A method for preparing a controllable molecular weight polycarbonate diol

Abstract

The application belongs to the technical field of polymer material synthesis, and discloses a preparation method of controllable molecular weight polycarbonate dihydric alcohol. The application uses excessive dimethyl carbonate to perform a reflux reaction with dihydric alcohol to generate an intermediate containing a methoxy group at an end, and accurately confirms the reflux reaction end point by detecting the relative abundance of characteristic molecular weight fragments of the intermediate by mass spectrometry, so as to ensure the controllability of the intermediate structure. The intermediate is further reacted with additional dihydric alcohol and polycondensed, and the hydroxyl value fluctuation range of the final product can be controlled within ±2 mgKOH / g.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis technology, specifically to a method for preparing polycarbonate diols with controllable molecular weight. Background Technology

[0002] Polycarbonate diol (PCDL) is an important raw material for synthesizing high-performance polyurethane. Polyurethane materials made from PCDL have excellent hydrolysis resistance, weather resistance, abrasion resistance and mechanical strength, and are widely used in coatings, adhesives, elastomers and synthetic leather.

[0003] Currently, the industrial production of polycarbonate diols mainly employs the transesterification method, where organic carbonates and aliphatic diols undergo transesterification and polycondensation reactions under the action of a catalyst to obtain the product. However, the traditional transesterification method involves a one-time mixing and reaction of raw materials. Due to the randomness of the transesterification reaction, the molecular weight and structure of the resulting intermediates are uncontrollable. This makes it difficult to precisely control the molecular weight of the polycarbonate diol obtained by further polycondensation of the intermediates, with batch-to-batch hydroxyl value fluctuations reaching ±5 mg KOH / g or more. This quality instability severely affects the stability and reproducibility of subsequent polyurethane synthesis, especially in high-end application fields with extremely high requirements for raw material consistency (such as pharmaceuticals and electronic materials), where existing technologies are insufficient to meet the demands.

[0004] To improve product quality stability, researchers have attempted a staged addition of raw materials. For example, a portion of the diol is first reacted with dimethyl carbonate, and then the remaining diol is added to continue the reaction. While this approach has made some progress in improving product transparency or flexibility, it still has significant shortcomings: Firstly, existing staged processes primarily focus on the physical state of the product (such as transparency and crystallinity), without establishing a quantitative correlation between intermediate structure and final molecular weight, making it impossible to achieve precise molecular weight design and control. Secondly, current technologies typically use dimethyl carbonate as a capping agent, making it difficult to accurately predict and control the product molecular weight by adjusting the intermediate chain length.

[0005] In addition, existing processes generally lack real-time monitoring of the structure of reaction intermediates, making it impossible to accurately determine the reaction endpoint and the degree of polymerization of intermediates, resulting in poor process controllability and significant batch-to-batch differences during scale-up production.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The present invention aims to solve at least one of the above technical problems, and provides a method for preparing polycarbonate diols with controllable molecular weight.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a polycarbonate diol with controllable molecular weight, comprising: Diol was mixed with excess dimethyl carbonate and refluxed under the action of a catalyst to remove excess dimethyl carbonate, thereby obtaining an intermediate with methoxy groups at the end, and the molecular weight of the intermediate was monitored. Diol was added to the reaction system to carry out the reaction. After removing the methanol generated in the reaction, polycondensation reaction was carried out under vacuum to obtain polycarbonate diol. The molar ratio of the diol used in the reflux reaction to dimethyl carbonate is 1:2-2.5, and the molar ratio of the diol used in the reflux reaction to the added diol is 1:0.5-1.

[0009] Preferably, the diol is selected from any one of 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, or 1,8-octanediol.

[0010] Preferably, the molecular weight of the intermediate is monitored by mass spectrometry, including detecting the relative abundance of characteristic molecular weight fragments corresponding to the diol. When the relative abundance reaches a preset range, the reflux reaction is confirmed to be complete.

[0011] Preferably, the catalyst is tetrabutyl titanate, and the ratio of the total mass of the diol to the mass of tetrabutyl titanate is 1:0.004-0.007.

[0012] Preferably, the reflux reaction is carried out at a temperature of 120-150°C for 4-5 hours.

[0013] Preferably, the reaction temperature for adding diol is 170-200℃, and the reaction time is 4-5 hours.

