CN114539455B - Preparation of polyvinyl ethers by cationic polymerization using continuous flow process and process - Google Patents
Preparation of polyvinyl ethers by cationic polymerization using continuous flow process and process Download PDFInfo
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Abstract
The present disclosure provides a process for preparing polyvinyl ethers by cationic polymerization using a continuous flow process comprising: providing an injector A and an injector B, wherein the injector A is filled with a cationic polymerization catalyst solution, the injector B is filled with a vinyl ether monomer and an initiator solution, and additives are optionally included; connecting the syringe A and the syringe B to two syringe pumps respectively, controlling the liquid flow rate by the syringe pumps, injecting the solutions in the syringe A and the syringe B into a mixer, mixing in the mixer, flowing into a tubular reactor, and carrying out cationic polymerization while continuously flowing in the tubular reactor to obtain the product polyvinyl ether.
Description
Technical Field
The disclosure belongs to the field of synthesis of high polymer materials, and particularly relates to a method for preparing polyvinyl ether by cationic polymerization by adopting a continuous flow method.
Background
The stereoregularity of polymers has a very significant impact on the performance of polymeric materials, and therefore, stereoselective polymerization of various types of monomers has been extensively explored over the past several decades, for example, coordination-insertion polymerization of alpha-olefins using chiral metallocene catalysts. However, these metallocene catalysts are often easily poisoned by polar groups on the monomer and lead to catalyst deactivation. Subsequently, late transition metal catalysts have appeared for the polymerization of polar vinyl ether monomers, but these methods have difficulty in achieving good control of stereoselectivity. At present, many researchers have taken radical polymerization or cationic polymerization to polymerize vinyl ether monomers, which is a great advantage in controlling polymer composition, molecular weight and molecular weight distribution, but still faces great challenges in stereo selectivity.
Cationic polymerization of vinyl ethers at low temperatures using some catalysts has also been known in the art, but the resulting polymers have only about 70% isotacticity. Although some polymerization systems can produce polymers with isotacticity of about 90%, there is also the problem of the inverse correlation between stereoselectivity of the polymer and monomer concentration. Based on these problems, the large-scale application of cationic polymerization of vinyl ethers is limited.
Disclosure of Invention
In view of the above technical problems, the present disclosure provides a method for preparing polyvinyl ether by cationic polymerization using a continuous flow process, which is intended to at least partially solve the above technical problems.
In order to solve the above technical problems, as one aspect of the present disclosure, there is provided a method for preparing polyvinyl ether by cationic polymerization using a continuous flow method, comprising:
providing a syringe A and a syringe B, wherein the syringe A is filled with a cationic polymerization catalyst solution, and the syringe B is filled with a vinyl ether monomer, an initiator solution and optionally an additive;
connecting the syringe A and the syringe B to two syringe pumps respectively, controlling the liquid flow rate by the syringe pumps, injecting the solution in the syringe A and the solution in the syringe B into a mixer, mixing in the mixer, flowing into a tubular reactor, and carrying out cationic polymerization while continuously flowing in the tubular reactor to obtain the product polyvinyl ether.
In one embodiment, the cationic polymerization catalyst comprises at least one of:
TiCl 2 (OAr) 2 、EtAlCl 2 、BF 3 Et 2 O、Et 2 AlCl、SnCl 4 wherein Ar is 2, 6-diisopropylphenyl.
In one embodiment, the solvents of the solutions in syringe a and syringe B are the same or different, and each comprises at least one of:
n-hexane, toluene, methylcyclohexane, dichloromethane.
In one embodiment, the vinyl ether monomer comprises at least one of:
isobutyl vinyl ether, tert-butyl vinyl ether, trimethylvinyloxysilane, n-butyl vinyl ether, cyclohexyl vinyl ether.
In one embodiment, the initiator is an addition product obtained by reacting HCl with any of the vinyl ether monomers described above.
In one embodiment, the additive comprises: 2, 6-di-tert-butyl-4-methylpyridine.
In one embodiment, the concentration of the cationic polymerization catalyst solution includes: 0.005-0.04M;
the concentrations of the above additives include: 0 to 0.006M;
the molar ratio of the above monomer to the above initiator includes: 24 to 144;
the reaction temperature of the tubular reactor comprises: -50 to-78 ℃;
the above cationic polymerization is carried out under an inert atmosphere.
In one embodiment, the mixer is a Y-mixer.
In one embodiment, the injection pump controls the fluid flow rate to include: 5-20 mL/h.
As another aspect of the present disclosure, there is provided a polyvinyl ether prepared by the above method.
