CN111116885B - Method for preparing polycaprolactone by ionic liquid modified kaolin through microwave catalysis - Google Patents
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Abstract
The invention provides a method for preparing polycaprolactone by ionic liquid modified kaolin catalysis through a microwave method, which comprises the following steps: preparing an ionic liquid: mixing N-methylimidazole with bromoethane, and preparing ionic liquid under microwave irradiation; kaolin activation: calcining kaolin, adding the calcined kaolin into a sulfuric acid solution for acidification, and filtering and washing the calcined kaolin for multiple times to adjust the pH value to be neutral to obtain activated kaolin; preparing ionic liquid modified kaolin: mixing the ionic liquid, sufficient deionized water and calcined and acidified kaolin for reaction to prepare ionic liquid modified kaolin; microwave ring-opening polymerization: the epsilon-caprolactone and the ionic liquid modified kaolin are uniformly mixed, the obtained mixture is subjected to ring-opening polymerization reaction under the conditions of microwave irradiation and no water and oxygen, and the polymer obtained by the reaction is subjected to post-treatment to obtain the poly epsilon-caprolactone.
Description
Technical Field
The invention relates to the technical field of polymer chemistry, in particular to a method for preparing polycaprolactone by ionic liquid modified kaolin through microwave catalysis.
Background
With the utilization of petroleum resources in large quantities, the polymer materials play an important role in promoting the development of social economy and improving the life of people. However, most of the synthetic high molecular polymers are produced by petrochemical products, and the synthetic durable polymers form a serious environmental pollution source, cause serious pollution to underground water and soil, prevent the growth of animals and plants, and even endanger the life health and survival of human beings. At present, polymer plastic products with long service life are still commonly used in the fields of engineering application, packaging, catering, surgery, sanitation and the like in human life, a large amount of difficultly-degraded polymer plastic wastes are formed after the polymer plastic wastes are used, and the polymer plastic wastes can generate a large amount of toxic emissions in the incineration process to bring serious environmental problems and energy consumption, so that the greening of polymer materials, namely, the degradable polymer is applied to replace the difficultly-degraded plastic products in the traditional plastic industrial field, and the polymer plastic products become the current popular research subject.
With increasing demands on the aspects of environment, medicine, biology and the like, biodegradable polymer materials are rapidly developed, for example, polycarbonate, polyorthoester, polyanhydride, polyamino acid, polyester and the like are produced accordingly, and the biodegradable polymer materials have great application potential in the aspects of drug carriers, tissue engineering, gene therapy, regenerative medicine, temporary implantation equipment, coating implantation and the like, so that the development of the biodegradable polymer materials which are beneficial to environmental protection is beneficial to rapidly and efficiently solving the problem of environmental pollution. Polycaprolactone (PCL) is biodegradable aliphatic polyester widely applied, can be widely applied to environmental protection materials such as daily shopping bags, agricultural mulching films, food packaging materials and the like on one hand, and can also be widely applied to the field of biomedicine such as orthopedic materials, surgical sutures, medicinal carriers and the like and the field of tissue engineering such as cell culture scaffolds and the like on the other hand, so that the pollution to the environment is effectively reduced, and the rapid development of the field of biomedicine is promoted.
The catalyst used in the synthesis of PCL is a metal complex, and toxic metal compound residues are easy to exist. Therefore, the preparation of a green and environment-friendly catalytic system which can be recycled and has high catalytic efficiency becomes a research hotspot. The ionic liquid is used as a novel green medium, has wide prospects in the fields of catalysis, new energy and the like, is composed of specific organic cations with relatively large volume and asymmetric structure and inorganic anions with relatively small volume, and has strong absorption capacity on microwaves. Kaolin is a natural layered silicate mineral, contains a large number of silicon-aluminum activation centers, and has the effect of catalyzing ring-opening polymerization of epsilon-caprolactone. A large number of experimental results show that the microwave polymerization can improve the reaction rate, shorten the reaction time and contribute to improving the molecular weight and the yield of a polymerization product. Therefore, the ionic liquid is adopted to carry out intercalation modification on the kaolin, and the modified kaolin is used for catalyzing ring opening polymerization of epsilon-caprolactone.