[0014] Preferably, the vacuum condition has a vacuum degree of -0.09 to -0.1 MPa, a polycondensation reaction temperature of 170-200°C, and a reaction time of 3-6 hours.

[0015] This invention also discloses a polycarbonate diol obtained by any of the above-described methods for preparing controllable molecular weight polycarbonate diols. The hydroxyl value of the polycarbonate diol fluctuates within the range of ±2 mg KOH / g.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes an excess of dimethyl carbonate to reflux with a diol, generating an intermediate with methoxy groups at the end. The relative abundance of characteristic molecular weight fragments of this intermediate (e.g., the relative abundance of molecular weights 206, 148, 90 or 220, 162, 104, etc.) is detected by mass spectrometry to precisely confirm the endpoint of the reflux reaction and ensure the controllability of the intermediate structure. This intermediate then reacts with additional diol and undergoes polycondensation, with the hydroxyl value of the final product controlled within ±2 mg KOH / g. This invention successfully obtains a molecularly stable polycarbonate diol by employing a staged addition of diol followed by a single excess addition of dimethyl carbonate.

[0017] This invention innovatively introduces mass spectrometry to monitor intermediates generated during the reflux reaction. By detecting the relative abundance of specific molecular weight fragments, the degree of polymerization and structural characteristics of the intermediates can be accurately determined, thereby precisely controlling the reaction endpoint. This process control method based on intermediate molecular weight monitoring achieves visualization and controllability of the reaction process, providing a new technical path for the molecular design of polycarbonate diols.

[0018] Since the polycarbonate diol obtained by the method of this invention has a stable and controllable molecular weight, when it is used as a raw material to synthesize polyurethane, the uniformity of the prepolymer structure can be ensured, and the mechanical property stability and processing repeatability of polyurethane products can be improved. It is particularly suitable for fields such as pharmaceuticals, high-end coatings and electronic adhesives where the batch stability of raw materials is extremely important. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The first embodiment of the present invention provides a method for preparing a controllable molecular weight polycarbonate diol, comprising: Diol was mixed with excess dimethyl carbonate and refluxed under the action of a catalyst to remove excess dimethyl carbonate, thereby obtaining an intermediate with methoxy groups at the end, and the molecular weight of the intermediate was monitored. Diol was added to the reaction system to carry out the reaction. After removing the methanol generated in the reaction, polycondensation reaction was carried out under vacuum to obtain polycarbonate diol. The molar ratio of the diol used in the reflux reaction to dimethyl carbonate is 1:2-2.5, and the molar ratio of the diol used in the reflux reaction to the added diol is 1:0.5-1.

[0021] In this embodiment, an excess of dimethyl carbonate is used to generate a short-chain carbonate intermediate with methoxy groups at the end of the reflux reaction. This intermediate is formed by transesterification of a diol and dimethyl carbonate, and its structural characteristics are directly related to the carbon chain length of the diol used.

[0022] It should be noted that the added diol in this embodiment can be the same diol or a different diol. The diol can be selected from any one of 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol or 1,8-octanediol.

[0023] This embodiment uses mass spectrometry to monitor the structure of intermediates generated during the reflux reaction. Since different diols have different molecular weights, the methoxy-terminated intermediates generated by their reaction with dimethyl carbonate have characteristic molecular weights. Therefore, it is necessary to detect the corresponding characteristic molecular weight fragments based on the type of diol selected.

[0024] Specifically, when 1,4-butanediol (molecular weight 90) is used, the resulting methoxy-terminated intermediates show characteristic peaks of 206 (methoxy-double-terminated carbonate), 148 (methoxy-single-terminated carbonate), and 90 in mass spectrometry; when 1,5-pentanediol (molecular weight 104) is used, the corresponding characteristic molecular weight fragments are 220, 162, and 104; when 1,6-hexanediol (molecular weight 118) is used, the corresponding characteristic molecular weight fragments are 234, 176, and 118; when 1,7-heptanediol (molecular weight 132) is used, the corresponding characteristic molecular weight fragments are 248, 190, and 132; and when 1,8-octanediol (molecular weight 146) is used, the corresponding characteristic molecular weight fragments are 262, 204, and 146.