Based on the technical scheme, the method for preparing polyvinyl ether by cationic polymerization by adopting a continuous flow method and the continuous flow method have the beneficial effects that at least one of the following effects is realized:
(1) In the embodiment of the disclosure, a continuous flow method is adopted to facilitate the sufficient contact between the cationic polymerization catalyst and the vinyl ether monomer in the flow process, and the polyvinyl ether polymer with higher isotacticity can be synthesized.
(2) In the embodiment of the disclosure, the preparation method provided by the disclosure can be adjusted according to different vinyl ether monomers and different reaction conditions (such as cationic catalyst, reaction temperature, solvent, initiator and the like) to prepare different vinyl ether polymers with different isotacticities, and the method has certain universality.
(3) In the embodiment of the disclosure, the polyvinyl ether polymer with higher isotacticity is prepared by adopting a continuous flow method through cationic polymerization, and the polyvinyl alcohol with higher isotacticity obtained by hydrolyzing the polymer can be applied to the fields of liquid crystal display, polarizing films and the like, so that the development and innovation of the polyvinyl alcohol industry can be driven.
Drawings
FIG. 1 is a schematic illustration of the process of the present disclosure for making polyvinyl ethers by cationic polymerization using a continuous flow process;
FIG. 2 is a schematic illustration of the mechanism of the present disclosure for making polyvinyl ethers by cationic polymerization using a continuous flow process;
FIG. 3 is a representation of a polyisobutyl vinyl ether polymer in example 1 of the present disclosure 13 C nuclear magnetic spectrum;
FIG. 4 is an X-ray diffraction pattern of a polyisobutyl vinyl ether polymer of example 1 of the present disclosure;
figure 5 is a differential scanning calorimetry test plot of the polymers of example 1 and example 13 of the present disclosure.
Detailed Description
To make the objects, technical solutions and advantages of the present disclosure more apparent, the present disclosure will be described in further detail below with reference to specific embodiments and the accompanying drawings.
The technical problems to be solved by the present disclosure are to improve the stereoselectivity in the polymerization process of vinyl ether monomers to obtain polyvinyl ethers with higher isotacticity, and to solve the problems of inverse correlation between polymer stereoselectivity and monomer concentration, and hopefully provide a new idea for large-scale controllable polymerization of vinyl ether monomers, and to explore the industrial production of high isotacticity polyvinyl ethers. Accordingly, the present disclosure provides a method for preparing polyvinyl ether by cationic polymerization using a continuous flow method, which realizes the synthesis of polyvinyl ether having a high isotacticity, wherein the isotacticity of the polyisobutyl vinyl ether prepared using isobutyl vinyl ether as a monomer is as high as 98%. The continuous flow method is adopted in the method, a plurality of experimental conditions can be simply adjusted in a flow chemical means, so that a plurality of polyvinyl ether polymers with different isotacticity can be obtained, and the method is simple to operate, effective and promising in further large-scale production.
FIG. 1 is a schematic illustration of the process of the present disclosure for making polyvinyl ethers by cationic polymerization using a continuous flow process.
According to an embodiment of the present disclosure, a syringe a containing a cationic polymerization catalyst solution and a syringe B containing a solution of a vinyl ether monomer, an initiator and optionally further including an additive are provided; connecting the syringe A and the syringe B to two syringe pumps respectively, controlling the liquid flow rate by the syringe pumps, injecting the solutions in the syringe A and the syringe B into a mixer, mixing in the mixer, flowing into a tubular reactor, and carrying out cationic polymerization while continuously flowing in the tubular reactor to obtain the product polyvinyl ether.
By the embodiment of the disclosure, in a glove box, a cationic polymerization catalyst solution with a certain concentration is prepared and sucked into one syringe A, a mixed solution of a monomer, an initiator and an additive with a certain concentration is prepared and sucked into the other syringe B, then the syringes A and B are taken out and installed on a programmed syringe pump, and the flow is started to carry out cationic polymerization at a set temperature and a set flow rate. The product was collected at the end of the tubular reactor and quenched by addition of ethanol and filtered to give the polymer. The continuous flow method is adopted to realize the full contact of the cationic polymerization catalyst and the vinyl ether monomer in the flow process, thereby being beneficial to synthesizing the polyvinyl ether polymer with higher isotacticity.
