A hyperbranched polycaprolactone-polylactic acid copolymer and its preparation method and application

Abstract

The present invention provides a hyperbranched polycaprolactone-polylactic acid copolymer and a preparation method and application thereof, belonging to the technical field of high molecular polymer synthesis. The copolymer is synthesized by using amino-terminated polylactic acid and 2,2-dihydroxymethylpropionic acid as starting materials to synthesize an intermediate terminal dimethylolpropionamide polylactic acid, and the terminal dimethylolpropionamide polylactic acid is then polymerized with ε-caprolactone. Polycaprolactone and polylactic acid are combined together in the form of chemical bonds, and the polymer with a hyperbranched structure has more free end groups, which can provide more lithium ion transmission channels and is conducive to the increase of ion conductivity. Due to the presence of polylactic acid, the crystallinity of polycaprolactone is reduced, which is conducive to the movement of polymer chain segments, thereby improving the mobility of lithium ions in the polymer. Compared with pure polycaprolactone electrolyte, it has better cycle performance and electrochemical stability.

Description

Technical Field

[0001] The invention belongs to the technical field of high molecular polymer synthesis, and specifically relates to a hyperbranched polycaprolactone-polylactic acid copolymer and a preparation method and application thereof. Background Art

[0002] Since the beginning of the 20th century, my country's main energy supply has been fossil fuels, which have a serious impact on the environment. Research on new green and sustainable energy has been put on the agenda. The invention of lithium batteries is very important for the policy of "carbon neutrality and carbon peak". Due to its high energy density, good cycle efficiency, green and sustainable advantages, it is the best energy storage device. In particular, liquid organic batteries are the most common. Today's new energy vehicles, mobile phones, laptops and other large and small electric devices are inseparable from lithium batteries.

[0003] However, there are safety risks behind the excellent lithium batteries. The "Samsung mobile phone explosion" incident many years ago and the "burning Tesla" incident in recent years have made it difficult for the public to believe in the safety of batteries. Liquid lithium-ion electrolyte batteries generally have the risk of being flammable and explosive at high temperatures, which greatly limits their development in power batteries and energy storage batteries.

[0004] Thus, polymer solid electrolytes came into being. Due to their extremely high safety and chemical stability, and the fact that they do not bulge or leak in the PACK, they are the future direction of electrolyte development. However, the research on polymer solid electrolytes is not mature and cannot be commercialized. The main reason is that most polymer structures are difficult to conduct electricity, and only a special part of polymers can obtain conductivity through modification and other methods.

[0005] As a polymer material, polycaprolactone (PCL) has become one of the most promising new electrolyte materials due to its excellent properties such as good stability to lithium, wide electrochemical stability window, low cost, and simple preparation method. However, polycaprolactone is a semi-crystalline polymer at room temperature. Due to its high crystallinity, the movement of chain segments is hindered and the ionic conductivity is low. In addition, the molecular chain structure of commercial polycaprolactone is a linear structure, which is not conducive to the movement of lithium ions in the polymer, limiting its application as an electrolyte. This requires modification of PCL. However, traditional physical blending modification is that two or more components are combined through weak van der Waals forces, which may lead to poor performance due to uneven dispersion, such as cracking, poor heat resistance, and easy short circuit. Summary of the invention

[0006] The purpose of the present invention is to provide a hyperbranched polycaprolactone-polylactic acid copolymer and a preparation method and application thereof in view of the above-mentioned deficiencies in the prior art, which can provide more lithium ion transmission channels and is conducive to increasing ion conductivity.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The first object of the present invention is to provide a hyperbranched polycaprolactone-polylactic acid copolymer, the structure of which is shown in Formula I:

[0009] Formula Ⅰ.

