A method is disclosed for reducing levels of residual halogen and Group IIIb metals in a crude poly(.alpha.-olefin) polymerized in the presence of a catalyst comprising the halogen and Group IIIb metals, wherein the method comprises: A) washing the crude poly(.alpha.-olefin) with water; B) separating the aqueous and organic phases; C) then adding an adsorbent selected from the group consisting of magnesium silicates, calcium silicates, aluminum silicates, aluminum oxides, and clays to the organic phase to form a slurry; D) heating the slurry under reduced pressure at a temperature of at least about 180.degree. C. for at least about thirty minutes; and then E) separating the adsorbent from the slurry.