A chain extender for polyurethane and its application

Abstract

A polyurethane chain extender and its application. The polyurethane chain extender comprises an aromatic diamine powder that reacts with vapor-phase acetyl chloride to amidate one or two amino groups of the aromatic diamine molecules on the surface of the aromatic diamine powder, producing a mixture of partially diacetylated and partially monoacetylated products. The aromatic diamine powder has a particle size of 20-800 microns. The surface-passivated MDA powder curing agent produced by the present invention reacts slowly or even non-reactively at room temperature, significantly extending the room-temperature operating time and even allowing the formulation of a one-component polyurethane system that can be cured by heating to 90-110°C.

Description

Technical Field

[0001] The present invention belongs to the field of chemical technology, and specifically relates to a polyurethane chain extender and application thereof, and especially relates to a surface chemical modification method of aromatic diprimary amine particles for polyurethane elastomer materials and application thereof. Background Art

[0002] Aromatic diamine chain extenders react with isocyanate-terminated (NCO-terminated) polyurethane prepolymers or polyisocyanates to produce polyurethaneureas or polyureas. Advantages include: the reaction rate of amino groups with NCO groups is faster than the reaction of hydroxyl groups / water with isocyanates, making it less likely to produce bubbles during elastomer preparation; the urea group has high polarity and can generate hydrogen bonds in the elastomer; and aromatic diamine chain extenders contain rigid benzene rings, which impart rigidity to the hard segments of the polyurethane (urea) macromolecules. The combined action of the rigid benzene rings and hydrogen bonds gives the polyurethane material better strength, heat resistance, and other properties.

[0003] Methylenediphenylmethanediamine (MDA) is a highly reactive, symmetrical aromatic diamine containing a double benzene ring. It is primarily used in the synthesis of diphenylmethane diisocyanate. MDA has a melting point of approximately 90°C. The urea groups formed by the reaction of MDA with NCO groups can form strong hydrogen bonds, resulting in high strength and heat resistance in polyurethane elastomers extended with these aromatic diamines.

[0004] Because the primary amino groups on the benzene rings of MDA are unhindered, they are highly reactive with NCO-terminated aromatic polyurethane prepolymers (hereinafter referred to as polyurethane prepolymers). If molten hot MDA is added to the polyurethane prepolymer, it will not have enough time to mix evenly, resulting in gelation in a short period of time. At room temperature, the gelation time of MDA dissolved in a medium (solvent, plasticizer, polyether polyol, etc.) with the polyurethane prepolymer is relatively short. If the prepolymer has a high NCO content, there will be no time for even mixing or pouring. If MDA powder is added to the hot polyurethane prepolymer, the surface layer will react with the prepolymer, releasing heat and causing the MDA to melt. If the prepolymer temperature is high or the NCO content is high, gelation can take anywhere from a few seconds to tens of seconds.

[0005] Chen Lilin and others from Sichuan University introduced a method for passivating the surface of MDA particles in the research paper "Preparation and Performance Research of Physical Surface Coated MDA and Polyurethane Elastomers" (see "Polyurethane Industry" Issue 5, 2019). The key points are to mix granular MDA and water in a mass ratio of 1:1, grind the obtained paste MDA on a ball mill for 24 hours, and then stir it evenly with polyvinyl pyrrolidone (PVP) powder not exceeding 10% of the MDA mass at room temperature. The PVP is dissolved and coated on the surface of the MDA particles. The mixture is vacuum dried at 45°C, and the non-agglomerated modified MDA sample is screened out. It is evenly mixed with the polyurethane prepolymer with a chain extension coefficient of 0.8 and reacted at 100°C to obtain a polyurethane urea elastomer.

[0006] Chen Ligui of Shaanxi University of Science and Technology, in "Acetylation Modification of MDA and Its Effect on the Properties of Synthetic Polyurea" (Guangzhou Chemical Industry, Issue 20, 2011), describes adding a mixture of glacial acetic acid and a small amount of phosphoric acid to molten MDA at a mass ratio of 3:1 at 120°C. The mixture is then heated at 120°C and refluxed for 8 hours. The generated water is evaporated and then refluxed. After a period of stagnation, the product is ground, washed, filtered, and thoroughly dried to obtain the diacetylated MDA. This bisamide chain extender can undergo a chain extension and curing reaction with MDI prepolymers, significantly delaying the gel time compared to pure MDA (from 45 seconds to 143 seconds). However, this method has disadvantages such as high reaction temperature and long reaction time, a melting point of the product well above 90°C, and a low yield. Summary of the Invention

[0007] The purpose of the present invention is to provide a polyurethane chain extender and application thereof.

