A low-yellowing ultraviolet-resistant copolycarbonate and a method for preparing the same

Abstract

This invention discloses a low-yellowness, UV-resistant copolycarbonate and its preparation method, belonging to the field of polymer material synthesis technology. The method involves melting bisphenol A, a resorcinol-based copolydihydroxy compound, and diphenyl carbonate, then adding a composite catalyst, and sequentially performing transesterification, pre-condensation, and final condensation reactions to obtain the low-yellowness, UV-resistant copolycarbonate. The resorcinol-based copolydihydroxy compound content is 5%–10%. This invention utilizes the microenvironmental regulation of a specific liquid composite catalytic system to effectively overcome the polymerization challenge of unifying transparency, low yellowness, UV resistance, and mechanical properties in copolycarbonate products. The copolycarbonate prepared by this method maintains excellent transparency and high molecular weight while reducing initial yellowness and significantly improving UV aging resistance, showing promising market prospects.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, specifically relating to a low-yellowness, UV-resistant copolycarbonate and its preparation method. Background Technology

[0002] Polycarbonate (PC) is widely used in optics, construction, automotive, and outdoor products due to its excellent transparency, impact resistance, and dimensional stability. However, conventional bisphenol A type polycarbonate is prone to yellowing under long-term ultraviolet (UV) irradiation, affecting the material's appearance and lifespan. To improve the weather resistance of polycarbonate, existing technologies typically employ the addition of UV absorbers or hindered amine additives, or introduce light-stabilizing structural units through copolymerization. Compared to added additives, the introduction of light-stabilizing aromatic diphenol structures through copolymerization can reduce additive migration, precipitation, and adverse effects on material transmittance, thus attracting increasing attention. Resorcinol and its derivatives are representative copolymer dihydroxy compounds; their introduction into the polycarbonate molecular chain helps improve the material's color stability under UV conditions. However, resorcinol comonomers present significant process challenges in the melt transesterification method for preparing polycarbonate. Because these monomers are highly sensitive to high-temperature alkaline environments, they are prone to side reactions under traditional catalytic conditions, leading to a darker color in the polymerization system and a higher initial yellowness in the resulting copolycarbonate, which fails to meet the base color requirements of high-end transparent products. While simply reducing the catalyst concentration can alleviate yellowing to some extent in existing technologies, it often results in decreased polymerization rate, incomplete polycondensation, and lower molecular weight, making it difficult to balance color, transparency, and mechanical properties. Furthermore, in resorcinol-based copolymer systems, uneven dispersion of the catalytic component in the melt and excessively strong local alkalinity can more easily induce side reactions and coloring. Therefore, controlling catalytic conditions, mitigating adverse side reactions of resorcinol comonomers, and maintaining high polymerization efficiency and product performance during the molten transesterification reaction are key issues in the preparation of this type of copolycarbonate.

[0003] Therefore, developing a melt preparation method suitable for resorcinol copolymer systems to achieve a balance of low initial yellowness, high transparency, and excellent UV aging color stability has significant application value. Summary of the Invention

[0004] To address the problems of side reactions and increased initial yellowness of resorcinol comonomers during melt transesterification polymerization, and the inability of prepared copolycarbonates to simultaneously achieve good color, transparency, and molecular weight, this invention provides a low-yellowing, UV-resistant copolycarbonate and its preparation method. Specifically, this invention employs a specific composite catalyst. By limiting the types of comonomers, copolymerization ratios, catalytic component combinations and their introduction methods, and polymerization process conditions, the resulting copolycarbonate maintains high molecular weight and transparency while exhibiting low initial yellowness, good UV aging color stability, and excellent mechanical properties.