Ionic liquids are a new class of compounds that have been developed in recent years. It is composed of specific anions and cations, is in a liquid state at room temperature, and is a green substitute of the traditional volatile organic solvent. Ionic liquids are of great interest as an environmentally friendly, "designable" solvent. Compared with the traditional solvent, the ionic liquid has the characteristics of no combustion, no explosion, difficult oxidation, good thermal stability and the like, and is widely applied to separation processes, chemical reaction processes and electrochemistry.
Kaolin (Kaolin) belongs to a layered silicate mineral, the unit cell comprising two atomic layers of octahedrally coordinated alumina and tetrahedrally coordinated silica, the two structures sharing a vertex to form 1: type 1 unit layer structure, eight surface layers with molecular formula of Al2(OH)6Its structure is similar to that of a hydroaluminum mineral, with adjacent aluminum atoms separated by hydroxyl groups at the top and bottom, respectively. The main mineral components are kaolinite and halloysite, and the chemical components of the kaolinite contain a large amount of Al2O3、SiO2. The calcined kaolin is modified to improve the porosity and the calcination activity, and is converted into an amorphous metakaolin structure, so that more active groups are exposed and surface active sites are exposed, and the chemical reaction activity is improved.
The kaolin exists in the form of tetrahedral aluminum during the calcination process and has obvious chemical activity, and the acid modified kaolin process is a process in which partial metal oxides such as aluminum oxide, iron oxide and the like react with acid to form effective pores on the surface of the kaolin, so that the specific surface, the porosity and active sites of the surface of the kaolin are increased. Especially metakaolin produced by high-temperature calcination is continuously dissolved in liquid-phase inorganic acid solution after reacting with inorganic acid through chemical reaction, but aluminum ions and the like leached subsequently are easily adsorbed on the surface of the kaolin to form Al2O3Such that the aluminum content of the kaolin surface is significantly increased. Thus, by varying the mineral acid solubility usedThe concentration and the type of the liquid can also effectively change the physicochemical properties and the structure of the kaolin.
Disclosure of Invention
The invention aims to solve the technical problems of residual catalyst toxicity, high production cost and poor thermal property in the conventional polycaprolactone, and provides a method for preparing polycaprolactone by microwave catalysis from ionic liquid modified kaolin.
The method for preparing polycaprolactone by the ionic liquid modified kaolin through microwave catalysis comprises the following steps:
s1, preparing ionic liquid: mixing N-methylimidazole with bromoethane, and preparing ionic liquid under microwave irradiation;
s2, kaolin activation: calcining kaolin, adding the calcined kaolin into a sulfuric acid solution for acidification, and filtering and washing the calcined kaolin for multiple times to adjust the pH value to be neutral to obtain activated kaolin;
s3, preparing ionic liquid modified kaolin: mixing the ionic liquid, sufficient deionized water and calcined and acidified kaolin for reaction to prepare ionic liquid modified kaolin;
s4, microwave ring-opening polymerization: the epsilon-caprolactone and the ionic liquid modified kaolin are uniformly mixed, the obtained mixture is subjected to ring-opening polymerization reaction under the conditions of microwave irradiation and no water and oxygen, and the polymer obtained by the reaction is subjected to post-treatment to obtain the poly epsilon-caprolactone.
Further, the ionic liquid is prepared by a microwave method, and the microwave method comprises the following steps: adding bromoethane into a flask, dropwise adding N-methylimidazole into the flask, uniformly mixing, magnetically stirring, condensing and refluxing, reacting for 5min under microwave irradiation at 160W and 80 ℃, cooling to room temperature, refrigerating for 24h to obtain light yellow crystals, washing with ethyl acetate for multiple times, removing bromide ions, and performing suction filtration to obtain the 1-ethyl-3-methylimidazolated bromide.
Further, in the step S2, the calcining temperature is 600-800 ℃, and the calcining time is 4-10 hours.
