Cyclic polyhemiacetal ester and synthetic method thereof

Abstract

The invention discloses a cyclic polyhemiacetal ester and a synthesis method thereof, the structural general formula of the cyclic polyhemiacetal ester is as follows: in the formula, n is selected from 10-10000; the synthesis method comprises the following steps: mixing a monomer and a catalyst, and carrying out solution polymerization without adding an initiator; the monomer is selected from 1, 3-dioxane-4-ketone, the structural general formula of the catalyst is MLx, and M is selected from one or more of rare earth metal, transition metal, IIA group metal and IIIA group metal; l is selected from one or more of trifluoromethanesulfonate radical, methanesulfonate radical, p-toluenesulfonate radical, chlorine, bromine, iodine, trifluoroacetate radical, acetate radical, phosphate radical and nitrate radical; x is selected from natural numbers of 1-3. The cyclic polyhemiacetal ester is successfully prepared for the first time, the molecular weight of the cyclic polyhemiacetal ester is large and adjustable, and the cyclic polyhemiacetal ester is a crystalline polymer. The synthesis method is mild in condition, simple, controllable and suitable for industrial production. # imgabs0 #

Description

Technical Field

[0001] The invention relates to the technical field of polymer synthesis, in particular to a cyclic polyhemiacetal ester and a synthesis method thereof. Background Art

[0002] Cyclic polymers have certain properties that are different from linear polymers, such as smaller hydrodynamic volume and low viscosity. The synthesis of cyclic polymers is usually very challenging. The main synthetic strategies are related to the cyclization method and the ring expansion method. The ring closure method is to synthesize cyclic polymers through coupling reactions of the chain end functional groups of linear polymers. It usually needs to be carried out in a dilute solution to avoid interchain reactions, and the products are often mixed with linear polymers that are difficult to separate (J Polym Sci. 2020, 58, 1481-1502). The ring expansion method refers to a method in which the active chain always maintains a cyclic topological structure during the polymerization process. This method can prepare high molecular weight cyclic polymers and mechanistically avoids the production of linear polymers in the product. Zwitterionic polymerization (including cationic and anionic) is a typical method for synthesizing cyclic polymers by ring expansion (Acc. Chem. Res. 2013, 46, 2585–2596).

[0003] Poly(hemiacetal ester) is a type of polymer material with a main chain containing hemiacetal ester bonds in the repeating unit. Since poly(hemiacetal ester) can be degraded under both acidic and alkaline conditions, it has broad application prospects in the field of degradable materials (Biomacromolecules, DOI: 10.1021 / acs.biomac.4c01229). The commonly used synthesis method of poly(hemiacetal ester) is the ring-opening polymerization of cyclic hemiacetal ester. The ring-opening polymerization of cyclic hemiacetal ester can follow a cationic or anionic mechanism, in which anionic polymerization is usually accompanied by the removal of small molecular aldehydes or ketones, resulting in the product being a polyester or polyester polyacetal copolymer rather than a poly(hemiacetal ester) (Polym. Chem., 2017, 8, 2990-2996; Polym. Chem., 2020, 11, 4928-4932; Acta Polymerica Sinica, 54(3): 356-364). Cationic polymerization generally does not remove aldehydes or ketones, and the product is polyhemiacetal ester (Ind. Eng. Chem. Res., 2016, 55, 11747-11755; Polym. Chem., 2019, 10, 4573-4583).

