Crystallization analysis fractionation of ethene/1-hexene copolymers made with the MAO-activated dual-site(l,2,4-Me3Cp)2ZrCl2 and(Me5Cp)2ZrCl2 system

摘要

Different poly(ethene-co-1-hexene)samples with varying amounts of 1-hexene were characterized by crystallization analysis fractionation(Crystal).The samples were synthesized with(l,2,4-Me_3Cp)_2ZrCl_2,(Me_5Cp)_2ZrCl_2,and a mixture of these two catalysts in a 1:1 molar ratio.In addition,preparative Crystaf was used to fractionate some of the samples made with the catalyst mixture into 1-hexene-rich and 1-hexene-poor fractions.These fractions were characterized by Crystaf,differential scanning calorimetry(DSC)and gel permeation chromatography(GPC),and compared with copolymers made under similar conditions using the individual catalysts.Both(l,2,4-Me_3Cp)_2ZrCl_2 and(Me_5Cp)_2ZrCl_2 produced copolymers with unimodal distribution of short chain branches(SCBD),as expected for single-site catalysts.The catalyst mixture produced copolymers with bimodal SCBDs when 0.38 mol/1 or higher concentrations of 1-hexene were used.The high temperature peak results from crystallization of polymer chains with few comonomer units,and these are attributed to(Me_5Cp)_2ZrCl_2.The low temperature peak results from crystallization of polymer chains made by(l,2,4-Me3Cp)2ZrCl2,and these chains contain many comonomer units.Direct evidence for relative activity enhancement of the(Me5Cp)2ZrCl2 catalyst in the dual-site system was observed.