Effects of aluminum trichloride and magnesium chloride on the synthesis of ladder polyphenylsilsesquioxane

Ladder polyphenylsilsesquioxane (Ph-LPSQ) has been synthesized at 80 °C through the hydrolysis and condensation of phenyltrichlorosilane (PhSiCl ₃), with aluminum chloride (AlCl ₃) or magnesium chloride (MgCl ₂) as an assistant reactant. The Ph-LPSQ obtained has been characterized and analyzed by SEM, FTIR, TGA, ²⁹Si-NMR, and MALDI-TOF MS, and the effects of AlCl ₃ and MgCl ₂ on the structure regularity of Ph-LPSQ and the condensation polymerization have also been studied. The results showed that Ph-LPSQ could be obtained in the AlCl ₃ and MgCl ₂ systems, respectively, but the experimental phenomena and results showed significant differences between the two systems. SEM observation revealed spherical Ph-LPSQ particles from the PhSiCl ₃/AlCl ₃ system, but irregular and agglomerated Ph-LPSQ particles from the PhSiCl ₃/1.5(MgCl ₂) system. TGA, ²⁹Si/NMR, and MALDI-TOF MS indicated that the ladder structure of Ph-LPSQ from the PhSiCl ₃/1.5(MgCl ₂) system was more regular. In the PhSiCl ₃/AlCl ₃ system, Al could be incorporated into the ladder chain structure through competing reactions between Si-O-Al and Si-O-Si, which slightly decreased the regularity of the ladder chain structure of Ph- -LPSQ. Mechanistic analysis suggests that the presence of AlCl ₃ or MgCl ₂ in the hydrolysis and condensation system favors the intermolecular condensation of intermediate products of polyhydroxyl silanol to form a regular ladder structure.