CN112028801B

CN112028801B - Chain extender and preparation method and application thereof

Info

Publication number: CN112028801B
Application number: CN202010720674.4A
Authority: CN
Inventors: 张超群; 王晓; 张怡; 卢其明; 罗颖
Original assignee: South China Agricultural University
Current assignee: South China Agricultural University
Priority date: 2020-07-24
Filing date: 2020-07-24
Publication date: 2021-07-09
Anticipated expiration: 2040-07-24
Also published as: CN112028801A

Abstract

The invention relates to a chain extender and a preparation method and application thereof. The chain extender has a structure shown as a formula (I) or a formula (II):

wherein, R, R₁、R₂And R₃Independently selected from alkyl, substituted alkyl, phenyl, substituted phenyl, heterocyclyl, alkylheterocyclyl or carbonyl. The chain extender provided by the invention has hydroxyl with a crosslinking function and carboxyl or tertiary amine with a hydrophilic function at the same time, is liquid at normal temperature and has the advantage of obvious compatibility; when the hydrophilic chain extender is used for preparing polyurethane, the waterborne polyurethane emulsion can be endowed with good storage stability, the biological content is up to 90 percent, and the mechanical property of the waterborne polyurethane is improvedAnd has a level comparable to or superior to that of the aqueous polyurethane material prepared from conventional commercial chain extenders.

Description

Chain extender and preparation method and application thereof

Technical Field

The invention belongs to the field of high polymer materials, and particularly relates to a chain extender and a preparation method and application thereof.

Background

Polyurethane (PU) is one of the most important polymers, and has been widely used in the fields of coatings, sealants, adhesives, foams and composites due to its excellent properties. Currently, most of hydrophilic chain extenders for preparing polyurethane are dimethylolbutyric acid (DMBA), 2-dimethylolpropionic acid (DMPA) and the like. These hydrophilic chain extenders have low solubility in organic solvents, resulting in the use of large amounts of solvents in the preparation of PU, and the generation of Volatile Organic Compounds (VOCs), including toluene, butanone, and the like, causing great damage to the environment and construction workers. On the other hand, the petrochemical resources are exhausted at present, so that the price fluctuation of the traditional hydrophilic chain extender is large. Therefore, the preparation of a novel, environment-friendly and low-cost hydrophilic chain extender is imperative.

Many researchers have been working on the synthesis of new chain extenders in recent years. The light click reaction is widely applied to the preparation of polyhydric alcohol, chain extender and the like due to the advantages of high efficiency, high speed, simple reaction conditions, easy purification and the like. Desroches et al studied the parameters and side effects of thiol-ene reaction by light click reaction of oleic acid with mercaptoethanol and succeeded in preparing rapeseed oil-based polyols and the resulting polyurethanes had the same heat resistance as the commercial polyurethanes. The novel plant oil-based polycarboxylic acid hydrophilic chain extender is successfully synthesized by carrying out sulfydryl-alkene click reaction on the plant oil and mercaptopropionic acid (university of Jiangxi Master) and the like.

The patents for preparing the novel hydrophilic chain extender reported at present are few, for example, the Chinese patent with the publication number of CN106046288A discloses the preparation and the application of the hydrophilic chain extender, the Chinese patent with the publication number of CN101240057A discloses the preparation method of the sulfonic acid type hydrophilic chain extender, and the patents are examples of successfully preparing the hydrophilic chain extender and applying the hydrophilic chain extender in the aspect of polyurethane, have excellent performance and are expected to replace the traditional chain extender. However, the above examples are all based on petroleum, and do not satisfy the requirement of sustainable development.

Therefore, the development of a novel hydrophilic chain extender which reduces or replaces non-renewable resources of petroleum has important research significance and economic value.

Disclosure of Invention

The invention aims to overcome the defect or deficiency that hydrophilic chain extenders selected in the prior art are all petrochemical resources as base materials and are not environment-friendly, and provides the hydrophilic chain extender. The chain extender provided by the invention has hydroxyl (at least 3) with a crosslinking effect and carboxyl or tertiary amine group with a hydrophilic effect, is liquid at normal temperature and has the advantage of obvious compatibility; when the hydrophilic chain extender is used for preparing polyurethane, the hydrophilic chain extender can endow the waterborne polyurethane emulsion with good storage stability and high biological content (up to 90 percent), and the mechanical property of the waterborne polyurethane is improved, so that the hydrophilic chain extender has the level equivalent to or superior to that of a waterborne polyurethane material prepared by a conventional commercial chain extender (such as DMPA and DMBA).

Another object of the present invention is to provide a method for preparing the chain extender.

The invention also aims to provide the application of the chain extender in preparing polyurethane.

In order to achieve the purpose, the invention adopts the following technical scheme:

a chain extender has a structure as shown in formula (I) or formula (II):

wherein, R, R₁、R₂And R₃Independently selected from alkyl, substituted alkyl, phenyl, substituted phenyl, heterocyclyl, alkylheterocyclyl or carbonyl.

The chain extender provided by the invention has hydroxyl with a crosslinking function and carboxyl or tertiary amine with a hydrophilic function at the same time, is liquid at normal temperature and has the advantage of obvious compatibility; when the hydrophilic chain extender is used for preparing polyurethane, the hydrophilic chain extender can endow the waterborne polyurethane emulsion with good storage stability, has the biological content as high as 90 percent, improves the mechanical property of the waterborne polyurethane, and has the level equivalent to or superior to that of a waterborne polyurethane material prepared by a conventional commercial chain extender (such as DMPA and DMBA).

The carbonyl group referred to in the present invention is-COR₄，R₄Is alkyl (e.g. C)_1～4Alkyl) phenyl or alkyl substituted phenyl.

Preferably, the alkyl group is C_1～10Alkyl groups of (a); the substituted alkyl is C_1～10Substituted alkyl of (a);

preferably, the heteroatom in the heterocyclic or alkylheterocyclic group is oxygen.

Preferably, the substituent in the substituted alkyl and the substituted phenyl is independently selected from one or more of hydroxyl, cyano, ester group or carboxyl.

