Highly Porous Polyhedral Silsesquioxane Polymers. Synthesis and Characterization

Polyhedral octahydridosilsesquioxanes, [HSiO1.5]8 (1) and [(HSiMe2O)SiO1.5]8 (3) were hydrosilylatively copolymerized with stoichiometric amounts of the octavinylsilsesquioxanes, [vinylSiO1.5]8 (2) and [(vinylSiMe2O)SiO1.5]8 (4) in toluene using platinum divinyltetramethyldisiloxane, “Pt(dvs)”, as catalyst. The degree of condensation of the resultant four copolymers ranges from 43% to 81% depending on intercube chain lengths, as determined by solid state 13C and 29Si MAS NMR analyses, using cross-polarization (CP) techniques. The presence of residual functional groups was confirmed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Polymer porosities were measured using nitrogen sorption, positron annihilation lifetime spectroscopy (PALS), and small angle X-ray scattering (SAXS) methods. The combination of these three techniques allows a relatively complete description of the pore sizes and pore size distributions in these materials. The pores in the cube interiors are ∼0.3 nm in diameter, while those between the cubes range from 1 to 50 nm in diameter (for polymer 3 + 4). Nitrogen sorption analyses give specific surface areas (SSAs) of 380 to 530 m2/g with “observable” pore volumes of 0.19−0.25 mL/g.