Lignin grafted polyoxazoline copolymer and preparation method thereof

Abstract

The invention discloses a lignin grafted polyoxazoline copolymer and a preparation method thereof, the structural general formula of the lignin grafted polyoxazoline copolymer is as follows: # imgabs 0 # imgabs 1 #, the polymerization degree n is equal to 5-200, n is an integer, and Lignin represents lignin. The preparation method comprises the following steps: hydroxylating lignin through a diluted hydrochloric acid solution, introducing benzyl bromide and other functional groups on the lignin through an esterification reaction, initiating cation ring opening polymerization of an oxazoline monomer by using the lignin as an initiator, and after the reaction is terminated, precipitating and drying in vacuum to obtain the oxazoline monomer. The lignin grafted polyoxazoline copolymer is obtained. The lignin grafted polyoxazoline copolymer prepared by the preparation method disclosed by the invention is terminated through cation ring opening polymerization of the oxazoline monomer and different terminators, so that the molecular weight of the copolymer can be controlled, the components of the copolymer can be adjusted, and the lignin grafted polyoxazoline copolymer has a wide application prospect in the fields of self-assembly, fluorescent probes, biomedicine and the like.

Description

Technical Field

[0001] The invention relates to the field of functional polymer modification and controllable synthesis of functional polymers, and in particular to a lignin grafted polyoxazoline copolymer and a preparation method thereof. Background Art

[0002] Lignin is a natural organic polymer with abundant reserves in nature. It is widely present in plant cell walls and has important resource value. However, the current industrial utilization rate of lignin is low. A large amount of lignin is burned or discharged as waste. Due to its poor water solubility, it not only causes a waste of resources, but also causes certain pollution to the environment. Therefore, lignin must be modified so that it can be used for processing and application. The current lignin modification methods mainly include chemical modification, physical modification and biological modification. Although chemical modification can improve the performance of lignin to a certain extent, it often requires the use of a large amount of toxic and harmful reagents, and the reaction conditions are harsh, which will cause great pollution to the environment; the physical modification method has limited effect and it is difficult to achieve a significant improvement in the performance of lignin; although the biological modification method is green and environmentally friendly, the reaction cycle is long and the modification efficiency is low, which cannot meet the needs of actual production. Therefore, there is an urgent need for a new method to improve the performance of lignin. Summary of the invention

[0003] The object of the present invention is to provide a lignin grafted polyoxazoline copolymer and a preparation method thereof, which solves the problem that the reaction activity of lignin is low and complex modification treatment is required to meet the needs of different application fields.

[0004] In one aspect of the present invention, the present invention provides a lignin grafted polyoxazoline copolymer. According to an embodiment of the present invention, its general structural formula is as follows:

[0005]

[0006] Wherein, the degree of polymerization n=5-200, n is an integer, and Lignin represents lignin.

[0007] In another aspect of the present invention, the present invention provides a method for preparing a lignin-grafted polyoxazoline copolymer. According to an embodiment of the present invention, the method comprises the following steps:

[0008] (1) hydroxylating lignin with a dilute hydrochloric acid solution to obtain hydroxylated lignin;

[0009] (2) chlorinating the reactant with disulfide sulfoxide, and then performing an esterification reaction with the hydroxylated lignin to obtain a lignin initiator, wherein the reactant is one of p-chloromethylbenzoic acid, p-bromomethylbenzoic acid, and p-iodomethylbenzoic acid;

[0010] (3) using lignin as an initiator to initiate cationic ring-opening polymerization of oxazoline in a solvent, reacting in an oil bath for 20 to 24 hours, adding a terminator to terminate the reaction, washing the resulting product with a poor solvent, and drying it until the mass remains unchanged, thereby obtaining the lignin-grafted polyoxazoline copolymer.

[0011] In addition, the method for preparing a lignin-grafted polyoxazoline copolymer according to the above embodiment of the present invention may also have the following additional technical features:

[0012] In some embodiments of the present invention, in step (1), the ratio of the dilute hydrochloric acid to the lignin is 10:1 to 20:1.

[0013] In some embodiments of the present invention, in step (2), the ratio of the disulfide sulfoxide, the reactant, and the hydroxylated lignin is (1.2-2): (1.0-1.5): (1.0-1.5).

[0014] In some embodiments of the present invention, in step (3), the solvent is one of N,N-dimethylacetamide, acetonitrile and toluene.

