JPS62195395A - Production of low-molecular-weight cellulose derivative having narrow molecular weight distribution - Google Patents

Abstract

PURPOSE:To easily obtain the titled substance useful as a filler for separation having high stability of quality, by heating a cellulose in an acidic aqueous solution to decrease the molecular weight, converting the decomposed cellulose to a derivative under a condition to maintain the molecular weight, reprecipitating in an organic solvent and fractionating a component having different molecular weight. CONSTITUTION:An acetylated cellulose is heated in an acidic aqueous solution such as dilute hydrochloric acid at 90 deg.C for 30min to obtain a cellulose having decreased molecular weight. The product is converted to a derivative by reacting with phenyl isocyanate, etc., under a mild condition to maintain its molecular weight. The derivative is reprecipitated in a hydrated or anhydrous organic solvent (e.g. methanol) to fractionate a component having different molecular weight. The objective low-molecular-weight cellulose derivative having a polymerization degree of 5-400 and narrow molecular weight distribution characterized by a (number-average molecular weight)/(weight-average molecular weight) ratio of <=3 can be produced by this process.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for obtaining a cellulose derivative having a low molecular weight and a narrow molecular weight distribution by derivatizing cellulose which has been heated in an acidic aqueous solution to reduce its molecular weight. Cellulose derivatives with low molecular weight and narrow molecular weight distribution have excellent physical properties such as low viscosity, high solubility, and uniform molecular chain length, so they have a wide range of applications, such as silica gel, etc. When adsorbed or chemically bonded to a carrier, a separating packing material that is easy to manufacture and has excellent quality stability can be obtained. Moreover, when used as a polymer liquid crystal, excellent performance is expected.

(Prior art and problems) Conventionally, the method for producing such low molecular weight cellulose derivatives is to depolymerize acetylated cellulose with acid, but the molecular weight distribution is not necessarily narrow and it is difficult to convert it to other derivatives. In this case, deacetylation was necessary.

On the other hand, microcrystalline cellulose (trade name: Avicel, etc.), which is a ■-type cellulose, and level-off cellulose, which is a ■-type cellulose whose molecular weight has been lowered in an acidic aqueous solution, are known as cellulose that has been heated in an acidic aqueous solution to lower its molecular weight. There is. The present inventors derivatized these low molecular weight cellulose obtained by heating cellulose in an acidic aqueous solution under mild conditions where the molecular weight does not change, and then analyzed this by gel permeation chromatography (GPC). They discovered that the peak was not a single peak, but rather a mixture of at least two components with different molecular weights, and as a result of intensive study of methods to separate these components, they discovered a method to completely separate them by reprecipitation, which led to the development of this book. The invention was completed.

(Means for Solving the Problems) That is, the present invention derivatizes cellulose which has been heated in an acidic aqueous solution to reduce its molecular weight under mild conditions, and then reprecipitates it in a water-containing or anhydrous organic solvent to obtain components with different molecular weights. This invention relates to a method for producing cellulose derivatives having a low molecular weight and a narrow molecular weight distribution, which is characterized by fractionating the cellulose derivatives. The raw material cellulose used in the present invention may be of any type, such as those normally obtained from cotton or pulp, or regenerated cellulose such as rayon. Further, in order to obtain a desired molecular weight, the raw cellulose may or may not be treated with an aqueous alkaline solution before lowering the molecular weight. The molecular weight of the low molecular weight cellulose used in the present invention can be adjusted by adjusting the type of cellulose used as a raw material, the time for reducing the molecular weight in an acidic aqueous solution, temperature, acid concentration, etc. In the present invention, the acidic aqueous solution used to lower the molecular weight of cellulose specifically refers to an aqueous solution of a strong acid. Any strong acid may be used, and examples thereof include sulfuric acid, hydrochloric acid, nitric acid, and perchloric acid. Further, the temperature can be appropriately selected along with the reaction temperature and reaction time depending on the desired molecular weight, but 1 to 5 normal is usually preferred.

Further, the heating temperature is preferably 40°C to the boiling point.

Examples of the cellulose used in the present invention, which has been heated in an acidic aqueous solution to lower its molecular weight under the above conditions, include:
Commercially available microcrystalline cellulose or, for example, Cellulose Chemistry and Technology Vol. 18, 4
Examples include level-off cellulose, which is obtained by lowering the molecular weight of regenerated cellulose (■-type cellulose) such as alcelized cellulose and rayon, as described on page 47 (1984). These are preferred because they are easily available. The cellulose derivative in the present invention refers to a cellulose with a substituent attached to the hydroxyl group.