[0008] To achieve the above-mentioned and other related objectives, the present invention provides a technical solution: a polyurethane chain extender, wherein the polyurethane chain extender is an aromatic diamine powder that reacts with gaseous acetyl chloride to amidate one or two amino groups of the aromatic diamine molecules on the surface of the aromatic diamine powder to generate a mixture of partially diacetylated products and partially monoacetylated products, wherein the aromatic diamine powder has a particle size of 20 to 800 microns.

[0009] The preferred technical solution is: the aromatic diamine powder is diphenylmethanediamine powder with a particle size of 50-500 microns.

[0010] The preferred technical solution is: the mass of the acetyl chloride is 0.5-2.2% of the mass of the aromatic diamine powder.

[0011] The preferred technical solution is: the mass of the acetyl chloride is 0.7-2% of the mass of the aromatic diamine powder.

[0012] The preferred technical solution comprises: a reaction vessel, an exhaust port of the reaction vessel being connected to an air inlet of a rotary drum reactor via a pipeline; pre-displacing the air in the rotary drum reactor with nitrogen, adding aromatic diamine powder into the rotary drum reactor, and starting the rotary drum reactor to rotate; heating acetyl chloride in the reaction vessel to obtain gaseous acetyl chloride, introducing the gaseous acetyl chloride into the rotary drum reactor using nitrogen as a carrier, maintaining the temperature in the rotary drum reactor at 40-65° C. After the acetyl chloride is introduced, nitrogen is stopped, the rotary drum reactor continues to rotate, and nitrogen is then introduced into the rotary drum reactor for 0.5-1 hour to drive away residual acetyl chloride or hydrogen chloride, until the nitrogen flow no longer turns a wet pH test paper red, thereby terminating the reaction, and discharging the material after cooling.

[0013] The preferred technical solution is: during the reaction process, when nitrogen is used as a carrier, the nitrogen flow rate is 50 to 150 ml / min; when nitrogen is introduced into the rotary drum reactor to drive away residual acetyl chloride or hydrogen chloride, the nitrogen flow rate is 0.2 to 1 liter / min.

[0014] The preferred technical solution is: the rotation rate of the rotary drum reactor is 10 to 60 revolutions per minute.

[0015] To achieve the above-mentioned and other related purposes, the present invention provides a technical solution: application of a polyurethane chain extender in the preparation of polyurethane urea or polyurea.

[0016] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0017] The surface-passivated modified MDA obtained by this invention can be used in heat-curing polyurethane systems, including polyurethane adhesives and cast elastomers. MDA has a relative density of approximately 1.15, similar to the relative density of polyurethane prepolymers (1.1-1.2). When mixed with prepolymers, the passivated MDA powder curing agent does not significantly settle or float in high-viscosity mixtures. It also reacts slowly or even inactively at room temperature, significantly extending the room-temperature operating time. It can even be used to formulate single-component polyurethane systems that can be cured by heating to 90-110°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the reaction apparatus.

[0019] In the above figures, 1, reaction vessel; 2, stirring device; 3, rotary drum reactor; 4, jacket; 5, second alkali liquid tank; 6, first alkali liquid tank; 7, acetic acid tank. DETAILED DESCRIPTION

[0020] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in these embodiments.

[0021] See also Figure 1 . It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they have no technical substantive significance. Any modification of the structure, change in the proportional relationship or adjustment of the size. The following examples are provided for a better understanding of the present invention, but are not intended to limit the present invention. The experimental methods in the following examples are all conventional methods unless otherwise specified. The experimental materials used in the following examples are all purchased from conventional biochemical reagent stores unless otherwise specified.

[0022] Unless otherwise specified, the reagents or materials described in the following examples are commercially available.

[0023] Example 1: A polyurethane chain extender and its application

[0024] A 5L stainless steel drum reactor with heating was filled with nitrogen to displace the air. 2kg of diphenylmethanediamine (MDA) with a particle size of approximately 200 microns (80 mesh) was added. The motor was turned on, rotating the reactor at 25 rpm to keep the powder in motion. Heating was then started to an internal temperature of 50°C.

