Systematic Investigation of Silicon Substitution on Single Macromolecule Mechanics

Four unsaturated poly(carbooligosilane)s(P1-P4) were prepared via acyclicdiene metathesis polycondensationof new oligosilane diene monomers (1-4). These novel polymers with varying main-chain Si incorporationhave high trans internal olefin stereochemistry (ca.80%) and molecular weights (9500-21,700 g mol(-1)). Postpolymerization epoxidation converted all alkene moieties toepoxides and rendered the polymers (P5-P8) more electrophilic, which allowed for single-molecule force spectroscopystudies via a modified atomic force microscope setup with a silicontip and cantilever. The single-chain elasticity of the polycarbooligosilanesdecreased with increasing numbers of Si-Si bonds, a findingreproduced by quantum chemical calculations.