Effect of molecular architecture of copolymer template on the morphology of mesoporous methylsilsesquioxane

Hybrid and mesoporous materials derived from methylsilsesquixoane (MSSQ) have been prepared by the evaporation-induced self-assembly (EISA) process using polystyrene-poly(2-vinyl pyridine) (PS-P2VP) block copolymers with linear (LA) and hetero-arm star (HA) molecular architectures as the templates. TEM and SAXS were used to characterize the morphology of the hybrid materials, LA/MSSQ (LB) and HA/MSSQ (HB), and their corresponding porous materials, LP and HP, obtained by pyrolysis. TEM images suggested that the morphology transformed from random spheres in LB hybrid to cylinders in the corresponding LP porous material. However, the sphere morphology was effectively preserved after the pyrolysis of HB. We proposed that MSSQ initially solubilized into the P2VP coronas of the copolymer micelles tended to be excluded from the coronal regions during the extensive curing of MSSQ on heating to the calcination temperature. This dewetting process competed against the crosslinking of MSSQ that could freeze the structure if the network formed readily prior to the abundant exclusion of MSSQ. In the hetero-arm system where several pairs of copolymer chains jointed to a common core, the exclusion of the MSSQ out of the corona regions became more restricted. Consequently, the initial micelle morphology was effectively fixed by the crosslinking reaction. The present study demonstrated that the molecular architecture of the structure-directing agent played an important role in the morphological formation of the MSSQ-based mesoporous materials.