Method for reducing acid value of polycaprolactone polyol

Abstract

The invention belongs to the field of polymer synthesis, and particularly discloses a method for reducing the polyalcohol acid value of polycaprolactone, which comprises the following steps: carrying out first-stage polymerization on polyalcohol and epsilon-caprolactone in the presence of an organic tin compound under the pressure maintaining condition of a protective atmosphere, and then carrying out second-stage polymerization under the purging condition of the protective atmosphere, and the low-acid-value polycaprolactone polyol with the acid value of less than 0.35 mgKOH / g is prepared. The invention creatively provides a brand new thought for controlling the acid value of the polycaprolactone polyol through gas control, and the acid value of the polycaprolactone polyol can be controlled on the premise that raw materials, reaction conditions and processes are not required to be adjusted accidentally through combined cooperation of pressure-maintaining first-stage polymerization in a protective atmosphere and purging second-stage reaction in the protective atmosphere. Therefore, the acid value of the polycaprolactone polyol can be effectively and controllably controlled.

Description

Technical Field

[0001] The invention belongs to the technical field of polyester polyol synthesis, and particularly relates to the field of polycaprolactone polyol preparation. Background Art

[0002] Polycaprolactone polyols, such as the common polycaprolactone diol, have high reactivity, low viscosity, excellent gloss, and low water content. These products are primarily used in the production of polyurethane elastomers, coatings, and adhesives. However, during the synthesis of polycaprolactone polyurethanes, the acid value of the polycaprolactone diol affects its reactivity with diisocyanates, thereby affecting the product performance of the polycaprolactone polyurethane. The higher the acid value of the polycaprolactone diol, the lower its reactivity with diisocyanates, and the poorer the product performance of the polycaprolactone polyurethane. Conversely, the lower the acid value of the polycaprolactone diol, the less impact it has on the reaction with diisocyanates, and the better the product performance of the polycaprolactone polyurethane. Typically, the acid value (measured in KOH) of the polycaprolactone diol should be less than 0.35 mg KOH / g.

[0003] The current main approaches to addressing the acid value of polycaprolactone polyols are to refine the raw materials and optimize the control of catalysts. For example, Xiong Tao et al. synthesized polycaprolactone diol using hydroquinone dihydroxyethyl ether as an initiator, butyl titanate, and organobismuth as catalysts. They identified the optimal reaction conditions: organobismuth as a catalyst, a reaction temperature of 150°C, a reaction time of 5 hours, and a catalyst dosage of 0.1%. The reported acid value of the polycaprolactone diol ranged from 0.43 to 0.63 mgKOH / g. Another example is CN114752049A, an organotin alcohol catalyst, its preparation, and its application in the preparation of low-acid-value polycaprolactone diols.

[0004] In summary, although there are some acid value acidification control methods in the existing technology, most of them still have shortcomings such as high material cost, difficult to control acid value, and complex process. The industry has not yet found an idea or process based on reaction atmosphere regulation to reduce acid value and achieve adjustable and controllable acid value. Summary of the Invention

[0005] In view of the defects in the preparation of polycaprolactone polyols in the prior art, the object of the present invention is to provide a method for reducing the acid value of polycaprolactone polyols, aiming to control the acid value of polycaprolactone polyols based on a simple idea and method.

[0006] A method for reducing the acid value of polycaprolactone polyol comprises the following steps: subjecting polyol and ε-caprolactone to a first-stage polymerization in the presence of an organotin compound and a protective atmosphere under pressure, and then subjecting the polymer to a second-stage polymerization under the purge of the protective atmosphere, to produce a low-acid-value polycaprolactone polyol having an acid value below 0.35 mgKOH / g.

[0007] The present invention innovatively provides a new approach to controlling the acid value of polycaprolactone polyols by controlling the gas flow. This innovative approach utilizes a combined polymerization stage (maintaining pressure under a protective atmosphere) and a second stage (purging with a protective atmosphere) to effectively and controllably control the acid value of polycaprolactone polyols without requiring adjustments to the raw materials, reaction conditions, or process.

[0008] In the present invention, the polyol is an organic small molecule polyol with a molecular weight of 62 to 700 g / mol, and can further be any one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, glycerol, trimethylolpropane, and pentaerythritol.