[0004] 1,3-Dioxane-4-one is a six-membered ring hemiacetal ester with the simplest structure. A Chinese patent document with application publication number CN116903835 A reports a polyester containing an acetal structure and a preparation method thereof. The polyester containing an acetal structure is represented by [A] x —[B] yThe technical solution uses acetal lactone monomer 1,3-dioxane-4-one as raw material, or uses acetal lactone monomer and lactone monomer as raw materials, and prepares linear polyester containing acetal structure through anionic ring-opening polymerization under the action of catalyst and / or initiator. The catalyst used is a Lewis base catalyst, including metal catalyst, organic catalyst and inorganic catalyst. The metal catalyst includes alkoxy rare earth or transition metal compound, and the organic catalyst includes organic base and organic acid. The polymerization is carried out at -70℃~80℃. According to the technical solution, Figure 1 From the NMR spectrum of poly(1,3-dioxane-4-one) prepared in Example 1, it can be seen that the prepared polymer is a crystalline polymer, and the characteristic peaks of the ester structure are basically not observed, which may be related to the low temperature polymerization temperature (-70°C) used. When the polymerization temperature is gradually increased, such as Figure 3 (Example 3, polymerization temperature -30°C), Figure 4 (Example 8, polymerization temperature 25°C), obvious characteristic peaks can be observed at 4.2ppm and 4.8ppm in the NMR spectrum, which are the characteristic peaks of the ester structure after formaldehyde removal, which also shows that in the system of this technical solution, higher polymerization temperature leads to increased formaldehyde removal and decreased crystallinity of the product. Therefore, if you want to prepare a crystalline polymer, you need to control the polymerization temperature at a low temperature (-40°C or below).

[0005] At present, there is no research on the preparation of poly (1,3-dioxane-4-one) by cationic polymerization, and there is no precedent for the synthesis of cyclic poly (1,3-dioxane-4-one). Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention successfully prepares cyclic polyhemiacetal ester for the first time, the molecular weight of the cyclic polymer is large and adjustable, and it is a crystalline polymer. The synthesis method of the present invention has mild conditions, is simple and controllable, and is suitable for industrial production.

[0007] The specific technical solutions are as follows:

[0008] A cyclic polyhemiacetal ester, the general structural formula is as follows:

[0009]

[0010] Wherein, n is selected from 10 to 10000.

[0011] The cyclic polyhemiacetal ester prepared by the present invention has a large and adjustable molecular weight, a narrow molecular weight distribution and strong controllability; no characteristic peak of the ester structure and no end group signal are observed in the cyclic polyhemiacetal ester prepared by the present invention, which proves that it has a cyclic structure.

[0012] Preferred:

[0013] The number average molecular weight of the cyclic polyhemiacetal ester is 1 to 1000 kg / mol, and the molecular weight distribution is not higher than 3.5.

[0014] More preferably, the number average molecular weight of the cyclic polyhemiacetal ester is 10 to 100 kg / mol, and the molecular weight distribution is not higher than 2.5.

[0015] Preferred:

[0016] The content of hemiacetal ester bonds in the main chain of the cyclic polyhemiacetal ester accounts for no less than 95 mol% of the total number of repeating units;

[0017] More preferably, the content of hemiacetal ester bonds in the main chain accounts for no less than 99 mol % of the total number of repeating units.

[0018] According to the DSC test results, the cyclic polyhemiacetal ester prepared in the present invention is a crystalline polymer.

[0019] The present invention also discloses a method for synthesizing the cyclic polyhemiacetal ester, comprising:

[0020] The monomers and the catalyst are mixed, and solution polymerization is performed without adding an initiator to prepare the cyclic polyhemiacetal ester;

[0021] The monomer is selected from 1,3-dioxane-4-one, and the structural formula is shown in the following formula (I):

[0022]

[0023] The catalyst has the general structural formula ML x , M is selected from one or more of rare earth metals, transition metals, Group IIA metals, and Group IIIA metals; L is selected from one or more of trifluoromethanesulfonate, methanesulfonate, p-toluenesulfonate, chlorine, bromine, iodine, trifluoroacetate, acetate, phosphate, and nitrate; x is selected from a natural number of 1 to 3.

[0024] In the prior art, since it is difficult to avoid the removal of small molecular formaldehyde during the ring-opening polymerization of 1,3-dioxane-4-one, the product is usually a copolymer of polyester and polyhemiacetal ester, and it is difficult to obtain a highly crystalline polyhemiacetal ester with a clear structure under mild conditions. In the present invention, under the action of a preferred catalyst and without the addition of an initiator, the selective ring-opening polymerization of 1,3-dioxane-4-one is successfully achieved, and a highly crystalline cyclic poly (1,3-dioxane-4-one) with a clear structure is prepared.