Specifically, cellulose carbamates, acylated cellulose, and cellulose ethers can be mentioned. Examples of derivatization methods under mild conditions where the molecular weight does not change include the following methods. That is, by reacting the low molecular weight cellulose obtained by the above method with various isocyanates or acid halides in lysine or triethylamine, the reaction system is prevented from becoming strongly acidic and the molecular weight is not changed. It can be made into cellulose carbamate derivatives and acylated cellulose. Furthermore, the degree of substitution of cellulose carbamate derivatives and acylated cellulose can be adjusted by appropriately changing the molar ratio of isocyanate or acid halide. In addition, a solvent that does not interfere with the reaction can be used if necessary, but as in the above example, using an excess of organic bases such as pyridine or triethylamine accelerates the reaction and prevents depolymerization of cellulose due to strong acidification. This is a preferred solvent because it can be avoided. The degree of polymerization of the obtained cellulose derivative is preferably 5 to 400, more preferably 10 to 250, which is the same as the degree of polymerization of low molecular weight cellulose before derivatization. Cellulose carbamate derivatives and acylated cellulose thus obtained include cellulose phenyl carbamate, cellulose-p-tolyl carbamate, cellulose-p-chlorophenyl carbamate, cellulose-〇-
Chlorophenyl carbamate, cellulose-3,4-dichlorophenyl carbamate, cellulose-2,6-dichlorophenyl carbamate, cellulose-p-bromophenyl carbamate, cellulose-p-fluorophenyl carbamate, cellulose-p-nide a phenyl carbamate, cellulose-3, 5-dimethylphenyl carbamate, cellulose-1)-)lifluoromethylphenyl carbamate, cellulose benzoate, cellulose-p-methoxybenzoate, cellulose-p-methylbenzoate, cellulose-m-methylbenzoate, cellulose-p-tertiary -Butyl benzoate, cellulose p-fluorobenzoate, cellulose 3,5-dichlorobenzoate, cellulose cinnamate, cellulose p-methyl cinnamate, cellulose acetate, cellulose phenylacetate, cellulose propionate, cellulose 〇-methylbenzoate , cellulose-4-phenylazophenyl carbamate, and the like.

Other cellulose ethers are also easily obtained, but
Preferred methods for its synthesis include alkylation using an alkyl halide, or ring-opening reaction of epoxides such as oxirane and oxetane. Examples of cellulose ethers include cellulose methyl ether,
Examples include cellulose ethyl ether, cellulose-n-propyl ether, cellulose benzyl ether, carboxymethyl cellulose, hydroxyethyl cellulose, and 2-hydroxypropyl cellulose.

However, the present inventors have derivatized the low-molecular-weight cellulose obtained by heating cellulose in an acidic aqueous solution under mild conditions that do not change the molecular weight. When analyzed by GPC, it was found that the peak was not a single peak but a mixture of at least two or more components with different molecular weights. However, for example, journal off
As described in Polymer Science Polymer Chemistry Edition, Vol. 12, p. 1065 (1974), the GPC pattern when cellulose nitrate is formed under extreme conditions is a broad single peak; It is thought that the molecular weight changed during the derivatization reaction. Now, these low molecular weight cellulose derivatives can be used in a wide range of applications due to their low viscosity and high solubility, but in order to obtain higher performance, it is necessary to make them more uniform. In other words, the cellulose derivative with a narrow molecular weight distribution, which is a feature of the present invention, means a uniform polymer with a single and narrow peak width in GPC, and in order to obtain such a polymer, it is generally necessary to process it in a hydrous or anhydrous π bale solvent. It is necessary to separate components with different molecular weights by reprecipitation. Any water-containing or anhydrous organic solvent may be used for reprecipitation for fractionation. That is, the reprecipitation solvent may be selected as appropriate depending on the type, molecular weight, degree of substitution, etc. of the obtained crude cellulose derivative, either alone or as a mixture. The reprecipitation method involves dissolving the cellulose derivative in a suitable solvent and transferring it to the reprecipitation solvent, but it is necessary to select the volume ratio of one volume for dissolution and the solvent for precipitation. Generally, components with lower molecular weights remain in solution and components with higher molecular weights precipitate, so that the components of the desired molecular weight do not contain other components. The monodispersity of the cellulose derivative having a narrow molecular weight distribution thus obtained is preferably such that the ratio of number average molecular weight 7 type weight average molecule in (MW/MN) is 3 or less. The low molecular weight cellulose carbamate derivatives, acylated celluloses, and cellulose ethers obtained in this way have high solubility and low viscosity, so they can be easily supported on carriers such as silica gel, and can be used as high-quality and uniform separation fillers. It is expected that it will be obtained, and it is also expected to have excellent performance as a polymer liquid crystal. Furthermore, if these cellulose derivatives can be easily reconverted to the original cellulose, cellulose with a low degree of polymerization and a narrow molecular weight distribution can be obtained.

