(563h) Design of Polymer Scaffolds for Supported Catalysts Using Molecular Simulations

Polynorbornene produced by Ring Opening Metathesis Polymerization (ROMP) has shown promise as a scaffold to support tethered homogeneous catalytic sites. Such catalyst supports provide the advantage of efficient homogeneous catalytic sites while making it easy to separate such catalysts from the reaction mixture. Molecular simulation has been applied to various isomers of this polymer to determine how the backbone structure affects the conformation of this polymer and consequently the degree to which the tethered catalyst sites are exposed to potential reactions. Previously, this ROMP polymer was assumed to adopt an expanded conformation similar to the vinyl-polymerization version of the same polymer. This assumption was based on the theory that polymers with alternating non-rotatable backbone bonds and bulky side groups formed elongated helical structures. This theory was derived from simulations of vinyl polymerized polynorbonene and substituted polyacetylenes. Simulations of ROMP polynobornene failed to exhibit this elongated helical structures because of the flexibility of the backbone cyclopentyl rings in this polymers. Simulations of ROMP poly(norbornene) in which the flexibility of the backbone cyclopentyl ring was reduced with a fused imide group did show signs of helical conformations, but only when a sufficiently large side chain was attached. Bulk simulations of this modified ROMP polynorbornene predicted the formation of intermediate bulk structure, which is often associated with helical conformations. The Wide-Angle X-Ray Diffraction (WAXD) pattern predicted from these simulations reproduced the experimentally measured one for a synthesized ROMP polynorbornene. These results provide useful heuristics for the design of optimal industrial catalyst platforms.