(R)-(+)-Binol-functionalized chiral periodic mesoporous organosilicas (PMOs) with different framework compositions were successfully synthesized by cocondensation of (R)-2,2'-di(methoxymethyl)oxy-6,6'-di(1-propyltrimethoxysilyl)-1,1'-binaphthyl (BSBinol) with 1,2-bis(trimethoxysilyl)ethane (BTME) and tetramethoxysilane (TMOS) using triblock copolymer P123 as a template in acidic solution. The mixture of BTME and BSBinol can result in a highly ordered mesostructure in an acidic medium but the mesoporous materials synthesized using a mixture of TMOS and BSBinol can only be obtained in a weak acidic buffer solution. All the materials are efficient catalysts (coordinated with Ti) for asymmetric addition of diethylzinc to aldehydes. The chiral PMO with ethane and (R)-(+)-Binol in the framework exhibits an enantioselectivity as high as 90% with a turnover frequency (TOF) of 104 h(-1), which is even higher than the homogeneous (R)-(+)-Binol catalyst (83% ee with TOF of 96 h(-1)) using toluene as solvent under similar conditions. This work demonstrates the positive effect of the rigid pore wall in increasing the enantioselectivity of the chiral PMOs.
The interactions between sodium polyacrylate (PANa) and mixed micelles of dodecyltrimethylammonium bromide (DTAB) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) were studied by isothermal titration calorimetry (ITC), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the interaction mechanism varies with the titration order. For titration of PANa/AOT by DTAB, DTAB monomers first participate in the formation of AOT/DTAB mixed micelles, then bind to polymer individually, and subsequently result in the polymerinduced micellization characterized by two endothermic peaks. Only one endothermic peak was observed for titration of PANa by AOT/DTAB mixed micelle, corresponding to binding of the mixed micelles to the polymer. Exothermic peaks were observed for both types of titration characterizing the cross-link of the polymer chains. These interaction mechanisms were also interpreted by a thermodynamic model and confirmed by the measurements of SEM and TEM.
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