The Polyvinyl Alcohol and Vinyl Acetate

Polyvinyl alcohol is a kind of can't directly through the polymerization of the monomers and polymers, because vinyl alcohol monomer is not exist alone, it is very unstable, under normal circumstances will spontaneously by intermolecular rearrangement into acetaldehyde, so can not use vinyl monomer polymerization of polyvinyl alcohol. The general method of polyvinyl alcohol preparation: first with vinyl acetate monomer by polymerization of poly vinyl acetate, and then poly vinyl acetate alcoholysis and hydrolysis of polyvinyl alcohol.

Vinyl acetate monomer for preparing poly vinyl acetate is solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization of four methods.

Bulk polymerization has the advantages of high purity, production fast, short process flow, simple process, but because no heat medium, along with the reaction, the viscosity of the system increases, the reaction heat to evaporate, easy to generate local overheating, the product color, even the implosion phenomenon, it is often used in a small amount of polymer laboratory studies of preparation, dynamical study. Solution polymerization method in the presence of solvents, chain transfer reaction is easy to happen, the low degree of polymerization, but its degree of polymerization and the molecular weight distribution is narrow, the products of good quality, and easy to heat dissipation, the industry generally by solution polymerization. Suspension polymerization is usually with water as medium, easy heat dissipation and temperature control, the degree of polymerization and the molecular weight is higher, but because of a small amount of residual suspension products, post treatment is complex, the cost of production. Emulsion polymerization with water as the dispersion medium, to facilitate heat dissipation and temperature control, and the polymerization rate, molecular quantity obtained high, but because the polymerized emulsion by condensation, washing, dehydration, drying after processing, the production cost is suspended high.

Vinyl acetate polymerization reaction is exothermic reaction (89.2KJ/mol), remove the reaction heat and the reaction was carried out with difficulty;, viscosity of polymerization system increases quickly, the stirring is difficult, hot issues shift intensified reaction, prone to implosion phenomena. This research used easy heat dissipation and temperature control solution to prepare poly vinyl acetate resin polymerization, solvent is methanol (reaction temperature and the boiling point close to), initiator azo isobutyronitrile (two, reaction temperature on the decomposition temperature range).