By controlling the hold up times, concentrations and temperatures for mixing the components of aluminum, titanium and magnesium based catalyst for solution polymerization it is possible to prepare a catalyst having a high activity, which prepares high molecular weight polyolefins. Generally, a catalyst loses activity and produces lower molecular weight polymer at higher temperatures. The catalyst of the present invention permits comparable polymers to be produced with higher catalyst activity and at higher reaction temperatures by increasing the concentration of the components used during the preparation of the catalyst.