A novel slurry reactor was used to investigate the copolymerization behavior of ethylene and 1-butene in the presence of 1 wt % Cr on Davison silica (Phillips-type) catalyst over the temperature range of 0-50 degrees C, space velocity of about 0.0051 [m(3) (STP)]/(g of catalyst) h, and a fixed ethylene to 1-butene feed mole ratio of 95 : 5. The effect of varying the ethylene to l-butene feed ratios, 100 : 0, 96.5 : 3.5, 95 : 5, 93 : 7, 90 : 10, 80 : 20, and 0 : 100 mol/mol at 50 degrees C was also studied. The addition of 1-butene to ethylene typically increased both copolymerization rates and yields relative to ethylene homopolymerization with the same catalyst, reaching a maximum yield for an ethylene : 1-butene feed ratio of 95 : 5 at 50 degrees C. The incorporation of 1-butene within the copolymer in all cases was less than 5 mol %. The average activation energy for the apparent reaction rate constant, k(a), based on total comonomer mole fraction in the slurry liquid for the ethylene to 1-butene feed mole ratio of 95 : 5 in the temperature range of 50-30 degrees C measured 54.2 kJ/mol. The behavior for temperatures between 30 to 0 degrees C differed with an activation energy of 98.2 kJ/mol; thus, some diffusion limitation likely influences the copolymerization rates at temperatures above 30 degrees C. A kinetics analysis of the experimental data at 50 degrees C for different ethylene to 1-butene feed ratios gave the values of the reactivity ratios, r(1) = 27.3 +/- 3.6 and r(2) congruent to 0, for ethylene and 1-butene, respectively.