Regulating and controlling method and synthesizing method for synthesizing EVA (ethylene vinyl acetate copolymer) with controllable release of free radicals, EVOH (ethylene vinyl alcohol) resin and sy
1. An EVOH resin characterized by having a bimodal gel permeation chromatography curve.
2. The EVOH resin according to claim 1, wherein a first peak of the double peaks has a weight-average molecular weight of 6.92 to 8.70 kg/mol;
the weight average molecular weight of the second peak in the double peaks is 4.38-7.15 kg/mol;
the molecular weight distribution PDI of the EVOH resin is 3.6-6.8;
the degree of branching of the EVOH resin being 1000 CH per molecule2The number of the medium-branched chains is less than or equal to 50.
3. A regulation and control method for synthesizing EVA is characterized by comprising the following steps:
a) setting the feeding mode and the feeding sequence of the ethylene and the vinyl acetate based on the initiation speed of the initiator to the ethylene and the vinyl acetate;
b) setting the selection, number and adding mode of the initiator based on the automatic acceleration effect of the free radical polymerization reaction;
c) setting the type and/or number of solvents based on the chain transfer constant of the solvent, the solubility of ethylene in the solvent, the solubility of vinyl acetate in the solvent and the distribution coefficient of ethylene in vinyl acetate and the solvent, thereby regulating and controlling the structure and/or molecular weight of the synthesized EVA;
when the number of the solvents is more than or equal to 2, the distribution coefficient of the vinyl acetate in the mixed solvent is also included in the step c);
d) setting a temperature rising mode of the synthesis reaction based on the relation between the free radical generated by the initiator and the temperature;
the steps of the regulation and control method are not in sequence.
4. The synthesis method of EVA based on the regulation and control method of claim 3, characterized by comprising the following steps:
1') adding ethylene, vinyl acetate and an initiator into a reaction device in batches and in sequence, and carrying out sectional polymerization reaction by pulse heating to obtain EVA;
wherein the adding mode of the solvent comprises one or more of separate adding, solution of ethylene and the solvent, solution of vinyl acetate and the solvent and solution of an initiator and the solvent;
the raw materials for synthesizing the EVA comprise ethylene, vinyl acetate, an initiator and a solvent.
5. The synthesis method according to claim 4, wherein the batch-wise sorting sequence is specifically:
firstly, adding a certain amount of vinyl acetate, introducing ethylene under a certain pressure for polymerization, heating, then adding a certain amount of vinyl acetate, and continuing polymerization;
alternatively, the first and second electrodes may be,
firstly adding vinyl acetate, then introducing ethylene under a certain pressure, and after a certain period of polymerization reaction, introducing a certain amount of ethylene, and continuing the polymerization reaction.
6. The synthesis process according to claim 4, characterized in that the initiator is added before and/or after the addition of vinyl acetate and/or before and/or after the addition of ethylene before the polymerization takes place;
the pulse heating is specifically heating to a certain temperature, standing for a certain time, cooling, standing for a certain time, heating, repeating in sequence, and controlling the temperature and the standing time.
7. The method of synthesis of claim 4, wherein the polymerization comprises free radical solution polymerization;
the initiator comprises one or two of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, azobis (2-methylbutyronitrile), hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, neopentyl peroxyneodecanoate, amyl peroxypivalate, butyl peroxyacetate and dibutyl peroxydicarbonate;
the solvent comprises one or more of n-hexane, petroleum ether, tetrahydrofuran, methanol, ethanol and propanol;
the volume ratio of the total amount of vinyl acetate to the solvent in the reaction device is (1-30): 1;
the total concentration of the initiator added in the polymerization reaction process is (2.2-9.8) multiplied by 10-3mol/L；
The temperature of the polymerization reaction is 45-125 ℃;
the polymerization reaction time is 2-8 h;
the pressure of the polymerization reaction is 0.5-15 MPa;
the pressure was kept constant during the polymerization.
8. A method for synthesizing EVOH is characterized by comprising the following steps:
1) heating and mixing EVA and methanol, adding a catalyst for reaction, adding methanol at the same time, keeping the concentration of the EVA in a reaction system constant, then adjusting the pH value, and separating out to obtain the EVOH.
9. The synthesis method according to claim 8, wherein the EVA contains 15-45 mol% of ethylene;
in the solution obtained by heating and mixing the EVA and the methanol, the molar concentration of the EVA is 5-35%;
the heating and mixing temperature is 50-120 ℃;
the mass ratio of the catalyst to the EVOH is (25-40): 1;
the catalyst is added for multiple times;
the times of the multiple times are 2-4 times;
the catalyst comprises one or more of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution and potassium carbonate solution;
the concentration of the catalyst is 20-100 g/L.
10. The synthesis method according to claim 8, wherein the reaction time is 3-10 h;
the regulator for regulating the pH value comprises one or more of boric acid, oxalic acid, acetic acid and citric acid;
the pH value is 5-8;
the concentration of the regulator is 0.5-1.5 mol/L;
the precipitation mode comprises precipitation in hot water;
the precipitation temperature is 55-95 ℃;
the precipitation time is 20-80 min;
the EVA comprises the EVA synthesized by the synthesis method of any one of claims 4-7.
Background
With the rapid development of the automotive industry, the consumption of fuel, in particular gasoline, is enormous and the demand is still increasing exponentially year after year. However, the main component of gasoline is volatile light hydrocarbon organic compounds (VOC), and since containers for storing gasoline, such as automobile fuel tanks, transportation tanks, storage tanks, etc., are made of metal, the barrier property against such VOC is very poor, and particularly after the gasoline volatilizes to form a certain vapor pressure in the containers, the VOC is more easily diffused and permeated out of the containers, thereby causing great harm to people, environment and organisms. Therefore, VOC treatment also becomes another important project after automobile exhaust treatment. By taking the method as a starting point, the barrier property of the gasoline container to light hydrocarbon organic matters is improved, VOC can be reduced, the load of the environment is reduced, the utilization efficiency of oil products is improved, the cost is saved, and the resource waste is reduced. EVOH (ethylene vinyl alcohol copolymer) is a semi-crystalline, high molecular material with excellent gas (e.g. oxygen, carbon dioxide, etc.) barrier properties and processability, and significantly reduces the permeation of light hydrocarbon VOCs by being used in oil containers in the form of an interlayer or coating. Industrially, EVOH is synthesized by using ethylene and vinyl acetate as raw materials, preparing EVA by initiating solution polymerization through free radicals, and obtaining EVOH after alcoholysis. The Nanjing Linification developed EVOH synthesis work (Lin chemical Commission, 1995, 6, 3-6; CN 91107038.9), and subsequently the China petrochemical group Sichuan Vinylon works also developed related work (CN 201510184602.1; CN 201310125550.1). At present, EVOH products are mainly prepared by directly processing and modifying purchased EVOH resins, and the EVOH synthesis technology does not reach the industrial production stage.
