Kinetic studies of the injection of comonomers during polymerization of ethene and propene with MgCl2-supported Ziegler-Natta catalysts

The effects of injecting ethene, propene, 1-hexene, 2-methylpropene, 3,3-dimethyl-1-butene, cis-2-butene, trans-2-butene, 2,3-dimethyl-2-butene, cyclopentene, styrene, 1,3-butadiene and 1,4-pentadiene during polymerizations of ethene and propene have been investigated. Catalysts used were a supported MgCl2/EB/TiCl2 ballmilled catalyst and precipitated MgCl2/2-EH/TiC1(4)/DIBP catalysts activated with triethylaluminium in presence of EB. (EB = ethyl benzoate, 2-EH = 2-ethylhexanol, DIBP = diisobutyl phthalate). The polymerizations were performed at 50 degrees C, in a heptane slurry at 1 atm (1.00 . 10(5) Pa) total pressure. The instantaneous polymerization rate was observed by continuous monitoring of the monomer consumption, the time resolution of the measurements being less than one second. Two different kinetic effects can be observed after injection of the comonomer First there is an immediate rate change, usually a rate reduction. Then a secondary effect may follow, which is a slow, and sometimes significant and persistent, activation. The two effects obviously have different causes, and for none of these we found single causes that can explain all the observations. The strongest immediate effect was observed after addition of dienes and indicates a direct association of the comonomer to the active center. A marked nonlinearity in the response may hint to inhomogeneity in the structural environment of the active centers. Addition of a-olefins during ethene polymerization gave the strongest secondary effect. In general the immediate effects were stronger during propene polymerization than during the polymerization of ethene. A significant difference in the effects of cis-2-butene and trans-2-butene in the polymerization of propene indicates that steric effects may be important.