Polymers are prepared by reaction between a polymer prepared by reaction between (A) an OH terminated reaction product of a polyacid chloride and an organic polymer having substituent groups condensable therewith and (B) a silane or siloxane having a group capable of reaction with substituent groups of the reaction product (A). Reaction product (A) is preferably derived from a polyoxyalkylene glycol and a diacid chloride. Silane or siloxane (B) is preferably an epoxy silane and preferably has at least one silicon- bonded hydrolysable group. Preferred polymers are employed in moisture curable composition, e.g. as sealants.