Preparation method of benzdioxane dimethyl ester monomer based on methyl protocatechuate and preparation method of copolyester of benzdioxane dimethyl ester monomer

Abstract

The invention relates to a method for modifying PBT (Polybutylene Terephthalate) and PBN (Polybutylene Nitrate) by using benzodioxane dimethyl ester, dimethyl terephthalate and 1, 4-butanediol or benzodioxane dimethyl ester, dimethyl 2, 6-naphthalate and 1, 4-butanediol as raw materials, and tetrabutyl titanate as a catalyst, and thermoplastic polyester is prepared through two-step melt polymerization. The preparation method comprises the following steps: 1) preparing a monomer benzdioxane dimethyl ester from methyl protocatechuate and methyl 2, 3-dibromopropionate; and 2) modifying the PBT polyester by using the benzdioxane dimethyl ester. And (3) modifying the PBN polyester by using the benzdioxane dimethyl ester. The method has the advantages that the raw materials are wide in source, low in price, renewable and low in production cost; the polyester synthesis process is simple, easy to operate, green and environment-friendly, high in yield and beneficial to industrial production; the prepared polyester material is high in glass transition temperature, high in mechanical strength, good in thermal stability, adjustable in performance and easy to realize structure and function diversification.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of green synthesis of renewable resources, and specifically relates to a method for preparing a mixture of 2,6-dimethyl-2,3-dihydro-1,4-benzodioxane-2,6-dicarboxylate and 2,7-dimethyl-2,3-dihydro-1,4-benzodioxane-2,7-dicarboxylate using a phenolic acid (methyl 3,4-dihydroxybenzoate) in many vegetables and fruits as a raw material. The two products are generated simultaneously, and the molar ratio is 6 ∶ The mixture of the two (referred to as benzodioxane dimethyl ester) is directly used as a third monomer for preparing polybutylene terephthalate (PBT) and polybutylene naphthalate (PBN) copolyesters without separation. BACKGROUND

[0002] At present, polymers synthesized from petroleum resources are indispensable in our life. However, fossil resources will eventually be exhausted, and the environmental problems caused by excessive use of fossil resources are becoming more and more serious, so it is very important to develop new high-performance polyesters using renewable resources. Polybutylene terephthalate (PBT) and polybutylene 2,6-naphthalate (PBN) are a pair of twin sisters, as important engineering plastics, have good mechanical properties and thermal stability, and are widely used in the fields of automobiles, mechanical equipment, precision instrument parts, electronic appliances and textiles. PBN has a higher glass transition temperature (T g ) and gas barrier performance than PBT, and is more used in high-end packaging and aerospace engineering fields. However, PBT and PBN also have some shortcomings, such as low T g , high melting point (T m ), low elongation at break, etc. Although PBN has higher mechanical strength and T g , the raw material dimethyl 2,6-naphthalate for synthesizing PBN is expensive and derived from fossil resources.

[0003] The purpose of the present application is to solve the above problems, and to use the bio-based monomer benzodioxane dimethyl ester based on protocatechuic acid to prepare PBT and PBN copolyesters. The introduction of benzodioxane dimethyl ester can increase the glass transition temperature of PBT and expand its application range. For PBN, partial substitution of 2,6-naphthalene dicarboxylic acid can reduce the production cost without reducing the overall performance of the material. SUMMARY

[0004] In order to improve the T gThis invention aims to enhance the value and expand the application range of PBN materials. Furthermore, to reduce production costs without compromising PBN material performance, this invention provides a copolymerization modification method. Using dimethyl benzodioxane to copolymerize and modify traditional PBT and PBN homopolymers, a bio-based polyester material exhibiting high glass transition temperature, high thermal stability, and high mechanical strength is obtained. This method features a simple synthesis process, high yield, mild reaction conditions, and inexpensive and environmentally friendly raw materials, making it easy to industrialize.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A benzodioxane dimethyl ester monomer based on protocatechuic acid and its copolyester, the monomer structure is as follows:

[0007]

[0008] The PBT and PBN copolyesters are copolymerized from dimethyl benzodioxane, dimethyl terephthalate (or dimethyl 2,6-naphthalenedicarboxylate), and 1,4-butanediol, respectively, and the copolyesters are composed of structural units represented as follows:

[0009]

[0010] or

[0011]

[0012] All copolyesters are random copolyesters with a number average molecular weight of over 40 kg / mol and a molecular weight distribution between 1.85 and 2.10.