Preferably, said R, R₁、R₂And R₃Independently selected from carbonyl, alkylheterocyclyl, methyl or ethyl.

More preferably, the carbonyl group is-COCH₃、-COCH₂CH₃、

More preferably, R₁is-COCH₃；R₂Is or-COCH₃；R₃Is ethyl.

The preparation method of the chain extender comprises the following steps: mixing oleum ricini

N-acetyl-L-cysteine and derivatives thereof

Mixing with initiator, and reacting under ultraviolet irradiationAnd obtaining the chain extender.

In general, the time for the mercapto group to completely convert the double bond of the vegetable oil is usually at least 3 hours. According to the invention, castor oil, N-acetyl-L-cysteine and derivatives thereof are used as raw materials to carry out sulfydryl-alkene light click reaction, double bonds can be completely converted within a short time at normal temperature, and the obtained chain extender can be used for preparing waterborne polyurethane with excellent performance.

For example, with N-acetyl-L-cysteine (NAC)

(R is-COCH)₃) The reaction is carried out by taking the raw materials, and the double bonds can be completely converted within 15 min. The other N-acetyl-L-cysteine derivatives are used as raw materials for reaction, and the reaction time is relatively short (about 10-60 min).

In addition, the preparation method of the invention takes renewable vegetable oil as raw material, has wide source and accords with the concept of green environmental protection; any petrochemical energy materials are not used, so that the pressure of excessive consumption of petrochemical energy is relieved; the natural N-acetyl-L-cysteine and the derivatives thereof are used as raw materials, so that the composition is safe and nontoxic; and the natural N-acetyl-L-cysteine and the derivatives thereof have small smell, and overcome the defect of large smell of the traditional mercapto acid.

Preferably, the molar ratio of double bonds in the castor oil to mercapto groups in the N-acetyl-L-cysteine and the derivatives thereof is 1: 1-6.

More preferably, the molar ratio of the double bond in the castor oil to the thiol group in the N-acetyl-L-cysteine and derivatives thereof is 1: 4.

Preferably, the photoinitiator is one or more of isopropyl thioxanthone ITX, 2-hydroxy-2, 2-dimethylacetophenone 1173, acetophenone, benzophenone, 4-benzoylbenzoic acid, 2-benzoylbenzoic acid, methyl 2-benzoylbenzoate, 4,4 '-bis (dimethylamino) -benzophenone, 4,4' -bis (diethylamino) -benzophenone, 1, 4-dibenzoylbenzene, diphenylhexanedione, hydroxycyclohexyl phenyl ketone, 2-ethylanthraquinone, photobase generator ketoxime ester, cobalt-amine complex, formamide, quaternary ammonium salt, 9-fluorenylcarbamate or 3-nitropentanylcarbamate.

More preferably, the photoinitiator is 2-hydroxy-2, 2-dimethylacetophenone 1173.

Preferably, the amount of the photoinitiator is 3-5% of the total mass of the castor oil, the N-acetyl-L-cysteine and the derivatives thereof.

Preferably, the reaction time is 10-60 min.

More preferably, the reaction time is 15-30 min.

Most preferably, the reaction time is 15 min.

Preferably, the castor oil, the N-acetyl-L-cysteine and the derivatives thereof and the initiator are mixed and dissolved in an organic solvent.

More preferably, the organic solvent is one or more of ethyl acetate, dichloromethane, petroleum ether, diethyl ether or tetrachloromethane.

Preferably, the reaction also comprises the steps of extraction, drying, filtration, evaporation and drying.

Specifically, the treatment process after the reaction is as follows: the reacted product was extracted with ethyl acetate, then dried over anhydrous magnesium sulfate, filtered and rotary evaporated to remove ethyl acetate, and then dried under vacuum at 45 ℃ overnight.

The application of the compound as a chain extender in the preparation of waterborne polyurethane is also within the protection scope of the invention.

The invention also discloses a preparation method of the waterborne polyurethane, which comprises the following steps: uniformly mixing polyol, diisocyanate and a catalyst, adding a chain extender with a structure shown as a formula (I) or a formula (II), and reacting to obtain the waterborne polyurethane.

The chain extender selected in the preparation method provided by the invention has hydroxyl with a crosslinking effect and carboxyl or tertiary amine with a hydrophilic effect at the same time, is liquid at normal temperature, has the advantage of obvious compatibility, and can be used for preparing aqueous polyurethane emulsion; the prepared aqueous polyurethane emulsion has good storage stability, high biological content (up to 90 percent) and excellent mechanical property, and has the level equivalent to or superior to that of the conventional commercial chain extender such as DMPA and DMBA and the prepared aqueous polyurethane material.

Polyols, diisocyanates and catalysts conventional in the art may be used in the present invention, and the reaction conditions may also be conventional controlled conditions.

Preferably, the polyol is one or more of polyester polyol, polyether polyol or vegetable oil-based polyol.

More preferably, the polyol is one or more of polypropylene glycol PPG, polycarbonate glycol PCDL, castor oil CO and derivatives thereof.

Preferably, the diisocyanate is one or more of isophorone diisocyanate (IPDI), Toluene Diisocyanate (TDI), diphenylmethane diisocyanate (MDI), 1, 6-Hexamethylene Diisocyanate (HDI) or L-Lysine Diisocyanate (LDI).

More preferably, the diisocyanate is isophorone diisocyanate, IPDI.

Preferably, the catalyst is one or more of dibutyltin laurate DBTDL, stannous octoate, zinc octoate or triethylene diamine.

More preferably, the catalyst is dibutyltin laurate DBTDL.

Preferably, the reaction temperature is 50-90 ℃. The time is 60-180 min.

Preferably, the molar ratio is 1.0: 1.5-2.5: 0.5-1.5 based on the molar value of OH or NCO in the structures of the polyol, the diisocyanate and the chain extender; the solid content of the waterborne polyurethane obtained after emulsification is 5-50%.

Preferably, the amount of the catalyst is 0.1-1% of the total mass of the reactants.

