Preparation method of low-free 4, 4 '-MDI type NCO-terminated prepolymer

Abstract

The invention discloses a preparation method of a low-free 4, 4 '-MDI type NCO-terminated prepolymer, which comprises the following steps: (1) adding polyether polyol, a plasticizer and 4, 4'-MDI, and reacting in the absence of a catalyst; (2) when the molar weight of OH in the reaction system is consumed by 35%-50%, adding a composite catalyst to continue the reaction; (3) when the NCO% content reaches a theoretical value, adding a stabilizer, uniformly mixing, and discharging; the composite catalyst is a mixture of an organic amine compound and an organic metal compound. The prepolymer synthesized by adopting the preparation method disclosed by the invention has relatively low viscosity and low MDI monomer content.

Description

Technical Field

[0001] The present invention relates to polyurethane prepolymers, and particularly to a method for preparing a prepolymer capped with NCO of low-free 4,4'-MDI type. Background Art

[0002] ‌The prepolymer method, semi-prepolymer method, and one-step method are three main methods in polyurethane production. The prepolymer method‌ involves first preparing a prepolymer with terminal isocyanate groups by reacting an excessive amount of isocyanate with a polyol polymer, and it has a wide range of applications in application fields such as polyurethane coatings, adhesives, elastomers, and foams. The polyurethane molecular chain segments prepared by the prepolymer method‌ are arranged relatively regularly, and it has obvious advantages in improving product quality and product performance.

[0003] Conventional MDI-type prepolymers generally contain about 5%wt of free MDI monomer. Although MDI has a low saturated vapor pressure, the residual MDI monomer still affects the performance of the elastomer. Currently, the methods for reducing free isocyanate in China mainly include chemical treatment methods (direct synthesis method and catalytic polymerization method) and physical treatment methods.

[0004] The direct synthesis method is to make the isocyanate monomer almost completely converted into the target product through precise formulation design and reasonable process control to achieve the purpose of reducing free isocyanate. A low-viscosity polyurethane prepolymer based on 2,4'-MDI disclosed in CN1724576A can reduce the monomer content to below 0.1%wt in the presence of a catalyst by utilizing the asymmetry of 2,4'-MDI. However, for the 4,4'-MDI-type prepolymer prepared by the same process, it has a high viscosity and a high free monomer content (above 1.4%wt). Therefore, this process is only limited to the synthesis of 2,4'-MDI prepolymers with low viscosity and low monomer content.

[0005] The catalytic polymerization method is to add a highly selective isocyanate self-polymerization catalyst in the later stage of the synthesis reaction to self-polymerize the unreacted free isocyanate into a polyisocyanate high polymer to achieve the purpose of reducing free isocyanate. CN101307127B discloses a method for reducing residual MDI in prepolymers. After the prepolymerization reaction is completed, 0.1% - 0.3% by mass of the theoretical remaining MDI of the trimerization catalyst tributylphosphine is added and the reaction continues, and then benzoyl chloride inhibitor is added to terminate the reaction. Finally, the free MDI mass fraction in the prepared prepolymer is reduced from 1.2% to 0.9%. The effect of this method is not obvious.

[0006] Physical treatment methods include molecular sieve absorption, azeotropic distillation, solvent extraction, ordinary vacuum distillation and thin film evaporation, and thin film evaporation is further divided into high vacuum scraper thin film evaporation and molecular distillation. CN1232555C discloses an MDI-based polyurethane prepolymer with low MDI monomer content. The patent adopts a high NCO / OH ratio (6~10:1, molar ratio), no catalyst, overnight reaction, and then vacuum distillation to remove free MDI to synthesize low free 4,4′-MDI type prepolymer. This method is complex and energy-intensive, and also involves the removal and recovery of excess isocyanate.

