Synthesis and characterization of ethoxy-terminated ladder-like polymethylsilsesquioxane oligomer

A fully ethoxy-terminated ladder-like polymethylsilsesquioxane oligomer (EtO-Me-T) has been synthesized and characterized for the first time using an effective transient catalyst (tetramethylammonium hydroxide, TMAH) via the dehydration alcoholysis reaction of hydroxy-terminated ladder-like polymethylsilsesquioxane (HO-Me-T) prepared by a modified stepwise coupling polymerization approach. Compared with the common acidic or basic catalysts, use of the transient catalyst TMAH can not only make the HO-Me-T molecules fully ethoxy-terminated but also enables the catalyst to be readily and thoroughly removed after completion of the alcoholysis reaction. It is noteworthy that the common acidic or basic catalysts widely used in the dehydration alcoholysis reaction are clearly unsuitable for the preparation of EtO-Me-T oligomer because the latter would be hydrolyzed unavoidably back to the parent HO-Me-T during the washing process. In addition, preliminary exploration indicates that, when compared with the tetraethyl orthosilicate (Si(OEt)(sub 4)) generally used as a crosslinking agent for the room-temperature vulcanization of silicone rubber (RTV-SR), the oligomer EtO-Me-T is a promising replacement which can greatly improve the mechanical properties of RTV-SR.