Modeling the Ethylene Sequence Length Distribution of Metallocene-Catalyzed Bimodal Polyethylene

The structure of bimodal poly-(ethylene-hexene) is presented in terms of the ethylene sequence length distribution. This distribution is determined by applying statistical modeling to molecular weight and short chain branching distributions obtained from gel permeation chromatography (GPC). We found that the ethylene sequence length distribution of bimodal polyethylene can have features different from molecular weight and short chain branching distributions (SCBD) in terms of bimodality. Using the successive self-nucleation and annealing (SSA) method, we demonstrate the model's ability to elucidate experimental data related to the crystallization and structure of copolymers. It was found that the average lamellar thickness inferred from the SSA results correlated with the weight-averaged ethylene sequence length and the ethylene sequence length distribution bimodal ratio. Combined crystallization of the high and low molecular weight populations was also evaluated through a combination of the ethylene sequence length distribution and the SSA results. The results show that such models are essential to link SSA results to the molecular structure.