Further, the step of acidifying at step S2 specifically includes: mixing with kaolinCalcining soil at 800 deg.C for 4 hr, mixing with 2mol/L sulfuric acid, and mixing with waterFixing device：VLiquid for treating urinary tract infectionStirring the mixture magnetically, condensing and refluxing the mixture at 80 ℃ for 6 hours, washing the mixture by deionized water to adjust the pH value to be neutral, and drying the mixture to obtain activated kaolin; the acid solution can also be one or two of hydrochloric acid and sulfuric acid.
Further, the specific steps for preparing the ionic liquid modified kaolin described in step S3 include: mixing imidazole ionic liquid, sufficient deionized water and calcined and acidified kaolin, and WIonic liquids:WKaolin clay10g of the modified kaolin is magnetically stirred, reacted at 80 ℃ for 48 hours and dried to obtain the ionic liquid modified kaolin.
Further, the microwave ring-opening polymerization in step S4 includes the specific steps of: weighing epsilon-caprolactone and ionic liquid modified kaolin according to a proportion, carrying out ultrasonic treatment for 15min, uniformly mixing, carrying out ring-opening polymerization reaction on the obtained mixture under the conditions of microwave irradiation and no water and no oxygen, adding dichloromethane and ice methanol into the polymer obtained by the reaction, refrigerating and standing for 24h to precipitate out a polymerization product from the solution, removing unreacted monomer byproducts, carrying out suction filtration, washing with methanol and deionized water, and drying to obtain the poly-epsilon-caprolactone.
Further, in the step S4, the power of the microwave irradiation is 240-480W, and the polymerization reaction time is 0.5-1 h.
Further, in the step S4, the anhydrous and anaerobic conditions are that the monomer and the ionic liquid modified kaolin are dried in vacuum, the whole reaction system is vacuumized until no bubbles are generated, and N is introduced2The whole reaction system is vacuumized again, and N is introduced2Obtaining an anhydrous and oxygen-free environment; the ratio of the catalyst to the monomer is 1/100-1/50.
Compared with the prior art, the invention has the advantages that:
1. the invention uses cheap and environment-friendly kaolin as a raw material, provides energy required by polymerization by microwave irradiation, replaces the traditional thermal polymerization, adopts the kaolin which is modified, calcined and acidified by ionic liquid as a catalyst for epsilon-caprolactone ring-opening polymerization, replaces expensive and toxic catalysts such as tin isooctanoate and the like, has the advantages of short polymerization reaction time, narrow molecular weight distribution, no toxic metal residue in the obtained polycaprolactone and the like, and is suitable for the fields of biomedicine, drug controlled release and sustained release, tissue engineering and the like.
2. In the invention, the ionic liquid (1-ethyl-3-methylimidazolium bromide) is prepared by microwave irradiation, the reaction time is greatly shortened, and the conversion rate is high.
3. Compared with thermal polymerization, the microwave polymerization can greatly shorten the reaction time, and has relatively high yield, and the prepared PCL has good thermal performance and relatively high molecular weight.
4. Compared with the traditional method for preparing the poly-epsilon-caprolactone by catalyzing with the traditional metal and organic catalyst in a traditional heating mode, the method for preparing the poly-epsilon-caprolactone by catalyzing with the ionic liquid modified kaolin as the catalyst has the advantages that the thermal property of the prepared poly-epsilon-caprolactone is obviously improved, the complex secondary composite processing process is effectively avoided, and the cost can be greatly saved.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a reaction scheme and flow diagram for the synthesis of ionic liquids according to the present invention;
FIG. 2 is a reaction scheme and a flow chart of the ring-opening polymerization of epsilon-caprolactone in the present invention;
FIG. 3 is a FT-IR chart of kaolin before and after modification by an ionic liquid prepared by a microwave method according to the present invention;
FIG. 4 is SEM photographs of ionic liquid modified kaolin prepared by a microwave method and polycaprolactone prepared in example 2;
FIG. 5 is a FT-IR plot of polycaprolactone made in example 2 of this invention;
FIG. 6 is a 1HNMR map of polycaprolactone prepared in example 2 of the present invention;
FIG. 7 is an XRD pattern of polycaprolactone prepared according to example 2 of the present invention;
FIG. 8 is a TG curve of polycaprolactone prepared according to 5 examples of the invention.
