Synthesis and rheological properties of some styrene/methacrylate copolymer latices

Copolymer emulsion latices based on styrene (St) with each of butyl acrylate (St/BuA), butyl methacrylate (St/BuMA), methyl methacrylate (St/MMA), and glycidyl methacrylate (St/GMA), were synthesized with different composition ratios (10/0, 7/3, 5/5, and 3/7) using potassium persulfate/sodium metabisulfite (KPS/NaMBS) as redox initiation system in the presence of a coemulsifier that consists of dodecyl benzene sodium sulfonate with polyvinyl alcohol (DBSS/PVA) and DBBS with polyoxyethylene glycol monomethyl ether (DBBS/POE). The obtained latices were characterized by H-1 NMR and rheological and morphological techniques. The rheological features for the obtained latices are strongly dependent on the type of the monomer used. The viscosity measurements showed that all latices behave as a non-Newtonian shear thinning (pseudoplastic). In addition, increasing the styrene ratio increases the apparent viscosity, pseudoplastic, and Bingham yield stress. The creep analysis for the latices demonstrated that the prepared latex using (DBSS/PVA) as a coemulsifier shows the least synersis effect than that obtained by using (DBSS/POE). Moreover, decreasing styrene content in the composition ratio improves the storage stability of copolymer latex. The morphological characteristics of the obtained latices clarify that the latex particles prepared in the presence of (DBSS/POE) as coemulsifier have the highest average volume particle diameter (D,) compared to that obtained for the latex prepared in the presence of (DBSS/PVA).