CN110746523A - A kind of lignin-based macromolecular photoinitiator and preparation method and application thereof - Google Patents

Abstract

The invention discloses a lignin-based macromolecular photoinitiator and a preparation method and application thereof. The invention firstly discloses a lignin-based macromolecular photoinitiator, which has a structural formula shown as the following formula I:wherein the content of the first and second substances,

Description

A kind of lignin-based macromolecular photoinitiator and preparation method and application thereof

technical field

The present invention relates to the technical field of photocuring. More specifically, it relates to a lignin-based macromolecular photoinitiator and its preparation method and application.

Background technique

Light curing technology is a high-efficiency, energy-saving, environmentally friendly and high-quality material surface treatment technology, and is known as a new technology for green industry in the 21st century. It has been widely used in printing, packaging, advertising, building materials and other industries. Its products mainly include UV ink, UV adhesive, photosensitive printing plate, photoresist, light rapid prototyping material, etc. In recent years, with the expansion of the demand for high-end customized products, especially the huge application prospects in life sciences, 3D printing based on optical technology has attracted people's attention due to its high printing accuracy, fast printing speed and high z-axis strength. wide attention. However, the existing photocurable materials often have many problems, which limit the application of this technology in high-end fields.

The photocuring system is mainly composed of photopolymerizable monomers, photoinitiators and additives. Among them, the photoinitiator is an important part of the formula of the photocuring system, which determines the curing speed and curing degree of the system, and then determines a series of macroscopic properties of the cured material. At present, light-curing products on the market mainly use organic small-molecule photoinitiators, whose main advantages are clear chemical structure and high initiation efficiency. However, there are also many problems in use, such as poor compatibility with monomers or oligomers in the photocuring system; photoinitiators and photolysis products are easy to migrate after curing, causing toxicity and yellowing; some small molecular photoinitiators Volatile and smelly. Therefore, the use of light curing technology in hygiene and food packaging materials is limited.

In order to overcome the above drawbacks of small molecular photoinitiators, the preparation of macromolecular photoinitiators has become an important research direction in the field of photocuring research. The most commonly used technical solution is to attach small molecular photoinitiators to polymer chains, such as: ①Condensation polymerization of a hydroxyl-substituted small-molecule photoinitiator and monomers or polymers containing isocyanate groups and epoxy groups to obtain the target product; ②Introducing unsaturated groups (usually vinyl groups) on the small-molecule photoinitiators , acryloxy), and then homopolymerization or copolymerization with other monomers to obtain the target product; ③ on the side chain of the host polymer by chemical modification grafting a photoinitiator group to obtain the target product. However, macromolecular photoinitiators often have the problems of high viscosity and low photoinitiating activity, which limit their large-scale application. Compared with the small-molecule initiator, its mobility is indeed significantly reduced, but its initiation efficiency is also significantly reduced. From the structural formula, KIP150 is equivalent to linking the small molecule photoinitiator 1173 to methyl ethylene oligomer, and the molecular weight is around 2000. Compared with 1173, KIP150 has the advantages of low migration, low odor and yellowing resistance, but its light The priming efficiency is only 25% of the 1173. Although sufficient high photoinitiation efficiency can be achieved by increasing the amount of KIP150, this move will significantly increase the viscosity of the photocurable formulation system, which is not conducive to the coating process, thus limiting its large-scale industrial application.

Therefore, it is necessary to provide a new idea or solution to construct and optimize the structure and properties of macromolecular photoinitiators to meet the practical needs of the photocuring industry.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide a lignin-based macromolecular photoinitiator with high photoinitiating activity, good thermal stability, good storage performance, low viscosity, low mobility, low toxicity and no volatility.

The second object of the present invention is to provide a preparation method of the above lignin-based macromolecular photoinitiator.

The third object of the present invention is to provide an application of the above lignin-based macromolecular photoinitiator.

To achieve the above object, the present invention adopts the following technical solutions:

The invention provides a lignin-based macromolecular photoinitiator, the structural formula of which is shown in the following formula I:

是木质素不含端羟基的分子骨架，M1是环氧卤代烷烃经环氧开环反应后不含端羟基与卤素原子的分子骨架，M2是助溶性化合物不含羟基的分子骨架，M3是裂解型光引发剂不含羟基的分子骨架；in,

It is the molecular skeleton of lignin without terminal hydroxyl groups, M1 is the molecular skeleton of epoxy halogenated alkanes without terminal hydroxyl groups and halogen atoms after epoxy ring-opening reaction, M2 is the molecular skeleton of solubilizing compounds without hydroxyl groups, and M3 is cracking. Type photoinitiator does not contain hydroxyl molecular skeleton;

n1, n2, x1, x2, y1 and y2 are integers ≥ 0 respectively and x1+x2=1; n3 is a natural number ≥ 1, n1+n2+n3=the number of terminal hydroxyl groups of lignin and y1+x2+n2≥ 1.