The excellent barrier property of EVOH benefits from the strong bonding effect between hydroxyl in molecules and intermolecular hydrogen bonds, the cohesive force is strong, molecular chains are tightly stacked, and small molecules cannot penetrate through the EVOH; on the other hand, the presence of ethylene segments imparts good processability to EVOH. At present, many reports exist for regulating and controlling the barrier property and the processing property of a polymer by controlling the content of ethylene in EVOH, however, the problems of poor controllability of the polymerization process, poor linearity of the polymer structure and the like, such as low molecular weight of the polymer, uneven distribution of hydroxyl groups on a main chain, or occurrence of hydroxyl groups on branched chains, high branching degree or uncontrollable branching and the like exist, and finally, the EVOH is low in molecular weight, unstable in batches and poor in structure controllability.
Therefore, how to realize the controllable polymerization of ethylene and vinyl acetate is of great significance for further improving the barrier property and the processability of EVOH and improving the batch stability of products, and is one of the problems to be solved by a plurality of researchers with prospective ideas in the field.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a method for regulating and controlling EVA synthesis, an EVOH resin and a method for synthesizing the same, and particularly a method for regulating and controlling EVA synthesis with controlled free radical release and a method for synthesizing the same. The regulation and control method of the EVA provided by the invention is characterized in that ethylene and vinyl acetate are used as raw materials, the EVA is prepared in a free radical solution polymerization system, and based on the relation between the dynamic characteristics of polymerization reaction and the concentration, the generation rate and the initiation efficiency of free radicals and the self-acceleration phenomenon, the structure of the EVA is regulated and controlled through the controllable release of the free radicals, so that the EVA of the EVOH can be better and controllably prepared.
The invention provides EVOH resin, which is characterized in that the gel permeation chromatography curve of the EVOH resin is in a bimodal form.
Preferably, the weight average molecular weight of the first peak in the double peaks is 6.92-8.70 kg/mol;
the weight average molecular weight of the second peak in the double peaks is 4.38-7.15 kg/mol;
the molecular weight distribution PDI of the EVOH resin is 3.6-6.8;
the degree of branching of the EVOH resin being 1000 CH per molecule2The number of the medium-branched chains is less than or equal to 50.
The invention provides a regulation and control method for synthesizing EVA, which comprises the following steps:
a) setting the feeding mode and the feeding sequence of the ethylene and the vinyl acetate based on the initiation speed of the initiator to the ethylene and the vinyl acetate;
b) setting the selection, number and adding mode of the initiator based on the automatic acceleration effect of the free radical polymerization reaction;
c) setting the type and/or number of solvents based on the chain transfer constant of the solvent, the solubility of ethylene in the solvent, the solubility of vinyl acetate in the solvent and the distribution coefficient of ethylene in vinyl acetate and the solvent, thereby regulating and controlling the structure and/or molecular weight of the synthesized EVA;
when the number of the solvents is more than or equal to 2, the distribution coefficient of the vinyl acetate in the mixed solvent is also included in the step c);
d) setting a temperature rising mode of the synthesis reaction based on the relation between the free radical generated by the initiator and the temperature;
the steps of the regulation and control method are not in sequence.
The invention provides an EVA (ethylene vinyl acetate) synthesis method based on the regulation and control method of the technical scheme, which comprises the following steps:
1') adding ethylene, vinyl acetate and an initiator into a reaction device in batches and in sequence, and carrying out sectional polymerization reaction by pulse heating to obtain EVA;
wherein the adding mode of the solvent comprises one or more of separate adding, solution of ethylene and the solvent, solution of vinyl acetate and the solvent and solution of an initiator and the solvent;
the raw materials for synthesizing the EVA comprise ethylene, vinyl acetate, an initiator and a solvent.
Preferably, the batch sorting sequence specifically comprises:
firstly, adding a certain amount of vinyl acetate, introducing ethylene under a certain pressure for polymerization, heating, then adding a certain amount of vinyl acetate, and continuing polymerization;
alternatively, the first and second electrodes may be,
firstly adding vinyl acetate, then introducing ethylene under a certain pressure, and after a certain period of polymerization reaction, introducing a certain amount of ethylene, and continuing the polymerization reaction.
Preferably, the initiator is added before and/or after the addition of vinyl acetate and/or before and/or after the addition of ethylene before the polymerization takes place;
the pulse heating is specifically heating to a certain temperature, standing for a certain time, cooling, standing for a certain time, heating, repeating in sequence, and controlling the temperature and the standing time.
Preferably, the polymerization comprises free radical solution polymerization;
the initiator comprises one or two of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, azobis (2-methylbutyronitrile), hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, neopentyl peroxyneodecanoate, amyl peroxypivalate, butyl peroxyacetate and dibutyl peroxydicarbonate;
the solvent comprises one or more of n-hexane, petroleum ether, tetrahydrofuran, methanol, ethanol, propanol and the like as a solvent, and preferably one or more of n-hexane, petroleum ether, tetrahydrofuran, methanol and ethanol;
the volume ratio of the total amount of vinyl acetate to the solvent in the reaction device is (1-30): 1;
the total concentration of the initiator added in the polymerization reaction process is (2.2-9.8) multiplied by 10-3mol/L；
The temperature of the polymerization reaction is 45-125 ℃;
the polymerization reaction time is 2-8 h;
the pressure of the polymerization reaction is 0.5-15 MPa;
the pressure was kept constant during the polymerization.
The invention provides a synthesis method of EVOH, which comprises the following steps:
1) heating and mixing EVA and methanol, adding a catalyst for reaction, adding methanol at the same time, keeping the concentration of the EVA in a reaction system constant, then adjusting the pH value, and separating out to obtain the EVOH.
Preferably, the content of ethylene in the EVA is 15-45 mol%;
in the solution obtained by heating and mixing the EVA and the methanol, the molar concentration of the EVA is 5-35%;
the heating and mixing temperature is 50-120 ℃;
the mass ratio of the catalyst to the EVOH is (25-40): 1;
the catalyst is added for multiple times;
the times of the multiple times are 2-4 times;
the catalyst comprises one or more of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution and potassium carbonate solution;
the concentration of the catalyst is 20-100 g/L.
