Using BF3 as probe, the surface of SiO2 was probed. The effects of the roast temperature on the SiO2 surface were investigated and a possible mechanism is suggested. Using SiO2 as starting material for supports, new supported catalysts for copolymerization of ethylene and propylene were prepared and their possible structures are discussed. It was found that higher polymerization productivity, for instance, 480 kg P/mol(Ti) h, can be obtained by using a SiO2/Al2Et3Cl3/TiCl4 catalytic system and addition of PhMgCl to this catalytic system can significantly increase polymerization activity. (C) 2000 John Wiley & Sons, Inc.