CN106519156B - A kind of environment-friendly preparation method thereof of cationic polychloroethylene film material - Google Patents

Abstract

The invention relates to a green preparation method of a vinyl chloride/dimethyldiallyl ammonium chloride copolymer as a separation membrane material, which is a copolymer formed based on free radical polymerization at a water/oil two-phase interface Synthesis technology, specially using a cationic surface active initiator to undergo redox reaction with potassium persulfate at room temperature, repeatedly generating free radicals at the interface and triggering independent polymerization of vinyl chloride and dimethyl diallyl ammonium chloride Reaction, the two chain segments are connected in series through the initiator molecule to form a multi-block copolymer. Experiments have proved that when the pH value of the aqueous medium is in the range of 4.5 to 5, the ratio of the monomer feed to the composition ratio of the copolymer Very consistent, the content of the dimethyl diallyl ammonium chloride segment in the copolymer is adjustable in the range of 5 to 16wt.%. The polymerization reaction conditions of this mode are mild and controllable, and the energy consumption is low. No other organic solvents and Emulsifier, the product is pure and fully meets the requirements of green chemistry.

Description

A kind of green preparation method of cationic polyvinyl chloride membrane material

technical field

The invention relates to the technical field of polymer material synthesis, in particular to a green preparation method of a cationic polyvinyl chloride membrane material. The copolymer is an amphiphilic polymer that can be used in the preparation of separation membrane materials. Its preparation method conforms to requirements of green chemistry.

Background technique

With the rapid development of membrane separation high-tech, its technology has been widely used in biological, medical and environmental engineering. In order to meet various separation requirements, the research work on the modification of membrane materials is very active at home and abroad, but mainly focuses on For some functional polymers with low output and high price, such as polysulfone, polyvinylidene fluoride, polyacrylonitrile, polysulfone amide, etc., and polyvinyl chloride is the second largest synthetic resin after polyethylene. It has the characteristics of low price, microbial erosion resistance, acid and alkali resistance, and good chemical stability. It is a membrane material worthy of promotion. Commercialized microfiltration membranes have appeared in foreign countries, and there are many reports on the research of ultrafiltration membranes. At present, considerable progress has been made in this area in China, and commercialized polyvinyl chloride ultrafiltration membranes have been developed. Polyvinyl chloride (PVC) is a hydrophobic polymer. Its hydrophilicity and toughness cannot meet the requirements of film materials. The gel film is prone to spontaneous shrinkage and wrinkling, and the film-forming performance is not ideal. Therefore, research on the modification of PVC has always been a direction of effort. Vinyl chloride is a monomer with low polymerization activity, and it is rarely copolymerized with other olefin monomers, which greatly limits the space for chemical modification through copolymerization. The water/oil two-phase interfacial polymerization technology can fundamentally solve this technical problem, making the synthesis of various vinyl chloride copolymer materials convenient and meeting the requirements of green chemistry.

The key to realizing interfacial polymerization is to use the cationic surfactant initiator as shown in Figure 1, which is at the interface of the water phase and the oil phase, and it can connect the polymerization reactions of the two phases of water/oil in series. An amphiphilic organic tertiary amine molecule can form a redox initiation system with water-soluble K ₂ S ₂ O ₈ , through repeated intramolecular charge transfer, free radicals are formed on the carbon atoms adjacent to the nitrogen atom, and the interface is free The base can not only initiate the polymerization reaction of the oil phase, but also the polymerization reaction of the water phase. As long as different monomers are added in a certain order, the polymerization can be initiated independently without interfering with each other, because the active species of the polymerization reaction all come from the same Initiator molecules, so the formed polymer chains are connected together, the basic principle is shown in Figure 2, it must be noted that, in order to ensure the smooth implementation of the copolymerization reaction, the combination of comonomers must be consistent with the structure of the initiator and match the pH of the aqueous medium. Polydimethyldiallylammonium chloride is a water-soluble polymer with a positive charge. Through the above polymerization method, the hydrophobic polyvinyl chloride chain and the hydrophilic polydimethyldiallyl Ammonium chloride is connected together to form a positively charged amphiphilic polymer, which completely overcomes the disadvantage of insufficient hydrophilicity of polyvinyl chloride, and is very suitable for use as a membrane material.