[0025] 25g of acetyl chloride was added to a 100mL four-necked reaction flask equipped with a stirrer, thermometer, nitrogen inlet, and gas outlet. The mixture was heated to approximately 30-45°C and nitrogen was introduced at a flow rate of 80 mL / min. The nitrogen gas introduced the highly volatile acetyl chloride through the hollow channel of the rotating shaft and into the rotary drum reactor. The acetyl chloride volatilized completely within 0.5-1 hour. The nitrogen flow was then stopped, and the mixture was rotated and mixed for 0.5 hour. Nitrogen flow was then continued for another hour, until the exhaust gas no longer turned wet pH paper red. The mixture was then cooled to below 40°C and discharged. The resulting modified MDA powder (labeled AMDA1) had an MDA weight gain of approximately 0.45% and an average amine value of approximately 557 mgKOH / g, as determined by titration.

[0026] Example 2: A polyurethane chain extender and its application

[0027] The raw material amounts, MDA particle size, and reaction conditions were essentially the same as in Example 1, except that the reactor temperature was changed to 60±2°C. The resulting acetylated MDA powder (labeled as AMDA2) had an MDA weight gain of approximately 0.49% and an average amine value of approximately 556 mgKOH / g, as determined by titration.

[0028] Example 3: A polyurethane chain extender and its application

[0029] The reaction conditions were essentially the same as in Example 1. The MDA particle size was 0.40-0.45 mm (45-40 mesh), and 16 g of acetyl chloride was used. The resulting acetylated MDA powder (labeled as AMDA3) had an MDA weight gain of approximately 0.31% and an average amine value of approximately 560 mgKOH / g, as determined by titration.

[0030] Example 4: A polyurethane chain extender and its application

[0031] The reaction conditions were essentially the same as those in Example 1. 2 kg of MDA with a particle size of 100-200 μm and 40 g of acetyl chloride were used to obtain acetylated MDA powder (labeled as AMDA4). The MDA weight gain was approximately 0.72%, and the average amine value determined by titration was 553 mgKOH / g.

[0032] Example 5 (application example):

[0033] Take 50g of PPG-TDI prepolymer with an NCO mass fraction of 5.0%, preheat it to a certain temperature, and add weighed pure MDA, AMDA1, AMDA2, AMDA3 and AMDA4 powder (about 5.33g) according to the chain extension coefficient of 0.9, stir evenly, and keep stirring. The results show that:

[0034] (1) The prepolymer was preheated to 50°C. The composition using pure MDA powder as the curing agent increased in viscosity within 30 seconds and gelled within about 50 seconds. The cured compositions of the passivation-modified products of Examples 1 to 4 were basically stable within 2 minutes and could be stirred evenly. The viscosity of the AMDA3 composition began to increase after 2 minutes and gelled in 5 minutes. The viscosity of the AMDA1 and AMDA2 compositions increased slightly, and the curing was slow in the early stage. The viscosity increased significantly in 6-7 minutes and gelled in about 10 minutes of mixing. There was no significant change in the AMDA4 composition within 0.5 hours. When heated to 90-95°C, the viscosity increased rapidly and gelled.

[0035] (2) The prepolymer was preheated to 80°C and stirred continuously. The viscosity of the pure MDA-prepolymer composition increased rapidly and gelled in 20-25 seconds. The viscosity of the AMDA1 and AMDA2 compositions increased slowly in the early stage of the stirring process and then accelerated in the later stage, gelling in 3-4 minutes. The AMDA3 composition could be stirred evenly within 30 seconds and gelled in about 2 minutes. The AMDA4 composition gelled in about 6 minutes. The cured product was strong and tough.

[0036] Example 6: A polyurethane chain extender and its application

[0037] A method for passivating and modifying the powder surface of highly active aromatic diamine MDA reduces the reactivity of MDA molecules on the surface of MDA particles while substantially retaining the molecular structure of most of the MDA particles, thereby allowing sufficient operating time for the MDA particles to react with polyurethane prepolymers for curing.

[0038] The present invention reacts MDA powder with vapor-phase acetyl chloride to amidate one or two amino groups on the surface of the MDA molecules, producing surface-passivated MDA particles with a thin skin layer that has a higher melting point than the MDA within. The acetylation-modified MDA particles significantly reduce their reactivity with aromatic isocyanate groups, allowing sufficient time for mixing with a warm prepolymer. The MDA particles melt in the later stages of the reaction and quickly solidify into a gel. This method allows MDA to be used in the curing of polyurethane prepolymers, resulting in high-strength polyurethaneurea elastomers.

