Characterization of pore structure of copolymer-templated periodic mesoporous organosilicas

摘要

The diameters of entrances to the large cage-like mesopores (7-10 nm) of triblock-copolymer-templated periodic mesoporous organosilicas (PMOs) with ethylene (-CH_2-CH_2-) bridging groups were determined on the basis of nitrogen and argon adsorption isotherms for unmodified and organosilane-modified materials. The polymers used for the PMO synthesis were Pluronic P123 poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (EO_(20)PO_(70)EO_(20)) and B50-6600 poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) (EO_(39)BO_(47)EO_(39)). Hysteresis loops of argon adsorption isotherms for unmodified PMOs closed at the lower limit of adsorption-desorption hysteresis, thus indicating the pore entrance diameter below 4 ran. The pores of the PMO templated with EO_(39)BO_(47)EO_(39) triblock copolymer were largely blocked after the surface modification with octyldimethylsilyl groups, thus suggesting the pore entrance size below ～2.9 μm. The PMO templated by EO_(20)PO_(70)EO_(20) copolymer still exhibited accessible porosity after the modification with the latter groups, which in combination with the results of argon adsorption points to the pore entrance diameter between 2.9 and 4.0 nm.