What the present invention relates to is a case of this novel polymerization method, and the initiator used is a kind of cationic surfactant initiator of special structure, and it can produce free radical at normal temperature under the action of K ₂ S ₂ O ₈ , In the absence of other surfactants, the polymerization of hydrophobic vinyl chloride and hydrophilic dimethyl diallyl ammonium chloride is respectively initiated to obtain a multi-block copolymer that is difficult to synthesize by other polymerization means, which is a kind of A new vinyl chloride copolymer material, and the preparation method of this material fully meets the standards of green chemistry: normal temperature reaction, low energy consumption, no use of organic solvents, and no other surfactants.

Contents of the invention

The primary technical problem to be solved by the present invention is to provide a free radical polymerization technology at the water/oil two-phase interface. The monomers are polymerized independently, and various chain segments are connected in series through initiator molecules to form new copolymers.

Another technical problem to be solved by the present invention is to provide the necessary cationic surfactant initiator for the above-mentioned interfacial free radical polymerization, which has the function of surfactant, and can form a redox initiation system with potassium persulfate, initiate Polymerization of various olefin monomers.

Another technical problem to be solved by the present invention is to provide a specific method for preparing vinyl chloride/dimethyldiallylammonium chloride multi-block copolymers by using the above-mentioned interfacial free radical polymerization method and specific surface active initiator .

1. The technical solution adopted by the present invention to solve the primary technical problem is: a kind of water/oil two-phase interface free radical polymerization technology, its basic principle is as shown in Figure 2, it is different from the general polymerization in water phase or oil phase Polymerization reaction, which is a free radical initiation method located at the interface of two phases, can make the polymerization reaction of the water phase or oil phase complete independently, and is connected in series with an initiator.

It is very beneficial that the polymerization of different monomers can be completed independently according to the homopolymerization method without interfering with each other, and the final result is a multi-block copolymer;

It is very beneficial that the composition of the copolymer can be simply controlled by the feed ratio of the monomers, avoiding the impact on the composition of the copolymer due to the difference in the activity of the monomers;

It is very beneficial that this technology can form a variety of monomers with different properties into copolymers, which provides a wide range of feasibility for the synthesis of copolymers for various purposes.

2. The technical solution adopted by the present invention to solve another technical problem is: a cationic surface-active initiator, the molecular structure of which is shown in Figure 1.

It is very beneficial that this initiator can be positioned at the interface of water/oil two phases, and has the ability to emulsify oily monomers, so it is no longer necessary to add other emulsifiers. Once the polymerization is initiated, it becomes the base of the polymer material. One part, there will be no emulsifier leakage problem, and no adverse effect on the performance of polymer materials;

It is very beneficial that the tertiary amine in the initiator can react with potassium persulfate at room temperature to generate interfacial free radicals, initiate the polymerization of water-based and oily monomers in two directions, and synthesize multi-block copolymers through multi-phase connection;

It is very beneficial that this initiator can generate free radicals on the α-carbon multiple times by continuously oxidizing nitrogen atoms, showing the characteristics of its chain initiation, and can flexibly control the polymerization reaction, so that various monomers can be polymerized in a certain order , which is very beneficial to the molecular design of polyolefin polymer materials.