Preferably, the neutralizing agent is one of triethylamine, acetic acid, hydrochloric acid, glycolic acid and lysine, and the neutralization degree is 60-150%.

The specific process of the reaction is as follows: mixing polyol and diisocyanate, stirring at 50-90 ℃, and then adding a catalyst for pre-reaction; and dissolving the chain extender in MEK (methyl ethyl ketone), stirring, and reacting for 10-60 min. Butanone was added after the reaction to reduce the viscosity of the system. And then cooling to room temperature, neutralizing by using a neutralizing agent (such as triethylamine TEA, tartaric acid and the like), stirring, emulsifying by using distilled water at a speed of 400-800 rpm for 60-120 min, and performing rotary evaporation to remove MEK to obtain 15-30 wt.% of aqueous polyurethane emulsion.

The waterborne polyurethane is prepared by the preparation method.

The use of the above aqueous polyurethanes in the preparation of coatings, sealants, adhesives, foams or composites is also within the scope of the present invention.

The application of the waterborne polyurethane in preparing waterborne polyurethane coating film is also within the protection scope of the invention.

An aqueous polyurethane coating film is prepared by the following steps: pouring the waterborne polyurethane into a mold, and drying to obtain the waterborne polyurethane coating.

Compared with the prior art, the invention has the following beneficial effects:

the chain extender provided by the invention has hydroxyl (at least 3) with a crosslinking effect and carboxyl or tertiary amine group with a hydrophilic effect, is liquid at normal temperature and has the advantage of obvious compatibility; when the hydrophilic chain extender is used for preparing polyurethane, the hydrophilic chain extender can endow the waterborne polyurethane emulsion with good storage stability and high biological content (up to 90 percent), and the mechanical property of the waterborne polyurethane is improved, so that the level of the waterborne polyurethane material prepared by the hydrophilic chain extender is equivalent to or superior to that of the conventional commercial chain extender, such as DMPA and DMBA.

Drawings

FIG. 1 is a schematic diagram of the reaction scheme and equipment for the preparation of the chain extender of example 1;

FIG. 2 is an FTIR spectrum (FIG. 2a), a Gel Permeation Chromatography (GPC) pattern (FIG. 2b) and a representation of the chain extender NACCO-p provided in example 1¹H-NMR chart (FIG. 2 c);

FIG. 3 shows the principle of initiation of different photoinitiators;

FIG. 4 is a drawing of the chain extender NACCO-T provided in example 1¹H-NMR chart (FIG. 4a), FTIR spectrum chart (FIG. 4b), Gel Permeation Chromatography (GPC)Graph (fig. 4c) and graph of conversion over time (fig. 4 e);

FIG. 5 is a drawing of the chain extender NACCO-m provided in example 1¹An H-NMR chart (fig. 5a), an FTIR spectrum chart (fig. 5b), a Gel Permeation Chromatography (GPC) chart (fig. 5c), and a conversion rate as a function of the molar ratio of mercapto groups/carbon-carbon double bonds (fig. 5 e);

FIG. 6 is a schematic diagram of the preparation of the aqueous polyurethane emulsion in example 3;

FIG. 7 is a particle size distribution diagram (FIG. 7a) and a transmission electron micrograph (FIG. 7b) of the aqueous polyurethane emulsion provided in example 3;

FIG. 8 shows the appearance (FIG. 8a), thermogravimetric analysis (FIG. 8b), differential scanning calorimetry (FIG. 8c) and dynamic thermomechanical analysis (FIG. 8d) of the waterborne polyurethane coating material provided in example 3;

FIG. 9 shows the results of mechanical property tests on the aqueous polyurethane coating material provided in example 3;

FIG. 10 shows the water contact angle (FIG. 10a) and the diiodomethane contact angle (FIG. 10b) of the aqueous polyurethane coating material provided in example 3.

Detailed Description

The invention is further illustrated by the following examples. These examples are intended to illustrate the invention and are not intended to limit the scope of the invention. Experimental procedures without specific conditions noted in the examples below, generally according to conditions conventional in the art or as suggested by the manufacturer; the raw materials, reagents and the like used are, unless otherwise specified, those commercially available from the conventional markets and the like. Any insubstantial changes and substitutions made by those skilled in the art based on the present invention are intended to be covered by the claims.

The chain extender, the aqueous polyurethane emulsion or the aqueous polyurethane coating material provided in each example were characterized as follows.

(1) Fourier transform infrared spectroscopy (FT-IR)

The functional groups of the chain extender were characterized using the Nicolet iS10 fourier transform infrared spectroscopy of the american siemer flyer. The spectral scanning range is 400-4000cm^-1。

(2) Nuclear magnetic resonance spectroscopy (NMR)

The samples were analyzed for hydrogen spectra using an AV600 NMR spectrometer from Bruker. The molecular structure of the chain extender is identified by using Tetramethylsilane (TMS) as an internal standard substance and dimethyl sulfoxide-D6 as a solvent. The conversion of carbon-carbon double bonds is calculated by the following formula:

wherein d and d' are the integrated areas of the carbon-carbon double bonds in the spectra of the crude vegetable oil and the resulting product, respectively, in the hydrogen spectra.

(3) Gel Permeation Chromatography (GPC)

The molecular weight of the sample was measured by using the Prominence GPC system of Shimadzu corporation. The system was equipped with a RID-10A differential refractive detector and Shodex KF804L and KF802.5 chromatography columns. Tetrahydrofuran was used as the mobile phase, and the flow rate and column temperature were 0.3mL/min and 30 ℃ respectively. Polystyrene standards were used.

(4) Mass spectrum (LC-MS)

The relative molecular weights of the products were obtained using AB Sciex API 3200.

(5) Measurement of acid value and hydroxyl value

The carboxyl group in the chain extender was measured according to AOCS Official Method Te 1a-64 Method. The specific operation is as follows: 1g of the chain extender and 15g of absolute ethanol were added to an Erlenmeyer flask and dissolved, and 3-5 drops of phenolphthalein indicator were added, followed by titration with 0.5mol/L potassium hydroxide solution.

