Polyhedral oligomeric silsesquioxane (POSS) containing sulfonic acid groups as a metal-free catalyst to prepare polycaprolactone

Organic-inorganic hybrid nano-building block of polyhedral oligomeric silsesquioxane (POSS) containing hyperbranched sulfonic acid groups was easily prepared within a day through oxidation reaction at room temperature. The desired product was fully characterized by ¹H, ¹³C{¹H} NMR, ²⁹Si CP/MAS NMR, FT-IR spectroscopy, and TGA-DSC analysis, confirming the complete formation of sulphonic acids while retaining the cubic structure of silsesquioxanes cage. Furthermore, the proton exchange capacities of POSS catalyst were determined to be 5.39 meq of H⁺/g, much greater than any previous silicon-based materials, leading to the catalytic preparation of polycaprolactone with well-controlled polymerization under the metal-free system and without the addition of any co-catalysts and solvents.