MMA/BA无皂乳液聚合机理研究--三阶段成粒机理

用Coulter LS230激光粒径分析仪研究MMA/BA无皂乳液共聚合中单分散粒子的成粒机理.根据理论和实验数据分析,其成核过程为均相成核机理.根据粒径分布和粒子数变化情况,把无皂乳液聚合过程分为3个阶段:第一阶段为成核-凝聚阶段,体系粒子数密度迅速增加,而粒径变化较小;第二阶段为成核-凝聚、增长-聚并共存阶段,当粒子数密度开始快速减少时,标志着第一阶段结束,第二阶段开始,当初级粒子开始消失时,标志着第二阶段结束;第三阶段为增长-聚并阶段.成核过程结束后,粒子迅速增长,较小粒子在增长过程中的优先聚并,导致粒径逐渐趋向均一,最终生成单分散性乳液.

Studies on Emulsifier-free Emulsion Polymerization Mechanism of MMA/BA--Three-stage Mechanism for Particle Formation

The particle formation mechanism of monodispersed particles in MMA/BA emulsifier free emulsion polymerization was investigated with Coulter LS 230 laser particle size analyzer. The nucleation mechanism of the system is homogeneous nucleation by theoretical and experimental analyses. A three stage mechanism of the particle formation mechanism of emulsifier free emulsion polymerization is proposed. Stage 1 is a homogeneous nucleation coagulation stage. The particle number density, N , increases rapidly in this stage, but the particle size changes less. Stage 2 is a nucleation coagulation propagation aggregation stage. When N begins to decrease rapidly, it marks the end of stage 1 and beginning of stage 2. Stage 3 is a propagation aggregation stage. When the particle nucleation process ends, it marks the beginning of stage 3. Particle size increases remarkably through propagation and aggregation. N tends to level off gradually. The precedent aggregation of smaller particles during the propagation leads to produce monodispersed particles.