The present invention also provides a preparation method of the above lignin-based macromolecular photoinitiator, comprising the following steps:

Dissolving or melting the hydroxy-containing solubilizing compound, adding a catalyst, then adding an epoxyhalogenated alkane to react, and removing the unreacted epoxyhalogenated alkane after the reaction is completed to obtain an intermediate product A;

Dissolving the lignin in the alkaline aqueous solution, heating to reflux, adding the intermediate product A to react, cooling after the reaction, adjusting the pH value to 7, and purifying and drying to obtain the intermediate product B;

The cracking type photoinitiator containing hydroxyl group is dissolved, and after adding the catalyst, the epoxyhalogenated alkane is added to react, and the unreacted epoxyhalogenated alkane is removed after the reaction is completed to obtain the intermediate product C;

The intermediate product B and the intermediate product C are dissolved, reacted under alkaline conditions, cooled after the reaction, adjusted to pH 7, purified and dried to obtain a lignin-based macromolecular initiator whose structural formula is shown in formula I.

Further, the structural formula of the intermediate product A is shown in formula II:

Wherein, M1 is the molecular skeleton of the epoxyhaloalkane without terminal hydroxyl and halogen after epoxy ring-opening reaction, M2 is the molecular skeleton of the solubilizing compound without hydroxyl, X is a halogen atom, and y3 is an integer ≥ 0.

Further, the structural formula of the intermediate product B is shown in formula III:

是木质素不含端羟基的分子骨架，M1是环氧卤烷烃经环氧开环反应后不含端羟基与卤素的分子骨架，M2是助溶性化合物不含羟基的分子骨架，n4为≥1的自然数，n5为≥0的整数且n4+n5＝木质素的端羟基数。in,

It is the molecular skeleton of lignin without terminal hydroxyl group, M1 is the molecular skeleton of epoxy haloalkane without terminal hydroxyl group and halogen after epoxy ring-opening reaction, M2 is the molecular skeleton of solubilizing compound without hydroxyl group, and n4 is ≥1 The natural number of , n5 is an integer ≥ 0 and n4+n5=the number of terminal hydroxyl groups of lignin.

Further, the structural formula of the intermediate product C, as shown in formula IV:

Wherein, M1 is the molecular skeleton of the epoxyhaloalkane that does not contain terminal hydroxyl groups and halogens after the epoxy ring-opening reaction, M3 is the molecular skeleton of the cracking photoinitiator that does not contain hydroxyl groups, and X is a halogen atom.

Further, the lignin includes but is not limited to one or more of sulfate lignin, alkaline lignin, sodium lignosulfonate and organic solvent-soluble lignin, preferably alkaline lignin;

Further, the molecular weight of the lignin is 5000-50000, and the hydroxyl content is 2.0-5.0 mmol/g.

Further, the epihaloalkanes include but are not limited to epichlorohydrin, epifluorohydrin, epibromohydrin, methyl epichlorohydrin, 4-bromo-1,2-epoxybutane, 6-bromo One or more of -1,2-epoxyhexane.

Further, the hydroxyl-containing solubilizing compounds include but are not limited to polyethylene glycol and its derivatives, polyvinyl alcohol and its derivatives, polymaleic acid and its derivatives, aqueous polyurethane and its derivatives, polyvinylpyrrolidone and its derivatives, water-soluble starch and its derivatives, sodium alginate and its derivatives, hyaluronic acid and its derivatives; preferably, the degree of polymerization of the hydroxyl-containing solubilizing compound is 5-7500, more preferably of 5 to 500.

Further, the cleavage-type photoinitiators containing hydroxyl groups include but are not limited to α-hydroxy ketone derivatives, α-amino ketone derivatives, benzoyl formates and acyl phosphorus oxides, preferably:

Further, the catalyst includes but is not limited to boron trifluoride ether, aluminum trichloride, triethylamine, sodium hydroxide, ferric chloride, titanium tetrachloride, preferably boron trifluoride ether, triethylamine , Sodium hydroxide.

Further, the solvent used for the dissolution includes, but is not limited to, one or more of alkaline aqueous solution, ethanol, dioxane, tetrahydrofuran, and dimethyl sulfoxide.

Further, the reaction molar ratio of the intermediate product C and the intermediate product B is 2:1 to 10:1.

Further, the mass fraction of the molecular skeleton of the solubilizing compound in the lignin-based macromolecular photoinitiator is 10-70 wt%, the mass fraction of the molecular skeleton of the cracking-type photoinitiator is 5-20 wt%, and the lignin-based macromolecule The solubility of the photoinitiator in water and/or organic solvent is ≥5wt%.

The present invention further provides the application of the above lignin-based macromolecular photoinitiator in a photocuring system.

Further, the photocuring system includes 0.1-20 parts of a lignin-based macromolecular photoinitiator whose structural formula is shown in formula I, 10-90 parts of a solvent, and 20-90 parts of a photopolymerizable monomer.

The photopolymerizable monomers are selected from polymerizable monomers with at least 1 functional group, including small and/or macromolecular polymerizable monomers containing monofunctional, bifunctional and multifunctional groups; preferably, they are selected from water-soluble polymerizable monomers. Photopolymerizable monomers, biomacromolecules that selectively modify polymerizable groups, and ester-soluble photopolymerizable monomers; more preferably, the water-soluble photopolymerizable monomers include but are not limited to epoxy (meth)acrylic acid one or more of esters, polyurethane (meth)acrylates, polyester (meth)acrylates, polyether (meth)acrylates, acrylated poly(meth)acrylates; the biological macromolecules Monomers include but are not limited to one or more of gelatin derivatives, hyaluronic acid derivatives, chitin derivatives, sodium alginate derivatives, cellulose derivatives, and xanthan gum derivatives; the ester solubility can be Photopolymerizable monomers include, but are not limited to, one or more of (meth)acrylates, vinyls, vinyl ethers, and epoxies.