[0009] In the present invention, the organotin compound is an organotin carboxylate. Conventional wisdom suggests that organotin carboxylates introduce a certain degree of acidity, but the present invention's innovative gas control method is also suitable for organotin carboxylates, still demonstrating excellent controllable acidity reduction.

[0010] In the present invention, the organotin compound is any one or more of stannous octoate, stannous acetate, and dibutyltin dilaurate.

[0011] In the present invention, at least one of the polyol, ε-caprolactone, and organotin compound is not pre-dehydrated. The method of the present invention does not require excessive refining of the raw materials, and thus can still achieve a good controllable acid value.

[0012] In the present invention, the amounts of polyol, ε-caprolactone, and organotin compound can be adjusted based on conventional reaction knowledge. For example, the molar ratio of ε-caprolactone to polyol is 1 to 100:1, further 3 to 70:1, and even further 5 to 20:1. The mass ratio of ε-caprolactone to organotin compound is 10,000:1 to 500:1, further 10,000:1 to 1,000:1.

[0013] In the present invention, the protective atmosphere is at least one of nitrogen and inert gas.

[0014] In the present invention, the pressure during the first stage polymerization is above 0.1 MPa, preferably 0.2 to 0.8 MPa.

[0015] In the present invention, the temperature of the first polymerization stage is 120-180°C, preferably 130-170°C;

[0016] Preferably, the first polymerization period is 3 to 8 hours.

[0017] In the present invention, the acid value of the first-stage polymerization system can be relatively high, for example, 0.5 to 2 mgKOH / g. Studies conducted by the present invention have shown that even with a relatively high acid value in the first-stage polymerization system, the acid value can still be effectively and controllably reduced by combining it with the subsequent second-stage polymerization process of the present invention.

[0018] In the present invention, the temperature of the second polymerization stage is 120 to 180°C, preferably 130 to 170°C.

[0019] In the present invention, the purge flow rate of the protective atmosphere in the second stage is 0.01m 3 / min or more, preferably 1m 3 / min or more, more preferably 1 to 13m 3 / min.

[0020] The present invention studies show that the purge time and the degree of reduction in acid value have a positive dependence, but considering the treatment efficiency, under normal circumstances, the treatment time of the second stage is more than 0.5h. Considering the treatment efficiency, it is preferably more than 2h, and more preferably 2 to 36h.

[0021] Beneficial effects

[0022] (1) The acid value of the final polycaprolactone diol product obtained is low, and can be within 0.35 mgKOH / g. Moreover, the acid value can be controlled by regulating the atmosphere. For example, the acid value of the polycaprolactone diol can be adjusted and controlled within the range of 0.01 to 0.35 mgKOH / g;

[0023] (2) The high acid value polycaprolactone diol can be further reduced in acid value to be converted into a low acid value polycaprolactone diol product, turning waste into treasure and improving economic benefits.

[0024] (3) The preparation of polycaprolactone diol has few steps, simple operation, low cost, and is suitable for large-scale production.

[0025] (4) The catalyst has high catalytic activity, a small amount of catalyst is required, and the resulting polycaprolactone diol is white in color. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the final product polycaprolactone diol obtained in Example 1.

[0027] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the final product polycaprolactone diol obtained in Example 2.

[0028] Figure 3 This is the hydrogen nuclear magnetic resonance spectrum of the final product polycaprolactone diol obtained in Example 3. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the following examples. This example is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process.

[0030] This invention is funded by the Science and Technology Innovation Program of Hunan Province, Project No. 2021RC3138.

[0031] The present invention provides a method for controlling the acid value of polycaprolactone polyol by controlling gas, which specifically includes a two-stage reaction process of pressure-maintaining reaction and atmosphere purging. The processing steps are, for example: under the conditions of 0.01-0.8 MPa nitrogen pressure, 120-180°C reaction temperature and organic tin compound catalysis, an organic small molecule polyol with a molecular weight of 62-700 g / mol initiates the ring-opening polymerization of ε-caprolactone to obtain a polycaprolactone polyol with an acid value of 0.5-2 mgKOH / g; then, under nitrogen purging conditions, the acid value of the polycaprolactone polyol gradually decreases, and the nitrogen flow rate during purging is 0.1-13 m 3 / min, nitrogen purge time 0.5 ~ 36h, and finally obtain the polycaprolactone polyol terminal product with an acid value of 0.01 ~ 0.35mgKOH / g.

