Easy and effective immobilization and activation of a range of Ti-based single-site catalysts for ethylene polymerization has been achieved, without methylaluminoxane or borate activators, using MgCl2/AlRn(OEt)3-n supports obtained by reaction of AlR3 with adducts of magnesium chloride and ethanol. The use of relatively low catalyst loadings leads to efficient uptake by the support and gives high catalyst activity. Catalyst immobilization using these MgCl2-based supports also leads to stable polymerization kinetics, with negligible decay in catalyst activity during polymerization. Metallocene, half-metallocene, and non-metallocene catalysts have been used, particularly high activities being obtained using cyclopentadienyl titanium trichloride and its analogues. The polyethylenes obtained have narrow molecular weight distribution, with generally in the range 2-3, indicating retention of single-site catalyst characteristics after immobilization. Spherical polymer particle morphology was achieved, without reactor fouling.