The hydroxyl group content of the sample was measured according to the Unilever method. The specific operation is as follows: 10g of a mixture of acetic anhydride and pyridine (mass ratio 1:9) and 1.0g of polyol were added to the Erlenmeyer flask. After the mixture was reacted at 90-100 ℃ for 1 hour, 25mL of pyridine and 10mL of deionized water were added. After further reaction for 20min, the product was titrated with 0.5mol/L potassium hydroxide solution under phenolphthalein as an indicator. Blank assays were performed in a similar procedure.

(6) Transmission Electron Microscope (TEM)

The morphology and particle size of the aqueous polyurethane emulsion were characterized using a Tecnai 12, Netherlands FEI Transmission Electron microscope in the Netherlands. The aqueous polyurethane emulsion was diluted with distilled water to a liquid concentration of 0.1% by mass and observed under a microscope.

(7) Stability of aqueous polyurethane emulsion

Aqueous polyurethane emulsion stability characterized by centrifuging the sample at 8000rpm for 30min using a Tomos 3-18 centrifuge from Shanghai Tomo scientific instruments.

(8) Particle size distribution and Zeta potential

The particle size distribution and Zeta potential of the aqueous polyurethane emulsion were measured with a Zeta-sizer Nano ZSE from malvern instruments ltd, u.k. the sample was diluted to about 0.01% by weight before the test.

(9) Contact angle

The contact angles of water and diiodomethane of the fixed coating film samples were measured at room temperature using a Powereach JC2000C1 contact angle meter of the digital technology equipment ltd, morning, shanghai. The mean was taken in triplicate for each sample.

(10) Thermogravimetric analysis (TGA)

The samples were measured using a TRIOS Discovery TGA 550 thermal analyzer. The sample was heated from 30 ℃ to 700 ℃ at a rate of 10 ℃/min under nitrogen. 5-10mg of sample was used in the test, and the sample was dried before the test.

(11) Mechanical Properties

The measurement was carried out by using Shimadzu AGS-X Universal tensile tester, Shimadzu corporation, Shimadzu, Japan. The test speed was 100 mm/min. The sample specification was 25mm × 10mm (length × width). Each sample was tested in 4 replicates and averaged.

(12) Dynamic Mechanical Analysis (DMA)

The measurement was carried out using a DMA 242C dynamic mechanical analyzer from sushi corporation. The stretching mode was used with the frequency set to 1 Hz. 20mm by 6mm (length by width) of the sample. The sample was raised from-60 ℃ to 140 ℃ at a rate of 5 ℃/min. Glass transition temperature (T)_g) From the temperature corresponding to the peak tan δ.

(13) Differential Scanning Calorimetry (DSC)

The glass transition temperature of the sample was measured using a DSC 214Polyma differential scanning calorimeter in Germany. In the test process, the temperature is firstly increased from 30 ℃ to 100 ℃ at the temperature increasing rate of 10 ℃/min, and then is reduced to-60 ℃ at the temperature reducing rate of 10 ℃/min to eliminate the heat. The dynamic temperature of the test is measured by raising the temperature to 100 ℃ at a temperature rise rate of 5 ℃/min at-60 ℃.

Example 1

This example provides a series of chain extenders, NACCO, prepared by a click reaction of Castor Oil (CO) and N-acetyl-L-cysteine (NAC), as follows.

First, NAC, CO and photoinitiator (4 wt.%) in the appropriate proportions were dissolved in absolute ethanol and transferred to a quartz tube. The reaction was carried out for a certain period of time under ultraviolet irradiation at a power of 350W (see FIG. 1 for reaction apparatus). After that, the product was extracted with ethyl acetate and dried over anhydrous magnesium sulfate. The product was filtered and rotary evaporated to remove ethyl acetate and then dried overnight at 45 ℃ under vacuum to give the chain extender naco.

Specifically, two photoinitiators (1173, ITX) are selected, 6 different reaction times (5min, 10min, 15min, 20min, 25min and 30min) and 6 different mercapto/double bond molar ratios (1:1, 2:1, 3:1, 4:1, 5:1 and 6:1) are carried out, and the obtained chain extenders are respectively named as NACCO-p, NACCO-T and NACCO-m, wherein p, T and m are respectively the photoinitiator, time and mercapto/double bond molar ratio, and the specific conditions are shown in table 1.

Table 1 preparation conditions of chain extender

NP stands for optional chain extender.

By using¹The structure of the product chain-extended NACCO is comprehensively characterized by H NMR, GPC and FTIR spectrums

FIG. 2 shows the characterization of NACCO-p.

FIG. 2a shows FTIR spectrum. As can be seen from the figure, when the photoinitiators ITX, 1173 were involved in the reaction, they were located at 3008cm from the original castor oil^-1The characteristic peak of carbon-carbon double bond at position (2) disappeared and was located at 1655cm^-1Where C is present ═Characteristic peaks of stretching vibration of O bond and deformation vibration of NH bond, and at 1535cm^-1In addition to this, a characteristic amide peak was observed at 3400cm^-1-3300cm^-1The characteristic peak of hydroxyl group (b) is shifted to the right, probably due to the introduction of N-H bond. All the above preliminarily show that NAC is successfully introduced into the double bond of castor oil through the light click reaction.

FIG. 2b shows a GPC chart. As can be seen from the figure, compared with the original castor oil, the retention time of the obtained product is shifted to the left (the retention time is between 17 and 18.5 min), which indicates that the molecular weight is increased, and when 1173 is taken as an initiator, the retention time is shortest, which indicates that the molecular weight is the largest and the reaction is the most complete. And also a small amount of oligomers was observed at 14.5-17min, which is likely a dimer of castor oil. Generally, under ultraviolet irradiation, the polymerization reaction is generated by the formation of hydroperoxides and cyclic peroxides according to an autoxidation mechanism. Wherein oligomers in the polyol can provide the hyperbranched molecular structure of the polyurethane.