Preferably, the reaction time is 3-10 h;
the regulator for regulating the pH value comprises one or more of boric acid, oxalic acid, acetic acid and citric acid;
the pH value is 5-8;
the concentration of the regulator is 0.5-1.5 mol/L;
the precipitation mode comprises precipitation in hot water;
the precipitation temperature is 55-95 ℃;
the precipitation time is 20-80 min;
the EVA comprises the EVA synthesized by the synthesis method in any one of the technical schemes.
The invention provides an EVOH resin, the gel permeation chromatography curve of which is bimodal. Compared with the prior art, the invention is based on the research that EVOH (ethylene-vinyl alcohol copolymer) has excellent gas barrier property and processing property, which depend on chain accumulation, molecular weight, main structure, branching degree and the like of the polymer, so that the barrier property and the processing property of the EVOH not only depend on the content of ethylene in the polymer, but also depend on the distribution and the position of hydroxyl groups, the crystallization property of the polymer and the like. And the EVOH is prepared by alcoholysis of EVA (ethylene-vinyl acetate copolymer), so that the controllable synthesis of the EVA has a dominant effect on the performance of the EVOH.
The invention provides a regulation and control method and a synthesis method for preparing EVA (ethylene-vinyl acetate copolymer) with a controllable structure. In particular, the prepared EVA is used for synthesizing EVOH (ethylene-vinyl alcohol copolymer) resin, and Gel Permeation Chromatography (GPC) tests show that the EVOH resin with bimodal distribution can be obtained by the regulation and control method provided by the invention. The method has the characteristics of strong controllability, mild conditions, simple operation and large-scale synthesis prospect. The invention realizes the controllable polymerization of ethylene and vinyl acetate, regulates and controls the polymer structure, the hydroxyl distribution and the like, is favorable for improving the high molecular weight of the polymer and improving the crystallization behavior (including crystal region distribution) of the polymer, and has important significance for further improving the barrier property and the processing property of EVOH and improving the batch stability of products.
Experimental results show that the EVA with controllable release of free radicals prepared by the invention can obtain high molecular weight, especially EVOH resin with bimodal distribution through alcoholysis reaction.
Drawings
FIG. 1 is a DSC of different EVOH resins;
FIG. 2 is a graph of the effect of pressure on the solubility of ethylene in butanol and the reaction system;
FIG. 3 is a graph of solubility parameters for different solvents;
FIG. 4 is a graph of the effect of reaction temperature/pressure on the reactivity ratio of monomers;
FIG. 5 is a graph of the effect of pressure and temperature on ethylene solubility;
FIG. 6 is a polymerization reaction characteristic in the present invention;
FIG. 7 is a nuclear magnetic hydrogen spectrum of EVA prepared in example 1 of the present invention;
FIG. 8 is a nuclear magnetic hydrogen spectrum of an EVOH produced in example 1 of the present invention;
FIG. 9 is a GPC chart of an EVOH resin produced in example 1 of the present invention;
FIG. 10 is a GPC chart of a bimodal distribution EVOH resin prepared in example 2 of the present invention;
FIG. 11 is a GPC chart of a bimodal distribution EVOH resin prepared in example 3 of the present invention;
FIG. 12 shows the method for characterizing and calculating the degree of branching of the EVOH resin prepared by 6 of the present invention (13C NMR)；
FIG. 13 is an external view of an EVOH resin and film produced by the present invention.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
All of the starting materials of the present invention, without particular limitation as to their source, may be purchased commercially or prepared according to conventional methods well known to those skilled in the art.
All the raw materials of the present invention are not particularly limited in purity, and industrial grade raw materials or purity requirements which are conventional in the field of production of EVA and EVOH may be preferably used in the present invention.
All the raw materials and the process of the invention belong to the conventional trade marks or the abbreviation, each trade mark or the abbreviation is clear and definite in the field of related application, and the technical personnel in the field can purchase the raw materials or prepare the raw materials or the abbreviation from the market or prepare the raw materials or the abbreviation by a conventional method or adopt corresponding equipment to realize the raw materials or the abbreviation according to the trade marks, the abbreviation and the corresponding application.
The invention provides an EVOH resin, the gel permeation chromatography curve of which is bimodal.
In the present invention, the weight average molecular weight of the first peak in the doublets is preferably 6.92 to 8.70kg/mol, more preferably 7.0 to 8.50kg/mol, more preferably 7.2 to 8.3kg/mol, and more preferably 7.5 to 8.0 kg/mol.
In the present invention, the weight average molecular weight of the second peak in the doublet is preferably 4.38 to 7.15kg/mol, more preferably 4.5 to 7.0kg/mol, more preferably 4.8 to 6.8kg/mol, more preferably 5.0 to 6.5kg/mol, more preferably 5.3 to 6.2kg/mol, more preferably 5.5 to 6.0 kg/mol.
In the present invention, the molecular weight distribution PDI (gel permeation chromatography) of the EVOH resin is preferably 3.6-6.8, more preferably 3.9-6.5, more preferably 4.2-6.3, more preferably 4.5-6.0, more preferably 4.8-5.7, more preferably 5.0-5.5.
In the present invention, the degree of branching of the EVOH resin is 1000 CH per molecule2The number of medium-branched chains is preferably 50 or less, more preferably 40 or less, and still more preferably 30 or less.
In the invention, the main chain structure of the EVOH resin is formed by random copolymerization of ethylene and vinyl acetate.
Referring to fig. 1, fig. 1 is a DSC diagram of different EVOH resins.
The invention provides a regulation and control method for synthesizing EVA, which comprises the following steps:
a) setting the feeding mode and the feeding sequence of the ethylene and the vinyl acetate based on the initiation speed of the initiator to the ethylene and the vinyl acetate;
b) setting the selection, number and adding mode of the initiator based on the automatic acceleration effect of the free radical polymerization reaction;
c) setting the type and/or number of solvents based on the chain transfer constant of the solvent, the solubility of ethylene in the solvent, the solubility of vinyl acetate in the solvent and the distribution coefficient of ethylene in vinyl acetate and the solvent, thereby regulating and controlling the structure and/or molecular weight of the synthesized EVA;
when the number of the solvents is more than or equal to 2, the distribution coefficient of the vinyl acetate in the mixed solvent is also included in the step c);
d) setting a temperature rising mode of the synthesis reaction based on the relation between the free radical generated by the initiator and the temperature;
the steps of the regulation and control method are not in sequence.