[0013] This invention provides a method for preparing benzodioxane dimethyl ester monomer and its copolyester, the method comprising the following steps:

[0014] Preparation of benzodioxane dimethyl ester monomer:

[0015] 1) Dissolve methyl 3,4-dihydroxybenzoate and anhydrous potassium carbonate in acetone, then add methyl 2,3-dibromopropionate dropwise, and stir at a certain temperature;

[0016] 2) After the reaction is complete, cool the mixture, filter the reaction mixture, evaporate the filtrate to dryness, and finally recrystallize it with methanol to obtain a white solid. Place the white solid in a vacuum oven to dry it; the white solid is benzodioxane dimethyl ester.

[0017] Preparation of copolyesters:

[0018] 3) Under inert conditions, benzodioxane dimethyl ester, dimethyl ester, and diol are added to the reactor to obtain a mixture;

[0019] 4) Melt the mixture until it becomes clear, then add the catalyst tetrabutyl titanate to carry out the esterification reaction;

[0020] 5) Perform polycondensation reaction;

[0021] 6) After the polycondensation is completed, the product is obtained. The product is cooled to room temperature and dissolved in chloroform. Finally, it is precipitated with methanol, filtered, and dried.

[0022] In the above technical solution, further, in step 1), the molar ratio of methyl 3,4-dihydroxybenzoate, methyl 2,3-dibromopropionate and anhydrous potassium carbonate is 1:1.1:2.5.

[0023] The diol is 1,4-butanediol.

[0024] The dimethyl ester is dimethyl terephthalate or dimethyl 2,6-naphthalenedicarboxylate.

[0025] In the above technical solution, further, the reaction temperature in step 1) is 50°C and the reaction time is 24h.

[0026] In the above technical solution, further, in step 2), the drying temperature is 50℃ and the drying time is 24h, and the melting point of the obtained benzodioxane dimethyl ester is (T). m The temperature is 90℃.

[0027] In the above technical solution, further, in step 3), the molar ratio of benzodioxane dimethyl ester, dimethyl ester and 1,4-butanediol is 1:1.5, and the inert gas is nitrogen.

[0028] In the above technical solution, further, in step 4), the molar ratio of benzodioxane dimethyl ester to the catalyst tetrabutyl titanate is 15:1, the melting temperature is 140℃, the esterification temperature is 210℃, and the esterification time is 6-8h.

[0029] In the above technical solution, further, the polycondensation reaction in step 5) is carried out under a vacuum of less than 60 Pa, and the polycondensation time is 6-8 h.

[0030] In the above technical solution, further, the drying temperature in step 6) is 50°C and the drying time is 24 hours.

[0031] The present invention provides benzodioxane dimethyl ester monomer and its copolyester obtained by the aforementioned preparation method.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1) The raw material methyl 3,4-dihydroxybenzoate involved in this invention is derived from biomass, which is widely available, inexpensive, and easy to obtain. The corresponding polymer materials synthesized from this raw material can reduce the dependence on fossil resources.

[0034] 2) The polyester monomer prepared by this invention has a simple and environmentally friendly synthesis process, which is conducive to industrial production;

[0035] 3) The polyester material provided by this invention has a high glass transition temperature and adjustable properties, reducing dependence on fossil resources. Attached Figure Description

[0036] Figure 1 The 1H NMR spectrum of Example 1;

[0037] Figure 2 The proton NMR spectrum of Example 2;

[0038] Figure 3 The DSC melt curve diagram for Example 2;

[0039] Figure 4 The hydrogen nuclear magnetic resonance spectrum of Example 3;

[0040] Figure 5 Here is the DSC melt curve of Example 3;

[0041] Figure 6 The proton NMR spectrum of Example 4;

[0042] Figure 7 Here is the DSC melt curve diagram for Example 4; Detailed Implementation

[0043] The specific implementation methods given below are only a further explanation of the present invention. It should be noted that the following implementation methods are only a further description of the present invention and should not be construed as a limitation on the scope of protection of the present invention. Non-essential changes made to the present invention by those skilled in the art, including the selection of catalysts and the adjustment of preferred high temperature and high vacuum conditions, are all within the scope of protection of the present invention.

