环硅氧烷负离子乳液聚合中活性中心浓度的变化规律

以八甲基环四硅氧烷(D4)为单体,十二烷基二甲基苄基氢氧化铵(BDAH)为乳化剂兼催化剂,进行环硅氧烷负离子乳液聚合,采用凝胶色谱(GPC)测定聚合产物的转化率及分子量.在此基础上,分析基元反应,提出活性中心生成机理,并应用环硅氧烷开环聚合普适动力学模型计算乳液聚合平衡之前的活性中心浓度变化规律.结果发现,聚合温度较低时,活性中心浓度随时间逐渐增加,最终恒定;聚合温度较高时,活性中心浓度随时间仅单调递增.结果与机理相符.

RULE OF ACTIVE CENTER CONCENTRATION CHANGE FOR ANIONIC POLYMERIZATION OF OCTAMETHYLCYCLOTETRASILOXANE IN AQUEOUS EMULSION

The anionic polymerization of cyclosiloxane in aqueous emulsion was performed with octamethylcyclotetrasiloxane(D_4) as monomer and benzyldimethyldodecylammonium hydroxide(BDAH) as catalyst and emulsifying agent.The innovation of this study includes:(1) Based on the analysis of elementary reaction,the forming mechanism of concentration of active center was proposed.(2) The changing rule of the concentration of active centers with reaction was quantitatively obtained according to the generalized kinetic model of ring-opening polymerization of cyclosiloxanes.Emulsion polymerization recipe used in this study consists of octamethylcyclotetrasiloxane,benzyldimethyldodecylammonium hydroxide and water.All materials were heated up to reaction temperature(w_ monomer ∶ w_ BDAH ∶w_ water =33∶1∶66).The mixture was then homogenized for 1 min to obtain emulsion.The emulsion was transferred to a glass reactor,and nitrogen was bubbled through the solution.The reaction temperature was adjusted with a constant temperature water bath.The polymerization was carried out under mechanical stirring(200 r/min).A certain amout of reactant was taken out during the course of polymerization and neutralized with glacial acetic acid to a pH near 8 in order to stop the reaction,and then used for measuring the needed data.The bulk polymerization of cyclosiloxane was performed with octamethylcyclotetrasiloxane(D_4) as monomer and benzyldimethyldodecylammonium hydroxide as catalyst.And the sample was periodically taken out for conversion measurements.The anionic polymerization of cyclosiloxane in aqueous emulsion was performed.The conversion and the molecular weight of synthesized polymer were examined by gel permeation chromatography(GPC).The forming mechanism of concentration of active center was proposed,and the changing rule of the concentration of active centers with reaction was quantitatively obtained.The results show that the concentration of active center gradually increases to a steady state when the temperature is relatively low,and that the concentration of active center only increases monotonously with time when the temperature is relatively high.