Detailed Description
For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
The method for preparing polycaprolactone by the ionic liquid modified kaolin through microwave catalysis comprises the following steps:
s1, preparing ionic liquid: as shown in figure 1, mixing N-methylimidazole with bromoethane, and preparing ionic liquid under microwave irradiation;
s2, kaolin activation: calcining kaolin, adding the calcined kaolin into a sulfuric acid solution for acidification, and filtering and washing the calcined kaolin for multiple times to adjust the pH value to be neutral to obtain activated kaolin;
s3, preparing ionic liquid modified kaolin: mixing the ionic liquid, sufficient deionized water and calcined and acidified kaolin for reaction to prepare ionic liquid modified kaolin;
s4, microwave ring-opening polymerization: as shown in figure 2, epsilon-caprolactone and ionic liquid modified kaolin are uniformly mixed, the obtained mixture is subjected to ring-opening polymerization reaction under the conditions of microwave irradiation, no water and no oxygen, and the polymer obtained by the reaction is subjected to post-treatment to obtain the poly epsilon-caprolactone.
The ionic liquid is prepared by a microwave method, the yield is up to 86%, and the microwave method comprises the following steps: adding bromoethane into a flask, dropwise adding N-methylimidazole into the flask, uniformly mixing, magnetically stirring, condensing and refluxing, reacting for 5min under microwave irradiation at 160W and 80 ℃, cooling to room temperature, refrigerating for 24h to obtain light yellow crystals, washing with ethyl acetate for multiple times, removing bromide ions, and performing suction filtration to obtain the 1-ethyl-3-methylimidazolated bromide.
The calcining temperature of the step S2 is 600-800 ℃, and the calcining time is 4-10 h; in order to make the polymerization reaction more complete, the calcination temperature was set at 800 ℃ and the calcination time was set at 4 hours.
The step of acidifying at step S2 specifically includes: calcining kaolin at 800 deg.C for 4h, and mixing with 2mol/L sulfuric acid (W)Fixing device：VLiquid for treating urinary tract infection1g:10mL), magnetically stirred, and condensed at 80 ℃ under refluxAnd 6h, washing with deionized water to adjust the pH to be neutral, and drying to obtain the activated kaolin. The acid solution can also be one or two of hydrochloric acid and sulfuric acid.
The specific steps for preparing the ionic liquid modified kaolin described in the step S3 include: imidazole ionic liquid, sufficient deionized water and calcined acidified kaolin (W)Ionic liquids:WKaolin clay1g:10g), magnetically stirring, reacting at 80 ℃ for 48h, and drying to obtain the ionic liquid modified kaolin.
Step S4, the microwave ring-opening polymerization specifically comprises the following steps: weighing epsilon-caprolactone and ionic liquid modified kaolin according to a proportion, carrying out ultrasonic treatment for 15min, uniformly mixing, carrying out ring-opening polymerization reaction on the obtained mixture under the conditions of microwave irradiation and no water and no oxygen, adding dichloromethane and glacial methanol into the polymer obtained by the reaction, refrigerating and standing for 24h to precipitate out the polymerization product from the solution, removing the unreacted monomer and other byproducts, carrying out suction filtration, washing with methanol and deionized water, and drying to obtain the poly-epsilon-caprolactone.
Step S4, the power of microwave irradiation is 240-480W, and the polymerization reaction time is 0.5-1 h; in order to make the polymerization reaction more complete, the power of microwave irradiation is set to 480W, and the ring-opening polymerization reaction time is 1 h.
Step S4, the anhydrous and anaerobic condition is that the monomer and the catalyst (i.e. the ionic liquid modified kaolin) are dried in vacuum, then the whole reaction system is vacuumized until no bubble is generated, and N is introduced2The whole reaction system is vacuumized again, and N is introduced2And obtaining the anhydrous and oxygen-free environment. The ratio of the catalyst to the monomer is 1/100-1/50.