[0044] Example 1

[0045] Weigh 10g (0.054mol) of methyl protocatechuate and 18.76g (0.136mol) of anhydrous potassium carbonate and dissolve them in 100-150mL of acetone. Then, add 14.69g (0.060mol) of methyl 2,3-dibromopropionate dropwise using a constant pressure dropping funnel. Incubate overnight in a round-bottom flask equipped with a magnetic stirrer and a reflux condenser at 50℃. After cooling and filtration, evaporate the filtrate to dryness and recrystallize it with methanol to obtain a white solid. Dry the solid in a vacuum oven for direct use.

[0046] After the experiment, the chemical structure of the rigid monomer benzodioxane dimethyl ester was determined by nuclear magnetic resonance.

[0047] Figure 1 The 1H NMR spectrum of benzo[a]dioxane dimethyl ester, a rigid monomer synthesized from methyl protocatechuate and methyl 2,3-dibromopropionate, was determined at room temperature using deuterated chloroform as the solvent. Analysis and assignment of the 1H NMR spectrum confirms the successful synthesis of this rigid monomer.

[0048] Example 2

[0049] 1) Weigh 10g (0.054mol) of methyl protocatechuate and 18.76g (0.136mol) of anhydrous potassium carbonate and dissolve them in 100-150mL of acetone. Then, add 14.69g (0.060mol) of methyl 2,3-dibromopropionate dropwise using a constant pressure dropping funnel. Incubate overnight in a round-bottom flask equipped with a magnetic stirrer and a reflux condenser at 50℃. After cooling and filtering, evaporate the filtrate to dryness and recrystallize it with methanol to obtain a white solid. Dry the solid in a vacuum oven for direct use.

[0050] 2) The rigid monomers benzodioxane dimethyl ester and 1,4-butanediol were used for polymerization, with an alcohol-ester molar ratio of 1.5:1.

[0051] 3) Weigh the reagents according to the corresponding alcohol-ester molar ratio and put them into a 100mL round-bottom flask. Prepolymerize the mixture at 140℃. After melting, heat to the corresponding transesterification temperature and add 3-4 drops of tetrabutyl titanate catalyst. Let it run for 6-8 hours.

[0052] 4) Perform polycondensation for 6-8 hours at the corresponding polymerization temperature.

[0053] 5) After the polycondensation is complete, cool the mixture to room temperature, add chloroform to dissolve it, and precipitate it with methanol.

[0054] 6) Collect the product by vacuum filtration and dry it.

[0055] After the experiment, the chemical structures of the rigid monomers benzodioxane dimethyl ester and 1,4-butanediol homopolymer were determined by nuclear magnetic resonance. The thermal properties of the products were characterized by DSC.

[0056] Figure 2 The 1H NMR spectrum is a homopolymer obtained by homopolymerization of the rigid monomers benzodioxane dimethyl ester and 1,4-butanediol, measured at room temperature using deuterated chloroform as solvent. Analysis and assignment of the 1H NMR spectrum confirms the successful synthesis of the homopolymer.

[0057] Figure 3The melting curves of homopolymer polyester obtained by homopolymerization of rigid monomers benzodioxane dimethyl ester and 1,4-butanediol were analyzed using a NETZSCH PC-200 differential scanning calorimeter. The test temperature ranged from -40℃ to 250℃, and the heating / cooling rate was 10℃ / min. The graph shows that the glass transition temperature of the polyester is 68℃, which is 26℃ higher than that of PBT (42℃) and comparable to that of PBN.

