Synthesis of a latex with bimodal particle size distribution for coating applications using acrylic monomers

Multipart emulsion polymerization of methyl methacrylate (MMA) and butyl acrylate (BA) was carried out in this work. The target was to achieve stability during the polymerization and to determine the proper hydrophilic–lipophilic balance (HLB) value for the stable system, using different types of non-ionic emulsifiers, sodium lauryl sulphate and their combinations. After determination of proper value of HLB (36.2), the best emulsifier combination on the basis of minimization of coagulum level was determined. This combination was 20 wt.% of KENON30 to SLS. The effect of monomer feed composition on the dry latex film properties was investigated to approach a monomer feed composition dealt with a proper T_g. The prepared latex showed a bimodal particle size distribution, due to the proper feeding policy in semibatch emulsion copolymerization process. The monomer feed composition of 45 wt.% MMA and 55 wt.% BA with a proper T_g was selected for the final improvement of coating properties such as UV resistance and adhesion. Adding acrylic acid (AA) and N-methylol acrylamide (NMA) to the reaction mixture improved the UV resistance and adhesion property of dry latex film. The flow and leveling, gloss, adhesion, UV resistance and water resistance of the produced bimodal latex showed good quality in comparison with the similar commercial resins used in coating applications.