【作者】 蔡娜；

【导师】 许湧深；

【作者基本信息】 天津大学 ， 材料学， 2007， 硕士

【摘要】 本文采用苯乙烯和丙烯酸丁酯共聚体系,讨论了不同浓度的乳化剂及助稳定剂;不同乳化剂与助稳定剂的摩尔比;超声后加入不同浓度的乳化剂;不同种类的助稳定剂以及不同引发体系对乳胶粒粒径的影响。研究证明,在微滴乳液聚合体系中乳化剂的主要作用是防止单体珠滴的聚并,而助稳定剂的主要作用是抑制Ostwald Ripening效应。通过测量预乳化阶段单体珠滴的尺寸以及聚合后乳胶粒的尺寸,定量地计算出微滴乳液体系中单体珠滴成核的几率,阐述了微滴乳液的成核机理。继而又通过与常规乳液聚合动力学的对比以及引入亚硝酸钠水相淬灭剂的方式进一步证明了微滴乳液在水溶性引发剂条件下,均相成核和单体珠滴成核同时存在,采用油溶性引发体系,均相成核受到抑制,单体珠滴成核几乎是体系中唯一的成核方式。引入甲基丙烯酸功能单体,在水溶性引发体系中,研究了其成核机理。结果发现,引入甲基丙烯酸单体后,单体珠滴成核的几率增加了。又对比了引入甲基丙烯酸单体前后体系的聚合动力学,研究发现,甲基丙烯酸的引入使体系的聚合速率降低了。主要是由于与先前没有引入甲基丙烯酸的体系相比,齐聚物自由基从水相中析出的临界聚合度相对较高。体系的均相成核的几率降低了,最终导致反应体系的聚合速率下降。在油溶性引发体系中,与采用水溶性引发体系相比,使用油溶性引发体系使单体珠滴成核的几率大大提高。还研究提高体系最终转化率的方法,研究发现,在聚合后期增加水溶性引发剂是最有效的方法。引入丙烯酸功能单体,由于丙烯酸单体的亲水性比甲基丙烯酸单体大,当[AA]>5%时,体系不稳定,聚合后有大量的凝胶产生。[AA]<5%时,体系与甲基丙烯酸体系相比,其成核机理和聚合动力学都与甲基丙烯酸体系类似。更多还原

【Abstract】 Miniemulsion polymerizations of styrene and butyl acrylate in the presence of sodium dodecyl sulfate (SDS) as the surfactant and stearyl methacrylate (SMA) as reactive co-stabilizer were carried out. Various factors were investigated, including effects of SDS and SMA concentration, various ratio of SDS to SMA, different amounts of SDS added before and after sonification, different type of co-stabilizers and two type of initiators on polymer particle size. The results show that the surfactant is necessary to retard droplet coalescence caused by Brownian motion and settling and the costabilizer prevents Ostwald Ripening. By comparison with the size of monomer droplets and polymer particle, the probability of monomer droplet nucleation can be illustrated. The kinetics of conventional emulsion polymerization and kinetics of miniemulsion polymerization with water phase scavenger also perform as an assistant evidence to illustrate the nucleation mechanism. It shows that both homogeneous nucleation and monomer droplets nucleation coexist in the presence of a water-soluble initiator. Meanwhile, using oil-soluble initiator, the possibility of homogeneous nucleation is depressed effectively. As a result, monomer droplets are definitely the main loci of particle nucleation.Miniemulsion polymerizations containing MAA were carried out by using KPS as a water-soluble initiator. The mechanism of nucleation was investigated. The results show that the probability of monomer droplet nucleation is enhanced in the presence of MAA. Compared with kinetics of miniemulsion polymerization without functional monomers, the polymerization with MAA is retarded, possibly because the critical chain length for MAA containing oligomeric radicals to precipitate out of the aqueous phase should be longer as compared with that obtained from the polymerization in the absence of MAA. As a result, the homogenous nucleation is retarded to some extent. When using an oil-soluble initiator, the probability of monomer droplet nucleation is enhanced sharply comparing with the same recipe and methods of preparation except using a water-soluble initiator. In addition, adding the water-soluble initiator at the later stage of polymerization is proved to be the most efficient way to enhanced the final conversion of monomers. Miniemulsion polymerizations containing AA were also carried out by using KPS as a water-soluble initiator and AIBN as an oil-soluble initiator, respectively. Because AA is more hydrophilic than MAA, the system containing AA is less stable than that containing MAA. When [AA]=5%, scraps present heavily. However, [AA]<5%,the mechanism of nucleation and kinetics of polymerization are much the same as the system containing MAA.更多还原