[0010] The second object of the present invention is to provide a method for preparing the above-mentioned hyperbranched polycaprolactone-polylactic acid copolymer, comprising the following specific steps:

[0011] Step S1, dissolving amino-terminated polylactic acid and 2,2-dimethylol propionic acid in a solvent, adding a catalyst and reacting to obtain a mixture A;

[0012] Step S2, washing the mixture A described in step S1 with water, and precipitating with a first precipitant to obtain a product of dimethylolpropionamide-terminated polylactic acid;

[0013] Step S3, polymerizing the dihydroxymethylpropionamide-terminated polylactic acid produced in step S2 with ε-caprolactone in a nitrogen atmosphere in the presence of a catalyst to obtain a mixture B;

[0014] Step S4, dissolving the mixture B described in step S3, and precipitating with a second precipitant to obtain a hyperbranched polycaprolactone-polylactic acid copolymer.

[0015] Furthermore, in step S1, the solvent is dichloromethane, and the catalyst is 1-hydroxybenzotriazole and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride.

[0016] Furthermore, the molar ratio of the amino-terminated polylactic acid to the 2,2-dihydroxymethylpropionic acid is 1: (0.9-1.1), the molar ratio of the 1-hydroxybenzotriazole to the 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1: (0.9-1.1), and the molar ratio of the catalyst to the 2,2-bis(hydroxymethyl)propionic acid is 3: (1.5-2.5).

[0017] Furthermore, in step S1, the reaction temperature is 20-40°C, and the reaction time is 8-12h.

[0018] Furthermore, in step S3, the catalyst is stannous isooctanoate, the mass ratio of the terminal dihydroxymethyl propionamide polylactic acid to ε-caprolactone is 1:(2-9), and the catalyst is 0.10-0.40% of the mass of ε-caprolactone.

[0019] Furthermore, in step S3, the reaction temperature is 140-150° C., and the reaction time is 5-6 hours.

[0020] Furthermore, in step S2, the washing solvent is distilled water, and the first precipitant is methanol; in step S4, the dissolving agent is dichloromethane, and the second precipitant is methanol.

[0021] The third object of the present invention is to provide an electrolyte comprising the hyperbranched polycaprolactone-polylactic acid copolymer.

[0022] A fourth object of the present invention is to provide an electrolyte battery comprising an anode, a cathode and a conductive electrolyte, wherein the conductive electrolyte comprises the above-mentioned electrolyte.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The hyperbranched polycaprolactone-polylactic acid copolymer provided by the present invention is prepared by synthesizing an intermediate terminal dimethylol propionamide polylactic acid using terminal amino polylactic acid and 2,2-dihydroxymethyl propionic acid as starting materials, and then polymerizing the terminal dimethylol propionamide polylactic acid with ε-caprolactone to obtain a hyperbranched polycaprolactone-polylactic acid copolymer. Polycaprolactone and polylactic acid are combined together in the form of chemical bonds, and the polymer structure is uniform. Both polycaprolactone and polylactic acid are biodegradable polymers, which are easy to recycle and conform to green and sustainable development.

[0025] (2) Compared with pure polycaprolactone electrolyte, the present invention provides a hyperbranched polycaprolactone-polylactic acid copolymer with better cycle performance and electrochemical stability.

[0026] (3) At the same time, polymers with hyperbranched structures have more free end groups, which can provide more lithium ion transmission channels and are conducive to the increase of ionic conductivity.

[0027] (4) Due to the presence of polylactic acid, the crystallinity of polycaprolactone is reduced, which is beneficial to the movement of polymer chain segments, thereby improving the mobility of lithium ions in the polymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A synthetic route diagram of a hyperbranched polycaprolactone-polylactic acid copolymer of the present invention;

[0029] Figure 2 A schematic diagram of lithium ion movement in the hyperbranched polycaprolactone-polylactic acid copolymer prepared in the present invention;

[0030] Figure 3 It is the nuclear magnetic hydrogen spectrum of the intermediate PLA-DMPA in the preparation process of the hyperbranched polycaprolactone-polylactic acid copolymer of the present invention;

[0031] Figure 4is the nuclear magnetic hydrogen spectrum of the hyperbranched polycaprolactone-polylactic acid copolymer PCL-PLA of the present invention;

