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Synthesis of Anion Exchange Resin (II)

Synthesis of Anion Exchange Resin (II)

  • 2022-10-25
Under the action of catalyst, chloromethylation of chloromethyl ether and polystyrene is easy to proceed. The reaction rate depends on the nature, amount and temperature of catalyst. When ZnCl2 is used as catalyst, the reaction rate constant is proportional to the amount of ZnCl2 used. For AICl3 and SnCl4, the logarithm of the reaction rate constant is proportional to its dosage. It can be seen that the amount of these two catalysts has a much greater impact on the reaction speed than ZnCl2.

The crosslinking structure of styrene diethylbenzene copolymer also has an obvious effect on chloromethylation. For example, the chlorine content of macroporous copolymers with crosslinking degree of 6, 8 and 10 after chloromethylation can reach 20.0%, 18.8% and 17.8% respectively. The higher the degree of crosslinking, the lower the chlorine content. The parent copolymer of common gel type anion exchange resin (cross-linking degree 7 or 8) reacts at 35~40 ℃ for 10h with the ratio of copolymer: chloromethyl ether: ZnCl=1:2.5:0.4, and the chlorine content can reach 13%~15%. In the case of high cross-linking, it is difficult to reach a high level of chlorine content, and the impact of polymer structure is not obvious

Copolymers with crosslinking degree of 43 and 100% pure p-DVB or m-DVB polymers, whether gel type anion exchange resin or macroporous anion exchange resin, have almost the same chlorine content. The reasons for this need to be further studied.

There are some different conclusions about the chloromethylation process of crosslinked polystyrene:

 (1) The distribution of functional groups in the sphere is uniform.

(2) The functional basis is mainly distributed in the surface layer of the sphere, and the thickness of the surface layer is related to the method of introducing the functional basis.
(3) Chlorine is mainly distributed on the surface of the sphere, independent of the method of introducing functional groups.

The explanation for shell distribution is that the post crosslinking of the DVB dangling double bond in the polymer chain due to polymerization during chloromethylation prevents the diffusion of ZnCl2 into the sphere. But compared with the results, this explanation is not satisfactory. The above different results are probably caused by the differences in experimental methods.

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