As shown in FIG. 2c, is¹H-NMR chart. As can be seen from the figure, compared with the original castor oil, the characteristic peak of the carbon-carbon double bond located at 5.2-5.5ppm in the main chain of the obtained chain extender is reduced or even completely disappears within 60 min. And, newly generated-CH group at 4.0ppm, and-CH at 2.8ppm in the spectrum₂Radical and-CH at 1.8ppm₃The characteristic peak of the group is from N-acetyl-L-cysteine, indicating that N-acetyl-L-cysteine was successfully grafted onto the fatty acid chain of castor oil by thiol-ene light click reaction. In addition, the-CH at 5.1-5.2ppm in castor oil₂-CH-CH₂The integrated area of the characteristic peak was defined as 1 and used as a standard for normalization, and the conversion of carbon-carbon double bonds was calculated by integrating the product. The results show that the highest reaction efficiency is obtained with 1173 as photoinitiator, with 98% conversion of the C ═ C double bonds and 93.78% yield, whereas the lowest reaction efficiency is obtained with ITX as initiator, with 64.36% conversion and 72.9% yield (specific data as shown in table 2). ITX and 1173 are typical hydrogen trapping initiators that can form a triplet state by photo-conversion. Triplet and triplet extraction functionThe hydrogen atoms of the C-H bonds in the molecule are further converted into free radicals and the grafting reaction is completed by coupling with functional molecule free radicals. In fact, photoinitiator 1173, upon initiation by ultraviolet light, generates two free radicals per molecule, which contribute to the formation of two thiophene groups during propagation; while the photoinitiator ITX generates only one radical by a hydrogen trapping reaction. In the absence of a photoinitiator, only one radical is formed by the cleavage of the SH group (see FIGS. 3 b-d). This result indicates that 1173 is the highest reaction efficiency of the photoinitiator.

TABLE 2 double bond conversion, yield and molecular weight of chain extenders under different conditions

FIG. 4 is a representation of NACCO-T.

As shown in FIG. 4a, is¹H-NMR chart. As can be seen from the figure, the characteristic peak of C ═ C double bonds between 5.2 and 5.5ppm in the nmr gradually decreased with increasing reaction time until it completely disappeared at 15 min.

FIG. 4c shows a GPC chart. As can be seen, the retention time of the product before 15min decreased with increasing time and was then unchanged.

FIG. 4b shows FTIR spectra. As can be seen from the figure, the product shows new characteristic peaks, which all indicate that the reaction is complete at 15 min.

The double bond conversion, yield and molecular weight of the chain extender are shown in table 2.

FIG. 5 shows the characterization of NACCO-m. As is clear from FIG. 5, the optimum reaction conditions are obtained when the molar ratio of mercapto group/carbon-carbon double bond is 4: 1.

From the above chart, it can be seen that the conditions for complete conversion of the carbon-carbon double bond are: the reaction time was 15min, the mercapto/double bond molar ratio was 4:1 in the presence of photoinitiator 1173, which is the optimum condition.

The physical and chemical properties of the chain extender obtained under the conditions (optimum conditions) were measured, and the results are shown in table 3.

TABLE 3 physical and chemical Properties of chain extender under optimal conditions

Under the condition, the full-bio-based chain extender with excellent performance is obtained, the acid value and the hydroxyl value are 87.82 +/-1.57 mg KOH/g and 184.86 +/-2.38 mg KOH/g respectively, the reaction efficiency is highest, and the energy consumption is least.

Examples 2 to 9

This example provides a series of chain extenders prepared by the click reaction of castor oil and N-acetyl-L-cysteine derivatives, whose structural parameters are shown in table 4.

TABLE 4N-acetyl-L-cysteine derivative structures

Click reaction of castor oil and N-acetyl-L-cysteine derivative

N-acetyl-L-cysteine derivatives (derivatives 1-8), CO and photoinitiator (4 wt.%) were dissolved in absolute ethanol and transferred to a quartz tube. The reaction was carried out for 15min under ultraviolet irradiation with a power of 350W. After that, the product was extracted with ethyl acetate and dried over anhydrous magnesium sulfate. And filtering and rotary evaporating the product to remove ethyl acetate, and then drying overnight at 45 ℃ in a vacuum environment to obtain the chain extender, which is recorded as examples 2-9 in sequence, wherein the performance characteristics are shown in table 5.

Table 5 acid number, hydroxyl number, and molecular weight of the chain extenders provided in examples 2-9

Example 10

This example provides a series of aqueous polyurethane emulsions prepared by the following procedure using NACCO (NACCO-4:1) provided in example 1 as the chain extender.

As shown in FIG. 6, polyol (PPG, PCDL, CO, castor oil derivative) and isophorone diisocyanate (IPDI) were added to a two-necked flask equipped with a mechanical stirrer and stirred and mixed at a temperature of 78 ℃ for 10 min. Then, dibutyltin laurate (DBTDL) (1% mass fraction of polyol) was added to the mixture, and then reacted for 20 min. Subsequently, the chain extender of NACCO was dissolved in Methyl Ethyl Ketone (MEK) and added dropwise to the mixture with stirring, the dropwise addition being completed within 60 min. The amounts of reactants used are shown in Table 6. After the reaction, 5-10mL of MEK was poured into the mixture to reduce the viscosity of the system. Then, when the temperature was cooled to room temperature, the system was neutralized with TEA and stirred for about 30 min. Finally, the mixture was emulsified with distilled water at a speed of 400 to 500rpm for 120min, and then excess MEK was removed by rotary evaporation to obtain an aqueous Polyurethane (PU) having a solid content of 15%. The aqueous polyurethane dispersions prepared are referred to as PU-p, where p denotes different polyols. Specifically, PU-CO164 represents castor oil with hydroxyl value of 164mg KOH/g of selected polyhydric alcohol; PU-PPG152 represents polypropylene glycol with hydroxyl value of 152mg KOH/g of selected polyalcohol; PU-PCDL224 represents a polycarbonate diol having a hydroxyl value of 224mg KOH/g of the selected polyol; PU-SCP represents the selected polyol, namely the polyol prepared from castor oil and soybean oleic acid, and the rest is analogized in the same way.