According to embodiments of the present disclosure, the cationic polymerization catalyst comprises at least one of: tiCl (titanium dioxide) 2 (OAr) 2 、EtAlCl 2 、BF 3 Et 2 O、Et 2 AlCl、SnCl 4 Wherein Ar is 2, 6-diisopropylphenyl, preferred cationic catalysts are TiCl 2 (OAr) 2 The structural formula of (A) is as follows:
by way of example of the present disclosure, with TiCl 2 (OAr) 2 By way of example, the electron pair shared by the initiator is further dissociated by the titanium metal central atom deficient in electrons on the cationic polymerization catalyst during the polymerization reaction to give the ion pair CH + -Cl - And thus facilitates subsequent coordination insertion of the vinyl ether monomer. When the vinyl ether monomer is inserted in a coordinated manner, the titanium metal central atom of the catalyst can also be coordinated with an oxygen atom on the pendant group of the vinyl ether monomer to form a cyclic transition state, and the spatial orientation of the pendant group during the insertion of the vinyl ether monomer is determined by the coordination transition state, so that the isotacticity of the polymer is improved. Similar mechanisms are true for other cationic polymerization catalysts, the only difference being the difference in the cationic catalyst and vinyl ether monomer, and the resulting polymers differing in isotacticity.
According to an embodiment of the present disclosure, the solvent of the solution in syringe a and syringe B is the same or different, each comprising at least one of: n-hexane, toluene, methylcyclohexane, and dichloromethane.
In embodiments of the present disclosure, organic solvents of different polarity have a significant effect on the isotacticity of the polymer. In nonpolar solvents, e.g. n-hexane, the dissociation of the CH-Cl bond and the CH is favoured + -Cl - The stable existence of ion pairs. In a polar solvent, the polar solvent molecules may also beWill interact with the ion pair, will compete with the coordination of the monomer, will destroy the ion pair and cyclic transition state stable existence, and is not conducive to monomer side group orientation control, so in polar solvent isotacticity is reduced.
According to embodiments of the present disclosure, the vinyl ether monomer includes at least one of: isobutyl vinyl ether, tert-butyl vinyl ether, trimethylvinyloxysilane, n-butyl vinyl ether, cyclohexyl vinyl ether, wherein the vinyl ether monomer is preferably isobutyl vinyl ether (IBVE) and has the following structural formula:
according to the embodiments of the present disclosure, the initiator is an addition product obtained by reacting HCl with any one of vinyl ether monomers, wherein, taking the addition product obtained by reacting HCl with isobutyl vinyl ether monomer as an example, the structural formula of the obtained addition product is as follows:
according to the embodiments of the present disclosure, the initiator may have an interaction with the active species at the end of the growing chain during the polymerization process, which may stabilize the active species at the end of the chain and maintain the polymerization activity; and can assist the titanium catalyst to control the spatial orientation of the side group when the vinyl ether monomer is inserted, thereby improving the isotacticity.
According to an embodiment of the disclosure, the additive comprises: 2, 6-di-tert-butyl-4-methylpyridine, wherein the structural formula of the 2, 6-di-tert-butyl-4-methylpyridine is as follows:
by way of example of the present disclosure, polyvinyl ethers prepared without the addition of additives have a lower isotacticity due to the presence of some trace impurities in the polymerization system, such as water, oxygen, etc., which would affect both initiation of the initiator and subsequent stereoselective polymerization in the absence of the additive; after the additive is used, the initiation of the initiator is facilitated, and the influence of trace impurities on the polymerization reaction is reduced, so that the isotacticity of the polymer is improved.
According to an embodiment of the present disclosure, the concentration of the cationic polymerization catalyst solution includes: 0.005-0.04M, wherein, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04M and the like can be selected.
In the examples of the present disclosure, the polyvinyl ether polymer prepared using the cationic polymerization catalyst solution in this concentration range has a high isotacticity, and when the concentration of the cationic polymerization catalyst solution is further increased, the effect of further increasing the isotacticity of the polyvinyl ether polymer is insignificant, while the isotacticity of the polyvinyl ether polymer prepared below this concentration range is decreased.
According to an embodiment of the present disclosure, the concentration of the additive includes: 0 to 0.006M, wherein 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006 and the like can be selected.
According to embodiments of the present disclosure, the molar ratio of vinyl ether monomer to initiator comprises: 24 to 144, wherein, 24.
By limiting the molar ratio of vinyl ether monomer to initiator within this range by embodiments of the present disclosure, on the one hand, higher monomer conversion and isotacticity of the polymer may be achieved, and on the other hand, higher molecular weight of the polymer may be achieved.
According to an embodiment of the present disclosure, the reaction temperature of the tubular reactor includes: -50 to-78 ℃, wherein, the temperature can be selected from-50, -58, -68, 78 ℃ and the like.
By way of example of the present disclosure, when the reaction temperature for preparing the polyvinyl ether polymer by cationic polymerization is higher, it is not beneficial to stably exist the cationic active species and the above mentioned cyclic transition state on the one hand, and it is also not beneficial to control the spatial orientation of the pendant group by the catalyst when the vinyl ether monomer is coordinately inserted, and the vinyl ether monomer is inserted more disorderly, so that the obtained polymer has lower isotacticity. When the reaction temperature of the cationic polymerization is lower, the stable existence of the cationic polymerization catalyst is facilitated, and the prepared polyvinyl ether has higher isotacticity. Where experimental conditions permit, the reaction temperature of the cationic polymerization can be further reduced to increase the isotacticity of the polyvinyl ether polymer.