The invention sets the feeding mode and the feeding sequence of the ethylene and the vinyl acetate based on the initiation speed of the initiator to the ethylene and the vinyl acetate. Specifically, a certain amount of vinyl acetate is added, ethylene under a certain pressure is introduced for polymerization, and a certain amount of vinyl acetate is added after the temperature is raised to continue the polymerization. Or, vinyl acetate is added firstly, then ethylene with certain pressure is introduced, and after a certain time of polymerization reaction, a certain amount of ethylene is introduced, and the polymerization reaction is continued.
The invention sets the selection, the number and the adding mode of the initiator based on the automatic acceleration effect of the free radical polymerization reaction.
In the present invention, the selection of the initiator preferably refers to a specific kind or a specific selection of the initiator.
The invention sets the type and/or number of the solvent based on the chain transfer constant of the solvent, the solubility of ethylene in the solvent, the solubility of vinyl acetate in the solvent and the distribution coefficient of ethylene in vinyl acetate and the solvent, thereby regulating and controlling the structure and/or molecular weight of the synthesized EVA.
Different solvents have different solubility parameters (solvent effect 1)
When the number of the solvents is more than or equal to 2, the distribution coefficient of the vinyl acetate in the mixed solvent is also included in the step c). Distribution ratio in mixed solvent (solvent effect 2)
Wherein the content of the first and second substances,
in the present invention, the kind of the solvent preferably refers to a specific selection of the solvent.
In the present invention, when the number of solvents is 2 or more, it is preferable that the number of solvents is a mixed solvent of two solvents, and therefore, the distribution coefficient of vinyl acetate in the mixed solvent is also included in the step c).
In the present invention, the solubility of the solvent is also correlated with the pressure of the reaction;
referring to fig. 2, fig. 2 is a graph showing the effect of pressure on the solubility of ethylene in butanol and the reaction system.
Referring to fig. 3, fig. 3 is a graph of solubility parameters for different solvents.
In the present invention, the control method preferably further comprises setting the values of the reaction temperature and the pressure based on the influence relationship of the reaction and the pressure on the solubility.
Referring to fig. 4, fig. 4 is a graph showing the effect of reaction temperature/pressure on the reactivity ratio of monomers.
Referring to fig. 5, fig. 5 is a graph of the effect of pressure and temperature on ethylene solubility.
The invention sets the heating mode of the synthesis reaction based on the relationship between the free radical generated by the initiator and the temperature. Specifically, pulsed heating may be employed. In the invention, the pulse heating can be heating to a certain temperature, cooling after staying for a certain time, heating after staying for a certain time, repeating the steps in sequence, and controlling the temperature and the staying time.
Referring to fig. 6, fig. 6 is a polymerization reaction characteristic in the present invention.
In the present invention, the above-mentioned regulation method is convenient to describe and illustrate in a stepwise manner, so that there is no precedence.
The invention provides an EVA (ethylene vinyl acetate) synthesis method based on the regulation and control method of the technical scheme, which comprises the following steps:
1') adding ethylene, vinyl acetate and an initiator into a reaction device in batches and in sequence, and carrying out sectional polymerization reaction by pulse heating to obtain EVA;
wherein the adding mode of the solvent comprises one or more of separate adding, solution of ethylene and the solvent, solution of vinyl acetate and the solvent and solution of an initiator and the solvent;
the raw materials for synthesizing the EVA comprise ethylene, vinyl acetate, an initiator and a solvent.
In the invention, the raw materials for synthesis are industrial-grade raw materials.
In the present invention, the batch-by-batch order may specifically be:
firstly adding a certain amount of vinyl acetate, introducing ethylene under a certain pressure for polymerization reaction, heating, then adding a certain amount of vinyl acetate, and continuing the polymerization reaction. Or, vinyl acetate is added firstly, then ethylene with certain pressure is introduced, and after a certain time of polymerization reaction, a certain amount of ethylene is introduced, and the polymerization reaction is continued.
In the present invention, the initiator is added before the polymerization reaction, before and/or after the addition of vinyl acetate.
And/or the presence of a gas in the gas,
the initiator is added before, before and/or after the addition of ethylene, before the polymerization reaction takes place.
In the invention, the pulse heating may be specifically heating to a certain temperature, cooling after staying for a certain time, heating after staying for a certain time, repeating the steps in sequence, and controlling the temperature and the staying time.
In the present invention, the polymerization preferably includes radical solution polymerization.
In the present invention, the initiator preferably includes one or two of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, azobis (2-methylbutyronitrile), hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, amyl neodecanoate peroxide, amyl pivalate peroxide, butyl acetate peroxide and dibutyl dicarbonateperoxide, more preferably azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, azobis (2-methylbutyronitrile), hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, amyl neodecanoate peroxide, amyl pivalate peroxide, butyl acetate peroxide or dibutyl dicarbonateperoxide.
In the present invention, the solvent preferably includes one or more of n-hexane, petroleum ether, tetrahydrofuran, methanol, ethanol, and propanol, and more preferably n-hexane, petroleum ether, tetrahydrofuran, methanol, ethanol, or propanol.
In the invention, the volume ratio of the total amount of vinyl acetate to the solvent in the reaction device is preferably (1-30): 1, more preferably (5-25): 1, more preferably (10 to 20): 1.
in the present invention, the polymerization has been carried outThe total concentration of the initiator added in the process is preferably (2.2-9.8) multiplied by 10- 3mol/L, more preferably (3.2 to 8.8). times.10-3mol/L, more preferably (4.2 to 7.8). times.10-3mol/L, more preferably (5.2 to 6.8). times.10-3mol/L。
In the invention, the polymerization reaction temperature is preferably 45-125 ℃, more preferably 55-115 ℃, more preferably 65-105 ℃, and more preferably 75-95 ℃.
In the invention, the time of the polymerization reaction is preferably 2-8 h, more preferably 3-7 h, and more preferably 4-6 h.
In the present invention, the reaction pressure is preferably derived from the pressure of a mixed gas of ethylene gas and a protective gas or the pressure of ethylene gas. Specifically, the reaction pressure is preferably 0.5 to 15MPa, more preferably 2.5 to 13MPa, and more preferably 5 to 10 MPa.
In the present invention, the protective gas preferably comprises nitrogen and/or an inert gas, more preferably nitrogen or an inert gas, and particularly may be nitrogen or argon.
In the present invention, the pressure is preferably kept stable during the polymerization reaction, and more preferably kept constant.
In the invention, the ethylene content in the EVA is preferably 15-45 mol%, more preferably 20-40 mol%, and more preferably 25-35 mol%.
