Physicochemical properties and preparation method of polydimethyldiallylammonium chloride (PDMDAAC) (1)

Polydimethyldiallylammonium chloride (PDMDAAC)

[Structural formula] The chemical structure of PDMDAAC has two kinds of one-five-membered ring structures and six-membered ring structures:

[Physical and chemical properties] Polydimethyldiallylammonium chloride (PDMDAAC or PDADMAC) is a white water-absorbent powder, soluble in water, methanol and glacial acetic acid , but insoluble in other solvents
.

PDMDAAC aqueous solution is stable in the range of pH=0.
5～14 at room temperature

[Preparation method] The preparation of polydimethyl diallyl ammonium chloride is mainly made by free radical polymerization reaction of dimethyl diallyl ammonium chloride.
The reaction formula is as follows:

The preparation methods of polydimethyldiallylammonium chloride include aqueous solution polymerization, non-aqueous solution polymerization, precipitation polymerization, emulsion polymerization and suspension polymerization.

Among them, the aqueous polymerization method has simple process and low cost, and the product can be directly applied.

(1) Aqueous polymerization

The preparation of polydimethyldiallylammonium chloride by aqueous solution polymerization can adopt chemical initiation, UV light initiation, γ-ray initiation, fluorescence initiation and other initiation methods
.

The initiators used in chemical initiation polymerization include inorganic peroxygens, such as potassium persulfate , ammonium persulfate, etc.

①Synthesis of DMDAAC by two-liquid method

It is completed by a two-step reaction, and the reaction formula is:

The intermediate product can be separated, and the sodium chloride impurities can be completely removed , and finally a high-purity solid cationic monomer can be obtained
.

The use of organic solvent two-liquid phase reaction can effectively inhibit the volatilization and self-polymerization of allyl chloride, and can easily separate the intermediate products, avoiding the time-consuming, volatilization loss, high-temperature self-polymerization and residues caused by distillation separation.
Loss and other unfavorable factors, in view of the fact that organic solvents can be repeatedly used, this method will not cause environmental pollution, and the excess allyl chloride can be recycled and used to reach or close to the level of gasless and liquid discharge

a.
Monomer preparation step In a three-necked flask equipped with a stirrer and a thermometer, add 150 mL 33% dimethylamine aqueous solution (1.
0 mol) and 100 mL organic solvent, stir vigorously to become milky white, add 82 mL allyl group dropwise within 3 hours Chlorine (1.
0mol) and 84g 50% sodium hydroxide aqueous solution (1.
05mol), slowly increase the temperature and maintain the system to reflux for 3h
.

After cooling, the upper organic phase was separated.

b.
Polymerization step Dissolve 6g DMDAAC solids and 14g acrylamide in 62g distilled water, add a certain amount of initiator, and initiate polymerization with an ultraviolet lamp at room temperature until the system temperature rises to the highest point (about 1.
5h, 47°C) , Cool, get elastic gel polymer
.

②Prepare DMDAAC in one step

The dimethyl diallyl ammonium chloride monomer was prepared by a one-step method, that is, the dimethyl monoallyl tertiary amine is firstly generated by the reaction of allyl chloride and dimethyl amine under strong alkaline conditions.
The amine is separated and allyl chloride is added again, and quaternary ammonium salt crystals are crystallized in acetone medium
.

However, the monomer solution obtained by this method contains a large amount of by-products such as sodium chloride, enol, alkenal, tertiary amine salt and unreacted allyl chloride, etc.

The principle of the experiment is that allyl chloride and dimethylamine undergo a nucleophilic substitution reaction to first generate tertiary amines, and then further react to obtain quaternary ammonium salts
.

The reaction formula is as follows:

It is polymerized by the above-mentioned monomers under a fixed initiator
.

Using aqueous solution as a flocculant, the larger the relative molecular mass, the better, and the longer the molecular chain, the better

Because the market price of raw material allyl chloride is relatively high, the market price of the product PDMDAAC is relatively high, but its volume is much smaller than that of HPAM
.

③Synthesized under microwave radiation

Dimethyldiallylammonium chloride was synthesized by one-step method, two-step crystallization method and phase transfer catalysis method respectively, and the microwave radiation-phase transfer catalysis effect was the best
.

When the DMDAAC monomer is prepared by the microwave radiation one-step method, the method is to drop all dimethylamine, sodium hydroxide solution, 50% to 80% of the total amount of chloropropene, under the power of 75 to 1000W microwave radiation, within 15 to 40 minutes
.
Add the remaining chloropropene and react with 75～1000W microwave radiation for 1～2h
.
Vacuum distillation, temperature 50～120℃, vacuum degree (0.
5～0.
8)×10 ⁶ Pa, use time 20～40min, filter at 80℃ to obtain the product
.

