Process for preparing highly viscous soluble polyvinylalcohols

Polyvinyl alcohol having a viscosity of more than 140 centipoises (4 per cent aqueous solution) is produced by hydrolysis of polyvinyl acetate prepared using 0.8 to 8 per cent of dioleyl peroxide (based on monomer) as catalyst. The polymerization may be a bulk, emulsion or granular process, and may include benzoyl peroxide as additional catalyst. In examples monomer and catalyst are added continuously and bulk and granular polymerizations (using the ammonium salt of styrene-maleic acid copolymer) are described. The polyvinyl alcohol may be obtained by acid or alkaline hydrolysis or by re-esterification, and complete or partial hydrolysis may be effected. The medium used may be aqueous, organic or a mixture thereof and the examples illustrate the use of methanol and methanolic sodium hydroxide. The products may be used in the preparation of dispersions and emulsions, in the formation of fibres, ribbons and foils, and may act as thickening agents in textile, pharmaceutical and cosmetic industries. Specification 462,165, [Group IV], is referred to.