Polymerization of ethylene by (α‐Diimine) nickel catalyst and statistical analysis of the effects of reaction conditions

Abstract

This article regards the ethylene polymerization catalyzed by a nickel catalyst and activated by ethylaluminum sesquichloride (EASC). The effects of the reaction conditions [polymerization temperature, cocatalyst (EASC) concentration, and ethylene concentration] on the average molecular weights of the final polymers and reaction yields were evaluated with the help of empirical statistical models. It is shown that reaction temperature and cocatalyst (EASC) concentration exert the most important effects on average molecular weights and catalyst activity. The polydispersities of the obtained polyethylenes are larger than the polydispersities of polyethylenes obtained with typical Brookhart catalysts. The analysis of polymer branching frequencies shows new types of short branching and significant amounts of long branches, which may explain the relatively large polydispersities of the obtained polymer samples. POLYM. ENG. SCI., 50:1797–1808, 2010. © 2010 Society of Plastics Engineers

Mathematical Modeling of MWD and CBD in Polymerizations with Macromonomer Reincorporation and Chain Running

“…It is also interesting to observe that the cocatalyst employed to activate the nickel catalyst also affects the running probabilities. As observed experimentally [39] and illustrated in Figure 9, branching frequencies are larger when MAO is used as cocatalyst and lower when EASC is the employed cocatalyst. Figure 9 shows unequivocally that the proposed model structure can be used successfully to describe the short CBD of polyolefins.…”

“…Figure 9 shows the short CBDs, as produced by the chainrunning mechanism during ethylene polymerizations performed with the analyzed nickel based catalyst. [39] As one can see in Figure 9, very good agreement between model predictions and available experimental data can be reached after the estimation of the model parameter q 1 and q. Two model parameters are required for improved fitting of available experimental data, indicating that the kinetics of running depends on the active carbon site, as discussed previously.…”

“…[ [15][16][17]24,[39][40][41][42] This might be due to the existence of multiple active sites, but was probably related to macromonomer reincorporation, as discussed elsewhere. [7][8][9][10][11][12][13][14][15][16][17][29][30][31][32][33][34][35][36][37][38][39][40][41][42] Based on the previous discussion and on the main effect analysis performed by Ferreira et al, [39] the following set of kinetic parameters was estimated for a single catalyst site using the experimental data presented by Ferreira et al: [39] propagation rate constant K Table 2.…”

“…Polymer chains obtained with the analyzed nickel (adiimine) catalyst system presented both short-chain branches (produced by the chain-running mechanism) and long-chain branches (probably produced by macromonomer reincorporation). [39] In addition, this catalyst led to production of polyethylenes with higher polydispersities than normally obtained with other similar catalysts.…”

“…Detailed description of the catalyst system and of the analyzed polymerization reactions are presented elsewhere. [39] However, it is important to emphasize that ethylene polymerizations were performed in semibatch mode at different pressures, different concentrations of catalyst and cocatalysts and different temperatures. Polymerizations were carried out with an a-diimine nickel catalyst and activated with ethylaluminum sesquichloride (EASC) in solution of toluene.…”