[0015] In some embodiments of the present invention, in step (3), the terminator is one of deionized water, pyrene methanol solution, methanol, propargyl alcohol, and sodium azide.

[0016] In some embodiments of the present invention, in step (3), the poor solvent is one of diethyl ether and n-hexane.

[0017] In some embodiments of the present invention, in step (3), the temperature of the oil bath is 110-130°C.

[0018] In some embodiments of the present invention, in step (3), the ratio of the lignin initiator to the oxazoline is 1:20 to 1:200.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) The present invention performs a series of treatments on lignin, hydroxylates it, modifies it, and introduces functional groups, thereby solving the problem that the reaction activity of lignin is low and complex modification treatments are required to meet the needs of different application fields, so that this natural polymer can be used in the preparation of functional polymers.

[0021] 2) The present invention proposes to use natural high molecular weight lignin from plant cell walls as an initiator for initiating oxazoline, thereby solving the problem of narrow application and difficulty in functionalization of oxazoline polymers.

[0022] 3) The present invention combines lignin and oxazoline together, so that various properties of oxazoline can be improved. In aqueous solution, oxazoline can be self-assembled into single-molecule micelles, thereby improving the loading capacity of polyoxazoline. At the same time, since lignin is a natural polymer, using it as an initiator can also reduce cytotoxicity, and has better prospects in drug applications.

[0023] 4) The present invention can increase the fluorescence intensity of lignin and oxazoline through the fluorescence overlap, thereby expanding the application of oxazoline polymers in the field of fluorescence. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the phosphorus spectrum of the hydroxylated lignin (a) and the lignin initiator (b) in Example 1 of the present invention;

[0025] Figure 2 is the H NMR spectrum of the lignin grafted diethylbisoxazoline copolymer in Example 1 of the present invention;

[0026] Figure 3 is an infrared spectrum of lignin (Lignin), hydroxylated lignin (Lignin-OH), lignin initiator (Lignin-Br) and the obtained polybisoxazoline (Lignin-PEtOx) in Example 1 of the present invention;

[0027] Figure 4 This is an AFM image of the lignin grafted diethylbisoxazoline copolymer in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Example 1

[0030] A method for preparing a lignin-grafted polyoxazoline copolymer comprises the following steps:

[0031] (1) Weigh 2.00 g of alkaline lignin, stir with 1.00 mol / mL dilute hydrochloric acid solution at room temperature for 30 min, and then filter. Repeat the above operation four times to obtain hydroxylated lignin, wherein the alkaline lignin has the structural formula:

[0032]

[0033] (2) Weigh 1.00 g of p-bromomethylbenzoic acid into a 250 mL two-necked bottle, add 0.66 g of disulfide, use dichloromethane as solvent, and stir the reaction in an oil bath at 55° C. under a N 2 atmosphere for 10 hours to obtain p-bromomethylbenzoyl chloride.

[0034] (3) Weigh 1.00 g of hydroxylated lignin and 0.50 g of p-bromomethylbenzoyl chloride and dissolve them in a two-necked flask with DCM (dichloromethane), add triethylamine to provide an alkaline environment, stir and react in a cold well at 0°C under N2 atmosphere for 10 hours, and use DCM to recrystallize to obtain the product lignin initiator with benzyl halide. Its synthesis route is as follows:

[0035] Wherein, X is Br.

[0036] (4) Preparation method of oxazoline polymerization initiated by modified lignin-modified initiator: weigh 50.00 mg of lignin initiator and 0.50 g of diethyl dioxazoline in a 10 mL Schlenk bottle, add 1 mL of DMAC (dimethylacetamide) as solvent, replace the system with nitrogen atmosphere, stir and react in a 120 ° C oil bath for 20 hours, and add deionized water to terminate the reaction. Use ether to wash and centrifuge to dry the oil pump to obtain a dark brown solid, that is, the polydiethyl dioxazoline product with lignin as the terminal group is obtained. Its synthesis route is as follows:

[0037]

[0038] Wherein, X is Br.

[0039] pass Figure 1 Phosphorus spectrum characterization of initiators, Figure 2 NMR characterization of polymers, with Figure 3 The infrared test verified the correctness of the product. At the same time, the elemental analysis was used to compare the obtained hydroxyl lignin and lignin initiator, which also proved that it was successfully prepared. Figure 4 It was proved that the polydiethylbisoxazoline product with lignin as the terminal group was a unimolecular micelle.