[0025] Among these characteristic molecular weight fragments, the largest fragment (such as 206, 220, 234, etc.) corresponds to methoxy-terminated carbonates formed by the reaction of a diol with two molecules of dimethyl carbonate; the middle fragments (such as 148, 162, 176, etc.) correspond to methoxy-terminated carbonates; and the smallest fragments (such as 90, 104, 118, etc.) correspond to unreacted diols.

[0026] By detecting the relative abundance of these characteristic molecular weight fragments, the degree of polymerization of the intermediate and the reaction endpoint can be determined. For example, when the relative abundance of the largest molecular weight fragment reaches 100%, and the relative abundance of the remaining fragments is in the range of 8%-20%, it indicates that the reflux reaction has reached the expected endpoint. At this point, the intermediate has a controllable molecular chain length and is suitable for the next chain extension reaction.

[0027] In this embodiment, the catalyst may be tetrabutyl titanate, and the ratio of the total mass of the diol to the mass of tetrabutyl titanate is 1:0.004-0.007. This ratio is merely illustrative, and those skilled in the art can adjust the amount of catalyst within this range according to the reaction rate requirements; all such adjustments are within the protection scope of this invention.

[0028] The reflux reaction temperature can be 120-150℃, and the time can be 4-5 hours; the reaction temperature after adding diol can be 170-200℃, and the time can be 4-5 hours. These temperature and time parameters are the key process parameters of this invention, which directly affect the quality of the intermediate and the efficiency of the subsequent chain extension reaction.

[0029] The polycondensation reaction is carried out under a vacuum of -0.09 to -0.1 MPa, at a temperature of 170-200℃, and for 3-6 hours. The vacuum condition helps remove methanol generated during the reaction, shifting the reaction equilibrium towards the formation of polycarbonate diol.

[0030] The second embodiment of the present invention provides a controllable molecular weight polycarbonate diol, which is prepared by the preparation method described in the first embodiment, and its hydroxyl value fluctuates within the range of ±2 mg KOH / g.

[0031] In this embodiment, the molecular weight of the polycarbonate diol is calculated using the hydroxyl value, and the calculation formula is as follows: ; where M n is the number average molecular weight, f is the hydroxyl functionality (value is 2), 56.1 is the molecular weight of KOH, I OH The measured hydroxyl value.

[0032] In this embodiment, the molecular weight of the polycarbonate diol can be in the range of 1800-2100, and the hydroxyl value can be 53-63 mgKOH / g.

[0033] The polycarbonate diol described in this embodiment has excellent batch stability, making it particularly suitable for the synthesis of high-performance polyurethanes where high consistency of raw materials is required, such as in pharmaceutical materials, high-end coatings, and electronic adhesives.

[0034] The preparation and properties of controllable molecular weight polycarbonate diols are described in detail below through several specific examples.

[0035] Example 1 180 g (2 mol) of 1,4-butanediol, 396 g (4.4 mol) of dimethyl carbonate and 2.02 g of tetrabutyl titanate were mixed and refluxed at 150 °C for 5 h. Excess dimethyl carbonate was removed by purging with nitrogen to obtain an intermediate. The molecular weight was determined by mass spectrometry to be 206, and the relative abundances of 148 and 90 were 100%, 10%, and 10%, respectively, confirming that the intermediate was a short-chain carbonate structure with methoxy groups at the end.

[0036] The temperature was raised to 180℃, and 135g (1.5 mol) of 1,4-butanediol was added to continue the reaction for 5h. After removing the methanol generated in the reaction, the vacuum degree was adjusted to -0.098MPa and the polycondensation reaction was carried out for 5h to obtain polycarbonate diol (1). The hydroxyl value was calculated to be 58.1mgKOH / g and the molecular weight was 1931.

[0037] Repeated experiments were conducted under the same process conditions, and polycarbonate diol (2) was found to have a hydroxyl value of 59.6 mgKOH / g and a molecular weight of 1883; polycarbonate diol (3) was found to have a hydroxyl value of 58.7 mgKOH / g and a molecular weight of 1911. The hydroxyl values ​​of the three experiments fluctuated within ±2 mgKOH / g, which proves that the experimental results are highly repeatable.

[0038] Example 2 180 g (2 mol) of 1,4-butanediol, 360 g (4 mol) of dimethyl carbonate and 2.02 g of tetrabutyl titanate were mixed and refluxed at 150 °C for 5 h. Excess dimethyl carbonate was removed by purging with nitrogen to obtain an intermediate. Mass spectrometry determined its molecular weight to be 206, and the relative abundances of 148 and 90 were 100%, 15%, and 15%, respectively.

