Dispersion polymerization of vinyl acetate

Dispersion polymerization is another kind of heterogeneous free radical polymerization of alene monomers except suspension polymerization and emulsion polymerization. Dispersion polymerization can be regarded as a polymerization between suspension polymerization and emulsion polymerization, and its characteristics are as follows:

1) Water or non-water solvent can be used as the medium. When water is used as a medium, the monomer must be insoluble in water or substantially insoluble in water.
2) The dispersion of monomers in water is achieved by intense agitation, and the protective colloid added to the system plays a role in preventing the agglomeration of dispersed phases.
3) Water-soluble initiators are required for dispersion polymerization with water as the medium.

In form, dispersion polymerization has many similarities with emulsion polymerization. But there are clear differences. Dispersion polymerization, for example, does not use typical emulsifiers but uses protective colloid to stabilize the polymerization system; The particles obtained by polymerization are larger than those obtained by emulsion polymerization. Let's wait.
The polymerization of vinyl acetate in water with polyvinyl alcohol as a protective colloid is a typical dispersion polymerization. Vinyl acetate is a water-soluble monomer with a solubility of about 2.5% in water at room temperature and is easily hydrolyzed. The hydrolysis product acetic acid can seriously interfere with the normal process of polymerization. Therefore, the dispersion polymerization of vinyl acetate has more complicated factors than the common emulsion polymerization. It is believed that the dispersion polymerization of vinyl acetate does not occur in micelles, but the monomer dissolved in water is first polymerized, and when the molecular weight reaches a certain level, the polymer precipitates from the water to form latex particles on the protective colloid. In order to improve the stability of the polymerization system and products, an appropriate amount of emulsifier is added in the dispersion polymerization of vinyl acetate, but the role of emulsifier in polymerization is auxiliary.

Attentions：

PVA usually has two specifications of 1788 and 1799 (17 indicates a degree of polymerization of 1700, 88 and 99 indicate an alcoholysis degree of 88% and 99%, respectively). When used as a dispersion polymerization protective colloid, it is best to use 1788, and the resulting product has good stability.
2. In the polymerization process, the monomer droplet acceleration should be slow and not fast. Generally, a slight reflux in the condenser is appropriate.
3. The boiling point of vinyl acetate is between 70-75℃. After adding drops, the heating rate should be slow, too fast and easy to caking.

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