Control of Sequence Distribution of Ethylene Copolymers: Influence of Comonomer Sequence on the Melting Behavior of Ethylene Copolymers

Abstract

New unbridged mixed-ligand zirconocenes were synthesized, characterized, and studied in the copolymerizations of ethylene−propylene (EP) and ethylene−1-hexene (EH). The MAO-activated metallocene [1-benzyl-2-(3‘,5‘-di-tert-butyl)phenylindenyl][2-phenylindenyl]zirconium dichloride (8) catalyzed EP and EH copolymerizations with products of reactivity ratios greater than one (rerp = 2.4, rerh = 2.2) to give rubbery, semicrystalline, high-melting polymers. Crystallinity was detected by differential scanning calorimetry (DSC) in both EP and EH copolymers containing only 50 mol % ethylene. Solvent fractionation of high ethylene content EH copolymers revealed that these copolymers were composed of a small ether-soluble fraction and heptane-soluble and heptane-insoluble fractions whose compositions and sequence distributions matched closely with those of the unfractionated polymer. Collectively, the reactivity ratios, DSC, and fractionation results gave evidence that these copolymers contained long crystallizable ethylene sequences. A comparison of the melting point behavior of a series of ethylene−1-hexene copolymers with 80 mol % ethylene revealed a sensitive dependence of the melting transition to the comonomer sequence distribution.