1. Aqueous solution polymerization

The monomer solution is generally about 60%. Under the condition of nitrogen deoxidization, polymerization is initiated with an appropriate amount of initiator within the appropriate temperature range of the initiator. Other additives can also be added in the polymerization process to improve the performance of the polymer. This method is the most widely used because of its simple process, low cost and direct application of the product without solvent recovery.

Inorganic peroxide initiators, such as potassium persulfate and ammonium persulfate, are mostly used as initiators; Oxidation-reduction initiation system, such as persulfate-fatty amine, persulfate-EDTA, etc; Water-soluble azo initiators are also used abroad. The pure persulfate initiator can oxidize Cl - in the monomer to form Cl radical and terminate the reaction, so the molecular weight of the polymer is not very high, and the molecular weight distribution is not easy to control. However, water-soluble azo initiators are expensive. Therefore, the redox initiation system is worthy of further study.

In order to improve the performance of the polymer and make the process as simple as possible, foreign researchers have made many attempts. For example, it can be polymerized without removing NaCl or even adding NaCl; Add F - to increase molecular weight and conversion; The cationic degree and molecular weight are controlled by adding comonomers and chain transfer agents in stages; Adding alkali metal or ammonium bisulfite to control the viscosity of the polymer; A new process is adopted to make the solution polymerize and dry at the same time at the temperature above the boiling point to obtain dry solid polymer, etc. These attempts have achieved certain results. However, China has not done much in this area, so it is necessary to do some work in this area to improve product quality and simplify the process.

2. Solution polymerization and precipitation polymerization of organic phase

The difference between organic phase solution polymerization and aqueous solution polymerization is that the solvent is not water but organic solvent, such as methanol, DMSO, etc. The solvent selection is more important: first, the solubility of monomers and polymers should be considered; Second, the chain transfer constant of solvent should be considered, and the solvent with small chain transfer constant should be selected, otherwise the molecular weight will decrease. The operation of this method is relatively complex, the product cannot be directly applied in the organic phase, and the solvent recovery is difficult. Therefore, this method is rarely used and is mainly used for laboratory research.

When the solvent used can only dissolve the monomer, but cannot dissolve the polymer or can only partially dissolve, the polymer will precipitate from the solution. In this case, this method can be classified as precipitation polymerization. Although the separation and purification of polymer by precipitation polymerization is simple and the molecular weight distribution is narrow, it is difficult to obtain polymer with high molecular weight. Therefore, its application is limited.

3. lotion polymerization and suspension polymerization

Because DMDAAC is highly water-soluble, lotion polymerization is mainly inverse lotion polymerization. The monomer emulsifier with low HLB value (such as sorbitol fatty acid salt, etc.) is used to make the monomer aqueous solution and solvent (benzene, xylene, mineral oil, etc. can be used) form a water in oil (W/O) lotion. If necessary, a stabilizer can be added to make it more stable, and then an oil soluble or water soluble initiator is added to initiate polymerization. This method has the characteristics of high polymerization rate, high polymer molecular weight (up to several million), narrow molecular weight distribution, and good product performance.

When DMDAAC is copolymerized with other monomers, the reactivity ratio is generally low, so the content of DMDAAC in the copolymer is low. To overcome this problem, some people use inverse micro lotion polymerization. Microemulsion can reduce the activity difference between monomers, so that the content of DMDAAC in the polymer is increased, the cationic degree is increased, and the performance of the polymer is improved.

When the monomer is suspended in the system in the form of small droplets, this polymerization method can be classified as suspension polymerization. This method uses dispersant or suspending agent instead of emulsifier. There are few reports of DMDAAC using suspension polymerization, and the performance of the product is not better than other methods.

Both lotion polymerization and suspension polymerization have the disadvantages of complicated operation, demulsification of solvent recovery, low production efficiency and low utilization of equipment. But if you want to get high-quality products, you can use lotion polymerization.

Related products: Poly(DMDAAC/AM) Series