| Ethylene and 1-butene in various proportions were copolymerized over a commercial titanium-based Ziegler-Natta catalyst in a semibatch gas-phase reactor. Activity of the catalyst was found to be sensitive to the exposure to the cocatalyst. Gas chromatographic analysis of the gas mixtures showed that 1-butene incorporation was limited to the early stages of the reaction, indicating that heterogeneity of branching frequency in linear low density polyethylene (LLDPE) was largely due to the changes in oxidation states of the active sites.;LLDPE samples were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and temperature rising elution fractionation (TREF). GPC results suggested that hydrogen was a more effective chain transfer agent for one type of active site than the other and that the kinetics of termination were of mixed-order. DSC studies revealed that major differences in crystallinity, melting temperature, and miscibility existed between the nascent reactor powder and the melt recrystallized resins. DSC fractionation was found to be quantitatively equivalent to the analytical TREF. |
