【作者】 舒适；

【导师】 吉静；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2010， 硕士

【摘要】 本文采用未经改性的二氧化硅水溶胶,在硅溶胶与聚合物静电相斥的情况下,通过简单的单体滴加聚合工艺制备了硅溶胶／聚丙烯酸酯复合乳液。系统的研究了具有不同物理性能的丙烯酸酯单体的比例对复合乳胶粒结构及复合乳液稳定性的影响,发现随着混合单体中甲基丙烯酸甲酯与丙烯酸丁酯的质量比例(MMA:BA)降低,无机-有机两相结合程度增大,当单体比例降到1：2时,可以形成硅溶胶粒子包裹丙烯酸酯聚合物的草莓型核壳结构复合乳胶粒。增大Si02的用量可以明显降低复合乳胶粒粒径,降低无皂乳液聚合的聚合反应速率,并且提高乳液稳定性。实验发现单体滴加工艺聚合的规律与传统的Pickering乳液聚合规律相反,因此深入讨论了无机-有机两相的结合机理。在研究了聚合过程粒径分布的基础上提出了无机-有机两相在静电相斥的情况下形成复合乳胶粒的机理,即在聚合反应初期,丙烯酸酯单体按照均相成核机理形成了初始聚合物微粒,由于自身的不稳定,初始微粒在高界面能的推动下与硅溶胶粒子发生吸附,继续聚合增长形成复合乳胶粒。通过对复合乳液涂膜的结构表征发现涂膜表层存在多孔结构,研究了乳胶粒粒径对涂膜孔结构的影响并讨论了成孔机理。对比了有皂乳液涂与无皂乳液涂膜的吸水率,发现采用无皂乳液聚合技术合成的乳液涂膜吸水率明显降低。随着Si02含量的提高,涂膜硬度提高,但抗冲击性、柔韧性并没有明显的降低,说明本试验工艺可以将纳米硅溶胶粒子均匀的分散在聚合物涂层之中。更多还原

【Abstract】 Silica sol/Polyacrylate composite latex was prepared through simple drop wise polymerization process under the condition of electrostatic repulsion between negative surface charge of silica and negatively charged polymer particle (derived from the anionic initiator KPS) without any surface modification. The influence of acrylate monomer ratio (MMA:BA) on structure of composite emulsion particles and stability of composite latex has been studied. The results indicated that the encapsulation of silica sol by polyacrylate increased with the monomer ratio (MMA:BA) decreased. The composite particle with core-shell structure can be synthesized when monomer ratio (MMA:BA) is 1:2, which silica particles served as shell and polyacrylate served as core. With the increase of amount of SiO2, polymerization rate and composite particle size had decrease trend. Also, the stability of composite emulsion was significantly improved due to the addition of silica sol.Based on experiment, it was found that the experimental law of drop wise processes was different from that of Pickering polymerization processes. Through the research on particle size distribution of polymerization process, a composite mechanism was proposed, that precursor particles of polyacrylate, which are formed in the early stage of soap-free emulsion polymerization, are very unstable, so they tend to be absorbed on colloidal silica particles to lower interfacial energy, thus forming composite particles.The structure of composite film was characterized by Scanning electron microscope (SEM). The images indicated that porous structure existed. Based on the discussion on the influence of composite particle size on porous structure, the mechanism of hollow formation was proposed. Water absorption of coating film of emulsion polymerization with emulsifier and emulsifier-free emulsion polymerization was studied and the result shows that water resistant property of coating film had obviously progress when there wasn’t any low-molecular-weight emulsifier involved. With the increase of silica amount, the hardness of coating film enhanced, but shock resistant and flexibility maintain a high-level, which is likely duo to the well-dispersed of silica particles in polymer matrix.更多还原