3, the technical scheme that the present invention adopts to solve another technical problem is: utilize above-mentioned cationic surfactant initiator to prepare the specific method of vinyl chloride/dimethyldiallyl ammonium chloride multi-block copolymer, its characteristic step is : 1) Dissolve the cationic surface active initiator in water, the concentration is generally in the range of 2.5-3.0‰, the dosage of the initiator is generally 2.5-3.0% of the weight of vinyl chloride, adjust the pH value of the aqueous solution to weak acidity, and ensure the cationic surface activity The emulsifying ability of the initiator, and then put the aqueous solution in a closed high-pressure reactor, and then pass nitrogen into the reactor to exclude the internal air; 2) inject the oil-soluble monomer vinyl chloride into the reactor, fully After stirring, add a saturated solution of potassium persulfate (the amount of potassium persulfate is generally 1.0-1.5% of the weight of the input monomer), and after about 5-10 minutes, the polymerization reaction occurs, and the polymer dispersion is formed quickly, the system temperature and The pressure rises and gradually falls after cooling. The polymerization reaction of the first stage generally lasts for 0.5 to 1 hour; 3) Add the 50% aqueous solution of the second monomer dimethyl diallyl ammonium chloride, The weight ratio of allyl ammonium chloride to vinyl chloride is in the range of 0.05 to 0.2, and the formed polyvinyl chloride particles are basically unchanged. After adding the second batch of potassium persulfate, the polymerization reaction starts again, and the dispersion of the particles is due to the hydrophilic It becomes better by strengthening, and the reaction lasts for 1 to 2 hours, and finally a well-dispersed amphiphilic copolymer is obtained, and the composition of the product can be controlled by the feed ratio of the monomers.

It is very beneficial that since free radicals are only generated at the interface, the concentration of oily monomers is high, so the polymerization reaction is fast and the conversion rate is high. During the polymerization process, the monomers can be added in sequence, and it is very easy to control the composition and structure of the polymer;

It is very beneficial that the polymerization reaction of vinyl chloride is carried out at normal temperature without high pressure, thus improving the safety factor of operation;

It is very beneficial that no other organic solvents are added in the whole polymerization process, no harsh conditions are required, and the requirements of green chemistry are fully met.

The advantages of the present invention are: 1) the independent homopolymerization of multiple monomers can be realized by utilizing the new interfacial free radical polymerization technology and connected in series, and the composition and structure of the polymer can be easily controlled; 2) the reactivity rate, monomer The restriction of physical property differences on traditional copolymerization methods is conducive to the preparation of more types of olefin copolymers, which greatly broadens the development space of polymer materials; 3) The polymerization reaction conditions are mild and controllable, low energy consumption, no other organic solvents and emulsifiers, and the product Pure and in full compliance with the requirements of green chemistry.

Detailed ways

Below in conjunction with embodiment the present invention is described in further detail.

The preparation of vinyl chloride/dimethyl diallyl ammonium chloride copolymer is carried out in the following steps:

a. Dissolve 1.5g cationic surfactant initiator in 500mL water, the concentration is generally in the range of 2.5-3.0‰, the amount of initiator is generally 2.5-3.0% of the weight of vinyl chloride, by adding different amounts of acetic acid and sodium phosphate mixture Adjust the pH value of the aqueous solution (pH=9 to 10; pH=7 to 8; pH=4.5 to 5.0), place the aqueous solution in a closed high-pressure reactor, and pass nitrogen into the reactor to remove the internal air;

b. Inject 55g of oil-soluble monomer vinyl chloride (boiling point is -13.4°C) into the reactor, stir well at room temperature and then add a saturated solution of potassium persulfate (the amount of potassium persulfate is generally 1.0-1.5% of the weight of the input monomer). %), after about 5 to 10 minutes, the polymerization reaction occurs, and a polymer dispersion liquid is formed quickly, the temperature and pressure of the system rise to some extent, and gradually fall back after cooling, and the polymerization reaction of the first stage generally lasts for 0.5 to 1 hour;

c. Add different amounts of the 50% aqueous solution of the second monomer dimethyl diallyl ammonium chloride, the weight ratio of dimethyl diallyl ammonium chloride to vinyl chloride is in the range of 0.05 to 0.2, and has formed The polyvinyl chloride particles remained basically unchanged. After adding the second batch of potassium persulfate, the polymerization reaction restarted, and the dispersibility of the particles became better. The reaction lasted for 1 to 2 hours, and finally a well-dispersed amphiphilic copolymer was obtained. Precipitate with methanol and then fully wash to obtain a powdery solid, which is dried for later use. The product is soluble in many organic solvents, which is convenient for further preparation of various separation membranes.

