Expandable mixtures that are devoid of isocyanates

An isocyanate-free foamable mixture comprising:

• (A) a mixture of prepolymers in which 50-99% of the chain ends are terminated by alkoxysilyl groups and 1-50% of the chain ends are terminated by groups of the formula [2]
• A1-R1 [2]
• where
• A1 is an oxygen atom, an N—R2 group or a sulfur atom,
• R1 is an alkyl, cycloalkyl, alkenyl, aryl or arylalkyl radical having 2-50 carbon atoms in which the carbon chain is optionally interrupted by nonadjacent oxygen atoms, sulfur atoms or N—R2 groups, and the carbon chain of R1 is optionally substituted by lateral alkyl groups having 1-10 carbon atoms or halogen atoms, and
• R2 is a hydrogen atom or an alkyl, alkenyl or aryl radical having 1-10 carbon atoms, and
• (B) a hydrocarbon blowing agent.