Using Probability Models to Design the Microstructure of Linear Olefin Block Copolymers

Olefin block copolymers (OBCs)─a new type of linear thermoplastic ethylene/1-olefin elastomer─are made via chain-shuttling polymerization using two catalysts with different reactivity ratios and a chain-shuttling agent. The microstructure of the OBCs has been analyzed using standard characterization techniques, but these methods cannot reveal the details of their molecular architectures, such as the distribution of the number of blocks in the polymer population; these finer microstructural features fall in the realm of mathematical models. In this article, we developed probability model equations to describe the microstructure of the OBCs and validated our solutions with Monte Carlo simulations. These new equations describe the distributions of molecular weight, chemical composition, number and length of blocks in OBCs made in a continuous stirred-tank reactor operated at steady-state conditions. We also developed a new method to predict the multimodality of the chemical composition distribution of OBCs (which can be experimentally measured) to assist in the design of new OBC materials.