[0039] The temperature was raised to 180℃, and 117.7g (1.31mol) of 1,4-butanediol was added to continue the reaction for 5h. After removing the methanol generated in the reaction, the vacuum degree was adjusted to -0.098MPa and the polycondensation reaction was carried out for 5h to obtain polycarbonate diol (1) with a hydroxyl value of 60.3mgKOH / g and a molecular weight of 1861.

[0040] Repeated experiments were conducted under the same process conditions, and polycarbonate diol (2) was found to have a hydroxyl value of 59.1 mgKOH / g and a molecular weight of 1898; polycarbonate diol (3) was found to have a hydroxyl value of 60.7 mgKOH / g and a molecular weight of 1848. The hydroxyl values ​​of the three experiments fluctuated within ±2 mgKOH / g, and the experimental results showed good repeatability.

[0041] Example 3 208 g (2 mol) of 1,5-pentanediol, 414 g (4.6 mol) of dimethyl carbonate and 1.72 g of tetrabutyl titanate were mixed and refluxed at 140 °C for 5 h. Excess dimethyl carbonate was removed by purging with nitrogen to obtain intermediates with molecular weights of 220, 162 and 104, with relative abundances of 100%, 16% and 14%, respectively.

[0042] The temperature was raised to 190℃, and 137.6g (1.32mol) of 1,5-pentanediol was added to continue the reaction for 4h. After removing the methanol generated in the reaction, the vacuum degree was adjusted to -0.098MPa, and the polycondensation reaction was carried out for 4h to obtain polycarbonate diol (1) with a hydroxyl value of 62mgKOH / g and a molecular weight of 1810.

[0043] Repeated experiments were conducted under the same process conditions, and polycarbonate diol (2) was found to have a hydroxyl value of 61.2 and a molecular weight of 1833, while polycarbonate diol (3) had a hydroxyl value of 60.7 mgKOH / g and a molecular weight of 1848. The hydroxyl values ​​of the three experiments fluctuated within ±2 mgKOH / g, indicating good repeatability of the experimental results.

[0044] Example 4 236 g (2 mol) of 1,6-hexanediol, 450 g (5 mol) of dimethyl carbonate and 2.41 g of tetrabutyl titanate were mixed and refluxed at 130 °C for 4 h. Excess dimethyl carbonate was removed by purging with nitrogen to obtain intermediates with molecular weights of 234, 176 and 118, with relative abundances of 100%, 12% and 8%, respectively.

[0045] The temperature was raised to 180℃, and 181g (1.53mol) of 1,6-hexanediol was added to continue the reaction for 4h. After removing the methanol generated in the reaction, the vacuum degree was adjusted to -0.098MPa, and the polycondensation reaction was carried out for 5h to obtain polycarbonate diol (1) with a hydroxyl value of 53.4mgKOH / g and a molecular weight of 2101.

[0046] Repeated experiments were conducted under the same process conditions, yielding polycarbonate diol (2) with a hydroxyl value of 54.6 mgKOH / g and a molecular weight of 2055, and polycarbonate diol (3) with a hydroxyl value of 53.9 mgKOH / g and a molecular weight of 2082. The hydroxyl values ​​of the three experiments fluctuated within ±2 mgKOH / g, indicating good repeatability of the experimental results.

[0047] Example 5 236 g (2 mol) of 1,6-hexanediol, 450 g (5 mol) of dimethyl carbonate and 2.41 g of tetrabutyl titanate were mixed and refluxed at 130 °C for 4 h. Excess dimethyl carbonate was removed by purging with nitrogen to obtain intermediates with molecular weights of 234, 176 and 118, with relative abundances of 100%, 12% and 8%, respectively.

[0048] The temperature was raised to 180℃, and 137.7g (1.53mol) of 1,4-butanediol was added and the reaction continued for 4h. The methanol generated in the reaction was removed, the vacuum degree was adjusted to -0.098MPa, and the polycondensation reaction was carried out for 5h to obtain polycarbonate diol (1) with a hydroxyl value of 54.2mgKOH / g and a molecular weight of 2070.