The specific embodiment of the above method is as follows:
in the following examples, the number average molecular weight and the molecular weight distribution index PDI of the polymer were determined at a temperature of 40 ℃ using a U.S. Waters breeze gel permeation chromatograph, using monodisperse polystyrene as a standard and corrected for universal values, N, N-Dimethylformamide (DMF) as a solvent, and a μ -Styragel packed column.
In the following examples, the ionic liquid used was an imidazole ionic liquid synthesized by microwave method, with a yield of up to 86%, and the method included the following steps: adding bromoethane into a flask, dropwise adding N-methylimidazole into the flask, uniformly mixing, magnetically stirring, condensing and refluxing, reacting for 5min under microwave irradiation at 160W and 80 ℃, cooling to room temperature, refrigerating for 24h to obtain light yellow crystals, washing with ethyl acetate for multiple times, removing bromide ions, and performing suction filtration to obtain the 1-ethyl-3-methylimidazolated bromide.
In the following examples, the kaolin used was calcined and acidified kaolin modified with ionic liquids prepared by microwave method, comprising the following steps: calcining kaolin crude ore at 800 ℃ for 4h, then placing the calcined kaolin into an acid solution with the concentration of 2mol/L, condensing and refluxing for 6h at 80 ℃, washing with deionized water to be neutral, and drying. Imidazole ionic liquid synthesized by a microwave method, sufficient deionized water and calcined acidified kaolin (W)Ionic liquids:WKaolin clay1g:10g), magnetically stirred, reacted at 80 ℃ for 48h, and dried.
Example 1
A method for preparing poly-epsilon-caprolactone by using imidazole ionic liquid modified kaolin prepared by a microwave method as a catalyst comprises the following steps:
(1) weighing bromoethane and N-methylimidazole (N)Bromoethane:nN-methylimidazole1.2:1), magnetically stirring, condensing, refluxing and reacting for 5min under the microwave irradiation of 160W at 80 ℃, cooling, and washing with ethyl acetate for multiple times to prepare the ionic liquid 1-ethyl-3-methylimidazolium bromide;
(2) the kaolin was calcined at 800 ℃ for 4 h. Then the mixture is mixed with 2mol/L H2SO4(WFixing device:VLiquid for treating urinary tract infection10mL) were mixed, magnetically stirred, condensed and refluxed for 6h, adjusted to neutral pH, and dried. (ii) ionic liquid, sufficient deionized water, calcined acidified kaolinIonic liquids:Kaolin clay1g to 10g), magnetically stirring, reacting at 80 ℃ for 48h, and drying to obtain the ionic liquid intercalation modified kaolin;
(3) according to the following steps of 100: 1-weight ratio of epsilon-caprolactone to ionic liquidUltrasonic treatment of kaolin for 15min under anhydrous and oxygen-free conditions2Protection and thermal polymerization reaction at 130 ℃ for 24 hours. Adding 10mL of dichloromethane and 50mL of glacial methanol, refrigerating and standing for 24h to precipitate out a polymerization product from the solution, removing side products such as unreacted monomers and the like, performing suction filtration, washing with methanol and deionized water, and drying to obtain the poly-epsilon-caprolactone.
The conversion of polyepsilon caprolactone prepared by the method described in this example was 20.3%, the number average molecular weight of polyepsilon caprolactone was 7060, and PDI was 1.27.