Microwave radiation two-step method, the method is all dimethylamine, solid sodium hydroxide, 50% to 80% of the total amount of chloropropene, power 75 to 1000W, microwave radiation for 5 to 10 minutes, the conversion rate of tertiary amine is based on the indicator 100 Phenolphthalein shows
.
For oil-water separation, use 40% to 120% of the total amount of solid sodium hydroxide for drying and dehydration.
After dehydration, the sodium hydroxide will react in the first step
.
In the second step, the above-mentioned dried tertiary amine and the remaining allyl chloride are added to 50%-200% acetone, and the mixture is allowed to stand at room temperature for 12-72 hours to obtain colorless needle-like crystals, that is, the quaternary ammonium salt monomer
.
After separation, it is refined by vacuum distillation, the temperature is 50-120℃, the vacuum degree is (0.
5-0.
8)×10 ⁶ Pa, and it takes 5-10min
.

Microwave radiation phase transfer catalysis method, the method is all dimethylamine, solid sodium hydroxide, 50% ~ 80% of the total amount of chloropropylene, power 75 ~ 1000W, microwave radiation 5 ~ 10min, the conversion rate of tertiary amine as indicator Thymolphthalein shows
.
Oil and water separation
.
Use 40%-120% of the total amount to obtain solid sodium hydroxide for drying and dehydration.
After dehydration, the sodium hydroxide will react in the first step
.
In the second step, the remaining propylene chloride is added and 20%-100% water is added as the phase transfer catalyst and the temperature is raised and refluxed for 1 to 3 hours
.
Vacuum distillation, temperature 50～120℃, vacuum degree (0.
5～0.
8)×10 ⁶ Pa, 10～20min
.

The polymerization method of polydimethyldiallylammonium chloride (PDMDAAC) uses microwave radiation-phase transfer catalysis to increase the reaction speed, increase the yield, and reduce the cost
.

Microwave radiation one-step method, using ice water bath to control the temperature, the reaction speed is half of the conventional reaction
.
Among them, microwave has obvious effect on tertiary amination, while quaternization has a general effect
.
Microwave radiation and phase transfer catalysis are combined with a two-step method, and the tertiary amination reaction is completed in 5-10 minutes.
The speed is fast, and side reactions such as hydrolysis and elimination are reduced
.
The purpose of oil-water separation is to remove sodium chloride by dehydration, using 40% to 120% of the total amount of solid sodium hydroxide for drying and dehydration.
After dehydration, the sodium hydroxide is reused in the first step of the reaction, and the effect of thorough desalination is good at low cost
.
The second step is crystallized in acetone.
Microwave radiation is not practical because it takes more than 1 hour, so it is not used, but it can obviously accelerate the reaction rate before the conversion rate is 50%
.

④Method 4

Take the mixed solution of alkali metal carbonate and complexing agent molar ratio (1-20):1 as the purifying agent, and wash the chloropropene one or more times with 0.
1%-0.
2% of the purifying agent aqueous solution; in the chloropropene solution Add dimethylamine solution and alkali metal hydroxide solution dropwise, the molar ratio of chloropropylene: dimethylamine: alkali metal hydroxide is 2.
1:1:1, and add a catalyst, the catalyst is alkali metal fluoride and high-efficiency complex The mixture molar ratio is (50:1)～(1:20) mixed solution; control temperature at 40～70℃, reaction time 2～4h, pump out water and low boiling point substances under reduced pressure to obtain DMDAAC; in DMDAAC solution , Add initiator, adjust the pH to about 6, and automatically polymerize at room temperature
.
The method has good raw material cleaning effect, easy control of the reaction, and high molecular weight polymers can be obtained
.

⑤Method 5

A synthetic method for high-purity dimethyl diallyl ammonium chloride
.

The process adopts the semi-dry alkali method at low temperature to quickly synthesize tertiary amines by autothermal catalysis
.
Then the oil and water are separated, dried, dehydrated, and desalinated
.
Finally, the oil phase crystallization or phase transfer catalytic reaction, vacuum distillation to obtain the product
.
The specific method is to add all dimethylamine, part of sodium hydroxide solution, appropriate amount of propylene chloride, react for a few minutes in an ice water bath or salt water bath (<5℃), add solid hydroxide in batches, and the sodium temperature control autothermal catalysis is completed quickly.
Tertiary amine reaction
.
Then the oil and water are separated, and the oil phase is dried with solid sodium hydroxide
.
Add the remaining propylene chloride and reflux for 1 to 3 hours, and then refining by distillation under reduced pressure for 10 to 30 minutes
.
After the monomer is prepared, an initiator is added for polymerization under certain conditions
.

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