Crosslinked polystyrene is the matrix for the synthesis of a variety of ion exchange resins. The benzene ring on its high molecular chain can carry out many substitution reactions like small molecular aromatic hydrocarbons, so as to introduce various ion exchange groups to make ion exchange resin with excellent performance.

1. Preparation of crosslinked polystyrene spheres

（1）Styrene monomer

The purity of industrial styrene is more than 99%. It can meet the requirements of synthetic ion exchange resin. In order to prevent self polymerization during storage and transportation, styrene is added with a certain amount of polymerization inhibitor (about 0.01% hydroquinone or p-tert-butyl catechol) when leaving the factory. The polymerization inhibitor shall be removed by distillation or washing with dilute alkali solution before use. A more convenient method is to make styrene pass through the column equipped with -- oh strong basic anion exchange resin, and the polymerization inhibitor is removed by the strong basic resin. Styrene with polymerization inhibitor removed should be used as soon as possible, and it will self polymerize slowly even if stored at low temperature. Styrene that has begun self polymerization cannot be used to synthesize ion exchange resins.

（2）Crosslinking agent

The most commonly used crosslinking agent is divinylbenzene (DVB). The diene monomer can be copolymerized with styrene, acrylate, acrylonitrile and other monomers to make the polymer chain into a cross-linked network structure. The crosslinking density and its uniformity have a great influence on the properties of ion exchange resin.

Industrial divinylbenzene has two main problems: one is low purity; Second, there are three isomers with different properties. The ion exchange resin produced by using divinylbenzene of different manufacturers and different quality as crosslinking agent must have certain differences in performance. Therefore, in the synthesis of ion exchange resin, we must first understand the quality of divinylbenzene.

The purity of general industrial divinylbenzene is between 40% ~ 60%. In addition to divinylbenzene (DVB), there are a considerable amount of ethyl styrene (EVB) and a small amount of diethylbenzene (DEB). Each component has meta - and para isomers.

The isomers of divinylbenzene show different reactivity when copolymerized with other monomers. This has a significant effect on the structure of copolymers and the properties of ion exchange resins prepared from these copolymers.