Process for producing an organosiloxane polymer and novel organosiloxane polymer compositions. The process according to the invention comprises hydrolyzing tetraalkoxysilane monomers in a hydrolysis step; and polymerizing said hydrolyzed monomers in a polymerization step by subjecting them to conditions conducive to polymerization to form an organosiloxane polymer. The hydrolysis step is conducted in a reaction medium comprising an organic compound with hydroxy groups. The invention allows for the synthesis of siloxane polymer compositions suitable for thin-film applications using a high content of tetra- and trifunctional silixane polymer precursors.