Propylene polymerization catalyst

A polymerization catalyst for propylene is made by (1) washing a co-crystallized TiCl3AlCl3 complex in which the mole ratio of TiCl3:AlCl3 is 3,0 to 1,0 with a solution of an Al (trialkyl) at a temperature of 20 DEG to 80 DEG C., and (2) mixing the solid residue from the washing with an Al (trialkyl) to give a product in which the mole ratio of Al (trialkyl) to TiCl3-AlCl3 is between 2,5:1 and 1:1. The solvent for the trialkyl is preferably a hydrocarbon. The cocrystallized TiCl3-AlCl3 is generally prepared by the reduction of TiCl4 with Al in the presence of a trace of AlCl3. The polymerization of propylene with the catalyst is generally effected in a hydrocarbon diluent, and a temperature of 60 DEG -135 DEG C. and a pressure of 130-200 p.s.i.