Effect of molecular weight on the mechanical properties of MSSQ films

Methylsilsesquioxane (MSSQ) of varied molecular weight were synthesized by a sol–gel method involving hydrolysis and condensation reaction in the presence of (CH3)2NH2 as catalyst at room temperature. The relationship between physical properties and molecular weight was investigated and discussed using nanoindentor and refractive index measurements for the MSSQ films coated on silicon substrate. The results demonstrate that as the molecular weight is increased, hardness, elastic modulus, and refractive index are decreased due to a low packing density. In addition, dynamic mechanical analysis shows a rapid and higher stiffness for the low molecular weight samples, indicating a high intermolecular interaction due to a high amount of reactive hydroxyl groups and a low entanglement between molecule chains.