According to an embodiment of the present disclosure, the cationic polymerization reaction is performed under an inert atmosphere, wherein the inert gas may be selected from nitrogen or argon.
By embodiments of the present disclosure, the use of an inert gas can provide an anhydrous, oxygen-free environment for the cationic catalyst.
According to an embodiment of the present disclosure, the mixer is a Y-type mixer.
Through this disclosed embodiment, choose for use Y type blender be convenient for the solution in syringe A and the syringe B and mix, make the solution intensive mixing even. Other shapes of mixer may be selected depending on the actual situation.
According to an embodiment of the present disclosure, a syringe pump controlled liquid flow rate includes: 5-20 mL/h, wherein 5, 10, 15, 20mL/h and the like can be selected, and corresponding adjustment can be carried out according to actual requirements.
By the embodiment of the disclosure, the flow rate of the liquid is controlled within 5-20 mL/h by using a syringe pump, higher polymer molecular weight and monomer conversion rate can be obtained, but the isotacticity of the polyvinyl ether polymers obtained at different flow rates is not obviously different.
To make the process of the present disclosure for preparing polyvinyl ethers by cationic polymerization using a continuous flow process clearer, the following explanation is made in conjunction with the mechanism of the cationic polymerization process.
FIG. 2 is a schematic illustration of the mechanism for preparing polyvinyl ethers by cationic polymerization using a continuous flow process according to the present disclosure.
The initiator is the addition product of the reaction of HCl with any one of the vinyl ether monomers. As shown in FIG. 2, firstly, the initiator is co-bonded with CH-Cl bond in the initiator with the help of the catalystFurther dissociation with electron pairs produces positive and negative ion pairs CH + ----Cl - Or alternatively Cl - Anion radical formed with the catalyst, subsequently, from CH + Cationic polymerization of vinyl ether monomers is initiated cationically, the chain ends remaining CH after coordinate insertion of the monomers + ---Cl - The active species is a cation. Repeating the monomer coordination insertion process to obtain polymer molecular chains, and finally carrying out chain termination reaction to finish the polymerization. In the polymerization process, the cationic polymerization catalyst also plays a role in controlling the spatial orientation of the side group when the vinyl ether monomer is coordinately inserted, so that the inserted side group of the vinyl ether monomer basically faces to one spatial direction, and further the polymer with high stereoregularity is obtained.
The method for preparing polyvinyl ether by cationic polymerization by adopting a continuous flow method comprises the following specific operation steps:
in the glove box, preparing a cationic polymerization catalyst solution with a certain concentration and sucking the solution into one syringe A, preparing a mixed solution of a monomer, an initiator and an additive with a certain concentration and sucking the mixed solution into the other syringe B, taking out the syringes A and B, installing the syringes A and B on a programmed syringe pump, and starting to flow at a set temperature and a set flow rate to carry out cationic polymerization. Collecting the product at the end of the tubular reactor, adding ethanol to quench the reaction, filtering to obtain a polymer, drying, and performing test analysis such as nuclear magnetism, DSC, GPC and the like. Wherein, GPC is gel permeation chromatography test, used to test the molecular weight and molecular weight distribution of the obtained polymer; DSC is differential scanning calorimetry, a thermal analysis method that measures the power difference (e.g., as heat) input to a sample and reference versus temperature at a programmed temperature to test the melting point of a polymer.
To make the objects, technical solutions and advantages of the present disclosure clearer, the technical solutions and principles of the present disclosure are further illustrated by specific embodiments and the accompanying drawings. It should be noted that the following specific examples are given by way of illustration only, and the scope of the disclosure is not limited thereto.
The test materials and reagents used in the following examples, etc., are commercially available unless otherwise specified.
Those skilled in the art who do not specify any particular technique or condition in the examples can follow the techniques or conditions described in the literature in this field or follow the product specification.
It should be noted that the synthesis of the catalyst and the polymerization process in the following examples were carried out in the absence of water and oxygen, all sensitive materials were stored in a glove box, and all solvents were strictly dried to remove water. All raw materials were purchased and used as received, unless otherwise specified.
The nuclear magnetic detection adopts a Bruker 400MHz nuclear magnetic instrument, the used deuterated reagent is deuterated chloroform, and the nuclear magnetic detection is carried out at room temperature; the element analysis is determined by the physicochemical center of the university of science and technology in China; molecular weight and molecular weight distribution were determined by GPC (polystyrene type column, HR2 and HR4, tank temperature 45 ℃ using Water 1515 and Water 2414 pumps; tetrahydrofuran as mobile phase at a flow rate of 1.0 ml per minute using polydispersed polystyrene as standard); the melting point was measured using a TA2000 type DSC instrument at a temperature rise rate of 10 deg.C/min, and the results of the second temperature rise test were analyzed.
