Effects of the Adding Methods of AA and its Concentration on the Properties of St-MMA-AA Soapless Latex Particles

Latex particles were obtained by soapless emulsion copolymerization of styrene (St) and methyl methacrylate (MMA) in the presence of functional monomer acrylic acid (AA) . The morphology, size and size distribution of the latex particles were observed or surveyed by TEM, and the distribution of -COOH in the latex was determined by conductometric titration and the density of surface -COOH was computed. Effects of the concentration of AA and its feeding process at different polymerization stages on the size and size distribution, density of surface -COOH of the latex particles were investigated. The results show that the average diameter (D) decreases and its dispersion parameter (D p) increases with increasing [AA] if AA was added in one batch before polymerization. D is larger and slightly decreases, and D p increases significantly with increasing [AA] if AA was added dropwise at the latter of nucleation stage. D and D p increase with increasing [AA] if AA was added dropwise after the steady stage and [AA] is winth a certain range. The density of surface -COOH (D c) increases with increasing [AA] no matter how AA was added, and D c is the largest when AA was added dropwise after the steady stage and it is the least when AA is added in one batch before polymer ization.