MMA/BA种子半连续乳液聚合成核过程及机理研究

NUCLEATION PROCESS AND NUCLEATION MECHANISM OF MMA/BA SEEDED SEMI-CONTINUOUS EMULSION POLYMERIZATION

引入一种不溶于水的染色剂(BL-S)作示踪剂,研究甲基丙烯酸甲酯(MMA)/丙烯酸丁酯(BA)种子半连续乳液聚合中各变量对成核过程及成核机理的影响,运用最终乳胶粒中染色剂的含量(Pdye)、最终乳胶粒子数(Npc)、胶束成核和均相成核所形成的粒子数目(Nm和Nh)等参数对聚合过程中的成核情况进行定量分析.结果发现,当引发剂浓度[I]增大时,Pdye、Nh、Nm和Nh/Npc均随之增大,同时Nm/Npc相应地减小,且Nm/Npc=-0.0262[I]+0.8833,表明均相成核随[I]的增大而增加,但胶束成核的比例减小.乳化剂浓度[E]在不同范围内对成核机理的影响不同,在[E]=0.7216×10-2mol.L-1时,体系中胶束成核和均相成核比例相等,各为50%;当[E]>0.7216×10-2mol.L-1时,随[E]增大,成核时间t1,2逐渐缩短,Nm/Npc增加,Nh/Npc减小,胶束成核所占比例大于均相成核,胶束成核逐渐上升为主要成核方式;反之当[E]<0.7216×10-2mol.L-1时,体系中胶束成核所占比例小于均相成核,均相成核为主要成核方式.当MMA的摩尔分率fMMA由0增至0.6时,Nm/Npc从80.93%下降至50%,体系中以胶束成核为主,均相成核为辅;当fMMA由0.6增至1时,Nm/Npc已降至40%,而Nh/Npc增至60%,体系中已转变成均相成核为主,胶束成核为辅.在常规和种子半连续乳液聚合中,t1,2分别为12min和6min,而Pdye变化较小,表明聚合方式只影响粒子的形成过程和成核时间的长短,对成核方式影响甚微.

A water-insoluble dye （BL-S） was used as a probe to study the influence of some factors on the process of nucleation and nucleation mechanism in seeded semi-continuous emulsion polymerization. Some parameters were analysed for quantitative study on nucleation mechanisms, the parameters include the amount of dye incorporated into the resultant latex particles （ Pare ）, number of the resultant latex particles （ Np ） and the different numbers of particles which are formed by micellar nucleation （ Nm ） and homogeneous nucleation （ Nh ）. The results of the study and analysis show that Pdye, Nh, Nm and Nh/Np^c all increase with increasing initiator concentration [I] ,but Nm/Np^c decreases as Nm/Np^c = -0.0262[I] ＋ 0.8833, which can illuminate the proportion of homogeneous nucleation increases while micellar nucleation decreases with increasing [I]. The influence of the emulsifier concentration [ E] on nucleation mechanisms is different at different concentration range, when [ E] equals to 0. 7216 × 10^-2 mol·L^-1, the proportion of homogeneous nucleation is equal to micellar nucleation, both of them are 50 % . When [ E ] is greater than 0. 7216 × 10^-2 mol·L^-1, the nucleation time t 1.2 decreases and Nm/Np^c increases with increasing [ E], Nh/Np^c decreases accordingly, and the proportion of micellar nucleation is larger than homogeneous nucleation, so that the micellar nucleation mechanism predominates gradually in the particle nucleation process; when [E] is less than 0.7216 × 10^-2 mol·L^-1 ,the proportion of micellar nucleation is less than homogeneous nucleation,the main nucleation mechanism becomes to homogeneous nucleation. In the system of MMA/BA copolymerization, when fMMA increases from zero to 0.6,the value of Nm/Np^c decreases from 80.93%to 50% ,which means that the proportion of micellar nucleation is larger than that of homogeneous nucleation, so that micellar nucleation plays a key role in the particle formation period. When fMMA increases from 0.6 to 1, Nm/Np^c is reduced to 40% and Nh/Np^c is raised to 60% ,but homogeneous nucleation is more important than micellar nucleation in this system. In addition,the t1.2 is 12 min and 6 min for the conventional and seeded semi-continuous emulsion polymerization, respectively, but Pdye change is less. All these show that the both semi-continuous emulsion polymerization techniques only have some effect on the formation process of particles and the neculeation time, but little effect on their specific nucleation.