Realistic molecular modeling of polyolefins and polyolefin mixtures.

摘要

In this thesis, molecular simulation techniques are used to describe realistic polyolefin melts and polyolefin mixtures of industrial importance. In order to study the systems of interest; a complete united atom force field is developed to study hydrocarbon mixtures and validated with experimental data. Then, new Monte-Carlo techniques are developed to study mixtures involving polyolefins. Specifically, we have developed osmotic-ensemble coupled with parallel tempering and variable connectivity Monte-Carlo techniques that greatly enhance simulations of realistic polyolefin mixtures.; Binary and ternary mixtures of ethylene/1-hexene/polyolefin have been simulated to observe the effect of polyolefin chain architecture on monomer sorption. In particular, we consider amorphous linear low density ethylene-1-hexene copolymers under typical gas-phase reactor conditions. Furthermore, we have used our simulation results to parameterize and test common polymer equations of states. In addition, we have developed a modified equation of state model to account for elastic constraints present in semi-crystalline polyolefins. This is essential because polyolefins are semi-crystalline below their melting temperature and reactor conditions are commonly below the polyolefin melting temperature. We have been able to show that this equation of state mapping from simulations technique accurately predicts experimental solubilities.; Using our new simulation techniques, we have studied long-range correlations for pure poly(ethylene-co-propylene) melts using the detailed united atom force field. These studies were not possible prior to the development of these new techniques due to computational limitations on simulating long-range correlations for realistic polymer models. These techniques provide a framework to begin studying polymer blends which are of industrial importance and are not fully understood.