Study of the compositional heterogeneity of ethylene/1-hexene copolymers produced over supported catalysts of different composition

Separation into narrow MWD fractions (liquidliquid fractionation) and preparative TREF (temperature rising elution fractionation) with subsequent analysis of fractions by GPC, FTIR, and 13C NMR spectroscopy were used to study the comonomer distribution of ethylene/1hexene copolymers produced over highly active supported titanium- and vanadium-magnesium catalysts (TMC and VMC) and a supported zirconocene catalyst. These catalysts produce PE with different MWD: Mw/Mn values vary from 2.9 for zirconocene catalyst, 4.0 for TMC, and 15 for VMC. 1-Hexene increases polydispersity to 25 for copolymer produced over VMC and hardly affects MWD of the copolymer produced over TMC and zirconocene catalysts. The most broad short chain branching distribution (SCBD) was found for ethylene/1hexene copolymers produced over TMC. VMC and supported zirconocene catalyst produce copolymers with uniform profile of SCB content vs. molecular weight in spite of great differences in Mw/Mn values (22 and 2.5 respectively). TREF data showed that majority of copolymer produced over supported zirconocene catalyst was eluted at 7090 degrees C (about 85 wt %). In the case of VMC copolymer's fractions were eluted in the broad temperature interval (40100 degrees C). Accordingly, TREF data indicate a more homogeneous SCBD in copolymer, produced over supported zirconocene catalyst. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012