[0025] The catalyst disclosed in the present invention can be specifically selected from one or more of lanthanum (III) trifluoromethanesulfonate, lutetium (III) trifluoromethanesulfonate, yttrium (III) trifluoromethanesulfonate, scandium (III) methanesulfonate, zinc (II) trifluoromethanesulfonate, iron (III) trifluoromethanesulfonate, magnesium (II) trifluoromethanesulfonate, iron (III) p-toluenesulfonate, zinc (II) p-toluenesulfonate, tin (II) p-toluenesulfonate, zinc (II) trifluoroacetate, scandium (III) nitrate, iron (III) phosphate, aluminum chloride (III), and indium bromide (III).

[0026] Preferred:

[0027] In the catalyst, M is selected from rare earth metals and / or transition metals, and L is selected from one or more of trifluoromethanesulfonate, methanesulfonate, and p-toluenesulfonate.

[0028] Further preferably, the catalyst is selected from one or more of lanthanum (III) trifluoromethanesulfonate, lutetium (III) trifluoromethanesulfonate, yttrium (III) trifluoromethanesulfonate, scandium (III) methanesulfonate, zinc (II) trifluoromethanesulfonate, iron (III) trifluoromethanesulfonate, iron (III) p-toluenesulfonate, zinc (II) p-toluenesulfonate, and tin (II) p-toluenesulfonate.

[0029] Preferred:

[0030] In the synthesis method of the present invention, the molar ratio of the catalyst to the monomer is 1:(20-10000); specifically, it can be selected from 1:20, 1:50, 1:100, 1:150, 1:200, 1:250, 1:500, 1:750, 1:1000, 1:2000, 1:2500, 1:5000, 1:7500, 1:10000 or any ratio within the above range;

[0031] More preferably, the molar ratio of catalyst to monomer is 1:(50-5000);

[0032] More preferably, the molar ratio of the catalyst to the monomer is 1:(50-500).

[0033] Preferred:

[0034] In the synthesis method of the present invention, the solvent used in the solution polymerization is selected from one or more of acetonitrile, dioxane, toluene, dichloromethane, chloroform, 1,2-dichloroethane, 1,1-dichloroethane, methyl tert-butyl ether, methyltetrahydrofuran, propylene carbonate, γ-butyrolactone, dimethyl sulfoxide, and dimethylformamide;

[0035] Further preferably, the solvent is selected from solvents having better solubility for the catalyst used.

[0036] Still more preferably, in order to further improve the solubility of the catalyst in the solvent, the catalyst can be first dissolved in a benign solvent and then added to the reaction system.

[0037] Preferred:

[0038] In the synthesis method of the present invention, the solution polymerization is carried out at a temperature of 0 to 50° C. and a time of 0.5 to 168 hours.

[0039] The synthesis method disclosed by the invention has mild reaction conditions and does not require low or high temperature.

[0040] Preferred:

[0041] In the synthesis method of the present invention, the solution polymerization also needs to be quenched by adding a terminator;

[0042] The terminator is selected from one or more of tri-n-butylphosphine, triphenylphosphine, piperidine, tetrahydropyrrole, triethylamine, and tri-n-butylamine.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The invention synthesizes poly(1,3-dioxane-4-one) with a cyclic structure for the first time. Compared with linear polymers, the cyclic polymer has low viscosity and good processing performance.

[0045] The synthesis method of the cyclic polyhemiacetal ester disclosed in the present invention is a cationic zwitterionic ring-opening polymerization, and the catalyst used is Lewis acid such as rare earth metal salts, transition metal salts and main group metal salts. These catalysts are commercial stable metal salts with strong universality and are suitable for large-scale industrial production. The polymerization conditions of the present invention are mild, no low temperature conditions (-40°C or below) are required, the yield is high, and it is more suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The H NMR spectrum of the product prepared in Example 1 of the present invention ( 1 H NMR);

[0047] Figure 2 The NMR carbon spectrum of the product prepared in Example 1 of the present invention ( 13 C NMR);

[0048] Figure 3 Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF) of the product prepared in Example 1 of the present invention;