[0039] Acetyl chloride, also known as chloroacetyl, is a highly volatile, colorless, transparent liquid with a boiling point of approximately 51°C and a saturated vapor pressure of 32 kPa at 20°C. It is a commonly used, highly active acetylation agent. However, it is highly irritating, so safety precautions and leak prevention are required during use. Because it readily hydrolyzes in contact with moisture to produce hydrogen chloride, it should be kept away from air. The MDA powder used in this invention should be virtually moisture-free.

[0040] If both amino groups of MDA are acetylated, the resulting diacetylated MDA product has a much higher melting point than MDA. However, the present invention aims to allow only a portion of the primary amino groups on the particle surface to participate in the reaction. Due to the strong hydrogen bonding of the amide groups, even a small amount of amidation can increase the melting point of the surface layer to a certain extent. This results in a thin layer of surface layer with a higher melting point and lower reactivity, which increases the barrier to the reaction between the MDA bulk and the prepolymer.

[0041] The indicative reaction formula for the acylation reaction of MDA with acetyl chloride is shown in reaction formula (I):

[0042] (I)

[0043] Acetyl chloride is highly reactive with amino groups. Excessive use of acetyl chloride can easily generate diacetylated MDA. The high melting point of diacetylated MDA increases the surface melting point of the particles, increasing their temperature resistance. This delays the melting reaction of the particles in the prepolymer below 100°C. At higher temperatures, it also hinders the contact reaction between the molten MDA liquid inside and the polyurethane prepolymer, potentially hindering curing. Therefore, it is important to control the amount of acetyl chloride used to prevent the generation of excessive diacetylated MDA.

[0044] Because amino groups are easily oxidized by air, nitrogen is used for protection, and nitrogen can also act as a carrier gas.

[0045] Although a gas-solid heterogeneous reaction can be carried out in a conventional three-necked flask under stirring, the uniformity is poor. The present invention uses a rotary drum reactor as the reaction vessel, reacting ground and sieved MDA powder with gaseous acetyl chloride at a temperature below the melting point of MDA. Alkaline MDA has an adsorption effect on acetyl chloride, which facilitates the reaction.

[0046] Since the melting point of the MDA acylation product is higher than that of MDA, the MDA powder particles will not agglomerate or clump during the continuous rotation mixing process.

[0047] The schematic diagram of the reaction device is shown in Figure 1 The invention relates to a rotary drum reactor 3, comprising a reaction vessel 1, which can be a three-necked flask as shown in the figure, with a stirring device 2 sealed and inserted into the middle opening. The air inlet is sealed and connected to a nitrogen inlet pipe, and the exhaust port is sealed and connected to a gas-phase acetyl chloride exhaust pipe. The gas-phase acetyl chloride exhaust pipe is connected to the air inlet of a rotary drum reactor. The rotary drum reactor 3 includes a reaction chamber, which is rotatably supported on a bracket and connected to a motor drive to drive its rotation. In order to provide heat to the material in the reaction chamber, a jacket 4 can be provided outside the reaction chamber; the exhaust port of the rotary drum reactor is connected to the acetic acid tank 7, the first alkali liquid tank 6, and the second alkali liquid tank 5 through pipelines in sequence.

[0048] Passivation reaction steps: First, replace the air in the reactor with nitrogen. Add MDA powder and maintain a rotating mixing state. Warm acetyl chloride in the reaction flask. Using low-pressure, low-velocity nitrogen as a carrier, slowly and continuously (or intermittently) introduce acetyl chloride into the rotary drum reactor through the hollow channel of the reactor shaft over 0.5-1 hour. Maintain the reactor temperature at 40-65°C for the reaction. After the acetyl chloride is introduced, stop the nitrogen flow and continue rotating mixing for 0.5 hour. Then, at a temperature of approximately 60°C, introduce nitrogen at a low rate for 0.5-1 hour to displace any residual acetyl chloride or hydrogen chloride until the nitrogen flow no longer turns damp pH paper red. The reaction is terminated, cooled, and discharged. The total reaction time is 1-2 hours.

[0049] In this embodiment, acetyl chloride was slowly and continuously introduced into a rotary drum reactor over 0.8 hours through the hollow passage of the reactor shaft using low-pressure, low-velocity nitrogen as a carrier. The reaction was conducted while maintaining the reactor temperature at 55°C. After the acetyl chloride was introduced, the nitrogen flow was stopped and rotary mixing was continued for 0.5 hours. Nitrogen was then introduced at a lower rate for 0.7 hours at a reactor temperature of approximately 60°C to remove any residual acetyl chloride or hydrogen chloride. The reaction was terminated, cooled, and discharged until the nitrogen flow no longer caused moist pH test paper to turn red. The total reaction time was 1.5 hours.