TABLE 6 amounts of polyols used

Note: a: hydroxyl molar equivalents of the polyol; b: hydroxyl molar equivalents of the chain extender.

And pouring the aqueous polyurethane emulsion into a silica gel mold and drying at room temperature to obtain a film for further analysis. All samples were dried at 60 ℃ for more than 12h prior to testing.

The measurement results are as follows.

(1) Stability of aqueous polyurethane emulsion

Stability was determined as provided previously. FIG. 7 is a particle size distribution diagram and a transmission electron microscope image of the aqueous polyurethane emulsion; table 7 shows the appearance, particle size and potential results for the aqueous polyurethane emulsion.

TABLE 7 appearance, particle size and potential of the aqueous polyurethane emulsion

As can be seen from the figures and tables, the dispersions of the polyurethane emulsions all exhibit excellent storage stability with a Zeta potential of less than-35.15 mV (Table 7). And no sample precipitation or delamination was observed after centrifugation at 3000rpm for 30 min. Furthermore, all dispersions remained unchanged after long-term storage in the laboratory environment for more than 2 years. Depending on the different polyols used, the dispersions showed different appearances (fig. 7). The larger the hydroxyl number of the polyol, the more transparent and stable the dispersion. For example, an aqueous polyurethane dispersion obtained from a castor oil derivative having a hydroxyl number of 208mg KOH/g showed a blue translucent appearance, while an aqueous polyurethane dispersion obtained from SCP having a hydroxyl number of 149mg KOH/g showed a milky appearance. Transmission electron microscopy results indicate that the polyurethane emulsion may self-assemble internally into nanoparticles, possibly due to the surface charge imparted by the carboxylic acid groups in the chain extender. The particle size of the PU-SCP dispersion was 150.00. + -. 20.00nm, whereas the PU-CO164 and PU-CO208 dispersions showed particle sizes of 100.00. + -. 10.00nm and 50.00. + -. 5.00nm, respectively. Polyurethane dispersions prepared from petroleum-based polyols (PPG and PCDL) show similar trends. These differences in particle size of the aqueous polyurethane dispersions are attributed to factors such as crosslink density, hydrophilicity, chain rigidity, and prepolymer viscosity.

(2) Thermodynamic property of polyurethane emulsion coating film

The thermodynamic properties of the polyurethane emulsion coating films were measured as provided above and the results are shown in FIG. 8 and Table 8.

As can be seen from the figures and tables, all film materials showed a transparent appearance (fig. 8 a). Most of these bio-based waterborne polyurethanesHigh biomass content can be as high as 90% and solids content can be as high as 45%. According to TGA characterization in the figure (fig. 8b), it is shown that all aqueous polyurethane coating materials undergo three degradation processes: the mass loss from 100 ℃ to 250 ℃ corresponds to the decomposition of the labile urethane groups. The weight loss from between 250 ℃ to 500 ℃ corresponds to the cleavage of the fatty acid chain. It is noteworthy that the thermal stability of the aqueous polyurethane coating film prepared from the bio-based Polyol and Polypropylene Glycol (PPG) decreases with increasing hydroxyl number due to the increase of urethane and higher unstable hard segments resulting from the high hydroxyl number. However, as the hydroxyl number increases, the thermal stability of the aqueous polyurethane coating film by polycarbonate diol (PCDL) increases. This may be associated with a higher crosslink density resulting from a higher hydroxyl number of the polyol PCDL 224. The mass loss of the aqueous polyurethane coating film above 500 ℃ is due to further thermal oxidation of the material. Generally, the temperature at which degradation will begin, i.e., the temperature at which 5% of mass is lost (T)₅) And temperature (T) at which degradation to the midpoint occurs₅₀) As a parameter for thermal stability (specific data are shown in table 8). T of PU-SCP and PU-CO films with increase in hydroxyl number from 149 to 208mg KOH/g₅The value was changed from 236.01 ℃ to 208.49 ℃ from T₅₀From 346.38 ℃ to 334.23 ℃. Aqueous polyurethanes prepared from the polyol PPG exhibit similar thermal behavior. This may be due to competition between higher unstable hard segments and increased crosslink density. However, T of PU-PCDL₅And T₅₀Increases with increasing hydroxyl number as a result of increasing crosslink density. Aqueous polyurethane coating materials made from bio-based polyols, polyesters and polyether polyols exhibit higher thermal stability than materials prepared by bulk reaction (PU-NACCO). Furthermore, the aqueous polyurethane coating materials made from polyester polyols have better thermal stability than materials made from polyether polyols. This is because of the stronger hydrogen bond formed by the urethane NH group and the ester group.

TABLE 8 thermodynamic Properties of aqueous polyurethane coating materials

Note: PCDL represents polycarbonate diol, and 224 and 112 represent hydroxyl values thereof, respectively; PPG represents polypropylene glycol, and 152 and 284 represent hydroxyl values thereof respectively; CO represents castor oil, and 208 and 164 represent hydroxyl values of the castor oil respectively; SCP is vegetable oil base polyalcohol obtained by the reaction of soybean oleic acid and castor oil; NACCO stands for the internal emulsifier prepared in this work, PU-NACCO stands for the aqueous polyurethane prepared from NACCO as polyol, and so on.

The DMA (fig. 8c) and DSC (fig. 8d) results show that all coating materials show a Tg in the DSC curve and there is no melting or crystalline transition, which is related to the amorphous nature of the resulting aqueous polyurethane coating material. As the hydroxyl value increased from 149mg KOH/g (SCP) to 208mg KOH/g (CO208), the Tg value of the resulting aqueous polyurethane coating film increased from 20.69 ℃ to 31.98 ℃. The same trend was observed for petroleum-based waterborne polyurethane films. As the hydroxyl number increases from 112mg KOH/g (PCDL112) to 284mg KOH/g (PPG284), the Tg value rises from-24.30 ℃ to 33.01 ℃ because the crosslink density increases with increasing hydroxyl number of the polyol, and therefore the glass transition temperature increases. The following table summarizes the Tg results for the aqueous polyurethane coating materials, wherein the DSC measured Tg values are about 10-20 ℃ lower than the DMA measured Tg values, which is related to the difference in the principles of the two test methods.