[0032] Figure 5 The DSC graphs of copolymers of various proportions in the preparation method of a hyperbranched polycaprolactone copolymer of the present invention;

[0033] Figure 6a and Figure 6b DMA graphs of copolymers of various proportions in a method for preparing a hyperbranched polycaprolactone-polylactic acid copolymer of the present invention;

[0034] Figure 7 The ionic conductivity diagram of the electrolyte battery prepared by using the hyperbranched polycaprolactone-polylactic acid copolymer of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention clearer, embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0036] In the present invention, 2,2-dihydroxymethylpropionic acid is also referred to as 2,2-bis(hydroxymethyl)propionic acid; 1-hydroxybenzotriazole is abbreviated as HOBt; 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is abbreviated as EDCI; stannous isooctanoate is abbreviated as Sn(Oct)2; polycaprolactone is abbreviated as PCL; polylactic acid is abbreviated as PLA; dihydroxymethylpropionamide-terminated polylactic acid is abbreviated as PLA-DMPA; and hyperbranched polycaprolactone copolymer is abbreviated as PCL-PLA.

[0037] like Figure 1 As shown in FIG. 1 , it is a synthetic route map of the hyperbranched polycaprolactone-polylactic acid copolymer of the present invention. The following embodiments are all implemented according to the synthetic route map. The specific synthetic steps are as follows:

[0038] (1) After amino-terminated polylactic acid and 2,2-dihydroxymethylpropionic acid are dissolved in dichloromethane, 1-hydroxybenzotriazole and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride are added to react at a temperature of 20-40° C. for a reaction time of 8-12 h to obtain a mixture A; the molar ratio of amino-terminated polylactic acid to 2,2-dihydroxymethylpropionic acid is 1:(0.9-1.1), the molar ratio of 1-hydroxybenzotriazole to 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1:(0.9-1.1), and the molar ratio of the catalyst to 2,2-bis(hydroxymethyl)propionic acid is 3:(1.5-2.5);

[0039] (2) washing the mixture A with water, and precipitating it with a first precipitant to obtain a product of dihydroxymethylpropionamide polylactic acid;

[0040] (3) polymerizing the dimethylolpropionamide-terminated polylactic acid and ε-caprolactone in a nitrogen atmosphere in the presence of stannous isooctanoate at a temperature of 140-160°C for a reaction time of 5-6 hours to obtain a mixture B, wherein the mass ratio of the dimethylolpropionamide-terminated polylactic acid to ε-caprolactone is 1:(2-9), and the amount of stannous isooctanoate added is 0.10-0.40% of the mass of ε-caprolactone;

[0041] (4) Dissolve the mixture B and precipitate it with methanol to obtain a hyperbranched polycaprolactone-polylactic acid copolymer.

[0042] like Figure 2 The figure shows the schematic diagram of lithium ion movement in hyperbranched polycaprolactone copolymer. Through this new synthesis method of polycaprolactone copolymer, a polycaprolactone copolymer containing a hyperbranched structure was successfully designed. The presence of the hyperbranched structure provides more channels for lithium ion transmission, and the molecular chain movement of the polymer is greatly enhanced, which makes the polymer electrolyte have higher ionic conductivity.

[0043] In some embodiments, the hyperbranched polycaprolactone-polylactic acid copolymer of the present invention can be used alone as an electrolyte, or as a raw material in an electrolyte material.

[0044] Example 1

[0045] This embodiment provides a method for preparing a hyperbranched polycaprolactone-polylactic acid copolymer PCL-PLA-10.

[0046] The specific steps are as follows:

[0047] (1) Synthesis of terminal dihydroxymethyl propionamide polylactic acid: 2 g (0.3 mmol) PLA-NH2 and 0.04 g (0.3 mmol) 2,2-bis (hydroxymethyl) propionic acid were added to a round-bottom flask in sequence and dissolved with dichloromethane. After dissolution, 0.06 g (0.45 mmol) HOBt and 0.086 g (0.45 mmol) EDCI were added to the reaction solution in sequence. After addition, the reaction was continued for 10 h. Distilled water was added for washing and methanol precipitation was performed to obtain the product PLA-DMPA.