The invention integrates and refines the whole technical scheme, better ensures the structure and the performance of a final product, provides a regulating method and a synthesizing method for synthesizing EVA by the controllable release of free radicals, and specifically comprises the following steps:
the invention takes ethylene and vinyl acetate as raw materials, prepares EVA in a free radical solution polymerization system, regulates and controls the structure of the EVA through the controllable release of free radicals based on the relationship between the dynamic characteristics of polymerization reaction and the concentration, the generation rate and the initiation efficiency of the free radicals and the self-acceleration phenomenon, and uses the EVA in preparing the EVOH.
Wherein the ethylene content in the EVA is 15-45 mol%.
The structure is controllable, particularly the polymerization rate, the polymer molecular weight and the branching degree are controllable, and particularly the EVOH with bimodal distribution can be prepared. The raw materials of the invention are industrial grade raw materials.
The radical solution polymerization is preferably performed by using one or two of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, azobis (2-methylbutyronitrile), hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, amyl neodecanoate peroxide, amyl pivalate peroxide, butyl acetate peroxide, dibutyl dicarbonate and the like as an initiator, preferably by using one or two of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, amyl neodecanoate peroxide, amyl peroxy pivalate, butyl acetate peroxide, more preferably azobisisobutyronitrile, methyl ethyl ketone peroxide, butyl peroxypivalate, methyl ethyl ketone peroxide, butyl peroxydicarbonate, methyl ethyl pivalate, methyl peroxypivalate, methyl tert-butyl peroxide, butyl peroxydicarbonate, methyl isobutyryl peroxide, methyl peroxyisobutyryl peroxide, methyl peroxypivalate, methyl isobutyryl peroxide, methyl peroxyisobutyryl peroxide, methyl isobutyryl peroxide, methyl peroxypivalate, methyl isobutyryl peroxide, methyl peroxyisobutyryl peroxide, methyl isobutyryl peroxide, methyl peroxyisobutyryl peroxide, methyl isobutyryl peroxide, methyl tert-methyl peroxyisobutyryl peroxide, methyl tert-butyl peroxide, methyl peroxyisobutyryl peroxide, methyl tert-butyl peroxide, methyl peroxyisobutyryl peroxide, methyl ether, methyl peroxyisobutyryl peroxide, methyl isobutyryl peroxide, methyl ether, methyl acetate, methyl ether, and methyl ether, Azodiisoheptanonitrile, hydrogen peroxide, ammonium persulfate, benzoyl peroxide tert-butyl ester, methyl ethyl ketone peroxide, amyl peroxyneodecanoate, amyl peroxypivalate or butyl acetate peroxide.
One or more of n-hexane, petroleum ether, tetrahydrofuran, methanol, ethanol, propanol, etc. is used as solvent, preferably one or more of n-hexane, petroleum ether, tetrahydrofuran, methanol, ethanol, more preferably one or more of n-hexane, tetrahydrofuran, methanol, ethanol.
The solution polymerization was initiated in a 500ml stainless steel autoclave with tetrafluoro liner to obtain EVA. Before reaction, checking the sealing performance of the reaction kettle, heating to 100 ℃, treating for 30min, replacing for 3-5 times by adopting nitrogen, and finally replacing for 3-5 times by using ethylene gas. Cooling to below 40 deg.C, and adding the raw materials.
The invention is initiated by free radicals, EVA is obtained by solution polymerization, and the EVA is realized by regulating and controlling a feeding mode, a solvent effect and pulse heating, and specifically comprises the following steps:
(1) adding the raw materials into a reaction kettle in batches according to different sequences according to different initiation speeds of an initiator on ethylene and vinyl acetate, wherein the initiation speeds are as follows: firstly adding a certain amount of vinyl acetate, introducing ethylene under a certain pressure, heating and then (continuously) adding a certain amount of vinyl acetate; or firstly adding vinyl acetate, then introducing ethylene under a certain pressure, reacting for a certain time, and then introducing a certain amount of ethylene.
(2) According to the automatic acceleration effect of the free radical polymerization reaction, the initiator is added into the reaction system in batches and in a small amount.
(3) According to different solvents, the chain transfer constant is different, and the solubility and distribution coefficient of ethylene and vinyl acetate in different solvents are different, a solvent or mixed solvent system is adopted to regulate and control the polymer structure and molecular weight.
(4) According to the dependence of free radicals generated by an initiator on temperature, pulse type heating is adopted, specifically, the temperature is raised to a certain temperature, the temperature is reduced after the temperature is raised for a certain time, the temperature is raised after the temperature is maintained for a certain time, and the temperature and the time are controlled repeatedly in sequence.
Controlling the volume ratio of the total amount of vinyl acetate to the solvent in the reaction system to be 1-30/1, preferably 3-28/1, and more preferably 5-25/1; the total amount of the added liquid in the reaction kettle is 80-150 ml, preferably 90-140 ml, and more preferably 95-135 ml; the total concentration of the added initiator is controlled to be 2.2-9.8 multiplied by 10-3mol/L, preferably 2.5 to 9.5X 10-3mol/L, more preferably 2.8 to 9.0X 10-3mol/L; the polymerization reaction temperature is 45-125 ℃, preferably 50-120 ℃, and more preferably 55-115 ℃; the reaction time is 2-8 h, preferably 2.5-7.5 h, and more preferably 2.5-7.5 h; the reaction pressure is 0.5 to 15MPa, preferably 1 to 13.5MPa, and more preferably 2 to 12.5 MPa. The pressure was kept constant during the reaction. And after the reaction is finished, drying the obtained EVA in a vacuum oven at 65 ℃ for later use.
The invention also provides a synthesis method of the EVOH, which comprises the following steps:
1) heating and mixing EVA and methanol, adding a catalyst for reaction, adding methanol at the same time, keeping the concentration of the EVA in a reaction system constant, then adjusting the pH value, and separating out to obtain the EVOH.
In the invention, the raw materials for synthesis are industrial-grade raw materials.
In the present invention, the EVA preferably includes EVA synthesized by the synthesis method according to any one of the above technical schemes.
In the invention, the ethylene content in the EVA is preferably 15-45 mol%, more preferably 20-40 mol%, and more preferably 25-35 mol%.
In the present invention, the molar concentration of EVA in the solution after heating and mixing EVA and methanol is preferably 5% to 35%, more preferably 10% to 30%, and still more preferably 15% to 20%.
In the invention, the heating and mixing temperature is preferably 50-120 ℃, more preferably 60-110 ℃, more preferably 70-100 ℃, and more preferably 80-90 ℃.
In the present invention, the mass ratio of the catalyst to the EVOH is preferably (25 to 40): 1, more preferably (28 to 38): 1, more preferably (30 to 35): 1.
in the present invention, the catalyst is preferably added in a plurality of times. Specifically, the number of times of the multiple times is preferably 2 to 4 times, and more preferably 3 to 4 times.