[0007] With the direct synthesis method, as the degree of reaction increases, a large number of prepolymers containing NCO groups exist in the system, the selectivity of the free monomer reaction becomes smaller, and the probability of the reaction between chains increases, resulting in a high content of free monomers that have not reacted completely and a high content of macromolecular prepolymers with a molecular weight exceeding the expected level. The apparent aspect is that the viscosity of the prepolymer increases significantly. Therefore, it is an urgent problem to develop a simple direct synthesis process to synthesize polyurethane prepolymers with low NCO content, high activity and low monomer content. Summary of the invention

[0008] In order to solve the problems existing in the prior art, the present invention provides a method for preparing a low-free 4,4′-MDI type NCO-terminated prepolymer. The prepolymer synthesized by the preparation method has lower viscosity and low MDI monomer content.

[0009] The technical solution of the present invention is as follows: A method for preparing a low-free 4,4′-MDI type NCO-terminated prepolymer comprises the following steps: (1) Add polyether polyol, plasticizer and 4,4′-MDI and react without catalyst; (2) When the molar amount of OH in the reaction system is consumed by 35% to 50%, the composite catalyst is added to continue the reaction; (3) When the NCO% content reaches the theoretical value, add stabilizer, mix evenly, and discharge; The composite catalyst is a mixture of an organic amine compound and an organic metal compound.

[0010] The room temperature viscosity of the prepolymer is low, and the free isocyanate monomer content is not higher than 0.5%wt.

[0011] The molar ratio of OH in the polyether polyol to NCO in 4,4′-MDI is selected from 0.35 to 0.65.

[0012] The polyether polyol described above is selected from one or more of polyethylene oxide polyol (PEG), polypropylene oxide polyol (PPG), and polytetrahydrofuran polyol (PTMG). The molecular weight of the polyether polyol is preferably 2000 to 20000. Polypropylene oxide polyol capped with ethylene oxide (PPG-PEG) is preferably used, and particularly preferably a polypropylene glycol, a polypropylene triol, or a combination of the two within the range of number average molecular weight of 2000 to 8000.

[0013] The plasticizer is one or more compositions of chlorinated paraffin, organic carboxylic acid ester, phenyl alkylsulfonate, and propylene carbonate. The dosage of the plasticizer is 10% to 15% of the mass of the prepolymer. The plasticizer is preferably an organic carboxylic acid ester, and the dosage of the plasticizer is preferably 10% to 12% of the mass of the prepolymer.

[0014] The 4,4′-MDI preferably has a 4,4 '-MDI content of ≥95%, and more preferably 4,4 '-MDI ≥97.5%.

[0015] The organic amine catalyst is preferably a tertiary amino compound, such as 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), N-alkylmorpholine, N,N'-dimethylpiperazine, 4-dimethylaminopyridine, N-methylimidazole, N-vinylimidazole, or 1,2-dimethylimidazole; the organometallic catalyst is preferably one or more of organotin, organobismuth, organolead, organozinc, and organomercury. The dosage of the composite catalyst is preferably 0.001% to 0.003% of the mass of the prepolymer, and the mass ratio of the organometallic compound to the organic amine is preferably 1:5 to 10.

[0016] The stabilizer includes one or more of organic acids, inorganic acids, or acyl chlorides. The inorganic acids are such as hydrochloric acid, sulfuric acid, phosphoric acid, or their derivatives, the organic acids are such as formic acid, acetic acid, or other alkanoic acids, and the acyl chlorides are such as formyl chloride, acetyl chloride, propionyl chloride, and benzoyl chloride. The dosage of the stabilizer is preferably 0.02% to 0.05% of the mass of the prepolymer.

[0017] The NCO% of the prepolymer ranges between 1.0% and 3.0%, preferably 1.6% to 2.5%.

[0018] In the step (1), the polyether polyol and the plasticizer are dehydrated before use until the water content is less than 500 ppm. The dehydration process can specifically be that, under stirring conditions, the temperature is raised to 100 °C - 110 °C, the vacuum pump is turned on, and dehydration is carried out for 2 - 3 h.

[0019] In the step (1), the reaction temperature is preferably 75 ºC to 80 ºC, and the reaction time is preferably 2 h to 4 h.