Further, the solvent includes but is not limited to one of deionized water, ethanol, acetone, methyl ethyl ketone, dimethyl sulfoxide, dimethylformamide, dichloromethane, chloroform, hexane, heptane or variety.

The beneficial effects of the present invention are as follows:

1. The lignin-based macromolecular photoinitiator of the present invention gives lignin a new structure and performance by modifying and attaching a solubilizing group and a cracking photoinitiator group on the lignin molecule at the same time, so that it can be used in water. It has sufficient solubility in conventional organic solvents and high photoinitiating activity, and can initiate the modification of monomers, oligomers and/or unsaturated double bonds containing unsaturated double bonds under UV-visible light exposure. The macromonomers undergo free radical polymerization or cross-linking reaction, and are used in the preparation of photocurable coatings, inks, adhesives, photoresists, printed circuit boards, optical fibers, 3D printing, biomedical hydrogels and other fields. It has good application prospects in the light curing industry.

2. The lignin-based macromolecular photoinitiator of the present invention has a hyperbranched structure. Compared with linear polymers of the same molecular weight, its viscosity is very low, so it will not significantly affect the viscosity of the photocurable formulation, which is beneficial to the coating film. Basic requirements for process or 3D printing rheological parameters.

3. The lignin-based macromolecular photoinitiator of the present invention is introduced into the photocuring formula as both a photoinitiator and a modified filler due to the polyphenylene ring and the three-dimensional cross-linked network structure of the lignin itself, thereby modifying the Macroscopic properties of photocurable materials, such as mechanical properties, thermal properties, and storage properties.

4. Compared with the small molecular photoinitiator, the lignin-based macromolecular photoinitiator of the present invention has large molecular weight, small mobility in the photocurable material, no volatility and low toxicity, and the safety of the photocurable material is improved. It is more suitable for applications in areas with higher security.

5. The lignin-based macromolecular photoinitiator of the present invention has the characteristics of simple synthesis route, easy high-volume synthesis and high yield.

Description of drawings

The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

Figure 1 shows the one-dimensional hydrogen NMR spectrum of the lignin-based macromolecular photoinitiator L-PEG-2959 in Example 2.

Figure 2 shows the infrared spectrum characterization of the lignin-based macromolecular photoinitiator L-PEG-2959 of Example 2.

3 shows the ultraviolet absorption spectrum of the lignin-based macromolecular photoinitiator L-PEG-2959 in Example 2.

4 shows the thermogravimetric analysis spectrum of the lignin-based macromolecular photoinitiator L-PEG-2959 in Example 2.

5 shows the gel permeation chromatogram of the lignin-based macromolecular photoinitiator L-PEG-2959 in Example 2.

FIG. 6 shows the photocurable formulation containing lignin-based macromolecular photoinitiator L-PEG-2959 in Example 7 and its photoinitiating performance.

FIG. 7 shows the mobility test of the lignin-based macromolecular photoinitiator L-PEG-2959 in the cured product in Example 7. FIG.

8 shows the mechanical strength test of the gelatin hydrogel by the lignin-based macromolecular photoinitiator L-PEG-2959 in Example 7.

Detailed ways

In order to illustrate the present invention more clearly, the present invention will be further described below with reference to the preferred embodiments and accompanying drawings. Similar parts in the figures are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not limit the protection scope of the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, biological materials, etc. used in the following examples can be obtained from commercial sources unless otherwise specified. The methods and equipment used are conventional in the art.

In the following examples, lignin was purchased from Sinopharm Chemical Reagent Co., Ltd., the content of lignin hydroxyl groups was measured by nuclear magnetic method, and the amount of hydroxyl groups was 2.0-5.0 mmol/g.

Example 1

This embodiment provides an ester-water amphiphilic lignin-based macromolecular photoinitiator L-PEG-2959, which is prepared according to the following steps:

1) 100g (0.1mol) of polyethylene glycol (PEG) with a molecular weight of 1000 was added to a there-necked flask of 500mL, and after being heated to 55° C. to be completely melted, 0.8g (0.005mol) of boron trifluoride ether was added under stirring conditions. The complex was then added dropwise with 4.626 g (0.05 mol) of epichlorohydrin (ECH) into the reaction flask, and the reaction temperature was maintained at 55°C to 60°C. After the dropwise addition was completed, the reaction was allowed to proceed in this temperature range for an additional 4 hours. Then, the unreacted epichlorohydrin was removed by rotary evaporation to obtain polyethylene glycol (PEG-ECH) with chlorine active groups at the end groups, and the yield of the obtained product was about 80 wt%.

2) Dissolve 20 g of alkaline lignin in 1 mol/L sodium hydroxide aqueous solution, and make the content of lignin 25% (w/w), add the product obtained in step 1) dropwise into the system, and then at 80 The reaction was carried out under the condition of ℃ for 4 hours. The obtained reaction solution was adjusted to pH 7 using hydrochloric acid, and then the product was extracted with butanone to extract unreacted polyethylene glycol, and then the remaining reaction solution was poured into a large amount of ethanol, stirred for 1 hour, and a small amount of brown-black solid was precipitated. The precipitate was removed by filtration, an appropriate amount of ethyl acetate was added to the remaining liquid, and a large amount of brown product was precipitated. The crude product L-PEG was obtained by filtration and drying, and the yield was about 70 wt%.