(3) Mechanical property of polyurethane emulsion coating film

The mechanical properties of the polyurethane emulsion coating were measured as provided above and the results are shown in FIG. 9 and Table 9.

TABLE 9 mechanical Properties of polyurethane emulsion coating films

Note: "/" indicates data for which no measurement can be made.

Fig. 9a shows the stress-strain behavior of the aqueous polyurethane coating material. The aqueous polyurethane coating material prepared from the polyol PCDL224, PPG284, CO208 and SCP shows obvious hard plastic stress-strain behavior and has strain softening and strain hardening behaviors before fracture. The aqueous polyurethane coating film material prepared from polyol PPG152 and CO164 exhibits only the elastic region and yield behavior of typical elastomeric polymers. It is clear that as the hydroxyl number of the polyol increases, the tensile strength (whether yield strength or strain stress) of the aqueous polyurethane coating material (excluding PU-SCP coating) prepared from the bio-based polyol increases, and the young's modulus and toughness as well as the elongation at break decrease. For example, the tensile strength, Young's modulus and toughness of PU-CO208 films were 18.56MPa, 210.99MPa, 37.02MP, respectively, while the corresponding values for PU-CO164 films were 10.67MPa, 64.14MPa and 18.24 MPa. Meanwhile, when the hydroxyl value was increased from 164mg KOH/g to 208mg KOH/g, the elongation at break was decreased from 255.81% to 241.56% (data as in Table 9). Generally, a high crosslink density results in better tensile strength and reduced elongation at break. Furthermore, although the hydroxyl number of polyol CO164 is higher than that of SCP, the aqueous polyurethane coating film prepared from polyol SCP exhibits better mechanical properties than the aqueous polyurethane film obtained with polyol CO 164. This may be related to the specific pre-cross-linked and hyperbranched structure of the polyol SCP, which may inhibit the aggregation of hard segments and promote the compatibility of hard and soft segments.

Similar tensile stress-strain behavior was observed for waterborne polyurethane films prepared from petroleum-based polyols. (PU-PCDL112 is too soft to perform the tensile test). As the hydroxyl number of the polyol increases, the tensile strength, Young's modulus and toughness of the aqueous polyurethane increase, while the elongation at break decreases. All aqueous polyurethane films showed elongation at break higher than 145%. Furthermore, the aqueous polyurethane prepared from the polyol PCDL has better mechanical properties than the aqueous polyurethane prepared from the polyol PPG. And PU-PCDL224 exhibits the highest tensile strength, young's modulus and toughness because it forms more hydrogen bonds between urethane and ester groups, which may result in PU-PCDL having a higher degree of phase mixing and a better crystal structure than PU-PPG.

To further evaluate the superiority of the waterborne polyurethane provided in this example, we compared it with other similar products in terms of mechanical properties. Waterborne polyurethanes based on vegetable oil based polyols were classified according to the different types of chain extenders used (fig. 9 b). In general, the aqueous polyurethane prepared with 2, 2-bis (hydroxymethyl) propionic acid (DMPA) as the chain extender has better mechanical properties than the sample prepared with N-Methyldiethanolamine (MDEA). The mechanical properties of the aqueous polyurethane prepared from 2, 2-bis (hydroxymethyl) butanoic acid (DMBA) and the chain extender provided in example 1 were comparable to those of the sample prepared using DMPA as the chain extender. Furthermore, it is noteworthy that the aqueous polyurethane prepared using the bio-based polyol and the chain extender provided in example 1 exhibited superior tensile strength and toughness compared to samples prepared using other chain extenders. Statistical data (fig. 9c) for waterborne polyurethanes prepared with petroleum-based polyols other than PCL show that the samples prepared using the chain extender provided in example 1 exhibit significant advantages in tensile strength and elongation at break compared to samples prepared using other chain extenders. Furthermore, it is worth emphasizing that the resulting aqueous polyurethane coating films have comparable or even higher mechanical properties compared to other solvent-based polyurethane coating films. These phenomena can be explained by the better compatibility of the chain extender provided in example 1 with polyols and IPDI compared to DMPA, DMBA and other chain extenders, resulting in a more uniform structure of the polyurethane. In addition, the carbon chains in the long and soft fatty acid chain extender (the chain extender provided in example 1) can prevent aggregation of the hard segments in the polyurethane and promote good compatibility of the soft and hard segments.

(4) Hydrophilic and hydrophobic property of polyurethane emulsion coating film

The hydrophilicity and hydrophobicity of the polyurethane emulsion coating film were measured according to the methods provided above, and the measurement results are shown in fig. 10 and table 10.

TABLE 10 contact angle data of aqueous polyurethane coating film

Fig. 10 shows the contact angles of the chain extender provided in example 1, the water-borne polyurethane coating film material of the different polyols of example 3, and water and diiodomethane. Specific contact angle results are shown in table 10. Aqueous polyurethane films from vegetable oil based polyols show a decreasing contact angle (except PU-SCP) with increasing hydroxyl number of the polyol. The water contact angle of PU-CO164 was 81.63 °, while PU-CO208 was 78.45 °. This is probably because the hydrophilic ionic groups and the crosslink density affect the hydrophobicity of the aqueous polyurethane film. As the hydroxyl number increases, the crosslink density of the aqueous polyurethane film increases, which results in an increase in contact angle. However, the hydrophilic ionic group increases with increasing chain extender content, resulting in increased hydrophilicity. The increase in hydrophilicity compensates for the decrease in hydrophilicity caused by the increase in crosslink density, resulting in a decrease in contact angle of the resulting membrane. A similar trend was observed for aqueous polyurethanes from Polyether Polyols (PPG) and polyester Polyols (PCDL). Both water and diiodomethane contact angles decrease with increasing hydroxyl number. For example, the water contact angle of PU-PPG decreased from 91.40 to 75.48 as the hydroxyl number increased from 152 to 284mg KOH/g, and likewise, the diiodomethane contact angle decreased from 44.08 to 37.40. Notably, the PU with the highest OH number of the PPG284 has the lowest contact angles of water and diiodomethane. This phenomenon confirms that the above conclusion is correct, and that the hydrophilic ionic groups govern the contact angle of the resulting film.