Example 1
In the embodiment, n-hexane is used as a solvent, the flow rate of the solution in the injection pump is 10mL/h, and the cationic polymerization reaction is carried out at-78 ℃, and the specific process is as follows:
in a glove box, 20mL of 0.02M TiCl was prepared 2 (OAr) 2 (Ar is 2, 6-diisopropylphenyl) catalyst in n-hexane was sucked into a20 mL syringe A, and a20 mL mixed n-hexane solution of isobutyl vinyl ether monomer concentration of 0.72M, initiator concentration of 0.01M, and additive concentration of 0.004M was prepared and sucked into another 20mL syringe B. Taking out the syringes A and B from the glove box, connecting to the 2mm inner diameter pipelines, respectively fixing on the injection pumps, programming the injection pumps to have a liquid flow rate of 10mL/h, placing the pipelines in a low temperature ethanol bath cooled to-78 deg.C, and cooling to-78 deg.CThe solutions in syringes A, B were mixed in a Y-type mixer and flowed into a tubular reactor to start the cationic polymerization. It should be noted that a nitrogen atmosphere is maintained throughout the process. Continuously flowing for a period of time at a set temperature and flow rate, receiving a product at the tail end of the tubular reactor, quenching by using ethanol to terminate the reaction, separating out a solid polymer, filtering, and drying in vacuum to constant weight. The polyvinyl ether polymers prepared were tested and the results are shown in table 1.
The monomer conversion was found to be 86%, the polymer molecular weight was 26400g/mol, the melting point was 136 ℃ and the isotacticity was found to be 98%.
FIG. 3 is a representation of a polyisobutyl vinyl ether polymer in example 1 of the present disclosure 13 C nuclear magnetic spectrum.
As shown in fig. 3, the isotacticity of the polymer is calculated by integrating the carbon peaks of the polyisobutyl vinyl ether polymer, wherein m = rmr + mmr + mmm =98%, which is much higher than the isotacticity of the polyisobutyl vinyl ether obtained by other current systems.
FIG. 4 is an X-ray diffraction pattern of the polyisobutyl vinyl ether polymer of example 1 of the present disclosure.
As shown in fig. 4, the X-ray diffraction pattern (XRD) indicates that the polymer is a semicrystalline polymer, indicating a crystalline state of the polymer.
Example 2
The same preparation as in example 1 was carried out, except that the monomer in example 2 was n-butyl vinyl ether, and the results of the relevant tests are shown in Table 1.
Example 3
The same preparation process as in example 1 was employed, except that the vinyl ether monomer in example 3 was cyclohexyl vinyl ether, and the results of the relevant tests are shown in Table 1.
Example 4
The same preparation as in example 1 was carried out, except that the vinyl ether monomer in example 4 was 2-vinyloxytetrahydrofuran, and the results of the tests are shown in Table 1.
Example 5
The same preparation as in example 1 was carried out, except that the monomer in example 5 was trimethylvinyloxysilane, and the results of the relevant tests are shown in Table 1.
Example 6
The same preparation process as in example 1 was employed, except that the vinyl ether monomer in example 6 was t-butyl vinyl ether, and the results of the relevant tests are shown in Table 1.
TABLE 1 Effect of different vinyl Ether monomers on cationic polymerization to prepare polyvinyl ethers
As can be seen from Table 1, the isotacticity of the polymer prepared using isobutyl vinyl ether is highest, up to 98%. The polyvinyl ether polymers prepared by cationic polymerization by using other vinyl ether monomers by using a continuous flow method also have different high isotacticity, which shows that the method for preparing the polyvinyl ether by using the continuous flow method provided by the disclosure has certain universality and potential for further large-scale production. In the case of 2-vinyloxytetrahydrofuran and trimethylvinyloxysilanes, the possible heteroatom-containing groups present on the monomer side groups poison cationic polymerization catalysts, such as TiCl 2 (OAr) 2 The catalyst is deactivated, resulting in no polymerization activity.
Example 7
In this example, a cationic polymerization was carried out at-78 ℃ using methylene chloride as a solvent and a solution flow rate of 10 mL/h.
