a process for polymerizing or copolymerizing a member of the group consisting of an alpha olefin or mixtures thereof , consisting of the steps of : polymerizing an alpha olefin in a polymerization reactor using a polymerization catalyst , a cocatalyst , and an amount of hydrogen adjusted for molecular weight control as measured by melt flow ; rapidly changing the melt flow of the polymerized alpha olefin from high to low melt flow by reacting a portion of the unreacted hydrogen in the reactor with a quantity of the alpha olefin present therein by interaction with a hydrogenation catalyst ; and removing the hydrogenation catalyst from the reactor through continuous exchange of the reactor contents .