Synthesis, in-situ membrane preparation, and good gas permselectivity of insoluble poly(substituted acetylene)s loosely cross-linked with short and soft siloxane and silanol linkages

Abstract

Insoluble but membrane-formable poly(substituted acetylene)s loosely cross-linked by short and soft Si–O–Si and SiOH---(OH)Si linkages have been synthesized from the corresponding monomers having one or two SiOH groups. These monomers have been polymerized in homogeneous systems to produce homogeneous polymer solutions in toluene. The resulting solutions were cast on polytetrafuluoroethylene sheets followed by evaporation of the solvent to give tough and flexible membranes which were completely insoluble. The membranes showed good oxygen and carbon oxide permselectivity and their plots in PO2 vs PO2/PN2 graph exceeded the 1991 Robeson's upper bound and very close to the 2008 Robeson's upper bound. The excellent selectivity are caused by enhancement of diffusion selectivity by the soft network structure which can create small pores (i.e., ultramicro pores) based on the short linkages. No drop in permeability may be due to the soft Si–O–Si and SiOH---(OH)Si linkages. In addition no change in PO2 and PO2/PN2 by aging was observed.