The catalyst system of claim 24 where the organometallic compound is at least one of:(a) di-sec-butylmagnesium; (b) n-butylmagnesium chloride; (c) aluminum triethyl and (d) compounds of the formula: (RV)n AlX.sub.(3-n) whereRV is at least one of an aliphatic, cycloaliphatic and aromatic radical of 1 to 8 carbon atoms, X is a halide and n is less than or equal to 3 but greater than 0. 26.