[0049] Repeated experiments were conducted under the same process conditions, yielding polycarbonate diol (2) with a hydroxyl value of 53.6 mgKOH / g and a molecular weight of 2093, and polycarbonate diol (3) with a hydroxyl value of 54.8 mgKOH / g and a molecular weight of 2047. The hydroxyl values ​​of the three experiments fluctuated within ±2 mgKOH / g, indicating good repeatability of the experimental results.

[0050] Comparative Example 1 180 g (3.2 mol) of 1,4-butanediol, 396 g (4.4 mol) of dimethyl carbonate and 2.02 g of tetrabutyl titanate were mixed and refluxed at 150 °C for 5 h. Then the temperature was raised to 180 °C and the reaction was continued for another 5 h. Nitrogen gas was then purged to remove excess dimethyl carbonate. The vacuum was adjusted to -0.098 MPa and the polycondensation reaction was carried out for 5 h to obtain polycarbonate diol (1) with a hydroxyl value of 60.3 mg KOH / g and a molecular weight of 1861.

[0051] Repeated experiments were conducted under the same process conditions, and polycarbonate diol (2) was found to have a hydroxyl value of 63.6 mgKOH / g and a molecular weight of 1764, while polycarbonate diol (3) had a hydroxyl value of 73 mgKOH / g and a molecular weight of 1536. The experimental results showed that the hydroxyl value fluctuated greatly between batches (±7 mgKOH / g) and the repeatability was poor, proving that the non-step feeding process could not achieve precise control of molecular weight.

[0052] Comparative Example 1 used a single addition of 1,4-butanediol without staged reaction and mass spectrometry monitoring. The results showed large fluctuations in hydroxyl values ​​between batches (±7 mg KOH / g) and poor reproducibility. This demonstrates that even when using a single diol, precise molecular weight control cannot be achieved without the staged addition and mass spectrometry monitoring process of this invention.

[0053] The comparison shows that the method of adding diols in stages, using excess dimethyl carbonate, and specific mass spectrometry monitoring (detecting characteristic molecular weight fragments for different diols) can significantly improve the molecular weight stability and batch repeatability of the product.

[0054] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a controllable molecular weight polycarbonate diol, characterized in that, include: Diol was mixed with excess dimethyl carbonate and refluxed under the action of a catalyst to remove excess dimethyl carbonate, yielding an intermediate with methoxy groups at the end. The molecular weight of the intermediate was monitored by mass spectrometry. Diol was added to the reaction system to carry out the reaction. After removing the methanol generated in the reaction, polycondensation reaction was carried out under vacuum to obtain polycarbonate diol. The molar ratio of the diol used in the reflux reaction to dimethyl carbonate is 1:2-2.5, and the molar ratio of the diol used in the reflux reaction to the added diol is 1:0.5-1.

2. The method for preparing controllable molecular weight polycarbonate diol as described in claim 1, characterized in that, The diol is selected from any one of 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, or 1,8-octanediol.

3. The method for preparing controllable molecular weight polycarbonate diol as described in claim 1 or 2, characterized in that, The molecular weight of the intermediate is monitored by mass spectrometry, including the detection of the relative abundance of characteristic molecular weight fragments corresponding to the diol. When the relative abundance reaches a preset range, the completion of the reflux reaction is confirmed.

4. The method for preparing controllable molecular weight polycarbonate diol as described in claim 1, characterized in that, The catalyst is tetrabutyl titanate, and the ratio of the total mass of the diol to the mass of tetrabutyl titanate is 1:0.004-0.

007.

5. The method for preparing controllable molecular weight polycarbonate diol as described in claim 1, characterized in that, The reflux reaction is carried out at a temperature of 120-150℃ for 4-5 hours.

6. The method for preparing controllable molecular weight polycarbonate diol as described in claim 1, characterized in that, The reaction is carried out at a temperature of 170-200℃ for 4-5 hours after the addition of diol.

7. The method for preparing controllable molecular weight polycarbonate diol as described in claim 1, characterized in that, The vacuum conditions are -0.09 to -0.1 MPa, the polycondensation reaction temperature is 170-200℃, and the reaction time is 3-6 hours.

8. A polycarbonate diol obtained by the method for preparing a controllable molecular weight polycarbonate diol as described in any one of claims 1-7.

9. The polycarbonate diol according to claim 8, characterized in that, The hydroxyl value of the polycarbonate diol fluctuates within the range of ±2 mg KOH / g.