[0032] As an example, the nitrogen holding pressure is 0.1-0.8 MPa, and the reaction temperature is 130-170°C.

[0033] As an illustrative embodiment, the organotin compound is an organotin carboxylate, more preferably any one or more of stannous octoate, stannous acetate, and dibutyltin dilaurate, and even more preferably stannous octoate with a purity of 99.45-99.99% and a stannous content of 27.30-29.30%.

[0034] As an illustrative embodiment, the organic small molecule polyol with a molecular weight of 62 to 700 g / mol is any one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, glycerol, trimethylolpropane, and pentaerythritol, and diethylene glycol is further selected.

[0035] As an example, the nitrogen flow rate during the purge is 1 to 13 m 3 / min.

[0036] As an illustrative embodiment, the nitrogen purge time is 2 to 36 hours.

[0037] In the present invention, the raw materials such as ε-caprolactone and diethylene glycol can be conventional commercial raw materials in the industry. For example, the water content of ε-caprolactone is 0.04% to 0.07%.

[0038] Example 1

[0039] Step (1):

[0040] 7000 g of ε-caprolactone, 996.02 g of diethylene glycol (DEG) and 0.71 g of stannous octoate (purity 99.45-99.99%, stannous content 27.30-29.30%) were respectively added to a polymerization reactor. After nitrogen replacement, the pressure was maintained at 0.5-0.8 MPa, the stirring speed was 56 r / min, the reaction temperature was 150-160°C, and the timing was started when the reaction temperature was reached.

[0041] First, the reaction was carried out under "nitrogen pressure" for 6 hours, and the acid value of the obtained polycaprolactone diol product was 0.98 mgKOH / g;

[0042] Step (2):

[0043] The polymerization reaction system was then purged with nitrogen (purging during the reaction).

[0044] At 12 h, the acid value of the product polycaprolactone diol was 0.41 mgKOH / g;

[0045] At 18 h, the acid value of the product polycaprolactone diol was 0.12 mgKOH / g;

[0046] The acid value of the final product polycaprolactone diol obtained after 24 hours is 0.04 mg mgKOH / g, and its H NMR spectrum is shown in the attached Figure 1 .

[0047] Example 2

[0048] 7200 g of ε-caprolactone, 896.4 g of diethylene glycol (DEG) and 0.79 g of stannous octoate (purity 99.45-99.99%, stannous content 27.30-29.30%) were respectively added to a polymerization reactor. After nitrogen replacement, the pressure was maintained at 0.5-0.8 MPa, the stirring speed was 56 r / min, the reaction temperature was 150-175°C, and the timing was started when the reaction temperature was reached.

[0049] First, the reaction was carried out under "nitrogen pressure" for 5 hours, and the acid value of the obtained polycaprolactone diol product was 1.53 mgKOH / g;

[0050] The polymerization reaction system was then purged with nitrogen (purging during the reaction).

[0051] At 10 h, the acid value of the product polycaprolactone diol was 0.71 mgKOH / g;

[0052] At 16.5 h, the acid value of the product polycaprolactone diol was 0.33 mgKOH / g;

[0053] At 22.5 h, the acid value of the product polycaprolactone diol was 0.17 mg mgKOH / g;

[0054] The acid value of the final product polycaprolactone diol obtained at 28.5h was 0.06mg mgKOH / g, and its H NMR spectrum is shown in the attached Figure 2 .

[0055] Example 3

[0056] 7000 g of ε-caprolactone, 470.12 g of diethylene glycol (DEG) and 0.72 g of stannous octoate (purity 99.45-99.99%, stannous content 27.30-29.30%) were respectively added to a polymerization reactor. After nitrogen replacement, the pressure was maintained at 0.5-0.8 MPa, the stirring speed was 56 r / min, the reaction temperature was 140-170°C, and the timing was started when the reaction temperature was reached.

[0057] First, the reaction was carried out under "nitrogen pressure" for 6 hours, and the acid value of the obtained polycaprolactone diol product was 0.86 mgKOH / g;

[0058] The polymerization reaction system was then purged with nitrogen (purging during the reaction).