[0020] In the step (2), the reaction temperature is preferably 75 ºC to 80 ºC, and the reaction time is preferably 30 min to 60 min.

[0021] Through the stepwise reaction and the application of the composite catalyst, the present invention effectively reduces the probability of intermolecular reaction of the polyurethane prepolymer, thereby achieving the effects of controlling the molecular weight distribution of the polyurethane prepolymer and reducing the content of free isocyanate. Compared with the prior art, the present invention has the following advantages: (1) The 4,4′-MDI type NCO-terminated prepolymer has a low room temperature viscosity; (2) The content of free isocyanate monomer in the 4,4′-MDI type NCO-terminated prepolymer is not higher than 0.5%wt; (3) The synthesis process of the 4,4′-MDI type NCO-terminated prepolymer is simple and the operation is convenient. Specific embodiments

[0022] The embodiments of the present invention are as follows, but are not limited thereto.

[0023] Example 1

[0024] Add 300 g of polyether 3600 (OH: 28 mgKOH / g, f = 3), 200 g of polyether DL4000D (OH: 28mgKOH / g, f = 2), and 62.4 g of diisodecyl phthalate (DIDP) into the reaction flask, dehydrate at 100 °C to 110 °C for 2 h, cool down to 70 °C, add 61.3 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 75 °C to 80 °C for 2 h, add 0.016 g of composite catalyst (dibutyltin dilaurate / dimorpholine diethyl ether = 1:8), continue to react for 1 h, test the NCO% to be 1.68% (the theoretical NCO% is 1.62%), add 0.13 g of benzoyl chloride, stir evenly, discharge, and store in a sealed manner.

[0025] Example 2

[0026] Add 300 g of polyether EP3600 (OH: 28 mg KOH / g, f = 3), 200 g of polyether TED28 (OH: 28 mg KOH / g, f = 2), and 76.6 g of diisononyl phthalate (DINP) into the reaction flask. Dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, add 62.0 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 75 °C - 80 °C for 4 h, add 0.008 g of a composite catalyst (dibutyltin dilaurate / dimorpholine diethyl ether = 1:10), continue to react for 1 h, test that the NCO% is 1.67% (the theoretical NCO% is 1.62 %), add 0.13 g of phosphoric acid, stir evenly, discharge, and store in a sealed manner.

[0027] Example 3

[0028] Add 300 g of polyether 2802 (OH: 28 mg KOH / g, f = 3), 100 g of polyether DL2000D (OH: 56 mg KOH / g, f = 2), and 50.9 g of phenyl alkylsulfonate (T50) into the reaction flask. Dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, add 58.5 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 75 °C - 80 °C for 4 h, add 0.013 g of a composite catalyst (dibutyltin dilaurate / N-vinylmorpholine = 1:8), continue to react for 1 h, test that the NCO% is 2.01% (the theoretical NCO% is 2.06 %), add 0.13 g of acetyl chloride, stir evenly, discharge, and store in a sealed manner.

[0029] Example 4

[0030] Add 300 g of polyether 2802 (OH: 28 mg KOH / g, f = 3), 200 g of polyether DL4000D (OH: 28 mg KOH / g, f = 2), and 64.2 g of phenyl alkylsulfonate (T50) into the reaction flask. Dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, add 77.8 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 75 °C - 80 °C for 4 h, add 0.018 g of a composite catalyst (dibutyltin dilaurate / N-vinylmorpholine = 1:10), continue to react for 1 h, test that the NCO% is 2.47% (the theoretical NCO% is 2.43 %), add 0.33 g of phosphoric acid, stir evenly, discharge, and store in a sealed manner.

[0031] Example 5

[0032] Add 350 g of polyether TEP240 (OH: 24 mg KOH / g, f = 3), 200 g of polyether TED28 (OH: 28 mg KOH / g, f = 2), and 68.2 g of diisononyl phthalate (DINP) into the reaction flask. Dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, add 64.2 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 75 °C - 80 °C for 3 h, add 0.018 g of a composite catalyst (bismuth isooctanoate / dimorpholine diethyl ether = 1:5), continue to react for 1 h, test the NCO% to be 1.73% (the theoretical NCO% is 1.62%), add 0.13 g of benzoyl chloride, stir evenly, discharge, and store in a sealed manner.