[0048] (2) Synthesis of hyperbranched copolymer: In a round-bottom flask, 10 wt% PLA-DMPA as an initiating macromolecule, ε-caprolactone, and 0.2 wt% Sn(Oct)2 were added in sequence, heated to 150°C under nitrogen atmosphere, and reacted for 3 h. The product PCL-PLA-10 was obtained by dissolving it in dichloromethane and precipitating it in methanol.

[0049] Example 2

[0050] This embodiment provides a method for preparing a hyperbranched polycaprolactone-polylactic acid copolymer PCL-PLA-15.

[0051] The specific steps are as follows:

[0052] (1) Synthesis of terminal dihydroxymethyl propionamide polylactic acid: 2 g (0.3 mmol) PLA-NH2 and 0.04 g (0.3 mmol) 2,2-bis (hydroxymethyl) propionic acid were added to a round-bottom flask in sequence and dissolved with dichloromethane. After dissolution, 0.06 g (0.45 mmol) HOBt and 0.086 g (0.45 mmol) EDCI were added to the reaction solution in sequence. After addition, the reaction was continued for 10 h. Distilled water was added for washing and methanol precipitation was performed to obtain the product PLA-DMPA.

[0053] (2) Synthesis of hyperbranched copolymer: In a round-bottom flask, 15 wt% PLA-DMPA as an initiating macromolecule, ε-caprolactone, and 0.2 wt% Sn(Oct)2 were added in sequence, heated to 150°C under nitrogen atmosphere, and reacted for 3 h. The product PCL-PLA-15 was obtained by dissolving it in dichloromethane and precipitating it in methanol.

[0054] Example 3

[0055] This embodiment provides a method for preparing a hyperbranched polycaprolactone-polylactic acid copolymer PCL-PLA-20.

[0056] The specific steps are as follows:

[0057] (1) Synthesis of terminal dihydroxymethyl propionamide polylactic acid: 2 g (0.3 mmol) PLA-NH2 and 0.04 g (0.3 mmol) 2,2-bis (hydroxymethyl) propionic acid were added to a round-bottom flask in sequence and dissolved with dichloromethane. After dissolution, 0.06 g (0.45 mmol) HOBt and 0.086 g (0.45 mmol) EDCI were added to the reaction solution in sequence. After addition, the reaction was continued for 10 h. Distilled water was added for washing and methanol precipitation was performed to obtain the product PLA-DMPA.

[0058] (2) Synthesis of hyperbranched copolymer: In a round-bottom flask, 20 wt% PLA-DMPA as the initiator macromolecule, ε-caprolactone, and 0.2 wt% Sn(Oct)2 were added in sequence, heated to 150°C under nitrogen atmosphere, and reacted for 3 h. The product PCL-PLA-20 was obtained by dissolving it in dichloromethane and precipitating it in methanol.

[0059] Example 4

[0060] This embodiment provides a method for preparing a hyperbranched polycaprolactone-polylactic acid copolymer PCL-PLA-25.

[0061] The specific steps are as follows:

[0062] (1) Synthesis of terminal dihydroxymethyl propionamide polylactic acid: 2 g (0.3 mmol) PLA-NH2 and 0.04 g (0.3 mmol) 2,2-bis (hydroxymethyl) propionic acid were added to a round-bottom flask in sequence and dissolved with dichloromethane. After dissolution, 0.06 g (0.45 mmol) HOBt and 0.086 g (0.45 mmol) EDCI were added to the reaction solution in sequence. After addition, the reaction was continued for 10 h. Distilled water was added for washing and methanol precipitation was performed to obtain the product PLA-DMPA.

[0063] (2) Synthesis of hyperbranched copolymer: In a round-bottom flask, 25 wt% PLA-DMPA as the initiator macromolecule, ε-caprolactone, and 0.2 wt% Sn(Oct)2 were added in sequence, heated to 150°C under nitrogen atmosphere, and reacted for 3 h. The product PCL-PLA-25 was obtained by dissolving it in dichloromethane and precipitating it in methanol.