From the above, it is understood that (1) the structure of the chain extender and its good compatibility impart good storage stability to the aqueous polyurethane emulsion. The functionality of the polyol has obvious influence on the appearance and the particle size of the emulsion, and as the hydroxyl value of the polyol is increased, the appearance of the dispersion is gradually clarified and transparent from milk white, and the particle size of the emulsion is gradually reduced.

(2) The waterborne polyurethane coating material obtained in example 3 has equivalent or even better mechanical properties than the coating materials obtained by commercial DMPA and DMBA. With the increase of the hydroxyl value of the polyol, the crosslinking density of the polyurethane coating material is increased, and the thermodynamic stability and the mechanical property are more excellent. In addition, the bio-based content of the obtained waterborne polyurethane coating material reaches 90 percent.

(3) The contact angle of the aqueous polyurethane coating material obtained in example 3 gradually decreased with the increase in the polyol hydroxyl value, indicating that the surface wettability increased. Where PU-PPG152 has the highest contact angle of 91.40.

Examples 11 to 18

The embodiment provides a series of aqueous polyurethane emulsions, which are prepared by respectively using the vegetable oil-based products provided in embodiments 2 to 9 as chain extenders through the following processes.

Mixing PPG and diisocyanate, stirring at 50-90 ℃, and adding a catalyst for pre-reaction; and then, respectively dissolving the plant oil-based chain extender prepared in the embodiment 2-9 in butanone (MEK), dropwise adding the solution into the mixture, stirring, and carrying out chain extension reaction for 10-60 min. The amounts of reactants used are shown in Table 11. Butanone was added after the reaction to reduce the viscosity of the system. And then cooling to room temperature, neutralizing by using a neutralizing agent, stirring, adding distilled water, emulsifying at the speed of 400-800 rpm, and performing rotary evaporation to remove excessive MEK so as to obtain the waterborne Polyurethane (PU) with the solid content of 15-35%.

TABLE 11 formulation parameters for aqueous polyurethane emulsions of examples 11-18

Note: a is the hydroxyl molar equivalent of the polyhydric alcohol; and b, hydroxyl molar equivalent of the chain extender.

Table 12 preparation Process parameters of the aqueous polyurethane emulsions of examples 11 to 18

The stability of the aqueous polyurethane emulsion was measured in the same manner as described above, and the results are shown in Table 13. As is clear from the table, the particle diameters of the examples other than example 11 were small, the influence of the increase in the ratio of the reactants on the particle diameters was large, and the Zeta potential absolute values of all the samples other than example 18 were larger than 34, indicating that the emulsion stability was good.

TABLE 13 particle diameter and Zeta potential of the aqueous polyurethane emulsions of examples 11 to 18

The polyurethane emulsion described above was poured into a silica gel mold and dried at room temperature to give a film for further analysis (thermodynamic properties). All samples were dried at 60 ℃ for more than 12h prior to testing.

The waterborne polyurethane coating materials provided in examples 11-18 all have good thermodynamic and mechanical properties.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A chain extender is characterized by having a structure shown as a formula (I) or a formula (II):

wherein, R, R₁、R₂And R₃Independently selected from alkyl, substituted alkyl, phenyl, substituted phenyl, heterocyclyl, alkylheterocyclyl or-COR₄，R₄Is alkyl, phenyl or alkyl substituted phenyl;

the preparation method of the chain extender comprises the following steps:

mixing oleum ricini

Compound 1 of the following structural formula:

and mixing and dissolving the chain extender and an initiator, and reacting under ultraviolet illumination to obtain the chain extender.

2. The chain extender of claim 1, wherein the alkyl group is C_1～10Alkyl groups of (a); the substituted alkyl is C_1～10Substituted alkyl of (a);

the heteroatom in the heterocyclyl or alkylheterocyclyl is oxygen;

the substituent in the substituted alkyl and the substituted phenyl is independently selected from one or more of hydroxyl, cyano, ester group or carboxyl.

3. The chain extender of claim 1, wherein said R, R is₁、R₂And R₃Independently selected from-COR₄Alkyl heterocyclic group, methyl group or ethyl group.

4. The chain extender of claim 1, wherein the molar ratio of the double bond in the castor oil to the mercapto group in the compound 1 is 1: 1-6; the amount of the photoinitiator is 3-5% of the total mass of the castor oil, the N-acetyl-L-cysteine and the derivatives thereof.

5. The chain extender of claim 1, wherein the photoinitiator is one or more of isopropylthioxanthone, 2-hydroxy-2, 2-dimethylacetophenone, acetophenone, benzophenone, 4-benzoylbenzoic acid, 2-benzoylbenzoic acid, methyl 2-benzoylbenzoate, 4,4 '-bis (dimethylamino) -benzophenone, 4,4' -bis (diethylamino) -benzophenone, 1, 4-dibenzoylbenzene, diphenylhexanedione, hydroxycyclohexylphenylketone, 2-ethylanthraquinone, photobase generator ketoxime ester, cobalt-amine complex, formamide, quaternary ammonium salt, 9-fluorenylcarbamate, or 3-nitropentylcarbamate.

6. The chain extender of claim 1, wherein the reaction time is 15-60 min.

7. The chain extender of claim 1, wherein the castor oil, compound 1 and the initiator are dissolved in an organic solvent.

8. The chain extender of claim 1, further comprising the steps of extracting, drying, filtering, evaporating, and drying after the reaction.

9. Use of a chain extender as claimed in any one of claims 1 to 8 in the preparation of a polyurethane.