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

Abstract

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(P_dye),number of the resultant latex particles(Nc_p)and the different numbers of particles which are formed by micellar nucleation(N_m)and homogeneous nucleation(N_h).The results of the study and analysis show that P_dye,N_h,N_m and N_h/Nc_p all increase with increasing initiator concentration [I],but N_m/Nc_p decreases as N_m/Nc_p=-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 N_m/Nc_p increases with increasing [E],N_h/Nc_p 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 f_MMA increases from zero to 0.6,the value of N_m/Nc_p 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 f_MMA increases from 0.6 to 1,N_m/Nc_p is reduced to 40% and N_h/Nc_p is raised to 60%,but homogeneous nucleation is more important than micellar nucleation in this system.In addition,the t_1,2 is 12 min and 6 min for the conventional and seeded semi-continuous emulsion polymerization,respectively,but P_dye 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.