聚硅氧烷/丙烯酸酯核/壳复合胶乳的粒径分布与成核机理

通过种子乳液法合成出具有高有机硅含量核 壳结构的聚硅氧烷 丙烯酸酯复合粒子 .研究了聚合方法、乳化剂浓度、引发剂浓度、单体滴加速度等工艺条件对复合乳液粒径尺寸、分布与形态的影响 ,并对复合乳液的成核机理进行了探讨 .研究表明 ,乳化剂浓度对乳液粒子的粒径分布和形态、结构有显著影响 ,引发剂浓度增加将使粒子粒径减小 ;相对一次投料法 ,种子乳液法生成的粒子分布窄 ,具有明显核壳结构 ,通过壳层单体滴加速度可以控制粒子的粒径尺寸和分布 ;而壳层丙烯酸酯聚合物主要是在聚硅氧烷种子表面的“过渡层”聚合、富集而成 .

PARTICLE SIZE DISTRIBUTION AND ITS FORMATION MECHANISM OF POLYSILOXANE/ACRYLATES CORE-SHELL COMPOSITE PARTICLES

The polysiloxane/acrylates copolymer latex with core-shell structure was prepared in the semi-batch emulsion polymerization of methyl methacrylate (MMA) in the presence of polysiloxane latex as seeds.The polysiloxane seeded latex was polymerized by octamethylcyclotetrasiloxane(D 4)and vinyl methylcyclotetrasiloxane (ViMeSiO) 4,and methyl triethoxysilane (MTES) as the crosslinking reagent.The effects of polymerization methods and preparation conditions (the concentrations of emulsifier and initiator,the adding mode and rate of MMA) on the average particle size,and its distribution,and the morphology of the obtained particles were studied.In comparison with batch process,the semi-batch process by adding MMA is more preferable for preparing a stable copolymer latex with smaller particle size and narrower distribution.The higher concentration of emulsifier and initiator will cause smaller particle size and narrower particle size distribution,the faster adding rate of MMA will cause smaller particle size,but wider particle size distribution.The TEM photos show that the composite particles prepared in the semi-batch process by adding MMA monomers have clear core/shell structure,but particles by batch method have irregular shape and no such structure.Besides the micelle nucleation during the seeded emulsion polymerization,the homogeneous nucleation can't be neglected because of the slight solubility of MMA in water.Under lower concentration of emulsifier and slower adding rate of MMA,the polymerization of shell monomers will be restricted in the “transition area" on the surface of the polysiloxane seeds.The particle size,distribution and morphology of the composite particles can be controlled by changing the concentration of the emulsifier and the adding rate of MMA.