Example 2
A method for preparing poly-epsilon-caprolactone by using imidazole ionic liquid modified kaolin prepared by a microwave method as a catalyst comprises the following steps:
(1) weighing bromoethane and N-methylimidazole (N)Bromoethane:nN-methylimidazole1.2:1), magnetically stirring, condensing, refluxing and reacting for 5min under the microwave irradiation of 160W at 80 ℃, cooling, and washing with ethyl acetate for multiple times to prepare the ionic liquid 1-ethyl-3-methylimidazolium bromide;
(2) the kaolin was calcined at 800 ℃ for 4 h. Then the mixture is mixed with 2mol/LH2SO4(WFixing device:VLiquid for treating urinary tract infection10mL) were mixed, magnetically stirred, condensed and refluxed for 6h, adjusted to neutral pH, and dried. Calcining acidified kaolin (W) with ionic liquid, sufficient deionized waterIonic liquids:WKaolin clay1g to 10g), reacting at 80 ℃ for 48h, and drying to obtain the ionic liquid intercalation modified kaolin;
(3) according to the following steps of 100: weighing epsilon-caprolactone and modified kaolin according to the mass ratio of 1, carrying out ultrasonic treatment for 15min, and reacting for 1h under the conditions of no water and no oxygen, N2 protection, 210 ℃ and 480W microwave irradiation. Adding 10mL of dichloromethane and 50mL of glacial methanol, refrigerating and standing for 24h to precipitate out a polymerization product from the solution, removing side products such as unreacted monomers and the like, performing suction filtration, washing with methanol and deionized water, and drying to obtain the poly-epsilon-caprolactone.
The conversion of polyepsilon caprolactone prepared by the method described in this example was 42.0%, the number average molecular weight of polyepsilon caprolactone was 8592, and PDI was 1.14.
Example 3
A method for preparing poly-epsilon-caprolactone by using imidazole ionic liquid modified kaolin prepared by a microwave method as a catalyst comprises the following steps:
(1) weighing bromoethane and N-methylimidazole (N)Bromoethane:nN-methylimidazole1.2:1), magnetically stirring, condensing, refluxing and reacting for 5min under the microwave irradiation of 160W at 80 ℃, cooling, and washing with ethyl acetate for multiple times to prepare the ionic liquid 1-ethyl-3-methylimidazolium bromide;
(2) according to the following steps of 100: weighing epsilon-caprolactone and modified kaolin according to the mass ratio of 1, and reacting for 0.5h under the conditions of no water and no oxygen, N2 protection, 210 ℃ and 480W microwave irradiation. Adding 10mL of dichloromethane and 50mL of glacial methanol, refrigerating and standing for 24h to precipitate out a polymerization product from the solution, removing side products such as unreacted monomers and the like, performing suction filtration, washing with methanol and deionized water, and drying to obtain the poly-epsilon-caprolactone.
The conversion of polyepsilon caprolactone prepared by the method described in this example was 32.6%, the number average molecular weight of polyepsilon caprolactone was 8559, and PDI was 1.13.
Example 4
A method for preparing poly-epsilon-caprolactone by using imidazole ionic liquid modified kaolin prepared by a microwave method as a catalyst comprises the following steps:
(1) weighing bromoethane and N-methylimidazole (N)Bromoethane:nN-methylimidazole1.2:1), magnetically stirring, condensing, refluxing and reacting for 5min under the microwave irradiation of 160W at 80 ℃, cooling, and washing with ethyl acetate for multiple times to prepare the ionic liquid 1-ethyl-3-methylimidazolium bromide;
(2) according to the following weight ratio of 50: weighing epsilon-caprolactone and modified kaolin according to the mass ratio of 1, and reacting for 1h under the conditions of no water and no oxygen, N2 protection, 210 ℃ and 480W microwave irradiation. Adding 10mL of dichloromethane and 50mL of glacial methanol, refrigerating and standing for 24h to precipitate out a polymerization product from the solution, removing side products such as unreacted monomers and the like, performing suction filtration, washing with methanol and deionized water, and drying to obtain the poly-epsilon-caprolactone.
The conversion of the polyepsilon caprolactone prepared by the method described in this example was 28.1%, the number average molecular weight of the polyepsilon caprolactone was 8238, and the PDI was 1.16.
