Molecular properties of silicon-substituted polymers for gas-separation membranes

Abstract

As shown by hydrodynamic, electrooptical, and computer-simulation studies, film-forming addition silicon-substituted polynorbornene and silicon-substituted poly(1-trimethylsilyl-1-propyne), which have close gas-permeability parameters, possess similar conformational properties of chains. The molecules of the these polymers are characterized by a heterogeneous microstructure due to energetically favorable spiralization of regular sequences of monomer units with the interrelated linear sizes of helical fragments and the equilibrium rigidity of chains. Despite different chemical structures, both polymers have the statistical Kuhn segment A = (44–47) × 10−10 m and a much smaller ((10–15) × 10−10 m) kinetic fragment freely orienting under application of an electric field. The hydrodynamic and electrooptical properties of silicon-substituted polynorbornenes synthesized from the same monomer (5-trimethylsilyl-2-norbornene) via addition and metathesis mechanisms are compared. It is found that there is a significant difference in the conformational characteristics of addition and metathesis analogs. This finding gives insight into the earlier observed difference in the properties of films based on these polymers.