In the present invention, the catalyst preferably includes one or more of a sodium hydroxide solution, a potassium hydroxide solution, a sodium carbonate solution, and a potassium carbonate solution, and more preferably a sodium hydroxide solution, a potassium hydroxide solution, a sodium carbonate solution, or a potassium carbonate solution.
In the invention, the concentration of the catalyst is preferably 20-100 g/L, more preferably 30-90 g/L, more preferably 40-80 g/L, and more preferably 50-70 g/L.
In the invention, the reaction time is preferably 3-10 h, more preferably 4-9 h, more preferably 5-8 h, and more preferably 6-7 h.
In the present invention, the pH adjusting agent preferably includes one or more of boric acid, oxalic acid, acetic acid, and citric acid, and more preferably boric acid, oxalic acid, acetic acid, or citric acid.
In the invention, the pH value is preferably 5-8, more preferably 5.5-7.5, and more preferably 6-7.
In the invention, the concentration of the regulator is preferably 0.5-1.5 mol/L, more preferably 0.7-1.3 mol/L, and more preferably 0.9-1.1 mol/L.
In the present invention, the precipitation is preferably performed in hot water.
In the invention, the precipitation temperature is preferably 55-95 ℃, more preferably 60-90 ℃, more preferably 65-85 ℃, and more preferably 70-80 ℃.
In the present invention, the precipitation time is preferably 20 to 80min, more preferably 30 to 70min, and still more preferably 40 to 60 min.
The invention integrates and refines the whole technical scheme, better ensures the structure and the performance of a final product, provides the application of the EVA with controllable release of free radicals in the synthesis of EVOH, and specifically comprises the following steps:
dissolving EVA in methanol, controlling the EVA concentration to be 5-35%, setting the heating temperature to be 50-120 ℃, after the reaction temperature is stable, slowly adding 20-60 ml of catalyst into a reaction system in 2-4 equal parts, and meanwhile, continuously adding methanol by using a constant-pressure dropping funnel to keep the EVA concentration of the system unchanged; the catalyst is a solution of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and the like, and the concentration of the catalyst is 20-100 g/L. After reacting for 3-10 h, adjusting the pH of the system to 5-8 by using solutions of boric acid, oxalic acid, acetic acid, citric acid (the concentration is 0.5-1.5 mol/L) and the like, transferring the product to 1000ml of deionized water for precipitation, filtering, treating with hot water at 50-100 ℃ for 10-90 min, and drying at 120 ℃.
Specifically, EVA is dissolved in methanol, and the concentration of the EVA is controlled to be 5-35%, preferably 10-30%, and more preferably 12-28%; setting the heating temperature to be 50-120 ℃, preferably 55-115 ℃, and more preferably 60-110 ℃; after the reaction temperature is stable, slowly adding 20-60 ml (preferably 25-55 ml, more preferably 30-50 ml) of catalyst into the reaction system in 2-4 equal parts, and meanwhile, continuously adding methanol by using a constant-pressure dropping funnel to keep the concentration of EVA (ethylene vinyl acetate) in the system unchanged; the catalyst is a solution of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and the like, preferably a solution of sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate, more preferably a solution of sodium hydroxide, potassium hydroxide and sodium carbonate, and has a concentration of 20-100 g/L, preferably 25-95 g/L, more preferably 30-90 g/L. Reacting for 3-10 h, preferably 3.5-9.5 h, more preferably 3.5-9.5 h; adjusting the pH of a system to be 5-8, preferably 5.5-7.5, more preferably 6-7, by using solutions of boric acid, oxalic acid, acetic acid, citric acid (the concentration is 0.5-1.5 mol/L, the concentration is preferably 0.8-1.3 mol/L, and the concentration is more preferably 1.0-1.2 mol/L) and the like; the solution is preferably boric acid, oxalic acid, acetic acid or citric acid solution, and the solution is more preferably boric acid, oxalic acid or acetic acid solution; and transferring the product into 1000ml of deionized water for precipitation, filtering, treating with hot water at 50-100 ℃ for 10-90 min, preferably 55-95 ℃, more preferably 60-90 ℃, preferably 20-80 min, more preferably 25-75 min, and finally drying the obtained product at 120 ℃.
The steps of the invention provide a regulation and control method for synthesizing EVA (ethylene vinyl acetate copolymer) with controllable release of free radicals, a synthesis method, EVOH (ethylene vinyl alcohol copolymer) resin and a synthesis method thereof. The invention realizes the regulation and control of EVA structure, molecular weight and the like by regulating and controlling a feeding mode, a solvent effect, pulse heating and a composite initiator based on the controllable release of initiator free radicals according to the relationship between the dynamic characteristics of polymerization reaction and the concentration, generation rate and initiation efficiency of the free radicals and the self-acceleration phenomenon. In particular, the prepared EVA is used for synthesizing EVOH (ethylene-vinyl alcohol copolymer) resin, and Gel Permeation Chromatography (GPC) tests show that the EVOH resin with bimodal distribution can be obtained by the regulation and control method provided by the invention. The method has the characteristics of strong controllability, mild conditions, simple operation and large-scale synthesis prospect. The invention realizes the controllable polymerization of ethylene and vinyl acetate, regulates and controls the polymer structure, the hydroxyl distribution and the like, is favorable for improving the high molecular weight of the polymer and improving the crystallization behavior (including crystal region distribution) of the polymer, and has important significance for further improving the barrier property and the processing property of EVOH and improving the batch stability of products.
Experimental results show that the EVA with controllable release of free radicals prepared by the invention can obtain high molecular weight, especially EVOH resin with bimodal distribution through alcoholysis reaction.
In order to further illustrate the present invention, the following will describe in detail a regulation and control method and a synthesis method for synthesizing EVA, an EVOH resin and a synthesis method thereof provided by the present invention with reference to examples, but it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and that detailed embodiments and specific procedures are given, only for further illustrating the features and advantages of the present invention, but not for limiting the claims of the present invention, and the scope of protection of the present invention is not limited to the following examples.