Product analysis: measure the actual effect of the initiator by comparing the consistency of the monomer feed ratio and the copolymer composition ratio after two polymerization reactions. After each polymerization, the reaction mixture per unit volume is precipitated with methanol to remove all possible Small molecule monomer, the obtained polymer is weighed after washing and drying to obtain the polymer output. The output M ₁ of polyvinyl chloride is obtained after the first polymerization, and the output M ₁ +M of the copolymer is obtained after the second polymerization ₂ , from which the mass composition ratio M ₂ /M ₁ of the two blocks in the copolymer can be calculated, and the feed ratio m ₂ /m ₁ is the mass ratio of the two monomers added in the experiment. The obtained experimental results are shown in Fig. 3 .

Control of product composition: Experimental data show that the relationship between the feed ratio and the composition ratio is related to the pH value of the polymerization medium. When the pH value is in the range of 4.5 to 5.0, the relationship between the feed ratio and the composition ratio is basically on the diagonal, indicating that Each polymerization reaction is relatively thorough, that is to say, the initiation efficiency of the initiator is relatively high. When the pH value is in the range of 7-8, the correlation curve between M ₂ /M ₁ and m ₂ /m ₁ deviates slightly below the diagonal line, and when the pH value is in the range of 9-10, the curve further deviates downward from the diagonal line, It shows that the emulsifying ability of the cationic initiator does not change much under alkaline conditions, but the reaction rate of the tertiary amine and potassium persulfate is accelerated, so that many free radicals fail to initiate the polymerization of dimethyl diallyl ammonium chloride in time , leading to a slight decrease in the initiation efficiency. However, when the pH value is less than 4, the protonation of the initiator causes the redox reaction to be hindered, and the initiation rate of the initiator is significantly reduced, which is not conducive to the progress of the polymerization reaction. Therefore, it is more appropriate to control the pH value of the medium in the range of 4.5-5.0.

Description of drawings

Fig. 1 Chemical structure of cationic surfactant initiator.

Fig. 2 Basic principle of free radical polymerization at water/oil two-phase interface.

Figure 3 Effect of medium pH on copolymer composition.

Claims (1)

1. a kind of preparation method of vinyl chloride/dimethyl diallyl ammonium chloride copolymer, it is characterised in that polymerisation uses Such as the cation surface activating initiator of lower structure：

The preparation method of the vinyl chloride/dimethyl diallyl ammonium chloride copolymer, operating procedure are followed successively by：

1) cation surface activating initiator is soluble in water, concentration is controlled in 2.5~3.0 ‰ ranges, cation surface activating The dosage of initiator is the 2.5~3.0% of vinyl chloride weight, adjusts the pH value of aqueous solution in 4~4.5 ranges, then will be water-soluble Liquid is placed in closed high-pressure reactor, then is passed through nitrogen to exclude internal air；

2) oil-soluble monomer vinyl chloride is injected into reactor, potassium peroxydisulfate saturated solution is added after being sufficiently stirred under room temperature, The dosage of potassium peroxydisulfate is to put into 1.0~1.5%, 5~polymerisation generation after ten minutes of monomer weight, and quickly form poly- Object solid dispersion is closed, polymerisation continues 0.5~1 hour；

3) second of monomer diallyldimethylammonChloride Chloride, the weight ratio of dimethyl diallyl ammonium chloride and vinyl chloride is added In 0.05~0.2 range, after second batch potassium peroxydisulfate is added, polymerisation can proceed with, and continue 1~2 hour, finally To well dispersed granular disintegration, after being washed and dried with methanol extraction, pulverulent solids product is obtained.