[0050] The nitrogen flow rate during the reaction process is 50 to 150 ml / min. The nitrogen flow rate in the later non-reactive stage can be controlled at 0.2 to 1 liter / min, which can be slow at first and then fast. In the present embodiment, the nitrogen flow rate during the reaction process is 100 ml / min. The nitrogen flow rate in the later non-reactive stage can be controlled at 0.6 liter / min, which can be slow at first and then fast.

[0051] The tail gas pipe outlet is passed into glacial acetic acid below the liquid surface to absorb and dissolve the residual acetyl chloride gas. The acetic acid containing acetyl chloride can be used to continue the acetylation reaction.

[0052] The hydrogen chloride gas produced by the reaction is then fed into a sodium hydroxide solution for absorption. After 1 to 2 liquid caustic soda tanks, the gas that does not turn a moist pH test paper red can be emptied. In the present embodiment, two liquid caustic soda tanks are specifically selected for use.

[0053] The reactor rotation speed can be 10 to 60 rpm, preferably 20 to 30 rpm. In this embodiment, the reactor rotation speed is 25 rpm.

[0054] The particle size of MDA is in the range of 20 to 800 microns, preferably 50 to 500 microns. The fineness of the raw MDA and acetylated modified MDA powder can be graded according to the specific application to keep the particle size within a relatively narrow range, such as 100 to 200 microns. In this embodiment, the particle size of MDA is 100 to 200 microns.

[0055] The amount of acetyl chloride used is in the range of 0.5% to 2.2% of the weight of the MDA powder, preferably 0.7% to 2%. If the amount of acetyl chloride exceeds 2%, the acetylation of the surface of the powder will reach saturation and the weight gain rate will increase slowly. In this embodiment, the amount of acetyl chloride used is in the range of 1.3% of the weight of the MDA powder.

[0056] In addition to controlling the reaction rate by controlling the amount and rate of acetyl chloride, the degree of acetylation can be roughly calculated by the rate of mass gain after the reaction or by measuring the amine value of the remaining amino groups. The molar mass of MDA is 198.3 g / mol. The molar mass of monoacetylated MDA (AMDA) produced by the reaction of one MDA molecule with one molecule of acetyl chloride is 240.3 g / mol. This means that if one amino group in an MDA molecule is acetylated, the molar mass increases by 42.0 g / mol, resulting in a theoretical weight gain of 21.2%. Because the reaction is limited to the surface of the powder particles, relatively little MDA actually participates in the reaction, while the MDA within the particles does not. Therefore, the reaction degree calculated based on the overall MDA is relatively low, resulting in a lower MDA weight gain and a slightly lower amine value than that of the starting MDA. As mentioned above, the acetylamino groups produced by amidation also react with NCO groups, but in small amounts. The overall average molecular weight of the product is similar to that of MDA, and can be used as a metric for polyurethane synthesis.

[0057] The above description is only used to explain the preferred embodiments of the present invention and is not intended to limit the present invention in any form. Therefore, any modifications or changes made to the present invention under the same inventive spirit should still be included in the scope of protection intended by the present invention.

Claims

1. A polyurethane chain extender, characterized in that: The polyurethane chain extender is a mixture of diphenylmethanediamine powder particles reacting with gaseous acetyl chloride to amidate one or two amino groups of aromatic diamine molecules on the surface of the diphenylmethanediamine powder particles to generate a mixture of partially diacetylated products and partially monoacetylated products. The particle size of the diphenylmethanediamine powder particles is 20-800 microns.

2. The polyurethane chain extender according to claim 1, wherein: The particle size of the diphenylmethanediamine powder is 50-500 microns.

3. The polyurethane chain extender according to claim 1, wherein: The mass of the gaseous acetyl chloride is 0.5-2.2% of the mass of the diphenylmethanediamine powder.

4. The polyurethane chain extender according to claim 3, wherein: The mass of the gaseous acetyl chloride is 0.7-2% of the mass of the diphenylmethanediamine powder.

5. Use of the polyurethane chain extender according to any one of claims 1 to 4 in the preparation of polyurethane urea or polyurea.

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