Utilization of cage germoxanes as templates for tuning pore characteristics of siloxane-based materials

Abstract

We demonstrate the utilization of cage germoxanes as templates for tuning the pore characteristics of siloxane-based materials. Molecular-scale composites of cage germoxanes and cage siloxanes are prepared by hydrosilylation reactions between SiH- and vinyl-modified cage siloxanes in the coexistence of vinyl-modified cage germoxanes. Subsequent acid treatments selectively removed the germoxane moiety, resulting in variation in the pore structures. These results contribute to developing a novel method for tuning the pore characteristics of siloxane-based nanoporous materials.

Direct cross-linking of silyl-functionalized cage siloxanes via nonhydrolytic siloxane bond formation for preparing nanoporous materials

“…The BET area ( S BET ) and the total pore volume ( V total ) were calculated to be 520 (±80) m 2 g −1 and 0.33 (±0.04) cm 3 g −1 for D4R-PR , and 489 (±23) m 2 g −1 and 0.35 (±0.02) cm 3 g −1 for D6R-PR . The hystereses of the isotherms were extended to low relative pressure ranges, which was also observed for porous materials composed of cage siloxanes cross-linked by Si–C linkages through hydrosilylation reactions, 5 h ,19,21 by Si–O–Si linkages through hydrolysis and polycondensation of terminal –Si(O i Pr) 2 CHCH 2 groups, 22 by the cross-linking of D4R silicate with dichlorodimethylsilane, 8 b and by the P–R reactions of D4R-SiMe 2 H with tetraethoxysilane; 11 however, it is rare that significant cavitation is not observed at around P / P 0 = 0.42. This N 2 adsorption–desorption behavior should have occurred due to the following reasons: (i) gas desorption was suppressed due to the presence of small pores, whose size was similar to N 2 , connecting larger pores; and/or (ii) insufficient time was allowed for the system to attain equilibrium.…”

“…In the cross-linking system of cage siloxanes by hydrosilylation reactions, 5 h ,19 D6R siloxane-based material showed higher BET area (701 m 2 g −1 ) and larger pore volume (0.51 cm 3 g −1 ) compared to the D4R siloxane-based material (573 m 2 g −1 and 0.40 cm 3 g −1 , respectively), whereas no significant difference was observed for D4R-PR and D6R-PR . Here, we discuss these differences based on the degree of the intramolecular condensation of the cage siloxanes.…”

“…The larger periodicity of D6R-PR is attributable to the larger size of the D6R siloxane than D4R siloxane, as we have shown in the previous reports. 5 h ,19 The SEM images of D4R-PR and D6R-PR (Fig. 2B) showed aggregates consisting of irregularly shaped particles with interparticle mesopores.…”

“…We recently prepared organically bridged cage siloxane-based porous materials via hydrosilylation reactions of D4R siloxanes or D6R siloxanes, and revealed that the D6R-based materials exhibited the higher BET area, larger pore volume, and higher degree of cross-linking. 5 h ,19 To achieve cross-linking of the D6R siloxanes by the P–R reactions, D6R-SiMe 2 OEt was synthesized by the reaction of D6R-SiMe 2 H with ethanol in the presence of a Pt catalyst. The 29 Si NMR spectrum of D6R-SiMe 2 OEt (Fig.…”