Example 1
Checking the air tightness of a 500ml stainless steel high-pressure reaction kettle with a tetrafluoro lining, heating to 100 ℃, treating for 30min, replacing 3 times by adopting nitrogen, and then replacing 3 times by using ethylene gas. Cooling the reaction kettle to below 40 ℃, adding 35ml of ethyl acetate, mixing an initiator azobisisobutyronitrile with 10ml of ethanol, adding the mixture into the reaction kettle, stirring while filling 4.0MPa of ethylene, heating to 75 ℃, continuously filling the ethylene to keep the pressure of the reaction system stable, after reacting for 1h, closing the ethylene, mixing 40ml of vinyl acetate, 20ml of tetrahydrofuran and methyl ethyl ketone peroxide, adding the mixture into the reaction kettle through a high-pressure pump, and continuing to react for 3h (controlling the concentrations of the azobisisobutyronitrile and the methyl ethyl ketone peroxide in the reaction system to be respectively 2.8 multiplied by 10 in the feeding process)-3mol/L and 4.0X 10-3mol/L). After the reaction is finished, the reaction product is cooled to room temperature, the pressure is released, the product is transferred to a vacuum oven and dried at 65 ℃ to obtain EVA, the ethylene content is 32% (NMR, mol), and the nuclear magnetic hydrogen spectrum is shown in figure 7.
Referring to fig. 7, fig. 7 is a nuclear magnetic hydrogen spectrum of EVA prepared in example 1 of the present invention.
Dissolving EVA in 200ml methanol (EVA concentration is 25 wt%), heating to 85 deg.C, dividing 20ml NaOH solution (concentration is 65g/L) into 4 equal parts, slowly adding into the reaction system every 30min, simultaneously, continuously adding methanol with constant pressure dropping funnel, keeping the EVA concentration of the system unchanged; after reacting for 6 hours, adjusting the pH value of the system to 6 by adopting 1.0mol/L oxalic acid solution; and transferring the product into 1000ml of deionized water for precipitation, filtering, treating with hot water at 80 ℃ for 70min, and drying the obtained product at 120 ℃ to obtain the EVOH resin. The molecular weight Mn was 13.2kg/mol and the distribution PDI was 1.17, as shown in FIGS. 8 and 9.
Referring to FIG. 8, FIG. 8 is a nuclear magnetic hydrogen spectrum of EVOH prepared in example 1 of the present invention.
Referring to FIG. 9, FIG. 9 is a GPC chart of EVOH resin produced in example 1 of the present invention.
Example 2
Checking the air tightness of a 500ml stainless steel high-pressure reaction kettle with a tetrafluoro lining, heating to 100 ℃, treating for 30min, replacing 5 times by nitrogen, and replacing 5 times by ethylene gas. Cooling the reaction kettle to below 40 ℃, adding 80ml of ethyl acetate, mixing an initiator azobisisobutyronitrile with 10ml of ethanol, adding the mixture into the reaction kettle, stirring while filling 3.5MPa of ethylene, heating to 75 ℃, continuously filling ethylene to keep the pressure of the reaction system stable, after reacting for 2 hours, closing the ethylene, mixing hydrogen peroxide with 20ml of n-hexane, adding the mixture into the reaction kettle through a high pressure pump, then continuously keeping the pressure of the reaction system through the ethylene, and continuously reacting for 3 hours (controlling the concentrations of the azobisisobutyronitrile and the hydrogen peroxide in the reaction system to be 3.6 multiplied by 10 respectively in the feeding process-3mol/L and 3.6X 10-3mol/L). After the reaction is finished, cooling to room temperature, releasing pressure, transferring the product to a vacuum oven, and drying at 65 ℃ to obtain EVA with the ethylene content of 28% (NMR, mol).
Dissolving EVA in 200ml methanol (EVA concentration is 20 wt%), heating to 75 deg.C, and after reaction temperature is stable, adding 40ml K2CO3Dividing the solution (with the concentration of 25g/L) into 4 equal parts, slowly adding the solution into the reaction system in turn every 30min, and simultaneously continuously adding methanol by using a constant-pressure dropping funnel to keep the EVA concentration of the system unchanged; after reacting for 4 hours, adjusting the pH value of the system to 7 by adopting 1.0mol/L acetic acid solution; and transferring the product into 1000ml of deionized water for precipitation, filtering, treating with hot water at 60 ℃ for 30min, and drying the obtained product at 120 ℃ to obtain the EVOH resin with bimodal distribution, as shown in figure 10.
Referring to FIG. 10, FIG. 10 is a GPC chart of a bimodal distribution EVOH resin prepared in example 2 of the present invention.
Example 3
Checking the air tightness of 500ml stainless steel high-pressure reaction kettle with tetrafluoro lining, heating to 100 ℃ for 30min, placing with nitrogenAfter 4 times of replacement, the reaction solution was replaced with ethylene gas 4 times. Cooling the reaction kettle to below 40 deg.C, mixing 10ml n-hexane, 10ml ethanol, initiator azobisisoheptonitrile and benzoyl peroxide, and adding into the reaction kettle (controlling the concentration of azobisisoheptonitrile and benzoyl peroxide in the reaction system to be 5.5 × 10 respectively-3mol/L and 2.5X 10-3mol/L), charging 3.0MPa ethylene, heating to 80 ℃ and keeping the pressure stable, after 30min, closing the ethylene, adding 115ml of ethyl acetate into the reaction kettle by a high-pressure pump, then introducing the ethylene to keep the pressure stable, stirring for reaction for 4h, cooling to room temperature, releasing the pressure, transferring the product to a vacuum oven, and drying at 65 ℃ to obtain EVA with the ethylene content of 17% (NMR, mol).
Dissolving EVA in 200ml methanol (EVA concentration is 20 wt%), heating to 90 deg.C, and adding 30ml Na after reaction temperature is stable2CO3Dividing the solution (with the concentration of 50g/L) into 3 equal parts, slowly adding the solution into the reaction system in turn every 30min, and simultaneously continuously adding methanol by using a constant-pressure dropping funnel to keep the EVA concentration of the system unchanged; after reacting for 6 hours, adjusting the pH value of the system to 6 by adopting 1.0mol/L oxalic acid solution; and transferring the product into 1000ml of deionized water for precipitation, filtering, treating with hot water at 90 ℃ for 60min, and drying the obtained product at 120 ℃ to obtain the EVOH resin with bimodal distribution, as shown in figure 11.
Referring to FIG. 11, FIG. 11 is a GPC chart of a bimodal distribution EVOH resin prepared in example 3 of the present invention.
