Effect of short chain-branching distribution on crystallinity and modulus of metallocene-based ethylene-butene copolymers

In this article, the short chain-branching distribution (SCBD) of some metallocene-based ethylene–butene copolymers was evaluated by DSC, and some conventional ethylene copolymers were also studied for the purpose of comparison. It is found that metallocene-based ethylene copolymers have a relative narrower SCBD. These copolymers were crystallized under different modes, and the crystallinity and initial modulus of them were examined. The metallocene-based ethylene copolymers contain less interfacial regions, and the melting temperatures of them decrease more rapidly with the decrease of density than those of conventional ethylene copolymers. Moreover, the metallocene-based and conventional ethylene copolymers of similar density have close initial modulus when they are quenched or annealed at 100°C, but conventional ethylene copolymers show higher initial modulus when stepwise crystallized from 120°C. These differences in crystallinity and initial modulus were explained based on their differences in short-chain branching distributions.