[0059] At 12.4 h, the acid value of the product polycaprolactone diol was 0.34 mgKOH / g;

[0060] At 18.9 h, the acid value of the product polycaprolactone diol was 0.21 mgKOH / g;

[0061] The acid value of the final product polycaprolactone diol obtained at 24.9 hours was 0.089 mg mgKOH / g, and its H NMR spectrum is shown in the attached Figure 3 .

[0062] Example 4

[0063] (1) 6000 g of ε-caprolactone, 335.88 g of diethylene glycol (DEG), and 6.050 g of stannous octoate (purity 99.45-99.99%, stannous content 27.30-29.30%) were added to a polymerization reactor. After nitrogen substitution, the pressure was maintained at 0.5-0.8 MPa, the stirring speed was 56 r / min, and the reaction temperature was 130-165°C. The timing was started when the reaction temperature was reached. The reaction was continued under "nitrogen pressure" for 7.7 hours. The acid value of the resulting polycaprolactone diol product was 0.93 mgKOH / g.

[0064] (2) A 248.18 g sample of the product obtained in Example 4 (1) was placed in a three-necked flask and purged with nitrogen. The timer was started when the temperature reached 145-150°C. The acid value of the polycaprolactone diol product was 0.67 mgKOH / g after 6 hours; 0.02 mgKOH / g after 13 hours; and 0.01 mgKOH / g after 19 hours.

Claims

1. A method for reducing the acid value of polycaprolactone polyol, characterized in that: The polyol and ε-caprolactone are polymerized in the presence of an organic tin compound and a protective atmosphere under pressure for the first stage, and then polymerized in the second stage under the purge of the protective atmosphere to obtain a low-acid polycaprolactone polyol with an acid value below 0.35 mgKOH / g.

2. The method for reducing the acid value of polycaprolactone polyol as claimed in claim 1, wherein: The polyol is an organic small molecule polyol with a molecular weight of 62 to 700 g / mol.

3. The method for reducing the acid value of polycaprolactone polyol as claimed in claim 2, wherein: The polyol is any one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, glycerol, trimethylolpropane, and pentaerythritol.

4. The method for reducing the acid value of polycaprolactone polyol as claimed in claim 1, wherein: The organotin compound is an organotin carboxylate.

5. The method for reducing the acid value of polycaprolactone polyol as claimed in claim 4, wherein: The organotin compound is any one or more of stannous octoate, stannous acetate, and dibutyltin dilaurate.

6. The method for reducing the acid value of polycaprolactone polyol according to claim 1, wherein: At least one of the polyol, ε-caprolactone and organotin compound has not been pre-dehydrated.

7. The method for reducing the acid value of polycaprolactone polyol according to any one of claims 1 to 6, wherein: The molar ratio of ε-caprolactone to polyol is 1-100:1, further 3-70:1, further 5-20:1; the mass ratio of ε-caprolactone to organotin compound is 10000:1-500:1, further 10000:1-1000:

1.

8. The method for reducing the acid value of polycaprolactone polyol according to claim 1, wherein: The protective atmosphere is at least one of nitrogen and inert gas.

9. The method for reducing the acid value of polycaprolactone polyol according to claim 1, wherein: The pressure during the first stage polymerization is above 0.1 MPa, preferably 0.2 to 0.8 MPa.

10. The method for reducing the acid value of polycaprolactone polyol according to claim 1 or 9, wherein: The temperature of the first polymerization stage is 120-180°C, preferably 130-170°C; Preferably, the first polymerization period is 3 to 8 hours.

11. The method for reducing the acid value of polycaprolactone polyol according to claim 1, wherein: The acid value of the first stage polymerization system is 0.5 to 2 mgKOH / g.

12. The method for reducing the acid value of polycaprolactone polyol according to claim 1, wherein: The temperature of the second polymerization stage is 120-180°C, preferably 130-170°C.

13. The method for reducing the acid value of polycaprolactone polyol according to claim 1 or 12, wherein: The purge flow rate of the protective atmosphere in the second stage is 0.01m 3 / min or more, preferably 1m 3 / min or more, more preferably 1 to 13m 3 / min.

14. The method for reducing the acid value of polycaprolactone polyol according to claim 1, wherein: The treatment time of the second stage is 0.5 h or longer, preferably 2 h or longer, and more preferably 2 to 36 h.

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