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Carboxylated polystyrene particles were synthesized by batch emulsion copolymerization of styrene (St) and methacrylic acid (MAA) at 70 °C for 7 h. The effects of introducing time and amount of emulsifier SDS on the polymerization and properties of polymer particles were investigated. Results showed that introducing SDS after initiating polymerization for 3 h was beneficial to forming latex particles with monodisperse size and smooth sphere, and the properties of the resultant particles, including size and size distribution, zeta potential as well as carboxyl distribution were hardly influenced by the amount of SDS in this situation. Furthermore, the mechanism of polymerization was briefly discussed Introduction Monodisperse polymer particles have been intensively studied in the past few decades due to their characteristics of microcosmic size, uniform distribution and high specific surface area [1-2]. These properties make it an exciting material in chromatography, catalyst carrier, biotechnology and electronic industry [3-6]. Since the pioneer synthetic method of monodispersepolymer particles was reported [7], global research and development effort has been done to extend the synthetic techniques and provide many valuable results [8-10]. Comparing with other polymerization techniques such as dispersion polymerization, precipitation polymerization, SPG membrane technique, and living radical polymerization method [11-14], emulsion polymerization belongs to simple technology, friendly environment, and stable quality, and is feasible for production in large scale. According to the concept of “particles design”, polymer particles could be endowed with diverse structures and properties, such as core-shell, porous, hair-like, sensitivity and surface modification, which make the polymer particles serve as functional materials in various fields [15-17]. Emulsifier is the most important controlling factors in emulsion polymerization. The previous researches were mostly focused on the effects of the amount of emulsifier on polymerization. With the aim of controlling the morphology of polymer particles and studying the relationship between the emulsifier and the particle morphology, the introducing time and the amount of the emulsifier on the polymerization and the properties of resultant P(St-MAA) particles were investigated in this study. In addition, the forming mechanism of latex particles was proposed based on the experiment results. Experimental Section Materials. Styrene (St) and methacrylic acid (MAA) (both A.R.grade, GuangFu Fine Chemical Industry Research Institute, Tianjin, China) were purified by distillation under reduced pressure and stored in an refrigerator. Ammonium persulfate (APS) (A.R.grade, GuangFu Fine Chemical Industry Research Institute, Tianjin, China) was purified by recrystallization twice. Sodium dodecyl sulfate (SDS), NaOH, and H2SO4 (all A.R.grade, ZhiYuan Chemical Regent Co., Ltd., Tianjin, China) were used as received. Deionized water was employed. Preparation of carboxylated PSt particles. Caboxylated PSt particles were prepared by emulsion polymerization in a 250 ml four-necked round bottom flask equipped with an inlet of nitrogen gas, a reflux condenser, a mechanical stirrer and a thermometer. 20 g of St and MAA (the mole ratio of St/MAA was 94:6) and 100 g of H2O were charged into the reactor, and polymerized at 2nd Annual International Conference on Advanced Material Engineering (AME 2016) © 2016. The authors Published by Atlantis Press 895 70 oC for 7 h. Meantime, 0.336 g APS dissolved in 25 g H2O was introduced at the beginning, 2 h and 4 h of polymerization with a ratio of 12:8:5. Certain amount of SDS dissolved in 10 g H2Owere introduced into the reactor at different time during the process of polymerization. Characterization. The monomer conversion of polymerization (Conv. wt%) were determined by gravimetric analysis. The hydrodynamic diameter (Dp), polydispersity Index (Poly. Index) and zeta potential (ζ) of the latex particles were measured on Zetasizer 3000HS (Malvern, UK). The number-average diameter (Dp) and morphology of the dried latex particles were characterized using transmission electron microscopy (TEM, JEOL JEM-2100EX, Japan) at 70 KV using 2% aqueous solution of phosphotungstic acid as staining agent. The surface appearance of the latex particles was observed by scanning electron microscope (SEM, JSM 7401F, Japan).The distribution of carboxyl groups in the emulsion system was determined by conductometric titration with DDS-307 conductometer (Leici, Shanghai, China) according to the literature [18].Sc, Fc and Ec represented the percentage of-COOH bounded on the surface of latex particles, free in the aqueous phase and embedded inside the latex particles respectively. Results and Discussion Introducing SDS at different time. In order to investigate the influences of SDS introducing time on the emulsion polymerization and particle properties, 0.467 g SDS which was 1.5 times of its critical micelle concentration (CMC) was added into the reaction system at different time of the polymerization. The results were given in Table 1, and morphology of the obtained products was shown in Fig. 1 and 2. Table 1. Influence of SDS introducing time on the properties of carboxylated PSt particles. Introducing time of SDS (h) Conv.(%) Dp(nm) Dp (nm) Poly. Index ζ (mV) 1 92.9 121 196 0.0220 40.1 2 93.3 -347 0.0847 35.8 3 92.6 236 314 0.0521 43.3 4 92.1 246 314 0.0020 46.6 Fig. 1. TEM photographs of caboxylated PSt particles prepared by introducing SDS at different time of polymerization process (a) 1h, (b) 2h, (c) 3h, (d) 4h

Effects of the Amount and Introducing time of Emulsifier on the Preparation of Carboxylated Polystyrene Particles