Polyvinylbutyral of reduced tackiness and improved tensile strength is prepared by acetalization of polyvinyl alcohol, which is capable of association, in the associated state with n-butyraldehyde in aqueous phase in the presence of an acid catalyst. In the process for its preparation from more highly saponified, associated polyvinyl alcohol having a vinyl acetate unit content of less than 1% by weight, the acetalization is started preferably at temperatures below 20.degree. C. and the temperature is raised to above 40.degree. C. in the course of the reaction. Use for the production of plasticized thermoplastic polyvinylbutyral films and use of the latter as the joining layer in laminated glass.