Abstract: Disclosed are support-activators and catalyst compositions comprising the support-activators for polymerizing olefins in which the support-activator includes a clay heteroadduct, also termed a composite, prepared from a colloidal phyllosilicate such as a colloidal smectite clay, which is chemically-modified with a surfactant. In an aspect, the clay composite can comprise the contact product of a colloidal smectite clay and a surfactant in a liquid carrier, but in the absence of any other reactant such as a cationic polymetallate, and their use as support-activators for metallocene precatalysts is also described. The use of surfactants with cationic polymetallates in forming clay-composites is also described.