【作者】 赵彬；

【导师】 李效玉；

【作者基本信息】 北京化工大学 ， 材料学， 2001， 硕士

【摘要】 本论文通过对分散聚合法制备微米级单分散聚甲基丙烯酸甲酯微球的研究，选择了合理的分散聚合聚合体系，考察不同聚合参数诸如：聚合时间，聚合温度，引发剂浓度，稳定剂浓度，单体浓度，分散介质，以及搅拌转速等因素对聚合体系的稳定性、微球粒径及其分布的影响和变化规律。目的在于能够根据研究的结果对微米级单分散聚甲基丙烯酸甲酯的合成提出合理化建议。通过研究，发现粒径随着聚合温度、聚合温度、引发剂浓度、单体用量的增加而增加；同时，它也随着稳定剂(PVP)的浓度的增大而减小。比较了不同聚合介质体系对聚合反应转化率以及聚合产物分子量的影响。 提出了以下的成核机理假设：分散聚合过程可分为以下三个阶段，起初，单体、分散剂和引发剂全部溶解于分散介质中，形成均相体系。(1)均相聚合期，温度上升到聚合温度后，引发剂分解产生自由基，并引发聚合，生成了溶于介质的齐聚物自由基。(2)成核期，当齐聚物链长超过临界链长后从介质中析出，多个齐聚物链团聚成聚合物核，核与核之间会聚并直至形成立构稳定的粒子，反应中生成的PMMA-PVP接枝共聚物以及未接枝的分散剂PVP共同对粒子起空间稳定作用。(3)粒子增长期，该阶段粒子数保持恒定，粒子的增长一方面靠吸收单体、引发剂和自由基在粒子相中聚合，另一方面靠吸附由连续相生成的齐聚物、接枝共聚物而增长，直至单体消耗完全。在分散聚合过程中，聚合反应由在连续相中的聚合转变到粒子相中的聚合。 通过对聚合物粒子的红外谱图和XPS谱图研究，对比，认为在分散聚合中，分散稳定剂存在物理吸附和化学吸附(PVP-g-PMMA的存在)两种形式，物理吸附可以在反应结束后进行长时间的溶剂清洗除去，该过程同时可以使粒子的表面光洁、干净；稳定剂的化学吸附在粒子经过长时间的清洗后仍然存在，不宜解析。通过对聚合体系进行10倍放大实验，在小体系中的规律仍然适用。 通过对聚合参数对粒径及对粒径分布影响的研究，得出了聚合2.8μm、5μm、7μm、8μm单分散PMMA粒子的标准配方。更多还原

【Abstract】 This paper was aimed at preparing the micro-size mono-disperse PMMA Particles by dispersion polymerization. Firstly, some pretty polymerization systems was chosen, and then, The influences of Polymerization parameters on particle size and particle size distribution were investigated to find out the reasonable polymerization way of PMMA mono-disperse particles.A series of experiments were conducted to get the effects of Polymerization parameters on particle size and mono-dispersion. The particle size was found to increase with increasing polymerization temperature, concentration of the initiator and monomer and prolonged reaction time. It also increased with decreasing concentration of the polymeric stabilizer-poly(vinyl pyrrolidone)(PVP). The influences of various polymerization parameters were explained by the proposed particle formation mechanism. Meanwhile we have found that different media system has a different influence on polymerization conversion rate and polymer particle size and polymer molecular weight distribution.From the results of the IR and XPS, it is concluded that PMMA-PVP graft-copolymer has been formed during the dispersion polymerization. A mechanism for particle formation and growth in dispersion polymerization is presented. The particle formation stage in dispersion polymerization consists of two steps: nuclei generation and aggregation. The oligomer chains grow in the continuous phase and precipitate to form the nuclei by either a self or aggregative mechanism. The nuclei are unstable and quickly aggregate with each other; concurrently, they adsorb the stabilizer molecules, and finally become mature(stable) particles. As long as enough mature particles are formed to capture all of the oligo-radicals and nuclei generated in the continuous phase, no more particles form and the particle formation stage will finish.The standard recipes for preparing 2.8 μm 5μm 7 μm 8 μm PMMA particles have been gotten.更多还原