[0049] Figure 4 This is the differential scanning calorimetry (DSC) curve of the product prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0051] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0052] The molecular weight and molecular weight distribution of the polymer in the present invention were determined by gel permeation chromatography (SEC, Waters 1515) (N,N-dimethylformamide containing 0.05 mol / L lithium bromide, 60° C., flow rate of 1.0 mL / min);

[0053] The nuclear magnetic resonance hydrogen spectrum ( 1 HNMR) was measured on a Bruker Avance DMX400 instrument using deuterated dimethyl sulfoxide as solvent and tetramethylsilane as internal standard;

[0054] The melting point of the polymer in the present invention is measured in a differential scanning calorimeter (DSC, Q200 TA).

[0055] Example 1

[0056] 0.204g (2mmol) of monomer 1,3-dioxane-4-one was dissolved in 2mL of dichloromethane, and 0.1mL of lanthanum trifluoromethanesulfonate (0.02mmol, 11.7mg) in propylene carbonate was added. After shaking, the mixture was placed in a 0℃ cold bath for reaction for 24h. After the polymerization was completed, tri-n-butylphosphine was added to terminate the polymerization. The polymerization solution was precipitated in methanol, filtered, and vacuum dried to constant weight to obtain polyhemiacetal ester with a yield of 57%.

[0057] After testing, the polymer product of this example has an SEC number average molecular weight of 24.1 kg / mol and a molecular weight distribution of 1.9. 1 H and 13 C NMR spectra (DMSO-d6) are shown as Figure 1 and Figure 2 As shown, the signal attribution is clear and the structure is clearly characterized, indicating that the obtained product is a polyhemiacetal ester without formaldehyde removal. No end group signal was observed in the NMR spectrum, and the MALDI-ToF spectrum ( Figure 3 ) indicates that the polymer is a ring structure. The DSC test results of the polymer are as follows Figure 4 As shown, the obtained polyhemiacetal ester is a crystalline polymer with a melting point of 53°C.

[0058] Example 2

[0059] The synthesis process is substantially the same as that in Example 1, except that the solvent is replaced with an equal volume of acetonitrile.

[0060] According to the test, the yield of the polymer product prepared in this embodiment is 48%, the SEC number average molecular weight is 19.3 kg / mol, and the molecular weight distribution is 3.3.

[0061] Example 3

[0062] The synthesis process is basically the same as in Example 1, except that:

[0063] The solvent was replaced with an equal volume of toluene, and the reaction temperature was changed to 10 °C.

[0064] Since poly(1,3-dioxane-4-one) has low solubility in toluene, the polymerization reaction is a heterogeneous polymerization. According to the test, the yield of the polymerization product prepared in this embodiment is 74%, the SEC number average molecular weight is 20.8 kg / mol, and the molecular weight distribution is 3.0.

[0065] Example 4

[0066] 0.204g (2mmol) of monomer 1,3-dioxane-4-one was dissolved in 1mL of dichloromethane, and 0.1mL of zinc trifluoromethanesulfonate (0.02mmol, 7.3mg) in propylene carbonate solution was added. After shaking, the mixture was placed in a 30°C oil bath for reaction for 15h. After the polymerization was completed, tri-n-butylphosphine was added to terminate the polymerization. The polymerization solution was precipitated in methanol, filtered, and vacuum dried to constant weight to obtain polyhemiacetal ester with a yield of 53%.

[0067] After testing, the SEC number average molecular weight of the polymer product prepared in this example is 80.6 kg / mol, and the molecular weight distribution is 2.4.

[0068] Example 5

[0069] The synthesis process is substantially the same as that in Example 4, except that:

[0070] The catalyst was replaced with an equimolar amount of iron p-toluenesulfonate, the polymerization temperature was replaced with 0° C., and the reaction time was replaced with 8 h.

[0071] According to the test, the yield of the polymer product prepared in this embodiment is 54%, the SEC number average molecular weight is 33.8 kg / mol, and the molecular weight distribution is 1.7.

[0072] Example 6

[0073] The synthesis process is substantially the same as that in Example 4, except that the catalyst is replaced with an equimolar amount of zinc trifluoroacetate.

