Radically polymerizable silane according to the general formula I in which R1 is a linear or branched aliphatic C1-C9-alkyl radical, phenyl or alkylated phenyl radical, R2, R3 independently of each other in each case are absent or are a linear or branched aliphatic C1-C20-alkylene radical, which can be interrupted by S or O atoms, R4, R5, R6 independently of each other in each case are —Cl, —O—CH3, —O—C2H5, —CH3 or —C2H5, X is CH2 or O, Y is absent, or is O or NR′, wherein R′ is H or a C1-5-alkyl radical, and Z is absent, or is O, NR″, —CO—O—, —CO—NR″—, —O—CO—O—, —O—CO—NR″—, or —NR″—CO—NR″—, wherein R″ is H or a C1-5-alkyl radical and wherein the radicals R2 and R3 cannot be absent at the same time and Z is absent if R2 or R3 is absent, polycondensates based thereon and fillers surface-modified therewith.