[0005] In a first aspect, the present invention provides a method for preparing a low-yellowness, UV-resistant copolycarbonate, specifically comprising the following steps: The main dihydroxy compound, the copolymer dihydroxy compound and the carbonate diester compound are added to the reaction vessel in a molar ratio of 1: (1~1.10), stirred and mixed evenly. After the monomer melts, a composite catalyst is added to the reaction system. After transesterification, pre-condensation and condensation reactions are carried out in sequence, low yellowness UV-resistant yellowing copolycarbonate can be obtained. The composite catalyst is added at a rate of 20-120 μL per mole of dihydroxy compound; The composite catalyst is prepared by mixing tetrabutylphosphonium acetate, sodium hydroxide and potassium dihydrogen phosphate in an aqueous medium.

[0006] Furthermore, in the liquid composite catalyst, the molar ratio of tetrabutylphosphonic acetate, sodium hydroxide, and potassium dihydrogen phosphate is 1 : (0.3-0.5) : (0.3-0.5).

[0007] Furthermore, after the polymerization reaction is completed, nitrogen gas is introduced into the reactor, and the low yellowness and UV-resistant yellowing copolycarbonate melt is extruded into the reactor at a temperature of 270-280℃. After water cooling and pelletizing, a high transparency and low temperature resistant copolycarbonate granule product is obtained.

[0008] Furthermore, in the composite catalyst, the concentration of component A is 0.8-1.5 mol / L, preferably 1.0-1.4 mol / L.

[0009] Furthermore, the main dihydroxy compound is bisphenol A; The copolymerized dihydroxy compound is a resorcinol compound with the following structural formula: R is independently selected from H, C1-C 20 Alkyl, C4-C 20 One of the aryl, amino, or halogen atoms.

[0010] Furthermore, the copolymerized dihydroxy compound is selected from one of 1,3-resorcinol, 2-aminoresorcinol, 4-methylresorcinol, 4-bromoresorcinol, and 5-fluororesorcinol.

[0011] Furthermore, the proportion of the copolymer dihydroxy compound in the sum of the main dihydroxy compound and the copolymer dihydroxy compound, in terms of mole fraction, is 5%-10%.

[0012] Furthermore, the carbonate diester compound is diphenyl carbonate.

[0013] Furthermore, the transesterification reaction is carried out at a temperature of 140-160°C, a pressure of 80-101 kPa, and a reaction time of 1-2 hours. The pre-polymerization reaction temperature is 230~255℃, the pressure is 3~60kPa, and the reaction time is 2-3h; The final polycondensation reaction temperature is 260~280℃, the pressure is 0.01~3kPa, and the reaction time is 1-2h.

[0014] Secondly, the present invention provides a method for preparing the above-mentioned composite catalyst, comprising the following steps: S1: Add the measured amount of potassium dihydrogen phosphate to deionized water and stir to disperse; then add sodium hydroxide and stir to generate a homogeneous and transparent mixed salt solution. S2: Add tetrabutylphosphonium acetate solution to the solution obtained in S1 and stir for 15-30 min to obtain the composite catalyst.

[0015] Furthermore, the concentration of tetrabutylphosphonic acetate in water in the composite catalyst is 1.0-1.4 mol / L.

[0016] Furthermore, the composite catalyst is added at a rate of approximately 33.3 μL per mole of total dihydroxy compound.

[0017] Preferably, the system obtained in steps S1 and S2 is a transparent homogeneous solution or a homogeneous dispersion.

[0018] Thirdly, the low yellowness and UV-resistant yellowing copolycarbonate prepared using the above scheme.

[0019] Furthermore, the number-average molecular weight of the copolycarbonate obtained by this preparation method is 2.6 × 10⁻⁶. 4 Up to 3.9×10 4 between Furthermore, the light transmittance of the copolycarbonate is not less than 89%; the initial yellowness index YI is not higher than 2.2. The increase in yellowness ΔYI after 120 hours of accelerated aging under 280-400nm ultraviolet light is no higher than 6.0.

[0020] Beneficial effects: This invention addresses the problem of initial yellowing of resorcinol comonomers during melt transesterification for polycarbonate preparation. By limiting the types of co-dihydroxy compounds, the copolymerization ratio, the combination of catalytic components, and the process conditions, the resulting copolycarbonate exhibits lower initial yellowness. Compared to directly adding catalytic components to the melt through physical mixing or using organic or inorganic strong base catalysts alone, this invention achieves a better balance between molecular weight, transmittance, and yellowness control.

