Polymer composition

A crosslinkable composition comprising:

• (A) a silyl polymer which is an organic polymer containing hydrolysable silane groups and is crosslinkable by the action of water in the presence of a silanol condensation catalyst and
• (B) a silanol condensation catalyst comprising a tin-containing polymer material having organic polymer chains bridged intermolecularly and/or intra-molecularly by tin-containing bridges comprising the unit:
• ##STR6## wherein R.sup.1 and R.sup.2 are the same or different hydrocarbyl groups, said polymeric material of (B) containing the tin bridges being derived from the group consisting of polymerised olefins, vinyl esters, unsaturated carboxylic acids, esters of unsaturated carboxylic acids and copolymers of two or more such monomers and having an average molecular weight in the range 1000 to 150,000, and the quantity of tin present in the polymeric material being in the range 1 to 42 weight percent, and
• The quantity of the tin-containing polymeric material of (B) being sufficient to provide 0.001 to 3.0 gramme atoms of tin per mole of silyl units in the silyl polymer.