Reaction engineering
Ali Ebrahimi; Saeid Ahmadjo; Mohsen Mohammadi; Mohammad-Mahdi Mortazavi; Mostafa Ahmadi
Abstract
Coordinative chain transfer polymerization (CCTP) has opened a new path for the development of novel products like olefin block copolymers and chain-end functional polyolefins. However, conflicting results are frequently reported on the catalyst performance including activity and comonomer selectivity ...
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Coordinative chain transfer polymerization (CCTP) has opened a new path for the development of novel products like olefin block copolymers and chain-end functional polyolefins. However, conflicting results are frequently reported on the catalyst performance including activity and comonomer selectivity under CCTP conditions. Here we have selected two catalysts including rac-ethylenebis(1-η5-indenyl)zirconocene and bis(imino) pyridine iron, with drastically different comonomer affinities. The effect of diethyl zinc as the chain transfer agent (CTA) on their individual performances is evaluated at different 1–hexene concentrations, in copolymerization with ethylene. Combined thermal fractionation and GPC results confirm that not all chains experience the reversible transfer reaction. Nevertheless, the metallocene catalyst shows twice activity and about 30% lower comonomer incorporation in the presence of CTA. Conversely, the late transition metal catalyst demonstrates lower activity and remains comonomer irresponsive. It could be concluded that, in addition to establishing a reversible transfer reaction, CTA affects the nature of active centers. This finding can help designing olefin copolymers with a more defined chemical composition based on CCTP reaction.
Characterization
Mostafa Ahmadi; Seyed Mohammad Mehdi Mortazavi; Saeid Ahmadjo; Majid Zahmati; Khosrow Valieghbal; Davoud Jafarifar; Reza Rashedi
Abstract
Ethylene / 1-butene copolymers at different comonomer levels were synthesized using Ziegler-Natta catalyst to evaluate the applicability of thermal fractionation methods in predicting chemical composition distribution (CCD). The continuous melting endotherms by DSC were converted to continuous CCD, and ...
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Ethylene / 1-butene copolymers at different comonomer levels were synthesized using Ziegler-Natta catalyst to evaluate the applicability of thermal fractionation methods in predicting chemical composition distribution (CCD). The continuous melting endotherms by DSC were converted to continuous CCD, and the average comonomer contents were compared with NMR results. DSC underestimated comonomer content specifically at higher levels and was more sensitive to the drawn baseline. The thermally fractionated melting endotherms by SSA method were deconvoluted and transformed into discrete CCDs. SSA method underestimated average comonomer content even more, however results were more reproducible. The main shortcoming of the thermal methods was the inability of short ethylene sequences in forming discernible lamella thicknesses at high comonomer levels. Calibration curves were created for converting the predicted comonomer contents into absolute values and used for studying industrial LLDPEs with different comonomer levels. It was shown that SSA provides more reliable results and correlates more reasonably to the measured densities.
