Theoretical study on the oligomerization mechanisms of bihydroxysilicone

Bihydroxysilicone SiO(OH)(2) is the simplest silicone monomer and can be condensed to various silica materials with diverse properties. The oligomerization mechanisms of SiO(OH)(2) were investigated systematically at B3LYP/6-311++G(d,p) level. All species including the monomers, dimers, trimers, and tetramers were fully optimized with CPCM solvation model to simulate the solvent environments in methanol. The Si=O bonds of silicones can couple via barrierless processes to form varied ringed structures, and bigger rings can be formed by dehydration and recyclization. The most stable trimer is the one with a hexagonal Si-O ring, and the energetically most favorable tetramer is the one with an octagonal Si-O ring and two hydroxyl groups on each Si atom.