[0064] Example 5

[0065] This embodiment provides a method for preparing a hyperbranched polycaprolactone-polylactic acid copolymer PCL-PLA-30.

[0066] The specific steps are as follows:

[0067] (1) Synthesis of terminal dihydroxymethyl propionamide polylactic acid: 2 g (0.3 mmol) PLA-NH2 and 0.04 g (0.3 mmol) 2,2-bis (hydroxymethyl) propionic acid were added to a round-bottom flask in sequence and dissolved with dichloromethane. After dissolution, 0.06 g (0.45 mmol) HOBt and 0.086 g (0.45 mmol) EDCI were added to the reaction solution in sequence. After addition, the reaction was continued for 10 h. Distilled water was added for washing and methanol precipitation was performed to obtain the product PLA-DMPA.

[0068] (2) Synthesis of hyperbranched copolymer: In a round-bottom flask, 30 wt% PLA-DMPA as the initiator macromolecule, ε-caprolactone, and 0.2 wt% Sn(Oct)2 were added in sequence, heated to 150°C under nitrogen atmosphere, and reacted for 3 h. The product PCL-PLA-30 was obtained by dissolving it in dichloromethane and precipitating it in methanol.

[0069] refer to Figure 3, is the H NMR spectrum of PLA-DMPA, an intermediate in the preparation process of hyperbranched polycaprolactone copolymer. It can be seen that the -CH3 signal peak and -CH2- signal peak of the terminal hydroxyl group appear at 1.26 ppm and 3.50 ppm respectively, and the -CH2- signal peak on the amide group is at 3.25 ppm. This shows that the -COOH in the DMPA structure and the -NH2 in the PLA-NH2 terminal group were successfully modified to obtain PLA-DMPA.

[0070] refer to Figure 4 , is the H NMR spectrum of hyperbranched polycaprolactone copolymer, in which a and b are PLA segment signals, and c, d, e, and f are PCL segment signals. The results show that in the presence of polylactic acid, caprolactone monomers successfully undergo ring-opening polymerization. The intensity of the -CH2- structure signal peak on the hydroxyl group at 3.50 ppm is relatively strong. Figure 3 The 3.50 ppm in the ε-CL monomer was greatly weakened, indicating that the polymerization of the ε-CL monomer was initiated by the -OH at the end of the PLA-DMPA structure, resulting in a decrease in the number of -OH groups. In addition, it can be calculated that Figure 3 The ratio of the integrated area at e to the integrated area at a is about 0.098. Figure 4 The ratio of the peak integrated areas of these two positions is 0.0157. By calculating (0.098 ~ 0.0157) / 0.098, it can be roughly obtained that the utilization rate of the hydroxyl group on -DMPA is 83.7%.

[0071] refer to Figure 5 The DSC data of hyperbranched polycaprolactone copolymers with different proportions prepared in Examples 1 to 5 show that as the amount of PLA added increases, the crystallinity of the system decreases, indicating that the proportion of the crystalline region of PCL decreases and the mobility of the polymer chain increases.

[0072] Comparative Example 1

[0073] This comparative example provides an electrolyte PCL.

[0074] 5 g of ε-CL monomer and 0.2 wt% Sn(Oct)2 were added to a round-bottom flask, heated to 150°C under nitrogen atmosphere, and reacted for 3 h. The product, pure PCL, was obtained by dissolving it with dichloromethane and precipitating it with methanol.

[0075] refer to Figure 6a , the DMA data of hyperbranched polycaprolactone copolymers with different proportions prepared in Examples 1 to 5 show that compared with pure PCL, the hyperbranched polycaprolactone copolymer exhibits a β transition at low temperature, indicating the existence of a hyperbranched structure, and the lower loss factor indicates that its chain motion ability is better.

[0076] refer to Figure 6b, the storage modulus of the hyperbranched polycaprolactone copolymer is higher, indicating that it has better thermomechanical properties as a solid electrolyte.