(Examples) Hereinafter, the present invention will be explained in detail with reference to Examples, but it goes without saying that the present invention is not limited thereto. In addition, the molecular weight in the examples was determined by the GPC method using a calibration curve for standard polystyrene. GPC column is TSK
G4000HXL and 5hodex KF-80
3 were connected, and tetrahydrofuran was used as the solvent.

Example 1 Arcelized cellulose (■-type cellulose) is heated at 90° C. for 30 minutes in dilute hydrochloric acid. After cooling, it is filtered and subsequently washed with water and methanol. The obtained low molecular weight cellulose was thoroughly dried and 16.2 g was weighed out. 324 ml of dry pyridine is added to this, and phenyl isocyanate 818 is added dropwise while heating slowly. Thereafter, the reaction temperature was raised to 100°C and the reaction was continued for 7 hours. After the reaction was completed, the mixture was cooled to 15° C. and left overnight, and then 30 ml of methanol was slowly added dropwise. , and transferred to a methanol-water (2:1) mixed solvent for precipitation. The obtained product was filtered and mixed with 500ml of methanol-water (2:1) mixed solvent.
After washing with l, dry. The light brown solid obtained had a density/MN of 2.37. Add this to 310 m of acetone
Dissolve in 900ml of ethanol and precipitate. After dissolving the precipitate again in 20 liters of acetone,
Transfer to 1 liter of methanol and precipitate. The precipitated white solid was separated and dried to give 18.7 g (44% yield). This white solid was confirmed to be cellulose trisphenyl carbamate by IR spectrum and NMR spectrum.

IR spectrum; 3500cm v NH, 330
0cm v Nll.

1700cm vc=0, 1530cm S N8
NMR spectrum; 18Hbroad single
tδ7゜7Hmultipulets δ6.0-3
．． 0 elemental analysis measurement value; C; 60.93χ, H; 4.68χ, N;
7.93χ theoretical value; C; 62.42%:, H; 4
．． 85%, N; 8.09% [(C2?H25N3
08)n] The molecular weight of the obtained cellulose trisphenyl carbamate was as follows.

MN=25900. Md/MN=1.35 (degree of polymerization 5
0) The resulting dope obtained from THF of cellulose trisphenyl carbamate appeared cloudy when observed with the naked eye, and had an iridescent and/or pearl-like appearance. Furthermore, when observed with an orthogonal polarization microscope, light transmitted through at least a portion of the sample in the THF dope.

Example 2 Rayon (■ type cellulose) was soaked in dilute hydrochloric acid for 1 hour and a half at 90°C.
After cooling, heat to °C and filter, followed by washing with water and methanol. The obtained low molecular weight cellulose is thoroughly dried and 1.5 g is weighed out. Add this to 50m of dry pyridine.
11.6 ml of dry triethylamine was added thereto, and a solution of 10.5 g of cinnamic acid chloride dissolved in 5 g of benzene was added dropwise while stirring. Then the reaction temperature was increased to 8
The mixture was heated to 5°C for 1.5 hours, then raised to 100°C and reacted for 3 hours. After the reaction is completed, the mixture is cooled to 15° C. and added dropwise to methanol for precipitation. The milled product is filtered, further washed with methanol, and then dried.

Yield was 5.0g. The light brown solid obtained was IR
It was confirmed from the spectrum and NMR spectrum that it was cellulose tricinnamate.

IR spectrum; around 3050 cm-1, olefinic C-H stretching vibration.

1640cm'''C=C, stretching vibration 1585.1500, 1460cm-1, skeletal vibration due to stretching between carbon and carbon in benzene ring.

1250 cm-1, C-0 stretching vibration of ester.

1040-1160 cm-1 C-0-C stretching vibration of cellulose.

990cnr 1 Olefinic C-H bending vibration.

675-900 cm-1 Out-of-plane bending vibration of benzene ring (measured after dissolving in methylene chloride, applying to common salt, and drying) Based on the OH group of cellulose, absorption near < 3450 cm-1 is almost non-existent. This was not observed, indicating that it was almost a trisubstituted product.

NMR spectrum; 5.9-7.8 ppm protons of the cinnamic acid moiety 3.2-5.5 ppm protons of the glucose ring and methylene at position 6 of cellulose (the intensity ratio of these absorptions was 3:1) .

Elemental analysis measurement values: C: 60.93", H: 4.68: ,
N; 7.93% theoretical value; C; 62.42X,
H; 4.85X, N; 8.09X [(C2tH2
sN30s)n] The molecular weight of this cellulose tricinnamate was as follows.