[0021] The method employed in this invention achieves a number-average molecular weight of 2.6 × 10⁻⁶ while maintaining high polymerization efficiency. 4 The above properties indicate good transparency, which meets the application requirements of transparent products.

[0022] The resorcinol-based copolycarbonate prepared by this invention exhibits a small increase in yellowness after accelerated UV aging, demonstrating good color stability and making it suitable for applications with high requirements for appearance and weather resistance. Detailed Implementation

[0023] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0025] The preferred embodiments of the present invention will now be described in detail with reference to specific examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and essence.

[0026] Test instrument model: (1) The optical testing instrument is HunterLab Pro (Hunterlab, USA).

[0027] (2) The molecular weight of the product was determined by GPC using a Waters GPC system equipped with a 1515 high performance liquid chromatography pump and a 2414 differential refractive index detector. Polystyrene was used as the standard sample and chromatographic grade tetrahydrofuran was used as the mobile phase. The molecular weight and molecular weight distribution of the product were characterized at 30 °C.

[0028] Preparation of liquid composite catalysts: KH₂PO₄ was added to deionized water and stirred to disperse it. Then, NaOH was added to form a homogeneous and transparent solution. While the resulting solution was still warm, a tetrabutylphosphonium acetate solution was added, and the mixture was vigorously shaken or ultrasonically stirred for 15 minutes to obtain a transparent and homogeneous liquid composite catalyst. The molar ratio of tetrabutylphosphonium acetate, NaOH, and KH₂PO₄ was 1:0.3:0.3; the concentration of tetrabutylphosphonium acetate in water was approximately 1.3 mol / L.

[0029] Example 1 (Comonomer: 1,3-resorcinol; Content: 5%) Weigh 325.00 g (1.425 mol) of bisphenol A, 8.3 g (0.075 mol) of resorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate, and place them in a 2 L pressure-resistant reactor. Replace the air and oxygen by applying vacuum and purging with nitrogen three times. After melting the mixture at 150 °C, inject 50 μL of the prepared composite catalyst solution into the melt using a pipette under nitrogen purging conditions. Continue stirring for 1 hour, during which the vacuum is slowly reduced to 80 kPa, the temperature is raised to 230°C, the vacuum is adjusted to 60 kPa and maintained for 10 minutes, then slowly reduced to 40 kPa and maintained for 10 minutes, then slowly reduced to 30 kPa and continued to react for 40 minutes. During this time, phenol is distilled into the collection tank, the temperature is raised to 235°C, the vacuum is adjusted to 22 kPa and reacted for 25 minutes, during which the vacuum is slowly reduced to 18 kPa and continued to be raised to 245°C, the vacuum is adjusted to 12 kPa and reacted for 15 minutes, during which the vacuum is slowly reduced to 8 kPa and continued to be raised to 255°C and reacted for 25 minutes, during which the vacuum is slowly adjusted to 3000 Pa and continued to be raised to 280°C and reacted for 45 minutes. During this time, the vacuum is first slowly reduced to 800 Pa and reacted until the phenol outflow decreases and the torque indicator increases. The vacuum is then adjusted to below 100 Pa. After the reaction is completed, the vacuum pump and stirrer are turned off, nitrogen is introduced to atmospheric pressure, the outlet is opened, and the product is obtained by water cooling the pull rod. The test results of various relevant performance aspects of the product are summarized in Table 1.

[0030] Example 2 (Comonomer: 4-methylresorcinol; Content: 5%) Weigh 325.30 g (1.425 mol) of bisphenol A, 9.31 g (0.075 mol) of 4-methylresorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1. The test results of various relevant properties of the product are summarized in Table 1.

[0031] Example 3 (Comonomer: 2-aminoresorcinol; Content: 5%) Weigh 325.30 g (1.425 mol) of bisphenol A, 9.38 g (0.075 mol) of 2-aminoresorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1. The test results of various relevant properties of the product are summarized in Table 1.

