核壳结构聚硅氧烷/丙烯酸酯复合乳液(Ⅰ) 乳化剂对乳液聚合过程及粒径分布和粒子形态的影响

Polysiloxane/acrylates core-shell composite emulsion(Ⅰ) Effect of emulsifiers on emulsion polymerization, particle size distribution and its morphology

采用种子乳液半连续法合成了具有高有机硅含量的聚硅氧烷/丙烯酸酯核壳结构复合乳液,研究乳化剂的种类、复配比例及质量浓度对有机硅/丙烯酸酯壳核乳液性能与乳胶粒径、分布和结构的影响.结果表明:阴离子乳化剂十二烷基硫酸钠(SDS)、十二烷基磺酸钠(SDS2)、十二烷基苯磺酸钠(SDBS)所合成的乳胶粒子粒径依次增大,SDS与非离子型乳化剂OP10复配使用时,随OP10质量分数的增加,聚合速率和转化率降低,化学稳定性增加,乳胶粒子粒径增大,分布变宽,确定了复合乳化剂的最佳配比.随复合乳化剂浓度的增加,聚合速率加快、转化率增加,乳胶粒子粒径减小而分布加宽.通过改变乳化剂加入方式可减小乳胶粒子的粒径分布.为减少壳层聚合物新粒子的产生,需严格控制乳化剂的浓度,使加入的壳层单体处于“饥饿”状态,在乳胶粒子表面富集、引发聚合,形成表层“过渡层”,最终形成核壳结构复合粒子.

The high organosilicone content polysiloxane/acrylates composite latex with core-shell structure was prepared in the semi-batch emulsion polymerization of methyl methacrylate （MMA） in the presence of polysiloxane latex as seed. The seed was polymerized by octamethylcyclotetrasiloxane （D4） and vinyl methylcyclotetrasiloxane （Vi- D4 ）, and methyl triethoxysilane （MTES） as crosslinking reagent. The effects of the type, compounding ratio and the weight concentration of emulsifiers on the properties of the emulsion and the average particle size, its distribution, and the morphology of the obtained latex particles were studied. The particle diameter increased in the order of three anionic emulsifiers： sodium dodecyl sulfate （SDS）, sodium dodecyl sulfonate （SDS-2） and sodium dodecyl benzenesulfonate （SDBS）. With decreasing compounding ratio of SDS/OP-10, the rate of polymerization and conversion of monomer reduced and the chemical stability of latex increased, while the latex particle size and its distribution increased. Conaidering all-around factors of emulsion, the best compounding ratio of SDS/OP-10 was 5 ： 1. Furthermore, a higher concentration of emulsifiers would cause smaller particle size, narrower particle size distribution, and faster rate of polymerization and higher conversion of monomer. The particle size distribution could be narrowed by changing the mode of adding emulsifier. In order to reduce the generation of new shell polymer particles the concentration of emulsifier must be strictly controlled to keep MMA in a “starvd” state. The polymerization of shell monomer would be restricted on the “transition area” on the surface of polysiloxane seeds to form core-shell structure composite particles.