkanoate with a non-solvent to isolate the substituted cellulose acetoacetate alkanoate. twenty two. The method of claim 21, wherein the non-solvent is selected from the group consisting of acetone, water, methanol, ethanol and 2-propanol. twenty three. The method of claim 21, wherein the substituted cellulose acetoacetate alkanoate is separated from the non-solvent by a method selected from the group consisting of filtering, drying, decanting and washing (filtering-washing-drying is a conventional method). twenty four. The method of claim 1, wherein the structure of the substituted cellulose acetoacetate alkanoate repeat unit is as follows:

Wherein, R ² , R ³ and R ⁶ are independently selected from hydrogen, acetoacetyl group and R ¹ C=O, provided that at least one of R ² , R ³ and R ⁶ is an acetoacetyl group, R ² , R ³ And at least one of ^R6 is alkanoic acid acyl, ^R1 is selected from alkyl or branched chain alkyl containing 1 to 20 carbon atoms, alkenyl or branched chain alkenyl containing 1 to 20 carbon atoms, benzene base and naphthyl. 25． A method for preparing substituted cellulose acetoacetate alkanoate comprising: (I) The mixture is formed by contacting cellulose with an acetylated compound selected from the group consisting of carboxylic acid anhydrides and acid chlorides in a carboxylic acid diluent, provided that the acid chlorides are used in combination with an acid acceptor. (II) For the mixture of step (I), at a temperature of 0°C to about 25°C, diketene, alkyl acetoacetate and 2,2,6-trimethyl-4H-1,3- an acetoacetylation compound of dioxin-4-one and a mineral acid catalyst are added thereto; and (III) Heating the mixture in step (II) to about 50°C to about 160°C to react the cellulose, acetylated compound and acetoacetylated compound to generate substituted cellulose acetoacetate alkanoate.