Molecular Weight Distribution of Ethylene/1‐Olefin Copolymers: Generalized Bimodality Criterion

Abstract

Two single‐site‐type metallocene catalysts can be combined to produce polymers with well‐controlled and broad molecular weight distributions (MWD). As polyolefins with unimodal and bimodal MWDs have different mechanical and rheological properties, a criterion to determine whether a system of two single‐site‐type catalysts produces polymers with unimodal or bimodal distributions is useful for product development and property optimization. In this work, a generalized MWD bimodality criterion is developed and represented as a comprehensive 3D map. The proposed criterion is validated with both simulated and previously reported experimental data. The effect of number average chain length and mass fraction on MWD bimodality criteria are also examined. The results show that unimodal MWDs are more likely to be observed when the mass fraction of one of the copolymers is much higher than the other and when both copolymers have similar average chain lengths. image