[0058] Example 3

[0059] 1) Weigh 10g (0.054mol) of methyl protocatechuate and 18.76g (0.136mol) of anhydrous potassium carbonate and dissolve them in 100-150mL of acetone. Then, add 14.69g (0.060mol) of methyl 2,3-dibromopropionate dropwise using a constant pressure dropping funnel. Incubate overnight in a round-bottom flask equipped with a magnetic stirrer and a reflux condenser at 50℃. After cooling and filtering, evaporate the filtrate to dryness and recrystallize it with methanol to obtain a white solid. Dry the solid in a vacuum oven for direct use.

[0060] 2) By controlling the feed ratio of dimethyl benzodioxane and dimethyl terephthalate to butanediol, copolyesters PBT with different molar compositions were synthesized. x D y x and y represent the molar percentages of dimethyl terephthalate and dimethyl benzo[a]dioxane, respectively.

[0061] 3) PBT copolyester was obtained by copolymerizing 50 mol% dimethyl benzo[a]oxane and 50 mol% dimethyl terephthalate with 1,4-butanediol. 50 D 50 The molar ratio of alcohol to ester is 1.5:1.

[0062] 4) Weigh the reagents according to the corresponding alcohol-ester molar ratio and put them into a 100mL round-bottom flask. Prepolymerize the mixture at 140℃. After melting, heat to the corresponding transesterification temperature and add 3-4 drops of tetrabutyl titanate catalyst. Let it run for 6-8 hours.

[0063] 5) Perform polycondensation for 6-8 hours at the corresponding polymerization temperature.

[0064] 6) After the polycondensation is complete, cool the mixture to room temperature, add chloroform to dissolve it, and precipitate it with methanol.

[0065] 7) Collect the product by vacuum filtration and dry it.

[0066] Figure 4 PBT is a copolyester composed of equimolar amounts of benzodioxane and dimethyl terephthalate, obtained by copolymerizing 50 mol% dimethyl benzodioxane and 50 mol% dimethyl terephthalate with 1,4-butanediol.50 D 50 The proton NMR spectrum was measured using deuterated chloroform as a solvent at room temperature. Analysis of the proton NMR spectrum confirmed that the molar composition of the copolyester was essentially consistent with the theoretical molar composition, indicating that the synthesis of the copolyester was successful.

[0067] Figure 5 The melting curve was obtained using a NETZSCH PC-200 differential scanning calorimeter. The test temperature ranged from -40℃ to 250℃, and the heating / cooling rate was 10℃ / min. The graph shows that the glass transition temperature of polyester is 51.2℃ and the melting point is 144℃. The glass transition temperature is higher than that of PBT, which significantly improves the thermal properties of PBT.

[0068] Example 4

[0069] 1) Weigh 10g (0.054mol) of methyl protocatechuate and 18.76g (0.136mol) of anhydrous potassium carbonate and dissolve them in 100-150mL of acetone. Then, add 14.69g (0.060mol) of methyl 2,3-dibromopropionate dropwise using a constant pressure dropping funnel. Incubate overnight in a round-bottom flask equipped with a magnetic stirrer and a reflux condenser at 50℃. After cooling and filtering, evaporate the filtrate to dryness and recrystallize it with methanol to obtain a white solid. Dry the solid in a vacuum oven for direct use.

[0070] 2) By controlling the feed ratio of dimethyl benzodioxane and dimethyl 2,6-naphthalenedicarboxylate to copolymerize with 1,4-butanediol, copolyesters PBN with different molar compositions were synthesized. x D y x and y represent the molar percentages of dimethyl 2,6-naphthalenedicarboxylate and dimethyl benzo[a]dioxane, respectively.

[0071] 3) PBT copolyester was obtained by copolymerizing 50 mol% dimethyl benzodioxane, 50 mol% dimethyl 2,6-naphthalenedicarboxylate, and 1,4-butanediol. 50 D 50 The molar ratio of alcohol to ester is 1.5:1.

[0072] 4) Weigh the reagents according to the corresponding alcohol-ester molar ratio and put them into a 100mL round-bottom flask. Prepolymerize the mixture at 140℃. After melting, heat to the corresponding esterification temperature and add 3-4 drops of tetrabutyl titanate catalyst. Let it run for 6-8 hours.

[0073] 5) Perform polycondensation for 6-8 hours at the corresponding polymerization temperature.