In a glove box, 20mL of 0.02M TiCl was prepared 2 (OAr) 2 (Ar is 2, 6-diisopropylphenyl) was sucked into one 20mL syringe A, and 20mL of a mixed solution of isobutyl vinyl ether monomer of 0.72M concentration, initiator of 0.01M concentration and additive of 0.004M in methylene chloride was prepared and sucked into another 20mL syringe B. Syringes A, B were removed from the glove box and connected to a syringe having an inner diameter of2mm pipelines are respectively fixed on injection pumps, the program of the injection pumps is set to ensure that the liquid flow rate is 10mL/h, then the pipelines are placed in a low-temperature ethanol bath which is cooled to-78 ℃, the solutions in two injectors are mixed in a Y-shaped mixer at the low temperature of-78 ℃ and then flow in a tubular reactor, and the cationic polymerization reaction is started. It should be noted that a nitrogen atmosphere is maintained throughout the process. Continuously flowing for a period of time at a set temperature and flow rate, receiving a product at the tail end of the tubular reactor, quenching by using ethanol to terminate the reaction, separating out a solid polymer, filtering, and drying in vacuum to constant weight.
It was found that the monomer conversion was 27%, the polymer molecular weight was 6300g/mol, the melting point was 97 ℃ and the isotacticity was 88%.
Example 8
The same preparation as in example 7 was used except that the organic solvent in example 8 was toluene. The polyvinyl ether polymers prepared were tested and the results are shown in table 2.
Example 9
The same preparation process as in example 7 was employed except that the organic solvent in example 9 was methylcyclohexane. The polyvinyl ether polymers prepared were tested and the results are shown in table 2.
TABLE 2 Effect of different organic solvents on the cationic polymerization for the preparation of polyvinyl ethers
As can be seen from Table 2, cationic polymerization using organic solvents of different polarities has a significant effect on the isotacticity of the polymer, with the highest isotacticity of 96. + -. 2% for the polymer obtained in a non-polar olefinic solvent such as n-hexane, and 91. + -. 1% for the polyisobutyl vinyl ether obtained using toluene as the solvent, and only 88. + -. 1% for the polymer obtained in a polar solvent such as dichloromethane. The non-polar organic solvent is favorable for dissociation of CH-Cl bonds and stable existence of ion pairs, and the existence of the polar solvent can cause polar solvent molecules to have interaction with the ion pairs and generate a competitive relationship with coordination of monomers, so that the stable existence of the ion pairs and a cyclic transition state is damaged, and the spatial orientation of monomer side groups is also not favorably controlled, so that the isotacticity is reduced in the polar solvent.
Example 10
In this example, a cationic polymerization was carried out at-78 ℃ using n-hexane as a solvent at a solution flow rate of 5 mL/h:
in a glove box, 20mL of 0.02M TiCl was prepared 2 (OAr) 2 (Ar is 2, 6-diisopropylphenyl) was sucked into one 20mL syringe A, and 20mL of a mixed solution of isobutyl vinyl ether monomer of 0.72M concentration, initiator of 0.01M concentration and additive of 0.004M concentration in n-hexane was prepared and sucked into the other 20mL syringe B. The syringes A and B were taken out from the glove box, connected to lines having an inner diameter of 2mm, and fixed to syringe pumps, respectively, and the syringe pumps were programmed to have a liquid flow rate of 5mL/h, and then the lines were placed in a low-temperature ethanol bath which had been cooled to-78 ℃ and the solutions in the two syringes were mixed in a Y-type mixer at a low temperature of-78 ℃ and then flowed into a tubular reactor to start a cationic polymerization reaction. It should be noted that a nitrogen atmosphere is maintained throughout the process. Continuously flowing for a period of time at a set temperature and flow rate, receiving a product at the tail end of the tubular reactor, quenching with ethanol to terminate the reaction, separating out a solid polymer, filtering, and drying in vacuum to constant weight.
Example 11
The same preparation method as in example 10 was employed except that the solution flow rate in example 11 was 20mL/h. The polyvinyl ether polymers prepared were tested and the results are shown in table 3.
Example 12
In the embodiment, n-hexane is used as a solvent, cationic polymerization is carried out by a discontinuous flow method, and the reaction temperature is-78 ℃.
In the handPreparing 20mL of a mixed solution of isobutyl vinyl ether monomer with the concentration of 0.72M, initiator with the concentration of 0.01M and additive with the concentration of 0.004M in a box, adding the mixed solution into a 100mLSchlenck bottle, taking out the bottle, putting the bottle into a low temperature of-78 ℃, and then preparing 20mL of TiCl with the concentration of 0.02M 2 (OAr) 2 (Ar is 2, 6-diisopropylphenyl) was added to a Schlenck flask, followed by initiation of cationic polymerization. The process also requires maintaining a nitrogen atmosphere, anhydrous and oxygen-free. After the same time of flowing condition, adding alcohol to quench and stop reaction, filtering polymer, vacuum drying to constant weight. The polyvinyl ether polymers prepared were tested and the results are shown in table 3.
