Chemical Composition Distribution Study in Ethylene/1-Hexene Copolymerization to Produce LLDPE Material using MgCl_2-TiCl_4-Based Ziegler-Natta Catalysts

摘要

The characteristic features of LLDPE poly-merization with ZN catalyst are the time drift effect dur-ing polymerization and the bending effect when tryingto decrease density of the copolymer by adding morecomonomer to the polymerization. The time drift inLLDPE polymerization is revealed by a constant decreaseof comonomer incorporation during polymerization time.The bending is revealed by difficulties in lowering thedensity of LLDPE material below the density of 920 kg/m3. With increasing comonomer content during polymer-ization, the density does not decrease, but the soluble frac-tion increases. To try to observe if these phenomena areconnected, two types of catalysts, SiO_2supported and pre-cipitated MgCl_2ZN catalysts, were studied. A short time (10 min) and an extended time (60 min) copolymerizationtest series where the polymerizations were performed inthe presence of a gradually increasing comonomeramount. Both catalysts show a strong bending when den-sity is presented as a function of 1-hexene both in 10- and60-min polymerization, indicating no connection betweentime drift and bending. The density, melting point, andcrystallinity results all indicate that both catalysts are mak-ing similar copolymer material with identical chemicalcomposition distribution.