[0032] Example 4 (Comonomer: 4-bromoresorcinol; Content: 5%) Weigh 325.30 g (1.425 mol) of bisphenol A, 15.08 g (0.075 mol) of 4-bromoresorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1. The test results of various relevant properties of the product are summarized in Table 1.

[0033] Example 5 (Comonomer: 5-fluororesorcinol; Content: 5%) Weigh 325.30 g (1.425 mol) of bisphenol A, 9.61 g (0.075 mol) of 5-fluororesorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1. The test results of various relevant properties of the product are summarized in Table 1.

[0034] Example 6 (Comonomer: 1,3-resorcinol; Content: 10%) Weigh 308.18 g (1.35 mol) of bisphenol A, 16.5 g (0.15 mol) of resorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1. The test results of various relevant properties of the product are summarized in Table 1.

[0035] Example 7 (Comonomer: 4-methylresorcinol; Content: 10%) Weigh 308.18 g (1.35 mol) of bisphenol A, 18.62 g (0.15 mol) of 4-methylresorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1. The test results of various relevant properties of the product are summarized in Table 1.

[0036] Example 8 (Comonomer: 2-aminoresorcinol; Content: 10%) Weigh 308.18 g (1.35 mol) of bisphenol A, 18.77 g (0.15 mol) of 2-aminoresorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1. The test results of various relevant properties of the product are summarized in Table 1.

[0037] Example 9 (Comonomer: 4-bromoresorcinol; Content: 10%) Weigh 308.18 g (1.35 mol) of bisphenol A, 30.15 g (0.15 mol) of 4-bromoresorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1. The test results of various relevant properties of the product are summarized in Table 1.

[0038] Example 10 (Comonomer: 5-fluororesorcinol; Content: 10%) Weigh 308.18 g (1.35 mol) of bisphenol A, 19.22 g (0.15 mol) of 5-fluororesorcinol, and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1. The test results of various relevant properties of the product are summarized in Table 1.

[0039] Comparative Example 1 (Preparation of Bisphenol A Polycarbonate) Weigh 342.20 g (1.50 mol) of bisphenol A and 347.05 g (1.62 mol) of diphenyl carbonate. The catalyst and other preparation steps are the same as in Example 1.

[0040] Comparative Example 2 (Physical Mixing) The polymerization formulation and process were the same as in Example 1. The difference was that no catalyst precursor solution was prepared. Equimolar amounts of tetrabutylphosphonium acetate solution, sodium hydroxide solution, and potassium dihydrogen phosphate solution were simultaneously added dropwise to the monomer melt using three separate pipettes.

[0041] Comparative Example 3 (only tetrabutylphosphonium acetate was added as a catalyst) The polymerization formulation is the same as in Example 1. Only tetrabutylphosphonium acetate is added as the catalyst (the amount of component A in Example 1), and inorganic components B and C are not added.

[0042] Comparative Example 4 (Sodium hydroxide was added as a catalyst only) The polymerization formulation is the same as in Example 1. The catalyst is supplemented only with sodium hydroxide, in the same amount as NaOH in Example 1 (the amount of component B in Example 1).

[0043] Table 1 Comparison of performance parameters of copolycarbonates in the examples. Note: Due to severe yellowing / brittleness of the initial sample, no subsequent aging tests were conducted.

[0044] As shown in Table 1, the resorcinol-based copolycarbonate prepared by the method of this invention achieves a good balance between number-average molecular weight, transmittance, and yellowness control. Compared with Comparative Example 2, the initial yellowness of the product is significantly reduced and the transmittance is significantly increased after adopting liquid composite catalytic conditions, indicating that introducing the catalytic component in a pre-prepared liquid system is more conducive to obtaining a product with a better appearance. Compared with Comparative Examples 3 and 4, this invention does not significantly sacrifice molecular weight due to the reduction in yellowness, indicating that the method of this invention is suitable for the preparation of high molecular weight resorcinol-based copolymer systems. Meanwhile, Comparative Example 1 shows that although the initial yellowness of the material is low when no resorcinol structure is introduced, the yellowness increases significantly after UV aging; while in the embodiments of this invention, after introducing a specific proportion of resorcinol comonomers, the yellowness increase value of the material after aging is low, showing good UV aging color stability.

