Co-polymers of acrylic acid and methyl methacrylate as stabilizers for suspension polymerization of styrene

Abstract

The synthesis of homo-polymers of acrylic acid and co-polymers of acrylic acid–methyl methacrylate as suspension agents (SA) was performed in aqueous media, and SA were used as stabilizer in the suspension polymerization of styrene. The behavior of water solutions in the interfacial tension of SA against styrene was studied. The composition of the co-polymers and their molecular weights are related to the Zykonski model coefficients and to the molecular configuration of the stabilizer at the interface. It was found that the molecular weight, the composition of SA, the concentration used in the reaction system and the time at which it was added had a marked effect on the stability of the suspension during the reaction and on the final particle size distribution of the polystyrene beads. The homo-polymers of acrylic acid do not prevent correctly the coalescence during the suspension polymerization, while the co-polymers of acrylic acid and methyl methacrylate are well adsorbed into the oil/water interface and then work as good stabilizers for styrene suspension polymerizations. Provided a good stabilizer was used, i.e., with a high molecular weight and enough hydrophobic character, its addition delayed up to the beginning of the sticky stage produced a quite narrow particle size distribution.