Hydrolysable and polymerizable or polyadditive silanes and methods of their production and the production of (hetero)silicic acid polycondensates or of polymers. The silanes in accordance with the invention are of general formulain which the groups and indices are equal or different and have the following meaning:R=hydrogen, R2-R1-R4-SiXxR33-x, carbonyl, alkyl, alkenyl, aryl, alkylaryl or arylalkyl;R1=alkylene, arylene, arylenealkene or alkenearylene;R2=alkylene, arylene, arylenealkene or alkenearylene;R3=Alkyl, alkenyl, aryl, alkylaryl or arylalkyl;R4=-(CHR6-CHR6)n-, where n=0 or 1, -CHR6-CHR6-S-R5-; -CO-S-R5-, -CHR6-CHR6-NR6R5-, -Y-CS-NH-R5-, -S-R5-, -Y-CO-NH-R5-, -CO-O-R5-, -Y-CO-C2H3(COOH)-R5-, -Y-CO-C2H3(OH)-R5- or -CO-NR6-R5-;R5=alkene, arylene, arylenealkene or alkenearylene;R6=hydrogen, alkyl or aryl with 1 to 10 carbon atoms;R9=hydrogen, alkyl, alkene, aryl, alkylaryl or arylalkyl;X=hydrogen, halogen, hydroxy, alkoxy, acyloxy, alkylcarbonyl, alkoxycarbonyl or NR''2, where R''=hydrogen, alkyl or aryl;Y=-O-, -S- or -NR6-;Z=-O- or -(CHR6)m-, where m=1 or 2;a=1, 2 or 3, with b=1 for a=2 or 3;b=1, 2 or 3, with a=1 for b=2 or 3;c=1 to 6;x=1, 2 or 3;a+x=2, 3 or 4.