[0074] According to the test, the yield of the polymer product prepared in this example is 9%, the SEC number average molecular weight is 6.5 kg / mol, and the molecular weight distribution is 2.1.

[0075] Example 7

[0076] The synthesis process is substantially the same as that in Example 4, except that:

[0077] The catalyst was replaced with an equimolar amount of indium bromide and the reaction time was changed to 24 h.

[0078] According to the test, the yield of the polymer product prepared in this embodiment is 37%, the SEC number average molecular weight is 8.4 kg / mol, and the molecular weight distribution is 2.3.

[0079] Example 8

[0080] The synthesis process is substantially the same as that in Example 4, except that:

[0081] The catalyst was replaced with an equimolar amount of magnesium trifluoromethanesulfonate, and the reaction time was changed to 24 h.

[0082] According to the test, the yield of the polymer product prepared in this embodiment is 19%, the SEC number average molecular weight is 4.4 kg / mol, and the molecular weight distribution is 1.9.

[0083] Comparative Example 1

[0084] The synthesis process is substantially the same as that in Example 4, except that:

[0085] The catalyst was replaced with an equimolar amount of cesium trifluoroacetate and the reaction time was changed to 24 h.

[0086] After testing, no polymer was obtained in this comparative example.

[0087] Comparative Example 2

[0088] The synthesis process is substantially the same as that in Example 4, except that:

[0089] The catalyst was replaced with an equimolar amount of potassium trifluoromethanesulfonate, and the reaction time was changed to 24 h.

[0090] After testing, no polymer was obtained in this comparative example.

[0091] What is disclosed above are preferred embodiments, but the protection scope of the present invention is not limited thereto. A person skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A cyclic polyhemiacetal ester, characterized in that The general structure is as follows: Wherein, n is selected from 10 to 10000.

2. The cyclic polyhemiacetal ester according to claim 1, characterized in that The number average molecular weight is 1 to 1000 kg / mol, and the molecular weight distribution is not higher than 3.

5.

3. The cyclic polyhemiacetal ester according to claim 1, characterized in that The content of hemiacetal ester bonds in the main chain is not less than 95 mol% of the total number of repeating units.

4. The cyclic polyhemiacetal ester according to claim 1, characterized in that It is a crystalline polymer.

5. A method for synthesizing a cyclic polyhemiacetal ester according to any one of claims 1 to 4, characterized in that: include: The monomers and the catalyst are mixed, and solution polymerization is performed without adding an initiator to prepare the cyclic polyhemiacetal ester; The monomer is selected from 1,3-dioxane-4-one, and the structural formula is shown in the following formula (I): The catalyst has the general structural formula ML x , M is selected from one or more of rare earth metals, transition metals, Group IIA metals, and Group IIIA metals; L is selected from one or more of trifluoromethanesulfonate, methanesulfonate, p-toluenesulfonate, chlorine, bromine, iodine, trifluoroacetate, acetate, phosphate, and nitrate; x is selected from a natural number of 1 to 3.

6. The method for synthesizing a cyclic polyhemiacetal ester according to claim 5, characterized in that: The molar ratio of the catalyst to the monomer is 1:(20-10000).

7. The method for synthesizing a cyclic polyhemiacetal ester according to claim 5, characterized in that: The solvent used in the solution polymerization is selected from one or more of acetonitrile, dioxane, toluene, dichloromethane, chloroform, 1,2-dichloroethane, 1,1-dichloroethane, methyl tert-butyl ether, methyltetrahydrofuran, propylene carbonate, γ-butyrolactone, dimethyl sulfoxide, and dimethylformamide.

8. The method for synthesizing a cyclic polyhemiacetal ester according to claim 5, characterized in that: The solution polymerization is carried out at a temperature of 0 to 50° C. and a time of 0.5 to 168 hours.

9. The method for synthesizing a cyclic polyhemiacetal ester according to claim 5, characterized in that: The solution polymerization also needs to be quenched by adding a terminator; The terminator is selected from one or more of tri-n-butylphosphine, triphenylphosphine, piperidine, tetrahydropyrrole, triethylamine, and tri-n-butylamine.

Images