Preparation of Macroporous Crosslinked Copolymer Spheres (Macroporous Ion Exchange Resin) (IV)
(3) Suspension copolymerization with mixed solvent as pore forming agent: macroporous ion exchange resins prepared by suspension copolymerization with good solvent or bad solvent as pore forming agent differ greatly in pore structure and performance, which indicates that the properties of pore forming agent have a very significant impact on the pore structure of copolymer. This effect is mainly attributed to the interaction between the porogen and the copolymer. The smaller the thermodynamic affinity of the porogen to the copolymer, the greater the porosity of the copolymer, and the pore structure is related to the second virial coefficient that can reflect the interaction between the polymer and the solvent. The solvability of mixed solvent to polymer is the sum of the solvability of its components according to the proportion of components. Therefore, using mixed solvent as porogen to prepare macroporous ion exchange resin is bound to obtain a new pore structure.
The so-called mixed solvent refers to the mixed pore forming agent of good solvent and bad solvent. The pore forming effect and the performance of macroporous ion exchange resin can be adjusted in a large range by selecting the type and proportion of solvent.
When toluene and hexane are used as pore forming agents, the solvability of the mixed system to the copolymer increases gradually when the amount of toluene in hexane increases gradually. This will inevitably affect the time when the phase separation occurs and the swelling state of the polymer phase. The more the content of toluene, the less the entanglement of macromolecular chains in the microgel core, and the improvement of the solvation degree of the microgel core, the more loose the internal structure of the microspheres, resulting in more and more pores. Therefore, when the amount of good solvent is gradually increased, the pore volume and pore diameter are gradually reduced, and the specific surface area is larger and larger.
The interaction between solvent and polymer can be understood from the solubility parameters, so the ratio of mixed solvent can also be selected from the solubility parameters.
(4) Suspension copolymerization with linear polymer as pore forming agent: Macroporous ion exchange resin can also be prepared by adding linear polymer into the comonomer. Linear polymers that can be used as pore forming agents include polystyrene, polyvinyl acetate, polyacrylate, etc. Before copolymerization, a certain amount of linear polymer is dissolved in the comonomer, and then suspension polymerization is carried out according to the usual method. When the monomer conversion reaches a certain degree, the cross-linked copolymer and the linear polymer dissolved in the monomer are separated [. As the monomer is continuously transferred into the copolymer, the linear polymer molecules that lose the solvent (monomer) are coiled into clusters. After the polymerization is completed, the linear polymer is extracted with the solvent to obtain a macroporous copolymer with large pore diameter.
When linear polymer polystyrene is used as the pore forming agent, the amount of polystyrene in the range of 10%~30% has the greatest impact on the apparent density. When it is less than 10%, the pore forming effect is not obvious, and when it is more than 30%, the impact on the apparent density is greatly reduced.
When polystyrene is used to prepare macroporous resin, the influence of crosslinking degree is less than that when solvent is used as pore forming agent. When the amount of DVB was more than 10%, the effect on apparent density disappeared. Like good solvent and bad solvent, the amount of linear polymer also has a critical value related to the amount of DVB.
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