Preparation of Macroporous Crosslinked Copolymer Spheres (Macroporous Ion Exchange Resin) (I)
The aforementioned suspension crosslinking copolymerization is an important method for preparing polymers. The copolymerization is carried out in a dispersed small ball. In fact, this is a micro bulk polymerization, and the product is a gel type transparent sphere. If a certain amount of inert solvent or linear polymer (collectively referred to as porogen) is added to the comonomer, the porogen will be wrapped in the copolymer sphere after the completion of copolymerization, and the porogen will be removed by distillation or solvent extraction, and macroporous copolymer will be obtained after drying. The performance of macroporous ion exchange resin is better than that of gel type ion exchange resin in terms of strength, exchange capacity and exchange speed.
The so-called inert solvent refers to the solvent that does not participate in polymerization. It can be divided into two types: one is a solvent that can be miscible with monomers and can also swell cross-linked copolymers, called good solvent. Second, it is a solvent that is miscible with monomers, but is a precipitator for polymers. It is called a bad solvent. The solvent used as pore forming agent shall be insoluble in water, and its boiling point shall be above the polymerization temperature. There are many solvents that can be used as porogen of macroporous ion exchange resin, but only a few are commonly used in industry. Such as toluene, gasoline, kerosene, paraffin, fatty acid, alcohol, etc.
Different from gel copolymer, macroporous copolymer is opaque or translucent milky white in dry state; The pore structure of pores with a certain diameter range (called physical pores or permanent pores) can be characterized by specific surface, pore volume, pore diameter and pore distribution. However, a clear distinction between gel type and macroporous copolymer cannot be drawn from the pore size (in the swelling state). Macroporous copolymers have a wide range of pore structures, including macropores and gel pores (Gelular), with pore diameters ranging from 50 to 105 nm and specific surfaces ranging from 1 to 1000 m/g. The pore volume generally varies between 10% and 90%. Therefore, the standard for distinguishing gel type ion exchange resin from macroporous type ion exchange resin is mainly the formation mechanism of pore structure, which is to see whether porogen is added during copolymerization.
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