[0045] Therefore, the method of the present invention can produce resorcinol-based copolycarbonates that have low initial yellowness, high transparency and good resistance to ultraviolet yellowing, and is suitable for the field of transparent products with high requirements for color and weather resistance.

[0046] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a low-yellowing, UV-resistant copolycarbonate, characterized in that, Includes the following steps: The main dihydroxy compound, the copolymer dihydroxy compound and the carbonate diester compound are added to the reaction vessel in a molar ratio of 1: (1~1.10), stirred and mixed evenly. After the monomer melts, a composite catalyst is added to the reaction system. After transesterification, pre-condensation and condensation reactions are carried out in sequence, low yellowness UV-resistant yellowing copolycarbonate can be obtained. The composite catalyst is prepared by mixing tetrabutylphosphonium acetate, sodium hydroxide and potassium dihydrogen phosphate in an aqueous medium.

2. The method for preparing the low yellowness and UV-resistant yellowing copolycarbonate according to claim 1, characterized in that, The composite catalyst is added at a rate of 20-120 μL per mole of total dihydroxy compound.

3. The method for preparing the low yellowness, UV-resistant yellowing-resistant copolycarbonate according to claim 1, characterized in that, In the composite catalyst, the molar ratio of tetrabutylphosphonic acetate, sodium hydroxide and potassium dihydrogen phosphate is 1:(0.3-0.5):(0.3-0.5).

4. The method for preparing the low yellowness, UV-resistant yellowing-resistant copolycarbonate according to claim 2, characterized in that, In the composite catalyst, the concentration of tetrabutylphosphonic acetate is 0.8-1.5 mol / L.

5. The method for preparing the low yellowness, UV-resistant yellowing-resistant copolycarbonate according to claim 1, characterized in that, The main dihydroxy compound is bisphenol A; The carbonate diester compound mentioned is diphenyl carbonate; The copolymerized dihydroxy compound is a resorcinol compound with the following structural formula: R is independently selected from H, C1-C 20 Alkyl, C4-C 20 One of the aryl, amino, or halogen atoms.

6. The method for preparing the low yellowness, UV-resistant yellowing-resistant copolycarbonate according to claim 5, characterized in that, The copolymer dihydroxy compound is selected from one of 1,3-resorcinol, 2-aminoresorcinol, 4-methylresorcinol, 4-bromoresorcinol, and 5-fluororesorcinol.

7. The method for preparing the low yellowness, UV-resistant yellowing-resistant copolycarbonate according to claim 1, characterized in that, The proportion of the copolymer dihydroxy compound in the sum of the main dihydroxy compound and the copolymer dihydroxy compound is 5%-10% by mole fraction.

8. The method for preparing the low yellowness, UV-resistant yellowing-resistant copolycarbonate according to claim 1, characterized in that, The transesterification reaction was carried out at a temperature of 140-160℃ and a pressure of 80-101 kPa for 1-2 hours. The pre-condensation reaction temperature is 230~255℃, the pressure is 3~60kPa, and the reaction time is 2-3h; The final polycondensation reaction temperature is 260~280℃, the pressure is 0.01~3kPa, and the reaction time is 1-2h.

9. A low-yellowing, UV-resistant copolycarbonate, characterized in that, It is prepared by any one of the preparation methods described in claims 1-8.

10. The low yellowness and UV-resistant yellowing copolycarbonate according to claim 9, characterized in that, The light transmittance of the low yellowness and UV-resistant yellowing copolycarbonate is not less than 89%; the initial yellowness index YI is not higher than 2.2; and the increase in yellowness ΔYI after 120 hours of accelerated aging under 280-400nm UV light is not higher than 6.0.

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