Method for forming flame-retardant clay-polyolefin composites

A method for forming polyolefin/clay composites by olefin polymerization which can be used as flame retardants in which at least one filler is combined with an early or late transition metal first catalyst component that becomes activated for olefin polymerization when in contact with the treated filler. An olefin is contacted by the activated catalyst-filler combination either (a) in the absence of an alkylaluminum second catalyst component or (b) in the presence an alkylaluminum second catalyst component when the first catalyst component is an early transition metal catalyst, whereby to form an clay-polyolefin composite incorporating platelets of said filler. The filler is preferably clay, exemplified by montmorillonite and chlorite. The first catalyst component is preferably a non-metallocene catalyst. A predetermined amount of one or more olefinic polymers can also be blended with a masterbatch to obtain a composite having a desired amount of loading.