Example 5
The preparation of poly epsilon-caprolactone by using ionic liquid prepared by a microwave method as a catalyst comprises the following steps:
(1) weighing bromoethane and N-methylimidazole (N)Bromoethane:nN-methylimidazole1.2:1), magnetically stirring, condensing, refluxing and reacting for 5min under the microwave irradiation of 160W at 80 ℃, cooling, and washing with ethyl acetate for multiple times to prepare the ionic liquid 1-ethyl-3-methylimidazolium bromide;
(2) according to the following steps of 100: weighing epsilon-caprolactone and ionic liquid in a mass ratio of 1 in the presence of anhydrous oxygen-free N2Protected, and reacted for 1h under 480W microwave irradiation at 210 ℃. Adding 10mL of dichloromethane and 50mL of glacial methanol, refrigerating and standing for 24h to precipitate out a polymerization product from the solution, removing side products such as unreacted monomers and the like, performing suction filtration, washing with methanol and deionized water, and drying to obtain the poly-epsilon-caprolactone.
The conversion of poly-epsilon-caprolactone prepared by the method described in this example was 37.2%, the number average molecular weight of poly-epsilon-caprolactone was 9082, and PDI was 1.21.
The following table 1 shows the polycaprolactones synthesized under different conditions. It has been found that microwave polymerization can greatly shorten the reaction time and has relatively high yield, molecular weight and distribution. Increasing the microwave power, increasing the reaction time, increasing the temperature within a certain range, and changing the catalyst to monomer ratio all contribute to the improvement of PCL yield.
FT-IR of kaolin before and after modification of the ionic liquid prepared by the microwave method is shown in figure 3. 1200cm-1-998cm-1Is the stretching vibration absorption band of O-Si-O and Si-O. 3176cm-1Is the expansion vibration peak of C-H bond on imidazole ring, 1460cm-1Is the in-plane bending vibration peak of saturated C-H, namely the kaolin is successfully modified by the ionic liquid.
FIG. 4 is SEM pictures of ionic liquid modified kaolin prepared by microwave method and polycaprolactone prepared by examples 2 and 5. (a) Is a morphology graph of ionic liquid modified kaolin, which is a regular lamellar structure; (b) the appearance is the appearance of example 5, and the PCL is in a laminated shape, the surface is regular and smooth, and the edges are uneven, which shows that the molecular chain grows along the two-dimensional direction; (c) is the topography of example 2, the PCL is in the form of a stack of sheets with holes.
FIG. 5 is a FT-IR plot of polycaprolactone prepared in example 2 of this invention. 1370cm-1The peak of bending vibration at 3440cm, which is attributed to-OH at the end of molecular chain of PCL-1The peak is the stretching vibration peak of-OH, which indicates that PCL with terminal hydroxyl group is generated.
FIG. 6 is a 1HNMR image of polycaprolactone prepared in example 2 of the present invention. The peak at 3.65ppm was assigned to the methylene hydrogen proton peak of-CH 2OH, indicating that the polymer product had a hydroxyl group at the terminal, indicating that epsilon-caprolactone underwent ring-opening polymerization.
FIG. 7 is an XRD pattern of polycaprolactone prepared in example 2 of the present invention. Diffraction peaks corresponding to 2 theta of 21.7 degrees, 22.3 degrees and 23.9 degrees are respectively (110), (111) and (200) crystal faces of PCL, and the polymerization product has certain crystallinity.
FIG. 8 is a TG curve of polycaprolactone prepared in example 2 of the present invention. The thermal decomposition process of PCL prepared under different conditions is divided into two steps. The decomposition temperature of the first step is 300-330 ℃, the weight loss rate is about 5 percent, and PCL is randomly broken into low molecular weight from high molecular weight. The second step has decomposition temperature of 330-480 deg.c and weight loss of PCL in low molecular weight into small molecular compound, such as H2O and CO2. The thermal decomposition temperature of the PCL prepared by the microwave method in the whole thermal degradation process is higher than that of the PCL prepared by thermal polymerization, which shows that the PCL prepared by the microwave method has more excellent thermal properties.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (7)
1. The method for preparing polycaprolactone by ionic liquid modified kaolin through microwave catalysis is characterized by comprising the following steps:
s1, preparing ionic liquid: mixing N-methylimidazole with bromoethane, and preparing ionic liquid under microwave irradiation;
s2, kaolin activation: calcining kaolin, adding the calcined kaolin into a sulfuric acid solution for acidification, and filtering and washing the calcined kaolin for multiple times to adjust the pH value to be neutral to obtain activated kaolin;
s3, preparing ionic liquid modified kaolin: mixing the ionic liquid, sufficient deionized water and calcined and acidified kaolin for reaction to prepare ionic liquid modified kaolin; the method comprises the following specific steps: mixing imidazole ionic liquid, sufficient deionized water and calcined and acidified kaolin, and WIonic liquids:WKaolin clay10g of kaolin modified by ionic liquid is obtained by magnetically stirring, reacting for 48 hours at 80 ℃, and drying;
s4, microwave ring-opening polymerization: the preparation method comprises the steps of uniformly mixing epsilon-caprolactone and ionic liquid modified kaolin, carrying out ring-opening polymerization reaction on the obtained mixture under the conditions of microwave irradiation, no water and no oxygen, and carrying out post-treatment on the obtained polymer to obtain poly epsilon-caprolactone, wherein the temperature condition of the polymerization reaction is 120 ℃.