Wherein, n ₄ is a natural number ≥ 1, n ₅ is a natural number ≥ 0, and n ₄ +n ₅ = the number of terminal hydroxyl groups of lignin.

3) Add 22.4g (0.1mol) small molecule photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) and 250mL ethanol to a 500ml three-necked flask , stir well to dissolve it uniformly, inject 0.8g (0.005mol) of boron trifluoride ether with a needle, and then slowly add 9.25g (0.1mol) of epichlorohydrin dropwise. After the dropwise addition, the reaction was continued at 55°C for 2 hours to stop the reaction. Then, the unreacted epichlorohydrin and ethanol solvent were removed by rotary evaporation of the reaction solution to obtain the crude product 2959-ECH.

4) in a 250 ml three-necked flask, add the product obtained in the above step 2) 5g and the product obtained in the above step 3) 5.6g and 100mL of ethanol, fully stir to mix uniformly, and then add 1 mol/L of hydrogen peroxide in the above solution dropwise. The pH was adjusted between 8 and 9 with sodium, heated to 80°C, and the reaction was continued at this temperature for 4 hours. After the reaction is completed, the temperature is naturally lowered, the pH of the reaction solution is adjusted to 7 with hydrochloric acid, the ethanol solvent is removed by rotary evaporation, the obtained product is extracted with a small amount of water, and the unreacted small molecule photoinitiator that is insoluble in water is filtered out. , retain the filtered brown aqueous solution, and then use a dialysis membrane with a molecular weight cut-off of 5kDa for 7 days to remove residual small molecule photoinitiators, generated salts and other impurities. The brown aqueous solution in the obtained dialysis membrane was poured into a large watch glass and dried under vacuum at 30°C for 7 days to obtain the pure final product L-PEG-2959.

Wherein, n1, n2, x1, x2, y1 and y2 are integers ≥ 0 respectively and x1+x2=1, y1+y2=1; n3 is a natural number ≥ 1, n1+n2+n3=terminal hydroxyl group of lignin number and y1+x2+n2≥1.

The product L-PEG-2959 was analyzed by thermogravimetric analysis to find that the molecular skeleton of lignin, the molecular skeleton of PEG-solubilizing compound and the molecular skeleton of Irgacure 2959 small-molecule photoinitiator accounted for the mass ratio of the macromolecular photoinitiator: 22.4:65.3:12.3.

Example 2

Similar to step 4) in Example 1, in a 500-milliliter three-necked flask, add 5 g of the product obtained in the above step 2) and 10 g of the product obtained in the above step 3) and 200 mL of ethanol, fully stir to mix uniformly, and then dropwise add 1 mol/L and adjust the pH between 8 and 9, heat to 80 °C and continue the reaction at this temperature for 4 hours. After the reaction, the temperature was naturally lowered, the pH of the reaction solution was adjusted to 7 with hydrochloric acid, the ethanol solvent was removed by rotary evaporation, the product was extracted with a small amount of water, and the water-insoluble unreacted small molecule photoinitiator was filtered. Go out, retain the filtered brown aqueous solution, and then use a dialysis membrane with a molecular weight cut-off of 5kDa for 7 days to remove residual small molecule photoinitiators, generated salts and other impurities. The brown aqueous solution in the obtained dialysis membrane was poured into a large watch glass and dried under vacuum at 30°C for 7 days to obtain the pure final product L-PEG-2959. The product L-PEG-2959 was analyzed by thermogravimetric analysis, and the molecular skeleton of lignin, the molecular skeleton of PEG-solubilizing compound and the molecular skeleton of Irgacure 2959 small-molecule photoinitiator accounted for the mass ratio of the macromolecular photoinitiator to 21.5:60.9: 17.6.

Figure 1 shows the one-dimensional hydrogen NMR spectrum of the macromolecular photoinitiator L-PEG-2959 prepared in this example, and Figure 2 shows the macromolecular photoinitiator L-PEG-2959 prepared in this example. Infrared spectroscopic characterization. It can be seen from Figure 1 and Figure 2 that the L-PEG-2959 macromolecular photoinitiator was successfully prepared by the method of the present invention.

Figure 3 shows the UV spectral test characterization of the macromolecular photoinitiator L-PEG-2959 prepared in this example. It can be seen from Figure 3 that in addition to retaining the UV absorption peak of the original lignin, the prepared L-PEG-2959 has an obvious new absorption peak at 250-300 nm, which is similar to the spectral properties of Irgacure 2959, indicating the photoinitiated activity. The groups were successfully introduced into the lignin molecular skeleton.

Figure 4 shows the thermogravimetric analysis spectrum of the macromolecular photoinitiator L-PEG-2959 prepared in this example. It can be seen from Figure 4 that a decomposition platform that can clearly distinguish different components of the material appears in Figure 4. From this, the composition of the macromolecular photoinitiator can be obtained, in which the mass fraction of photoinitiator groups is 17.6 wt%, and its A considerable amount of grafting ensures high initiation activity of macroinitiators.

