Polymers based on exo-silicon-substituted norbornenes for membrane gas separation

Silicon-substituted polynorbornenes are an unusual class of polymeric membrane materials, combining the properties of both glassy and rubbery polymers. They exhibit an attractive performance for CO2/N-2 separation and for separation of gaseous hydrocarbons. However, addition polynorbornenes with Si-groups (for examples, having Si-O-C, or Si-O-Si-spacers) often suffer from poor film-forming properties due to low molecular weights of the polymers. Herein, by using a new simple and efficient approach to the synthesis of such polymers, we prepared two sets of novel high-molecular-weight polymers based on pure exo-isomers of Si-containing norbornenes and studied their gas transport properties in detail. The desired metathesis and addition polynorbornenes with (C2H5)(3)Si-, (CH3)(3)SiO(CH3)(2)Si- and ((CH3)(3)SiO)(2)(CH3)Si-side groups were readily obtained in good or high yields via selective hydrosilylation of norbornadiene-2,5 by commercial silanes followed by polymerization over Ru- or Pd-catalyst. Diffusion (D) and permeability (P) coefficients of these polynorbornenes were determined for permanent gases (He, H-2, O-2, N-2, CO2) and C-1-C-4 alkanes. The influence of exo-/endo-orientation of substituents on gas transport properties and the relationship between nature of side-groups and membrane properties were evaluated. The data on BET, SEM, WAXD, and fractional free volumes of the polymers are also reported and discussed.

Automated summary

Silicon-substituted polynorbornenes are polymeric membrane materials with combined properties of glassy and rubbery polymers, showing attractive performance in CO2/N-2 separation and separation of gaseous hydrocarbons. A new synthesis approach allowed preparation of high-molecular-weight polymers based on pure exo-isomers of Si-containing norbornenes, and their gas transport properties were studied. The influence of substituent orientation and nature on membrane properties was evaluated, with additional data on BET, SEM, WAXD, and fractional free volumes reported.