The anionic polymerization of octamethylcyclotetrasiloxane (D4) catalyzed by tetramethyl ammonium hydroxide (TMAH) in the presence of water under the conditions of high temperature and oxygen-off was investigated. The conversion of polymerization and the molecular mass of the polymer were examined by Gel Permeation Chromatography (GPC). Based on mechanism analysis

the calculation model of terminated hydroxy concentration (cOH) was obtained. And the result of the increase of cOH with conversion was observed by using the model. Then the influence of reaction conditions on the change of the value of cOH with conversion was investigated.The increase of the hydroxy terminated rate was greater than that of the polymerization rate with increasing temperature.The increase of the polymerization rate was greater than that of the hydroxy terminated rate with the concentration of catalyst increasing. With the concentration of water increasing

the polymerization rate decreased and the hydroxy terminated rate increased.