Figure 5 shows the gel permeation chromatogram of the macromolecular photoinitiator L-PEG-2959 prepared in this example. It can be seen from Figure 5 that the prepared lignin-based macromolecular photoinitiator has a relatively large molecular weight, meets the requirement of low macromolecular mobility, and is still a typical hyperbranched molecular structure, which is easy to achieve effective photoinitiation performance and low molecular weight. Viscosity properties.

Example 3

Similar to step 4) in Example 1, in a 500-milliliter three-necked flask, add 5 g of the product obtained in the above step 2) and 15 g of the product obtained in the above step 3) and 200 mL of ethanol, fully stir to mix well, and then dropwise add 1 mol/L The sodium hydroxide solution was adjusted to pH 8-9, heated to 80°C, and the reaction was continued at this temperature for 4 hours to obtain the crude product of the final product. After the reaction, the temperature was naturally lowered, the pH of the reaction solution was adjusted to 7 using hydrochloric acid, the ethanol solvent was removed by rotary evaporation, the product was extracted with a small amount of water, and most of the unreacted small molecule photoinitiators that were insoluble in water were removed. After filtration, the brown aqueous solution was retained, and then dialyzed with a dialysis membrane with a molecular weight cut-off of 5 kDa for 7 days to remove the residual small molecule photoinitiator and the generated salts and other impurities. The brown aqueous solution in the obtained dialysis membrane was poured into a large watch glass and dried under vacuum at 30°C for 7 days to obtain the pure final product L-PEG-2959.

The product L-PEG-2959 is analyzed by thermogravimetric analysis, wherein the molecular skeleton of lignin, the molecular skeleton of PEG-solubilizing compound and the molecular skeleton of Irgacure 2959 small molecule photoinitiator account for the mass ratio of the macromolecular photoinitiator to 24.5: 55.7:19.8.

Example 4

1) Add 27.6g (0.1mol) of TPO-OH containing hydroxyl group and 200mL of dimethyl sulfoxide (DMSO) to a 500ml three-necked flask, stir well to mix well, and inject 0.8g (0.005mol) with a syringe Boron trifluoride ether, and then slowly add 9.25 g (0.1 mol) of epichlorohydrin dropwise to the mixed solution. After the dropwise addition, the reaction was continued at 55°C for 2 hours. After the completion of the reaction, the unreacted epichlorohydrin was removed by rotary evaporation, washed with a large amount of water, precipitated, and filtered to obtain the crude product TPO-ECH.

2) in a 250 ml three-necked flask, add the product obtained in step 2) in the above-described embodiment 1) 5g and the product obtained in the above step 1) 5.6g and 100mL of dimethyl sulfoxide and water mixed solution, fully stirred to mix well, Then, 1 mol/L aqueous sodium hydroxide solution was added dropwise to the above solution to adjust the pH between 8 and 9, heated to 80° C., and the reaction was continued at this temperature for 4 hours. After the reaction, the temperature was naturally lowered, the pH of the reaction solution was adjusted to 7 with hydrochloric acid, and the reaction solution was washed with a small amount of water, filtered, and the brown aqueous solution was retained, and then dialyzed for 7 days using a dialysis membrane with a molecular weight cut-off of 5 kDa to remove residual small molecules. Photoinitiators, solvents, salts formed, and other impurities. The brown aqueous solution in the obtained dialysis membrane was poured into a large watch glass and dried under vacuum at 30°C for 48 hours to obtain the final pure product L-PEG-TPO.

Wherein, n1, n2, x1, x2, y1 and y2 are integers ≥ 0 respectively and x1+x2=1, y1+y2=1; n3 is a natural number ≥ 1, n1+n2+n3=terminal hydroxyl group of lignin number and y1+x2+n2≥1.

Thermogravimetric analysis of the product L-PEG-TPO in which the molecular skeleton of lignin, the molecular skeleton of the PEG-solubilizing compound and the molecular skeleton of the TPO small molecule photoinitiator accounted for the mass ratio of the macromolecular photoinitiator to 31.5:56.7 : 11.8.

Example 5

This embodiment provides a water-soluble lignin-based macromolecular photoinitiator L-PVA-2959, which is prepared according to the following steps:

1) Add 15g of low molecular weight 13,000-23,000, 86-89% hydrolyzed polyvinyl alcohol (PVA) and 300mL of water to a 500mL there-necked flask, heat up to 70° C. At this temperature, 0.008 g (0.00005 mol) of boron trifluoride diethyl ether complex was added as a catalyst with a syringe, and then 0.04626 g (0.0005 mol) of epichlorohydrin (ECH) was slowly added dropwise to the reaction flask. After the dropwise addition was completed, the reaction was continued for 4 hours. After the reaction, the unreacted epichlorohydrin was removed by rotary evaporation to obtain a crude product PVA-ECH with a yield of about 90 wt%.

Wherein, n ₆ is a natural number ≥ 1, and n ₆ +n ₇ = the number of hydroxyl groups of polyvinyl alcohol.

2) 5 g of alkaline lignin is dissolved in 1 mol/L aqueous sodium hydroxide solution, and the content of lignin is 25% (w/w), and the product obtained in the above 1) step and the aqueous alkaline lignin solution are added to the solution. In a 500 mL three-necked flask, the temperature was raised to 80° C., and the mixture was fully dissolved by high-speed mechanical stirring, and then reacted under this condition for 4 hours. After the completion of the reaction, the pH of the obtained reaction solution was adjusted to 7 using hydrochloric acid. Then, the Soxhlet extractor was used for repeated extraction under the condition of water as solvent and heating for 3 days, and finally dried in a vacuum drying oven for 48 hours to obtain a pure L-PVA copolymer product with a yield of about 70%.

