Methods of forming blocked-mercapto alkoxy-modified silsesquioxanes are provided. The blocked-mercapto alkoxy-modified silsesquioxane compounds contain an alkoxysilane group that participates in an alkoxysilane-silica reaction as a silica dispersing agent in rubber, with the release of zero to about 0.1% by weight of the rubber as alcohol (a volatile organic compound (VOC)), during compounding and further processing. The blocked-mercapto alkoxy-modified silsesquioxane compounds also contain a blocked mercapto group which, when de-blocked, allows the mercapto group to interact with the polymer(s) in a rubber composition. Further described are rubber compounds containing the blocked-mercapto alkoxy-modified silsesquioxanes.