[0033] Example 6

[0034] Add 350 g of polyether TEP240 (OH: 24 mg KOH / g, f = 3) and 42.6 g of diisononyl phthalate (DINP) into the reaction flask. Dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, add 33 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 75 °C - 80 °C for 3 h, add 0.010 g of a composite catalyst (bismuth isooctanoate / N-vinylmorpholine = 1:5), continue to react for 1 h, test the NCO% to be 1.65% (the theoretical NCO% is 1.62%), add 0.13 g of benzoyl chloride, stir evenly, discharge, and store in a sealed manner.

[0035] Example 7

[0036] Add 480 g of polyether 330N (OH: 35 mg KOH / g, f = 3), 200 g of polyether DL4000D (OH: 56 mg KOH / g, f = 2), and 87.2 g of phenyl alkylsulfonate (T50) into the reaction flask. Dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, add 104.5 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 70 °C - 75 °C for 3 h, add 0.12 g of a composite catalyst (T12 / DBU = 1:10), continue to react for 1 h, measure the NCO% to be 1.75 (the theoretical NCO% is 1.62), add 0.13 g of benzoyl chloride, stir evenly, discharge, and store in a sealed manner to obtain pre-7.

[0037] Comparative Example 1 Add 300 g of polyether 3600 (OH: 28 mg KOH / g, f = 3), 200 g of polyether DL4000D (OH: 28 mg KOH / g, f = 2), and 62.4 g of diisodecyl phthalate (DIDP) into the reaction flask. Dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, add 61.3 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 75 °C - 80 °C for 2 h, add 0.016 g of a composite catalyst (bismuth isooctanoate / N-vinylmorpholine = 1:2), continue to react for 1 h, test the NCO% to be 1.61% (theoretical NCO% is 1.62%), add 0.33 g of phosphoric acid, stir evenly, discharge the material, and store it sealed.

[0038] Comparative Example 2 Add 300 g of polyether 3600 (OH: 28 mg KOH / g, f = 3), 200 g of polyether DL4000D (OH: 28 mg KOH / g, f = 2), and 62.4 g of diisononyl phthalate (DINP) into the reaction flask. Dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, add 61.3 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 75 °C - 80 °C for 2 h, add 0.016 g of a composite catalyst (dibutyltin dilaurate / N-vinylmorpholine = 1:15), continue to react for 1 h, test the NCO% to be 1.99% (theoretical NCO% is 1.62%), add 0.33 g of phosphoric acid, stir evenly, discharge the material, and store it sealed.

[0039] Comparative Example 3 Add 300 g of polyether 2802 (OH: 28 mg KOH / g, f = 3), 200 g of polyether DL4000D (OH: 28 mg KOH / g, f = 2), and 62.4 g of diisodecyl phthalate (DIDP) into the reaction flask. Dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, add 61.3 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), react at 75 °C - 80 °C for 5 h (OH consumption is 58.5%), add 0.008 g of a composite catalyst (dibutyltin dilaurate / diethyl ether of dimorpholine = 1:8), continue to react for 1 h, test the NCO% to be 1.63% (theoretical NCO% is 1.62%), add 0.13 g of benzoyl chloride, stir evenly, discharge the material, and store it sealed.

[0040] Comparative Example 4 (low free synthesis process) Add 300 g of polyether 2802 (OH: 28 mg KOH / g, f = 3) to the reaction flask, dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, design the NCO / OH ratio to be 8:1 (molar ratio), add 150 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), 0.036 g of dibutyltin dilaurate, react at 75 °C - 80 °C for 3 h, and remove the free MDI monomer through a thin-film evaporator to obtain a 4,4′-MDI-polyether triol prepolymer with an NCO% of 1.97%.

