Computational Linear Rheology of Metallocene-Catalyzed High Density Polyethylene Predicted by Two Alternative Hierarchical Models
Xue Chen and Ronald G. Larson. Chemical Engineering, University of Michigan, 2300 Hayward St.3074 H.H. Dow Building, Ann Arbor, MI 48105
We compare the predictions of a “hierarchical model” for commercial long-chain-branched polymers, developed by Park and Larson with another publicly available model that incorporates similar physical mechanisms developed by Das et al. (2005). Both models include reptation, primitive path fluctuations of chain ends, and constraint release by “constraint release Rouse motion” or “dynamic dilution.” The model of Das et al. also accounts for branches on branches, i.e., hyper-branching. These two models are applied to single-site metallocene catalyzed high density polyethylene (mHDPE) to predict the effect of long-chain branching on the linear viscoelastic properties. We generate the distributions of molecular weight and of long chain branching for mHDPE using a Monte Carlo simulation of Costeux et al. (2002), where the simulation parameters are obtained from the average molecular weight and the degree of LCB. Besides the algorithm differences described by Das et al. (2005), we compare the parameters needed in the two models. The prediction results show the differences between these two models in accuracy and efficiency.