In accordance with one embodiment of this invention, a chromium catalyst supported on an aluminum phosphate-containing base is used in conjunction with a boron component either as a part of the base or as a cocatalyst. The resulting catalyst is unique both in its favorable sensitivity to molecular weight control agents such as hydrogen and in its ability to produce a fundamentally different olefin polymer. In accordance with another embodiment of this invention, the chromium is supported on a phosphate base produced using a melt of the aluminum salt.