[0041] Similarly, add 200 g of polyether DL4000D (OH: 28 mg KOH / g, f = 2) to the reaction flask, dehydrate at 100 °C - 110 °C for 2 h, cool down to 70 °C, design the NCO / OH ratio to be 8:1 (molar ratio), add 100 g of diphenylmethane diisocyanate (4,4′-MDI ≥ 99%), 0.025 g of dibutyltin dilaurate, react at 75 °C - 80 °C for 3 h, and remove the free MDI monomer through a thin-film evaporator to obtain a 4,4′-MDI-polyether diol prepolymer with an NCO% of 1.87%.

[0042] Mix the two prepolymers and add 10% of the total mass of the plasticizer DIDP, mix evenly to obtain a mixed 4,4′-MDI polyether prepolymer.

[0043] Performance testing: The NCO content is determined according to GB / T12009.4 - 1989; The viscosity is determined according to GB / T12008.7 - 2010, and the measurement temperature is 25 °C; The content of free diisocyanate monomer is detected by gel permeation chromatography.

[0044] The test results of the examples and comparative examples are shown in the following table:

[0045] From the data of Examples 1 to 7, it can be seen that by using this process, the free monomer content of the synthesized low-NCO prepolymer can be controlled within 0.5%. Comparative Example 1 and Comparative Example 2 show that when there is too much organotin catalyst or too much amine catalyst, the viscosity of the prepolymer is too high or the reaction cannot proceed completely, and the free monomer content is relatively high. Examples 1 and 2 and Comparative Example 3 illustrate that this process requires selecting the appropriate addition time of the catalyst according to the reaction progress. When the consumption of hydroxyl groups in the system exceeds 50%, the intermolecular reaction increases, the viscosity of the prepolymer increases, and the free monomer content also increases accordingly. Comparative Example 4 uses a low-free synthesis process and removes the excess isocyanate monomer by means of thin-film evaporation. Although the monomer content is low, the reaction does not proceed completely and the process is complex.

Claims

1. A method for preparing a low-free 4,4′-MDI type NCO-terminated prepolymer, comprising the following steps: (1) Add polyether polyol, plasticizer and 4,4′-MDI and react without catalyst; (2) When the molar amount of OH in the reaction system is consumed by 35% to 50%, the composite catalyst is added to continue the reaction; (3) When the NCO% content reaches the theoretical value, add stabilizer, mix evenly, and discharge; The composite catalyst is a mixture of an organic amine compound and an organic metal compound.

2. The preparation method according to claim 1, characterized in that: The free isocyanate monomer content of the prepolymer is not higher than 0.5%wt.

3. The preparation method according to claim 1, characterized in that The molar ratio of OH in the polyether polyol to NCO in 4,4′-MDI is selected from 0.35 to 0.

65.

4. The preparation method according to claim 1, characterized in that: The polyether polyol is selected from one or more of polyethylene oxide polyol (PEG), polypropylene oxide polyol (PPG), and polytetramethylene glycol (PTMG).

5. The preparation method according to claim 1, characterized in that: The plasticizer is one or more combinations of chlorinated paraffin, organic carboxylic acid ester, alkyl phenyl sulfonate and propylene carbonate.

6. The preparation method according to claim 1, characterized in that: The organic amine catalyst is a tertiary amino compound; the organic metal catalyst is preferably one or more of organic tin, organic bismuth, organic lead, organic zinc and organic mercury.

7. The preparation method according to claim 1, characterized in that: The mass ratio of the organometallic compound to the organic amine is preferably 1:5-10.

8. The preparation method according to claim 1, characterized in that: The stabilizer is selected from one or more of organic acids, inorganic acids or acid chlorides.

9. The preparation method according to claim 1, characterized in that The prepolymer NCO% ranges from 1.0% to 3.0%.

10. The preparation method according to claim 1, characterized in that In the step (1), the reaction temperature is 75 ºC to 80 ºC; in the step (2), the reaction temperature is 75 ºC to 80 ºC.

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