Wherein, n8, n9, n10 are integers ≥ 0, n ₆ is a natural number ≥ 1, and n6+n8+n9=the number of hydroxyl groups of polyvinyl alcohol, and n8+n10=the number of terminal hydroxyl groups of lignin;

3) in the there-necked flask of 500mL, add the obtained product 5g in the above-mentioned 2), the obtained product 2959-ECH1.0g and 200mL 1mol/L in the step 3) described in Example 1 The aqueous sodium hydroxide solution of 1mol/L is heated to 80 ℃ again. The reaction was carried out under these conditions for 4 hours. After the reaction, the temperature was naturally lowered, and the pH of the reaction solution was adjusted to 7 using hydrochloric acid, and the Soxhlet extractor was used for repeated extraction under heating and reflux conditions for 3 days, and then the dialysis membrane with a molecular weight cut-off of 5kDa was used for dialysis for 7 days. , and finally dried in a vacuum drying oven for 48 hours to obtain the final pure product L-PVA-2959.

Among them, n1, n2, n9, x1, x2, y1, y2, z1 and z2 are integers ≥ 0 respectively and x1+x2=1, z1+z2=1, y1+y2+n9+1=raw polyvinyl alcohol The hydroxyl number of ; n3 is a natural number ≥ 1, n1+n2+n3=the number of terminal hydroxyl groups of lignin and y1+x2++z2+n2≥1.

The product L-PVA-2959 was analyzed by thermogravimetric analysis in which the molecular skeleton of lignin, the molecular skeleton of PVA co-solubilizing compound and the molecular skeleton of Irgacure2959 small molecule photoinitiator accounted for the mass ratio of the macromolecular photoinitiator to 27.8:63.5 : 8.7.

Example 6

Similar to step 3) in Example 5, add 5 g of the product obtained in the above step 2), 2 g of the product obtained in step 3) in Example 1 and 200 mL of ethanol into a 500-milliliter three-necked flask, heat and stir to mix uniformly, and then dropwise Add 1 mol/L aqueous sodium hydroxide solution and adjust the pH to 8-9, heat to 80° C. and continue the reaction at this temperature for 4 hours. After the reaction is finished, the temperature is naturally cooled, and the pH of the reaction solution is adjusted to 7 using hydrochloric acid, and then the Soxhlet extractor is used for repeated extraction for 3 days under the condition that water is a solvent and heated to reflux, and then the dialysis with a molecular weight cut-off of 5kDa is used. The membrane was dialyzed for 7 days and finally dried in a vacuum oven for 48 hours to obtain the final pure product L-PVA-2959.

The product L-PVA-2959 was analyzed by thermogravimetric analysis in which the molecular skeleton of lignin, the molecular skeleton of PVA co-solubilizing compound and the molecular skeleton of Irgacure2959 small molecule photoinitiator accounted for the mass ratio of the macromolecular photoinitiator to 30.9:56.8 : 12.3.

In the above-mentioned embodiment, the above-mentioned experimental content is repeated and the "alkaline lignin" is replaced with another one selected from the group consisting of sulfate lignin, alkaline lignin, sodium lignosulfonate and organic solvent-soluble lignin, and The performance of the final lignin-based macromolecular photoinitiator is not affected.

In the above embodiment, repeat the above experiment content and replace "epichlorohydrin" with other selected from epifluoropropane, epibromopropane, methyl epichlorohydrin, 4-bromo-1,2-epoxy One of butane and 6-bromo-1,2-epoxyhexane does not affect the performance of the finally obtained lignin-based macromolecular photoinitiator.

In the above-mentioned embodiment, repeat the above-mentioned experimental content and replace "polyethylene glycol" or "polyvinyl alcohol" with other selected from polymaleic acid and its derivatives, water-based polyurethane and its derivatives, polyvinylpyrrolidone and its derivatives. Derivatives, water-soluble starch and its derivatives, sodium alginate and its derivatives, hyaluronic acid and its derivatives, do not affect the performance of the finally obtained lignin-based macromolecular photoinitiator.

In the above example, the above experimental content was repeated and the "2959" or "TPO-OH" was replaced with another one selected from the group consisting of α-hydroxy ketone derivatives, α-amino ketone derivatives, benzoyl formates, and acyl phosphorus oxidation. One of them does not affect the performance of the final lignin-based macromolecular photoinitiator.