TABLE 3 Effect of different flow rates of the solutions on the preparation of polyvinyl ethers by cationic polymerization
As can be seen from Table 3, when the flow rate of the solution in syringes A, B is 5mL/h, the conversion of isobutyl vinyl ether monomer is >97%, and the molecular weight of the resulting polymer is higher (38200 g/mol); when the flow rate of the solution in syringes A, B was 20mL/h, the conversion of isobutyl vinyl ether monomer was 73%, and the molecular weight of the resulting polymer was lower (22200 g/mol), but the flow rate of the solution in the syringes had no significant effect on the isotacticity of the polyvinyl ether polymer. At a flow rate of 10mL/h, the obtained polyisobutyl vinyl ether has the highest isotacticity, which reaches 96 +/-2%.
It can also be found from Table 3 that the isotacticity of the polyvinyl ether polymer prepared by cationic polymerization using the continuous flow method can reach 96. + -. 2% under the same reaction conditions, while the isotacticity of the polyvinyl ether polymer prepared by the conventional polymerization method (i.e., non-flow method) is only 91. + -. 1%, which indicates that the cationic catalyst and the monomer are more sufficiently contacted in the cationic polymerization using the continuous flow method, which is a continuous reaction process, and the isotacticity of the polymer is further improved. In addition, the polyisobutyl vinyl ethers obtained by the continuous flow process have a higher melting point and a greater enthalpy of fusion than the polyisobutyl vinyl ethers obtained by the conventional (non-flowing) polymerization processes
Figure 5 is a differential scanning calorimetry test plot of polymers of example 11 and example 13 of the present disclosure.
As shown in fig. 5, the polyisobutyl vinyl ether prepared by the continuous flow method (flow chemistry method) has a higher melting point of 136 deg.c, compared to the polyisobutyl vinyl ether prepared by the conventional method (non-flow method).
Example 13
In this example, n-hexane was used as a solvent, the solution flow rate was 10mL/h, and the cationic polymerization was carried out at-50 ℃:
in a glove box, 20mL of 0.02M TiCl was prepared 2 (OAr) 2 (Ar is 2, 6-diisopropylphenyl) in n-hexane, was taken up into a20 mL syringe, and 20mL of a mixed solution of isobutyl vinyl ether (IBVE) monomer at 0.72M, initiator at 0.01M, and additive at 0.004M in n-hexane was prepared and taken up into another 20mL syringe. The syringes were taken out from the glove box, connected to a line having an inner diameter of 2mm, fixed to a syringe pump, programmed to have a liquid flow rate of 10mL/h, and then the line was placed in a low-temperature ethanol bath which had been cooled to-50 ℃, and the solutions in the two syringes were mixed in a Y-type mixer at a low temperature of-50 ℃ and then flowed into a tubular reactor to start a cationic polymerization reaction. It should be noted that a nitrogen atmosphere is maintained throughout the process. Continuously flowing for a period of time at a set temperature and flow rate, receiving a product at the tail end of the tubular reactor, quenching by using ethanol to terminate the reaction, separating out a solid polymer, filtering, and drying in vacuum to constant weight. The polyvinyl ether polymers prepared were tested and the results are shown in table 4.
TABLE 4 Effect of different cationic polymerization temperatures on the preparation of polyvinyl ethers by cationic polymerization
As can be seen from Table 4, the isotacticity of the polymer decreases with increasing temperature of the cationic polymerization. The cationic polymerization reaction can obtain the polyisobutyl vinyl ether polymer with the isotacticity of 96 +/-2% at the temperature of-78 ℃, and when the temperature is increased to-50 ℃, the isotacticity of the polymer is only 79 +/-2% at the highest. It is shown that at higher temperatures, this is not conducive to the stable presence of cationic active species and cyclic transition states, and is not conducive to the steric orientation of pendant groups controlled by the catalyst during monomer coordination insertion, and the monomer insertion is more disordered, resulting in lower isotacticity of the resulting polymer.
Example 14
In the same manner as in example 1, but with no additives used in the only difference in example 14, the results of the relevant tests are given in Table 5.
TABLE 5 Effect of additives on the cationic polymerization for the preparation of polyvinyl ethers
As can be seen from Table 5, the isotacticity of the polymer obtained with the additive 2, 6-di-tert-butyl-4-methylpyridine (DTBMP) is 96. + -. 2%, while that without the additive is only 85. + -. 2%, all other things being equal. The reason for this is that, after the use of additives, the initiation of the initiator is favored on the one hand, and on the other hand, the effect of traces of impurities on the polymerization is minimized, thereby increasing the isotacticity of the polymer.