[0074] 6) After the polycondensation is complete, cool the mixture to room temperature, add chloroform to dissolve it, and precipitate it with methanol.

[0075] 7) Collect the product by vacuum filtration and dry it.

[0076] Figure 6 PBT is a copolyester composed of equimolar amounts of benzodioxane dimethyl ester and 2,6-naphthalenedicarboxylate, obtained by copolymerizing 50 mol% 2-benzodioxane dimethyl ester and 50 mol% 2,6-naphthalenedicarboxylate with butanediol. 50 D 50 The proton NMR spectrum was measured using deuterated chloroform as a solvent at room temperature. Analysis of the proton NMR spectrum confirmed that the molar composition of the copolyester was essentially consistent with the theoretical molar composition, indicating that the synthesis of the copolyester was successful.

[0077] Figure 7 The melt curve was obtained by analysis using a NETZSCH PC-200 differential scanning calorimeter. The test temperature was -40℃ to 250℃, and the heating / cooling rate was 10℃ / min. The graph shows that the glass transition temperature of polyester is 71℃, which is close to that of PBN (72℃). This indicates that dimethyl benzodioxane can partially replace dimethyl 2,6-naphthalenedicarboxylate.

[0078] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A method for modifying PBT and PBN with benzodioxane dimethyl ester, using benzodioxane dimethyl ester, dimethyl terephthalate and 1,4-butanediol or benzodioxane dimethyl ester, dimethyl 2,6-naphthalenedicarboxylate and 1,4-butanediol as raw materials, and tetrabutyl titanate as catalyst, to prepare thermoplastic polyester through two-step melt polymerization, the steps of which are as follows: 1) Preparation of monomeric benzodioxane dimethyl ester from protocatechuic acid methyl ester and 2,3-dibromopropionate methyl ester Add methyl protocatechuate and anhydrous potassium carbonate to a three-necked flask, dissolve in acetone, then add methyl 2,3-dibromopropionate dropwise using a constant pressure dropping funnel. Incubate overnight in a round-bottom flask equipped with a magnetic stirrer and reflux condenser at 50°C. After cooling and filtration, evaporate the filtrate to dryness and recrystallize with methanol to obtain a white solid. 2) Preparation of PBT copolyester Alcohol and ester were added sequentially in a three-necked flask at a molar ratio of 1.5:1, along with dimethyl benzo[a]dioxane, dimethyl terephthalate, 1,4-butanediol, and tetrabutyl titanate. The mixture was heated to 180°C under a nitrogen atmosphere and stirred continuously. Vacuum polycondensation began when 95% of the theoretical methanol was distilled off. Polyester material was prepared when the rod-climbing phenomenon occurred. 3) Preparation of PBN copolyester Alcohol and ester were added sequentially in a three-necked flask at a molar ratio of 1.5:1, along with monomers benzodioxane dimethyl ester, 2,6-naphthalenedicarboxylate dimethyl ester, 1,4-butanediol, and tetrabutyl titanate. The mixture was heated to 180°C under a nitrogen atmosphere and stirred continuously. Vacuum polycondensation began when 95% of the theoretical methanol was distilled off. Polyester material was prepared when the rod-climbing phenomenon occurred.

2. The method for preparing monomeric benzodioxane dimethyl ester from methyl protocatechuate and methyl 2,3-dibromopropionate according to claim 1, characterized in that: The ratio of protocatechuic acid methyl ester, 2,3-dibromopropionate methyl ester, anhydrous potassium carbonate, and acetone is 10g:14.69g:18.76g:150mL.

3. The method for modifying PBT polyester with monomer benzodioxane dimethyl ester according to claim 1, characterized in that... The mass of the catalyst, tetrabutyl titanate, is 0.05% of the total mass of the reactants.

4. The method for modifying PBN polyester with monomer benzodioxane dimethyl ester according to claim 1, characterized in that... The mass of the catalyst, tetrabutyl titanate, is 0.05% of the total mass of the reactants.

5. In the preparation process of the polyester, the catalyst is preferably tetrabutyl titanate; the vacuum degree of post-curing is 0.03-0.05 mbar.

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