St-MMA无皂乳液共聚合的研究

SOAP-FREE EMULSION COPOLYMERIZATION OF STYRENE AND METHYL METHACRYLATE

在70℃下进行了苯乙烯和甲基丙烯酸甲酯的无皂乳液共聚合,研究了单体初始总浓度[M]_0、引发剂浓度[K_2S_2O_8]和总离子强度I对乳胶拉平均直径d_w与粒子数N_p的影响,其关系式为: lgd_w=lg([M]_0^(0.795)[K_2S_3O_8]^(-0.193)I^(0.346))-0.213 N_p=0.762×10^(15)[K_2S_2O_8]^(0.579)[M]_0^(-1.385)I^(-1.038)发现平均聚合速率随[M]_0及I的增大而减小,随[K_2S_2O_4]的增大而增大;在成核过程中,同时存在着两种相反因素,即新柱子的生成与柱子聚并。粒子间的有限聚并平衡既可提高乳液的稳定性,又是导致乳胶拉子单分散性的主要原因。

The soap-free emulsion copolymerization of styrene (St) and methyl methacrylate (MMA) was carried out at 70°C. The effects of initial monomers concentration [M]0, initiator concentration [K2S2O8] and total ionic strength / on the diameter of latex particles dw and the final number of latex particles Np were investigated in the case of a fixed monomer ratio . They are related as follows : Igdw=lg ([M]00.795[K2S2O8]0.193I0.346)-0.213 (1)NP=0.762 × 1015 [K2S2O8]0.579[M]0-1.385I-1.038 (2)According to Equation (1) and (2), potassium persulfate plays the double contradictory roles during the polymerization because it acts both an initiator and an electrolyte .The study of emulsion polymerization kinetics shows that the average polymerization rate decreases as increasing in [M]0 and I , but increases as increasing in [K2S2O8] . This is due to the effect of particle numbers .The study of latex particle nucleation kinetics also shows that the curves of transient particle number Npversus time t have a common character during the period of nucleation, i .e .after striding over a peak ,these curves will gradually become constant values . This is because there are two opposite tendencies in the course of nucleation,namely, the formation of new particles which causes to increase the particle number and to decrease the Zeta electric potential ,and the limited coalescence of initial nuclei which results in reduction of the particle number with increasing in surface charge density .Finally they will reach an equilibrium state and hereafter the number of par tides remains constant throughout the later reaction .After that , the particles begin to compete growing . The parameters [M]0 ,[K2S2O8] and I all affect the peak values of the curves and the nucleation intervals . The limited coalescence of initial nuclei and the competitive growth are the main reason for monodispersion of latex particles in soap-free emulsion systems .