[0077] Example 6

[0078] This embodiment provides an electrolyte battery.

[0079] The prepared pure PCL, PCL-PLA-10, PCL-PLA-15, PCL-PLA-20, PCL-PLA-25 and PCL-PLA-30 were dissolved in DMC respectively, and 20wt% of lithium salt LiTFSI and 20wt% of nano-Al2O3 were added as fillers, and stirred thoroughly to make the solution composition uniform. Film was cast, and a solid electrolyte membrane was obtained after DMC volatilized for a period of time. Finally, the electrolyte membrane was assembled into a button battery in the order of negative electrode cover-spring-gasket-electrolyte membrane-gasket-positive electrode cover.

[0080] refer to Figure 7 , is a graph of the ionic conductivity of electrolyte batteries prepared using hyperbranched polycaprolactone copolymers of different proportions prepared in Examples 1 to 5. It can be seen from the figure that the electrolyte battery prepared using PCL-PLA-20 has the highest ionic conductivity, that is, the hyperbranched polycaprolactone copolymer has the best conductive performance when the PLA addition amount is 20wt%.

[0081] For matters not mentioned above, the prior art applies.

[0082] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art to which the present invention belongs may make various modifications or supplements to the specific embodiments described or replace them in a similar manner, but they will not deviate from the direction of the present invention or exceed the scope defined by the attached claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A hyperbranched polycaprolactone-polylactic acid copolymer, characterized in that: The structure is shown in Formula I, Formula Ⅰ.

2. A method for preparing a hyperbranched polycaprolactone-polylactic acid copolymer as claimed in claim 1, characterized in that: The specific steps include: S1, dissolving amino-terminated polylactic acid and 2,2-dimethylol propionic acid in a solvent, and then adding a catalyst to react to obtain a mixture A; S2, washing the mixture A described in step S1 with water, and precipitating with a first precipitant to obtain a product, dimethylolpropionamide-terminated polylactic acid; S3, polymerizing the product of step S2, dimethylolpropionamide-terminated polylactic acid, and ε-caprolactone in a nitrogen atmosphere in the presence of a catalyst to obtain a mixture B; S4, dissolving the mixture B described in step S3, and precipitating with a second precipitant to obtain a hyperbranched polycaprolactone-polylactic acid copolymer.

3. The preparation method according to claim 2, characterized in that: In step S1, the solvent is dichloromethane, and the catalyst is 1-hydroxybenzotriazole and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride.

4. The preparation method according to claim 3, characterized in that The molar ratio of the amino-terminated polylactic acid to the 2,2-dihydroxymethylpropionic acid is 1:(0.9-1.1), the molar ratio of the 1-hydroxybenzotriazole to the 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1:(0.9-1.1), and the molar ratio of the catalyst to the 2,2-bis(hydroxymethyl)propionic acid is 3:(1.5-2.5).

5. The preparation method according to claim 4, characterized in that: In step S1, the reaction temperature is 20-40°C and the reaction time is 8-12h.

6. The preparation method according to claim 2, characterized in that: In step S3, the catalyst is stannous isooctanoate, the mass ratio of the terminal dihydroxymethyl propionamide polylactic acid to ε-caprolactone is 1:(2-9), and the catalyst is 0.10-0.40% of the mass of ε-caprolactone.

7. The preparation method according to claim 6, characterized in that: In step S3, the reaction temperature is 140-160° C., and the reaction time is 5-6 hours.

8. The preparation method according to claim 2, characterized in that: In step S2, the washing solvent is distilled water, and the first precipitant is methanol; in step S4, the dissolving agent is dichloromethane, and the second precipitant is methanol.

9. An electrolyte, characterized in that The invention comprises the hyperbranched polycaprolactone-polylactic acid copolymer as claimed in claim 1.

10. An electrolyte battery comprising an anode, a cathode and a conductive electrolyte, characterized in that: The conductive electrolyte comprises the electrolyte as claimed in claim 9.

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