Example 7: The use of lignin-based macromolecular photoinitiator L-PEG-2959 for photoinitiated gum derivatives to prepare biocomposite hydrogels

Glycidyl methacrylate modified gelatin (Gel-GMA) was used as a water-soluble macromonomer (with a double bond grafting rate of 74%), which was first dissolved in hot water to keep the content at 20 wt%, and then added The macromolecular photoinitiator L-PEG-2959 synthesized in Example 2 (with respect to the monomer, its content is about 5wt%, 10wt% and 15wt%, converted into the content of the photoinitiator component in the formula is about 1wt%, 2 wt %, 3 wt %), and then the lignin-gelatin composite hydrogel was obtained by initiating polymerization for 10 minutes under the irradiation of an ultraviolet light source with a maximum absorption wavelength of 365 nm and a light intensity of 20 mw/cm ² . As a reference sample, small molecule Irgacure 2959 was added as the corresponding small molecule photoinitiator at 1 wt% (relative to the monomer), and then photopolymerized under the same experimental conditions to obtain a homopolymerized gelatin hydrogel. The prepared sample was ultrasonically extracted with unreacted photoinitiator or its cleavage residue in a certain amount of ethanol, and then the extraction amount was determined by high pressure liquid chromatography and ultraviolet spectroscopy to quantitatively determine the amount of photoinitiator in the photocurable material. mobility. Table 1 shows the formulation of the photocuring system containing the macromolecular photoinitiator L-PEG-2959 obtained in Example 2, the gelatin derivative macromonomer, and water as the solvent.

Table 1 Light curing system formula

A in Figure 6 shows the photocurable formulations composed of different formulations containing different amounts of L-PEG-2959. It can be seen from the figure that L-PEG-2959 can be well miscible with gelatin derivatives under the condition of deionized water within a large addition range (5-15wt%);

B in FIG. 6 is the lignin-gelatin composite hydrogel obtained after curing with ultraviolet light. It can be seen from the figure that L-PEG-2959 can initiate the photopolymerization of water-soluble bio-based macromers (gelatin derivatives), demonstrating its photoinitiating ability. The two have good compatibility within the composition range, and with the increase of lignin content, the color of the mixed hydrogel gradually becomes darker.

FIG. 7 shows the test characterization results of the exudation amount of the residual photoinitiator or its post-photoinitiated cleavage residue in the photocurable composite hydrogel after ultrasonic extraction with ethanol. It can be seen from the figure that the amount of photoinitiator that can be extracted by the macromolecular photoinitiator L-PEG-2959 is significantly smaller than that of the corresponding small molecule photoinitiator Irgacure 2959, indicating its migration in the curing system. The stability is significantly reduced, thereby increasing the safety of the cured material.

Figure 8 shows the test characterization results of the effect of L-PEG-2959 as a filler on the mechanical strength of gelatin hydrogels. It can be seen from the figure that the mechanical strength of the homopolymerized gelatin hydrogel is very weak, and its Young's modulus can be significantly improved after the introduction of lignin, and the modulus of the mixed hydrogel increases significantly with the increase of the lignin content. big.

Example 8: L-PEG-2959, a lignin-based macromolecular photoinitiator, is used for photoinitiating commercial acrylate monomers to prepare 3D products

Under light-proof conditions, polyethylene glycol diacrylate (PEGDA) with a molecular weight of 1000 was dissolved in dimethyl sulfoxide (DMSO) as a photopolymerizable monomer, and then a certain amount of macromolecular photoinitiator L- PEG-2959, fully stirred to make it completely dissolved; wherein, Table 2 shows the light containing the macromolecular photoinitiator L-PEG-2959, PEGDA oligomer monomer and DMSO obtained in any of Examples 1-3 as solvents. Curing system formulation. Then, the above-mentioned light-curing formula was placed in a 3D printer machine gun, certain instrument parameters were set, and then 3D printing materials with certain shapes and specifications were obtained under the exposure of ultraviolet-visible light sources.

Table 2 Light curing system formula

Example 9: Use of lignin-based macromolecular photoinitiator L-PEG-2959 for water-based photocurable coatings

50-70 parts of commercial water-based polyurethane acrylate (Bayer U54), 10-15 parts of tripropylene glycol diacrylate (TPGDA) emulsion, 5-40 parts of deionized water, 0.05-1 part of macromolecular photoinitiator L-PEG-2959 and 5 to 20 parts of pigments, fillers, additives and other solid powder substances that may be contained are connected, and after grinding and dispersing, a slurry dispersion is formed, which is applied to the substrate and fixed after drying. , and then cured by ultraviolet light to obtain a photocurable coating. Table 3 shows the macromolecular photoinitiator L-PEG-2959 containing any of the obtained examples 1-3, water-based polyurethane acrylate as an oligomer, and TPGDA as a reactive diluent. The formula of the photocurable system, and the water-based photocurable coating can be obtained through the formula in this table.

Table 3 Light curing system formula

Example 10: L-PEG-TPO, a lignin-based macromolecular photoinitiator, is used for photoinitiating commercial acrylate monomers to prepare 3D products

Under light-proof conditions, polyethylene glycol diacrylate (PEGDA) with a molecular weight of 1000 was dissolved in dimethyl sulfoxide (DMSO) as a photopolymerizable monomer, and then a certain amount of the macromolecule prepared in Example 4 was added. Molecular photoinitiator L-PEG-TPO, fully stirred to make it completely dissolved; among them, Table 4 shows the photocuring system containing macromolecular photoinitiator L-PEG-TPO, PEGDA oligomer monomer and DMSO as solvent formula. Then, the above-mentioned light-curing formula was placed in a 3D printer machine gun, certain instrument parameters were set, and then 3D printing materials with certain shapes and specifications were obtained under the exposure of ultraviolet-visible light sources.