2. The method for preparing polycaprolactone by microwave catalysis of ionic liquid modified kaolin according to claim 1, wherein the ionic liquid is prepared by a microwave method, and the microwave method specifically comprises the following steps: adding bromoethane into a flask, dropwise adding N-methylimidazole into the flask, uniformly mixing, magnetically stirring, condensing and refluxing, reacting for 5min under microwave irradiation at 160W and 80 ℃, cooling to room temperature, refrigerating for 24h to obtain light yellow crystals, washing with ethyl acetate for multiple times, removing bromide ions, and performing suction filtration to obtain the 1-ethyl-3-methylimidazolated bromide.
3. The method for preparing polycaprolactone through microwave catalysis of ionic liquid modified kaolin according to claim 1, wherein the calcination temperature in step S2 is 600-800 ℃, and the calcination time is 4-10 h.
4. The method for preparing polycaprolactone through microwave catalysis of ionic liquid modified kaolin according to claim 1, wherein the step of acidification in step S2 specifically comprises: calcining kaolin at 800 deg.C for 4h, mixing with 2mol/L sulfuric acid, and mixing with waterFixing device：VLiquid for treating urinary tract infection10mL, magnetically stirred, condensed and refluxed at 80 ℃ for 6h, washed with deionized water to adjust pH to neutrality, and dried to obtain activated kaolin.
5. The method for preparing polycaprolactone by microwave catalysis of ionic liquid modified kaolin according to claim 1, wherein the microwave ring-opening polymerization in step S4 comprises the following specific steps: weighing epsilon-caprolactone and ionic liquid modified kaolin according to a proportion, carrying out ultrasonic treatment for 15min, uniformly mixing, carrying out ring-opening polymerization reaction on the obtained mixture under the conditions of microwave irradiation and no water and no oxygen, adding dichloromethane and ice methanol into the polymer obtained by the reaction, refrigerating and standing for 24h to precipitate out a polymerization product from the solution, removing unreacted monomer byproducts, carrying out suction filtration, washing with methanol and deionized water, and drying to obtain the poly-epsilon-caprolactone.
6. The method for preparing polycaprolactone through microwave catalysis of ionic liquid modified kaolin according to claim 1, wherein the power of microwave irradiation in step S4 is 240-480W, and the polymerization reaction time is 0.5-1 h.
7. The method for microwave catalytic preparation of polycaprolactone from ionic liquid modified kaolin according to claim 1, wherein the anhydrous and anaerobic conditions of step S4 are obtained by first vacuum drying the monomer and ionic liquid modified kaolin, and then subjecting the whole to reverse reactionVacuumizing the reaction system until no bubbles are generated, and introducing N2The whole reaction system is vacuumized again, and N is introduced2Obtaining an anhydrous and oxygen-free environment; the ratio of the catalyst to the monomer is 1/100-1/50.
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| CN102604050A (en) * | 2012-02-15 | 2012-07-25 | 中国地质大学（武汉） | Method for preparing poly(epsilon-caprolactone) with attapulgite as catalyst |
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