Example 4
Checking the air tightness of a 500ml stainless steel high-pressure reaction kettle with a tetrafluoro lining, heating to 100 ℃, treating for 30min, replacing 5 times by nitrogen, and replacing 5 times by ethylene gas. Cooling the reaction kettle to below 40 ℃, adding 90ml of ethyl acetate, mixing an initiator azobisisobutyronitrile with 15ml of methanol and 10ml of tetrahydrofuran, adding the mixture into the reaction kettle, charging 3.2MPa of ethylene while stirring, heating to 70 ℃, reacting for 0.5h, cooling to 50 ℃, keeping for 0.5h, heating to 70 ℃, keeping for 1.5h, mixing the initiator azobisisobutyronitrile with 10ml of methanol (the concentration of the added azobisisobutyronitrile is 4.0 multiplied by 10 respectively in two times)-3mol/L and 1.5X 10-3mol/L) is added into the reaction kettle through a high-pressure pump, and then is reducedHeating to 50 ℃, keeping the temperature for 0.5h, then heating to 70 ℃, introducing ethylene to keep the pressure of the reaction system constant, and continuing to react for 2 h. After the reaction is finished, cooling to room temperature, releasing pressure, transferring the product to a vacuum oven, and drying at 65 ℃ to obtain EVA with the ethylene content of 22% (NMR, mol).
Dissolving EVA in 200ml methanol (EVA concentration is 15 wt%), heating to 75 deg.C, dividing 40ml KOH solution (concentration is 40g/L) into 4 equal parts after reaction temperature is stable, slowly adding into reaction system every 30min, simultaneously, continuously adding methanol with constant pressure dropping funnel, keeping EVA concentration of system unchanged; after reacting for 6 hours, adjusting the pH value of the system to 7 by adopting 1.1mol/L acetic acid solution; and transferring the product into 1000ml of deionized water for precipitation, filtering, treating with hot water at 90 ℃ for 30min, and drying the obtained product at 120 ℃ to obtain the EVOH resin. The molecular weight Mn was 12.09kg/mol and the distribution PDI was 6.76.
Example 5
Checking the air tightness of a 500ml stainless steel high-pressure reaction kettle with a tetrafluoro lining, heating to 100 ℃, treating for 30min, replacing 3 times by adopting nitrogen, and then replacing 3 times by using ethylene gas. Cooling the reaction kettle to below 40 ℃, adding 50ml of ethyl acetate, mixing initiator hydrogen peroxide and 10ml of ethanol, adding the mixture into the reaction kettle, filling 2.0MPa of ethylene while stirring, heating to 75 ℃, reacting for 0.5h, cooling to 50 ℃ and keeping for 0.5h, then mixing 40ml of vinyl acetate, 10ml of ethanol and hydrogen peroxide, and adding the mixture into the reaction kettle through a high-pressure pump (the concentration of hydrogen peroxide added twice is respectively 3.5 multiplied by 10)-3mol/L and 3.5X 10-3mol/L), introducing ethylene to adjust the reaction pressure to 4.0MPa, then heating to 75 ℃ and keeping the pressure stable, and continuing the reaction for 3 hours. After the reaction is finished, cooling to room temperature, releasing pressure, transferring the product to a vacuum oven, and drying at 65 ℃ to obtain EVA with the ethylene content of 35% (NMR, mol).
Dissolving EVA in 200ml methanol (EVA concentration is 25 wt%), heating to 80 deg.C, dividing 40ml NaOH solution (concentration is 25g/L) into 4 equal parts, slowly adding into the reaction system every 30min, simultaneously, continuously adding methanol with constant pressure dropping funnel, keeping the EVA concentration of the system unchanged; after reacting for 4 hours, adjusting the pH value of the system to 6 by adopting 1.2mol/L boric acid solution; and transferring the product into 1000ml of deionized water for precipitation, filtering, treating with hot water at 80 ℃ for 40min, and drying the obtained product at 120 ℃ to obtain the EVOH resin. The molecular weight Mn was 10.72kg/mol and the distribution PDI was 6.53.
Example 6
Checking the air tightness of a 500ml stainless steel high-pressure reaction kettle with a tetrafluoro lining, heating to 100 ℃, treating for 30min, replacing 5 times by nitrogen, and replacing 5 times by ethylene gas. When the reaction kettle is cooled to below 40 ℃, 50ml of ethyl acetate is added, then the initiator azobisisobutyronitrile, hydrogen peroxide and 10ml of methanol are mixed and added into the reaction kettle (the concentrations of the azobisisobutyronitrile and the hydrogen peroxide are controlled to be 1.5 multiplied by 10 respectively)-3mol/L and 3.0X 10-3mol/L), charging 2.0MPa ethylene while stirring, heating to 80 ℃, continuously charging ethylene to keep the pressure of the reaction system stable, after 2 hours of reaction, closing ethylene, and mixing 40ml vinyl acetate, 10ml ethanol, hydrogen peroxide and azobisisobutyronitrile (controlling the concentrations of azobisisobutyronitrile and hydrogen peroxide to be 1.5 multiplied by 10 respectively)-3mol/L and 3.0X 10-3mol/L) is added into the reaction kettle through a high-pressure pump, then ethylene is introduced to adjust the reaction pressure to 3.0MPa and keep stable, and the reaction is continued for 2 hours. After the reaction is finished, cooling to room temperature, releasing pressure, transferring the product to a vacuum oven, and drying at 65 ℃ to obtain EVA with the ethylene content of 23% (NMR, mol).
Dissolving EVA in 200ml methanol (EVA concentration is 15 wt%), heating to 70 deg.C, dividing 20ml NaOH solution (concentration is 35g/L) into 4 equal parts, slowly adding into the reaction system every 30min, simultaneously, continuously adding methanol with constant pressure dropping funnel, keeping the EVA concentration of the system unchanged; after reacting for 8 hours, adjusting the pH value of the system to 6 by adopting 1.0mol/L boric acid solution; and transferring the product into 1000ml of deionized water for precipitation, filtering, treating with hot water at 85 ℃ for 60min, and drying the obtained product at 120 ℃ to obtain the EVOH resin. The molecular weight Mn was 14.51kg/mol and the distribution PDI was 5.90.
The EVOH resin prepared in inventive example 6 was characterized and calculated.
Referring to FIG. 12, FIG. 12 is a graph showing the degree of branching of an EVOH resin prepared according to 6 of the present inventionAnd a calculation method (13C NMR)。
Referring to FIG. 13, FIG. 13 is an external view of an EVOH resin and film produced by the present invention.
The present invention provides a method for controlling and synthesizing EVA with controlled release of free radicals, an EVOH resin and a method for synthesizing the same, which are described in detail above, and the specific examples are used herein to explain the principles and embodiments of the present invention, and the above description is only used to help understand the method and the core ideas of the present invention, including the best mode, and also to enable any person skilled in the art to practice the present invention, including making and using any device or system, and performing any combination of methods. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention. The scope of the invention is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