MN=7200. MW/MN=1.53 (, degree of polymerization 1
3) Example 3 Rayon is heated in dilute hydrochloric acid to 90° C. for one and a half hours. After cooling, it is filtered and subsequently washed with water and methanol. The obtained low molecular weight cellulose is thoroughly dried and 1.5 g is weighed out. To this was added 60 ml of dry pyridine, and while stirring, a solution of 11.7 g of benzoyl chloride dissolved in 5 g of benzene was added dropwise. After that, the reaction temperature was increased to 80°C.
The mixture was heated to 100° C. for 5 hours and then reacted for 3 hours. After the reaction is completed, the mixture is cooled to 15° C. and added dropwise to methanol for precipitation.

The milled product is filtered, further washed with methanol, and then dried. The yield was 4.3g.

The molecular weight of this cellulose tribenzoate was as follows.

MN=7700. /MN=1.40 (degree of polymerization 16)
Example 4 Microcrystalline cellulose (E, Avicel manufactured by Merck) was thoroughly dried and 25 g was weighed out. Dry and add 500 ml of lysine to this, boil and heat, then dropwise add 100 g of lylisocyanate (I)-). Then, reduce the reaction temperature to 1
Raise the temperature to 10°C and react for 7 hours. After the reaction was completed, the mixture was cooled to 15° C. and 20.1 methanol was slowly added dropwise. - After standing overnight, it is transferred to a mixed solvent of 3.21 parts of methanol and 1.6 parts of water to precipitate. The obtained milled product is filtered, further washed with 200 ml of methanol, and then dried. The obtained light brown solid had a MW/MN of 9.2. After dissolving it in 500 ml of acetone, it was again dissolved in 4 ml of ethanol.
1 and precipitate. The precipitated white solid was 81 g after being separated and dried. The obtained white solid was found to be cellulose tris-
It was confirmed that it was p-)lyl carbamate. The molecular weights were as follows.

MN=51000. Bi/MN=1.59 (i synthetic leather 91
) The resulting dope obtained from THF of cellulose tris-p-)lyl carbamate appeared cloudy when observed with the naked eye, and had an iridescent and/or pearl-like appearance. Furthermore, when observed with an orthogonal polarization microscope, light transmitted through at least a portion of the sample in the THF dope.

Example 5 Microcrystalline cellulose (1: Avicel manufactured by Jlerck)
Dry thoroughly and weigh out 21.7 g. Add 434 ml of dry pyridine to this, and slowly heat until the p-
After dropping 100 g of chlorophenylisocyaner, the reaction temperature was raised to 100°C and the reaction was continued for 9 hours. After the reaction was completed, the mixture was cooled to 15° C. and 70 ml of methanol was slowly added dropwise. - After standing overnight, the mixture is transferred to methanol-water (1:1) mixed solvent 61 to precipitate. The obtained product is I
This crude product, which is filtered, further washed with 11 methanol-water (1:1) mixed solvent, and then dried, has a MW/MN=9.
It was 95. This was dissolved again in 500 ml of acetone, and 3.85 ml of ethanol-water (10: 1) mixed solvent was added.
1. The precipitate was filtered and dried to yield 56 g of homogeneous polymer.

The molecular weights were as follows.

MN”45900, nail/MN=1.73 (degree of polymerization 7
4) Example 6 Microcrystalline cellulose (E, Avicel manufactured by Merck) was thoroughly dried and 15.8 g was weighed in 7.1 portions. Add 300 ml of dry pyridine to this and heat slowly for 30 minutes.
, 65 g of 5-xylyl isocyanate were added dropwise, and then the reaction temperature was raised to 95°C and the reaction was continued for 5 hours. After the reaction 1
Cool to 5°C and slowly add 130ml of methanol dropwise. - After incubation overnight, transfer to methanol 51 and precipitate. The obtained crude product was filtered and further mixed with methanol 1
After washing with step 1, dry. Again, 500m of acetone
1 and added to ethanol 31 to precipitate. The precipitate is filtered and dried to yield 45.6g of homogeneous polymer.
Obtained. On the other hand, the solid matter obtained by distilling off the f liquid is 5.
It was 78.

The molecular types were as follows.

Claims (1)

[Claims] A degree of polymerization characterized by derivatizing cellulose that has been heated in an acidic aqueous solution to reduce its molecular weight under mild conditions where the molecular weight does not change, and then re-precipitating in a water-containing or anhydrous organic solvent to separate components with different molecular weights. is 5 to 400,
A method for producing a low molecular weight cellulose derivative with a narrow molecular weight distribution and a number average molecular weight/weight average molecular weight ratio of 3 or less.