Example 15
The same preparation method as that of example 1 was used except that the concentration of the cationic polymerization catalyst solution in example 15 was 0.005, and the results of the relevant tests are shown in Table 6.
Example 16
The same preparation method as that in example 1 was used except that the concentration of the cationic polymerization catalyst solution in example 16 was 0.03, and the results of the relevant tests are shown in Table 6.
Example 17
The same preparation method as that of example 1 was used except that the concentration of the cationic polymerization catalyst solution in example 17 was 0.04, and the results of the relevant tests are shown in Table 6.
TABLE 6 Effect of different cationic polymerization catalysts on the cationic polymerization for the preparation of polyvinyl ethers
As can be seen from Table 6, the isotacticity of the polyvinyl ether polymers prepared by the cationic polymerization catalyst in the range of 0.005 to 0.04M was 95% or more, and even 98%, and the isotacticity of the polymers did not significantly decrease as the concentration of the cationic polymerization catalyst increased.
Example 18
The same preparation as in example 1 was carried out, except that in example 18 the molar ratio of vinyl ether monomer to initiator was 24.
Example 19
The same procedure as in example 1 was followed, except that in example 19 the vinyl ether monomer to initiator molar ratio was 48, and the results of the relevant tests are shown in Table 7.
Example 20
The same preparation as in example 1 was carried out, except that in example 20 the molar ratio of vinyl ether monomer to initiator was 144, 1, and the results of the tests are shown in Table 7.
TABLE 7 Effect of vinyl Ether monomer to initiator molar ratio on preparation of polyvinyl Ether by cationic polymerization
As can be seen from Table 7, the isotacticity of the polymer can reach 98% at a molar ratio of the monomer to the initiator of 72, and as the concentration of the monomer to the initiator is further increased, the isotacticity of the polymer is still maintained at 92% or more, which is still higher than that of the polymer prepared by the conventional method (non-flow method).
In view of the foregoing, the present disclosure provides a method for preparing polyvinyl ether by cationic polymerization using a continuous flow process, wherein the polymer has an isotacticity of up to 98% under preferred conditions. In addition, the continuous flow method can be easily adjusted for various monomers, various solvents, cationic polymerization reaction temperature and other parameter conditions, and shows that the method has certain universality. And due to the unique advantages of the flow chemical means in industrial production, the continuous controllable synthesis of the high isotacticity polyvinyl ether in a large scale is hopefully realized, and a new thought is provided for obtaining the high isotacticity polyvinyl ether through the large-scale continuous controllable polymerization of the vinyl ether monomer.
In addition, a means of introducing a flow chemistry into a fixed bed reactor may be considered, and a catalyst or the like is supported on a carrier and fixed on the fixed bed, and then a flow chemistry reaction is performed, which is more favorable for the exploration of industrial production.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.
Claims (5)
1. A process for preparing polyvinyl ethers by cationic polymerization using a continuous flow process comprising:
providing a syringe A and a syringe B, wherein the syringe A is filled with a cationic polymerization catalyst solution, and the syringe B is filled with a vinyl ether monomer, an initiator solution and an optional additive;
connecting an injector A and an injector B to two injection pumps respectively, controlling the liquid flow rate by the injection pumps, injecting the solutions in the injector A and the injector B into a mixer, mixing in the mixer, flowing into a tubular reactor, and carrying out cationic polymerization while continuously flowing in the tubular reactor to obtain a product polyvinyl ether;
wherein the cationic polymerization catalyst comprises at least one of:
TiCl 2 (OAr) 2 、EtAlCl 2 、BF 3 Et 2 O、Et 2 AlCl、SnCl 4 wherein Ar is 2, 6-diisopropylphenyl;
the initiator is an addition product obtained by reacting HCl with any one of the vinyl ether monomers, wherein the vinyl ether monomer comprises at least one of the following:
isobutyl vinyl ether, n-butyl vinyl ether;
the concentrations of the cationic polymerization catalyst solution include: 0.005 to 0.04M;
the molar ratio of the vinyl ether monomer to the initiator comprises: 24 to 144;
the solvents of the solutions in syringe a and syringe B are the same or different, each comprising at least one of:
n-hexane, toluene, methylcyclohexane, dichloromethane;
the reaction temperature of the tubular reactor comprises: -50 to-78 ℃;
the syringe pump controlled liquid flow rates include: 5 to 20mL/h.
2. The method of claim 1, wherein the additive comprises: 2, 6-di-tert-butyl-4-methylpyridine.
3. The method of claim 1, wherein,
the concentrations of the additives include: 0 to 0.006M;
the cationic polymerization reaction is carried out under an inert atmosphere.
4. The method of claim 1, wherein the mixer is a Y-mixer.
5. A polyvinyl ether produced by the method according to any one of claims 1 to 4.
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