Synthesis of Siloxyalumoxanes and Alumosiloxanes Based on Organosilicon Diols

We have drawn a few interesting conclusions while studying reaction products of Ph2Si(OH)2 with Al(iBu)3 and tetraisobutylalumoxane. In the first place, this is the production (at Ph2Si(OH)2 and Al(iBu)3 equimolar ratio) of oligomer siloxyalumoxane structure with alternating four- and six-member rings, as well as isobutyl and phenyl groups migration between aluminum and silicon due to the formation of intramolecular four-member cyclic complex [Ph2(OH)SiO]Al(iBu)2 → [(iBu)Ph(OH)SiO]Al(iBu)Ph. Ph2Si(OH)2 interaction with Al(iBu)3 not only starts from intramolecular complex production, but the chain is terminated for the same reason, which in the case of Ph2Si(OH)2 reaction with tetraisobutylalumoxane results in failure of obtaining high-polymer siloxyalumoxane compounds. When Al(iBu)3 interacts with α- and γ-diols, no oligomer compounds are produced. Al(iBu)3 reaction with α, γ-diols results in monomer compounds that are likely to have cyclic structure. Notably at Al(iBu)3 interaction with α-diol only double excess of Al(iBu)3 allows full replacement of  hydrogen in α-diol hydroxyl groups by aluminum alkyl residue with 1,3-bis(diisobutylalumoxymethyl)-1,1,3,3-tetramethyldisiloxane production. At equimolar ratio of initial reagents the second isobutyl radical at Al does not interact with the second hydroxyl group of α-diol, apparently due to the steric hindrance and 1-(diisobutylalumoxymethyl)-3-(hydroxymethyl)-1,1,3,3-tetramethyl-disiloxane is produced. Al(iBu)3 reactions with γ-diol also result in monomer compounds but the presence of a chain consisting of three СН2-groups between Si and hydroxyl group facilitates interaction between the second hydroxyl group of γ-diol and the second isobutyl radical Al(iBu)3. Tetraisobutylalumoxane reaction with α- and γ-diols results in oligomer compounds.

Synthesis of Siloxyalumoxanes and Alumosiloxanes Based on Organosilicon Diols

We have drawn a few interesting conclusions while studying reaction products of Ph2Si(OH)2 with Al(iBu)3 and tetraisobutyl alumoxane. In the first place, this is the production (at Ph2Si(OH)2 and Al(iBu)3 equimolar ratio) of oligomer alumoxanesiloxane structure with alternating four- and six-member rings, as well as isobutyl and phenyl groups migration between aluminum and silicon due to formation of intramolecular four-member cyclic alumosiloxane complex [Ph2(OH)SiO]Al(iBu)2 → [(iBu)Ph(OH)SiO]Al(iBu)Ph. Ph2Si(OH)2 interaction with Al(iBu)3 not only starts from intramolecular alumosiloxane complex production, but the chain is terminated for the same reason, which in the case of Ph2Si(OH)2 reaction with tetraisobutylalumoxane results in failure of obtaining high-polymer alumosiloxane compounds. When Al(iBu)3 interacts with α- and γ-diols, no oligomer compounds are produced. Al(iBu)3 reaction with α, γ-diols results in monomer compounds that are likely to have cyclic structure. Notably at Al(iBu)3 interaction with α-diol only double excess of Al(iBu)3 allows full replacement of hydrogen in α-diol hydroxyl groups by aluminum alkyl residue with 1,3-bis(diisobutylalumoxymethyl)-1,1,3,3-tetramethyldisiloxane production. At equimolar ratio of initial reagents the second isobutyl radical at Al does not interact with the second hydroxyl group of α-diol, apparently due to steric hindrance and 1-(diisobutylalumoxymethyl)-3-(hydroxymethyl)-1,1,3,3-tetramethyl-disiloxane is produced. Al(iBu)3 reactions with γ-diol also result in monomer compounds but the presence of a chain consisting of three СН2-groups between Si and hydroxyl group facilitates interaction between the second hydroxyl group of γ-diol and the second isobutyl radical Al(iBu)3. Tetraisobutylalumoxane reactions with α- and γ-diols results in oligomer compounds.

Effects of Surfactants on the Preparation of MnO2 and its Capacitive Performance

Amorphous hydrated manganese dioxide (MnO2) was prepared as an electrode material for supercapacitors by liquid co-precipitation in the presence of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and sodium dodecylbenzenesulfonate (SDBS) respectively. The obtained samples were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and electrochemical methods. Physical characterizations confirmed that the addition of surfactants played an important role in the preparation of MnO2. The specific surface areas of MnO2 with the addition of PEG, SDBS and PVP were 169.92 m2/g, 137.40 m2/g and 196.64 m2/g, respectively, and the corresponding capacitances were 207.9 F/g, 187.5 F/g and 238.7 F/g. Compared with the sample without surfactants, the specific surface area and capacitance of the sample with the addition of PVP were improved by 92.2% and 53.1%, respectively. Moreover, the electrode showed good cycle stability at the current density of 120 mA/g, and 91.1% of its specific capacitance still remained after 500 cycles. It was concluded that this performance improvement was attributed to the electrostatic stabilization of the multivariate alkyl residue and cyano group (—NCO) as anchoring group, as well as the steric hindrance effect from lateral polarity groups of pentabasic ring in PVP structure.