Synthesis of amino-containing oligophenylsilsesquioxanes

A series of aminophenylsilsesquioxanes were prepared from octaphenylsilsesquiox-ane (OPS), dodecaphenylsilsesquioxane (DPS) and two polyphenylsilsesquioxanes, one a low molecular weight LMW oligomer (PPS) and the other a high molecular weight (HMW) PPS (Mn of 1.3×103, PPS) and two polyhedral materials. LMS and HMW PPS were obtained by polycondensation of PhSi(OEt)3 to form oligomeric, incompletely-condensed frameworks. The oligomer was used as is for nitration to produce LMW polynitrophenylsilsesquioxane (PNPS). However, optimization of hydrolysis and condensation processes using KOH as catalyst, led to a route to HMW PPS (Mn of 2.5×104, Mw of 6.1×104), which was best prepared in EtOH. PS, LMW PPS (Mn of 1.3×103), and HMW PPS (Mn of 2.5×104), were nitrated using 90% fuming HNO3, and then reduced using triethylamine, formic acid, and 5% Pd/C in THF. The products were characterized using 1H, 13C, and 29Si NMR, GPC, FT-IR, and TGA. Amino groups (NH2) were introduced primarily in meta and ortho positions in a 70:25 ratio with the remainder being para. It was determined that little or no OPS or DPS cage cleavage occurred coincident with nitration or reduction if the latter process was run at 40 °C, whereas the MW of HMW PPS decreased to 1.6×103 after nitration and reduction. The Mn suggests that for both LMW and HMW PPS, the same PAPS product forms, which consists of monomer, dimer, and trimer species.