Reduction of Volatile Organic Compound Emission for Silica Compounding Part II: Synthesis and Characterization of Alkoxy-modified Silsesquioxane

The preparation and characterization of a class of alkoxy-modified silsesquioxane (AMS) compounds containing less than five weight percent of latent alcohol is described. The AMS derived from octyl triethoxysilane behaves as a shielding agent in silica-filled rubbers while significantly reducing the volatile organic compounds (VOC) that are released during the manufacture of rubber articles. Analysis of AMS by HPLC and 29Si NMR shows that it has a plethora of structures present that can best be described as a highly condensed opened oligomeric, branched arrangement of silsesquioxanes units. This structure is moisture stable, hydrocarbon soluble and reactive with silica at compounding temperatures. The AMS has been prepared by acid or base catalyzed hydrolysis and condensation in alcohol solution to form a product that often separates from the lower density reaction mixture. The kinetics of the AMS formation was examined and showed two separate rate processes occurring. The co-AMS prepared from octyl triethoxysilane and 3-mercaptopropyl trimethoxysilane yielded an effective shielding agent and coupling agent when used in silica-filled vulcanizates.