Silane-modified polyvinyl acetals are obtained by copolymerizing a) vinyl esters of C1-15 alkylcarboxylic acids having from 1 to 15 carbon atoms, and optionally (meth)acrylates C1-15 of alcohols, olefins, dienes, vinylaromatics, or vinyl halides, with b) from 0.02 to 20.0 % by weight of an ethylenically unsaturated, hydrolyzable silicon compounds or hydrolyzable mercaptosilanes; hydrolyzing the resulting vinyl ester copolymers to 50 mol % or more of vinyl alcohol units; and acetalizing vinyl alcohol units with a C1-15 aliphatic or aromatic aldehydes, wherein from 5 to 50 % by weight of a mixture of comonomers a) and silane comonomers b), based on the total weight of comonomers a) and b), is used as an initial charge, and the remainder is metered in during polymerization, such that the ratio between the comonomers a) and silane comonomers b) remains constant throughout the polymerization, resulting in a homogeneous polymer.