[0040] Example 2

[0041] A method for preparing a lignin grafted polyoxazoline copolymer, which differs from Example 1 only in that: in step (4), the mass of diethylbisoxazoline is 1.00 g, and the other parameters and steps are the same as those in Example 1.

[0042] Example 3

[0043] A method for preparing a lignin grafted polyoxazoline copolymer, which differs from Example 1 only in that: in step (4), the mass of diethylbisoxazoline is 1.50 g, and the remaining parameters and steps are the same as those in Example 1.

[0044] Example 4

[0045] A method for preparing a lignin grafted polyoxazoline copolymer, which differs from Example 1 in that: in step (4), pyrene methanol solution is added to terminate the reaction, and the remaining parameters and steps are the same as those in Example 1.

[0046] Its synthetic route is as follows:

[0047]

[0048] Example 5

[0049] A method for preparing a lignin grafted polyoxazoline copolymer, which differs from Example 1 only in that in step (4), sodium azide is added to terminate the reaction, and the remaining parameters and steps are the same as those in Example 1.

[0050] Its synthetic route is as follows:

[0051]

[0052] Example 6

[0053] A method for preparing a lignin grafted polyoxazoline copolymer, which differs from Example 1 only in that: in step (4), the mass of the lignin initiator is 50.00 mg, 0.50 g of diethyldioxazoline is replaced by 0.50 g of dimethyldioxazoline, and the remaining parameters and steps are the same as those in Example 1, and finally a polydimethyldioxazoline product with lignin as the terminal group is obtained.

[0054] Its synthetic route is as follows:

[0055]

[0056] Example 7

[0057] A method for preparing a lignin-grafted polyoxazoline copolymer, which differs from Example 1 only in that: in step (4), the mass of the lignin initiator is 50.00 mg, 0.50 g of diethyldioxazoline is replaced by 0.50 g of diisopropyldioxazoline, and the remaining parameters and steps are the same as those in Example 1, and at most a polydiisopropyldioxazoline product with lignin as the terminal group is obtained.

[0058] Its synthetic route is as follows:

[0059]

[0060] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A lignin-grafted polyoxazoline copolymer, characterized in that The general structure is as follows: Wherein, the degree of polymerization n=5-200, n is an integer, and Lignin represents lignin.

2. A method for preparing the lignin-grafted polyoxazoline copolymer according to claim 1, characterized in that: The following steps are involved: (1) hydroxylating lignin with a dilute hydrochloric acid solution to obtain hydroxylated lignin; (2) chlorinating the reactant with disulfide sulfoxide, and then performing an esterification reaction with the hydroxylated lignin to obtain a lignin initiator, wherein the reactant is one of p-chloromethylbenzoic acid, p-bromomethylbenzoic acid, and p-iodomethylbenzoic acid; (3) using lignin as an initiator to initiate cationic ring-opening polymerization of oxazoline in a solvent, reacting in an oil bath for 20 to 24 hours, adding a terminator to terminate the reaction, washing the resulting product with a poor solvent, and drying it until the mass remains unchanged, thereby obtaining the lignin-grafted polyoxazoline copolymer.

3. The method for preparing a lignin-grafted polyoxazoline copolymer according to claim 2, wherein: In step (1), the molar ratio of the dilute hydrochloric acid to the lignin is 10:1 to 20:

1.

4. The method for preparing a lignin-grafted polyoxazoline copolymer according to claim 2, wherein: In step (2), the molar ratio of the disulfide sulfoxide, the reactant, and the hydroxylated lignin is (1.2-2): (1.0-1.5): (1.0-1.5).

5. The method for preparing a lignin-grafted polyoxazoline copolymer according to claim 2, wherein: In step (3), the solvent is one of N,N-dimethylacetamide, acetonitrile and toluene.

6. The method for preparing a lignin-grafted polyoxazoline copolymer according to claim 2, wherein: In step (3), the terminator is one of deionized water, pyrene methanol solution, methanol, propargyl alcohol, and sodium azide.

7. The method for preparing a lignin-grafted polyoxazoline copolymer according to claim 2, wherein: In step (3), the poor solvent is one of diethyl ether and n-hexane.

8. The method for preparing a lignin-grafted polyoxazoline copolymer according to claim 2, wherein: In step (3), the temperature of the oil bath is 110-130°C.

9. The method for preparing a lignin-grafted polyoxazoline copolymer according to claim 2, wherein: In step (3), the ratio of lignin initiator to oxazoline is 1:20 to 1:200.

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