The preparation of ion exchange resin by polycondensation is the earliest method to synthesize organic ion exchanger. Although most of the ion exchange resins produced today are additive type functionalized copolymers, the polycondensation method is still very useful. Some polycondensation ion exchangers are still widely used. The early polycondensation resin was made into block polymer by bulk polymerization, and then crushed and sieved to obtain amorphous particles. The hydraulic properties of this resin in column operation are not very good, so the method of suspension polymerization was also used to prepare spherical resin later.
The monomers used in the synthesis of polycondensation resin are water-soluble, so water cannot be used as the dispersion medium. The substances suitable for dispersion medium of polycondensation reaction include o-dichlorobenzene, transformer oil, liquid paraffin, diethyl phthalate, dioctyl phthalate, carbon tetrachloride [52], etc. This suspension polycondensation reaction in non-aqueous medium is called reverse suspension polymerization.
1. Strong acid cation exchange resin
These resins can be synthesized in two ways. The first is to add concentrated sulfuric acid to phenol, stir at 100 ℃ for 4h, generate phenol sulfonic acid, and leave some phenol. Adjust the mixture to alkaline, add 35% formaldehyde aqueous solution, react at 100 ℃ for 5h, adjust it to acidic, then add it to chlorobenzene at 100 ℃, disperse it to appropriate particle size, heat it for 1h, and obtain spherical resin. The exchange capacity can reach 3meq/g.
The other method is condensation polymerization of 2,4-benzenesulfonic acid formaldehyde, resorcinol and formaldehyde. This reaction can be carried out under acidic conditions or in alkaline solution. The exchange capacity of the obtained resin is 2.8 meq/g.
The heat resistance, oxidation resistance and mechanical strength of the condensed sulfonic acid based ion exchange resin are inferior to those of the styrene based strong acid resin, so it is gradually replaced by the latter.
In addition, sulfonated cation exchange resin can also be obtained by condensation polymerization of p-hydroxybenzyl sulfonic acid with phenol and formaldehyde. This resin has weak acidity and few practical uses.
English