Table 4 Light curing system formula

Example 11: Use of lignin-based macromolecular photoinitiator L-PVA-2959 for waterborne photocurable coatings

Prepare 50-70 parts of commercial water-based polyurethane acrylate (Bayer U54), 10-15 parts of tripropylene glycol diacrylate (TPGDA) emulsion, 5-40 parts of deionized water, and 0.05-1 part of Example 5 The macromolecular photoinitiator L-PVA-2959 and 5-20 parts of solid powder substances such as pigments, fillers, and additives that may be contained are connected to form a slurry dispersion after grinding and dispersing, and the construction is coated on the substrate. After drying, it was fixed, and then cured by ultraviolet light to obtain a photocurable coating. Table 5 shows the light containing macromolecular photoinitiator L-PVA-2959, water-based polyurethane acrylate as oligomer, and TPGDA as reactive diluent. Curing system formulations, and water-based light-curable coatings can be obtained from the formulations in this table.

Table 5 Light curing system formula

Obviously, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Changes or changes in other different forms cannot be exhausted here, and all obvious changes or changes derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims (10)

1. a lignin-based macromolecular photoinitiator, is characterized in that, its structural formula is shown in the following formula I: in,

It is the molecular skeleton of lignin without terminal hydroxyl groups. M1 is the molecular skeleton of epoxyhalogenated alkane without terminal hydroxyl group and halogen atom after epoxy ring-opening reaction, M2 is the molecular skeleton of the solubilizing compound without hydroxyl, M3 is the molecular skeleton of the cracked photoinitiator without hydroxyl; n1, n2, x1, x2, y1 and y2 are integers ≥ 0 respectively and x1+x2=1; n3 is a natural number ≥ 1, n1+n2+n3=the number of terminal hydroxyl groups of lignin and y1+x2+n2≥1. 2. a preparation method of lignin-based macromolecular photoinitiator as claimed in claim 1, is characterized in that, comprises the following steps: The hydroxyl-containing solubilizing compound is dissolved or melted, a catalyst is added, an epoxyhaloalkane is added to react, and the unreacted epoxyhaloalkane is removed after the reaction to obtain an intermediate product A; the structural formula of the intermediate product A is as shown in formula II. Show: Wherein, X is a halogen atom, and y3 is an integer ≥ 0; Dissolving lignin in an alkaline aqueous solution, heating to reflux, adding intermediate product A to react, cooling after the reaction, adjusting the pH value to 7, and reacting to obtain intermediate product B; the structural formula of the intermediate product B is shown in formula III:

Wherein, n4 is a natural number ≥ 1, n5 is an integer ≥ 0, and n4+n5=the number of terminal hydroxyl groups of lignin; The cracking-type photoinitiator containing hydroxyl group is dissolved, a catalyst is added, an epoxyhaloalkane is added to react, and the unreacted epoxyhaloalkane is removed after the reaction to obtain an intermediate product C; the structural formula of the intermediate product C is shown in formula IV: The intermediate product B and the intermediate product C are dissolved, reacted under alkaline conditions, cooled after the reaction is completed, the pH value is adjusted to 7, and the lignin-based macromolecular photoinitiator is obtained by the reaction after purification. 3. The preparation method according to claim 2, wherein the lignin comprises one or more of sulfate lignin, alkaline lignin, sodium lignosulfonate and organic solvent soluble lignin , preferably alkaline lignin; more preferably, the molecular weight of the lignin is 5000-50000, and the hydroxyl content is 2.0-5.0 mmol/g. 4. preparation method according to claim 2 is characterized in that, described epihaloalkane comprises epichlorohydrin, epifluorohydrin, epibromohydrin, methyl epichlorohydrin, 4-bromo-1 , One or more of 2-epoxybutane and 6-bromo-1,2-epoxyhexane; the catalyst includes boron trifluoride ether, aluminum trichloride, triethylamine, sodium hydroxide, Ferric chloride and titanium tetrachloride, preferably boron trifluoride ether, triethylamine and sodium hydroxide. 5. The preparation method according to claim 2, wherein the hydroxyl-containing solubilizing compound comprises polyethylene glycol and derivatives thereof, polyvinyl alcohol and derivatives thereof, polymaleic acid and derivatives thereof , water-based polyurethane and its derivatives, polyvinylpyrrolidone and its derivatives, water-soluble starch and its derivatives, sodium alginate and its derivatives, hyaluronic acid and its derivatives; The degree of polymerization of the compound is 5-7500, more preferably 5-500. 6. The preparation method according to claim 2, wherein the cleavage-type photoinitiator containing hydroxyl group comprises α-hydroxy ketone derivatives, α-amino ketone derivatives, benzoyl formates and acyl phosphorus oxides, preferably:

7 . The preparation method according to claim 2 , wherein the reaction molar ratio of the intermediate product C to the intermediate product B is 2:1 to 10:1. 8 . 8 . The preparation method according to claim 2 , wherein the mass fraction of the molecular skeleton of the solubilizing compound in the lignin-based macromolecular photoinitiator is 10-70 wt %, and the molecular skeleton of the cracking photoinitiator The mass fraction is 5-20wt%, and the solubility of the lignin-based macromolecular photoinitiator in water and/or organic solvent is ≥5wt%. 9. The application of the lignin-based macromolecular photoinitiator as claimed in claim 1 in a photocuring system. 10. The application according to claim 9, wherein the photocuring system comprises 0.1-20 parts of a lignin-based macromolecular photoinitiator whose structural formula is shown in formula I, 10-90 parts of a solvent, 20- 90 parts of photopolymerizable monomers.

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