苯乙烯与甲基丙烯酸甲酯在聚乙二醇水溶液中无皂乳液共聚的粒径变化

利用高倍光学显微镜、库尔特粒径测试仪、TEM及zeta电位跟踪观测了苯乙烯(St)与甲基丙烯酸甲酯(MMA)在聚乙二醇(PEG)水溶液无皂乳液共聚过程中的粒径、粒径分布以及zeta电位变化.聚合物粒径会经历由小到大(某些粒径甚至超过1000μm,分布在0.04～2000μm的极宽范围内),再由大变小(形成的数均分布在0.04～0.18μm)过程,且粒径分布也由宽变窄,最终粒径数均分布集中在0.04～0.18μm窄范围内.结合聚合转化率数据,根据PEG水溶液中进行的St/MMA无皂乳液共聚粒径变化过程,以及zeta电位在聚合过程中异于普通无皂乳液的现象,认为该体系在反应初期形成的粒子会形成粒子堆,并随着聚合反应的继续,带有离子片段的自由基链段不断扩散进入粒子堆表面的小粒子,使其zeta电位不断增强,最终脱离粒子堆.提出了PEG水溶液中St/MMA无皂乳液共聚聚并脱析成核机理.

PARTICAL SIZE EVOLUTION IN SURFACTANT-FREE EMULSION COPOLYMERIZATION OF STYRENE AND METHYL METHACRYLATE IN AQUEOUS SOLUTION OF POLY(ETHYLENE GLYCOL)

The surfactant-free emulsion polymerization(SFEP) of styrene and methyl methacrylate carried out in the aqueous solution of poly(ethylene glycol)(PEG) was studied.With high power optical microscope,Coulter counter and transmission electron microscopy,particle size,particle size distribution and zeta potential were measured in the process of polymerization.It is interesting to observe that the polymer particle size experiences a process from small to large,which can be more than 1000 μm,and then from large to small,which is back to a range of 0.04 ~ 0.18 μm.When the particle size returns to nanometer scale,the system has an obvious temperature rising.This phenomenon is different from the traditional nucleation mechanism of SFEP.The particle,which is formed by the homogeneous nucleation or oligomer micelle nucleation mechanism that is popularly received as traditional nucleation mechanism of SFEP,usually has a trend to become bigger and bigger to the end in the process of SFEP.It is obviously found that the freshly formed particles are first coalesced to form a particle pile,which is bigger than 1000 μm and even seen with eyes,and then corrupted into tinny ones,which are smaller than 0.04 μm and even beyond the ability of high power optical microscope.With transmission electron microscopy(TEM),it was clearly proven the existence of paricle pile which was composed of a lot of little particles ranging from 40 nm to 80 nm.And by use of Coulter zeta potential measurement,it was found that the zeta potential of particles had a trend from low to high level,and experenced abruptly increase in zeta potential at 60 min which was just the time that the little particle seperated from the paricle pile.This phenomenan was very different from the system that SEFP was carryed out in water without PEG,in which the zeta potential of particle was keeping about-50 mV and just changed a little after 50 min.It was reasonble to think that the potential increase was the driving force to make the little particles to escape from the particle pile.Therefore,the mechanism of coalescence-separate nucleation is proposed.