Conversion improvement of high solids waterborne alkyd–acrylic nanoscale hybrid systems and its effect on nanostructure

GOIKOETXEA, MONIKA; MINARI, ROQUE J; BERISTAIN, ITXASO; PAULIS, MARÍA; BARANDIARAN, MARÍA J.; ASUA, JOSÉ M.

Madrid (España)

Conferencia; 6Th Ecnp Conference on Nanostructured Polymers and Nanocomposites; 2010

The European Centre for Nanostructured Polymers (ECNP)

Recent efforts have been made to produce waterborne coating systems which combine the positive properties of alkyd resins and acrylic latexes. The best way of combining the positive properties of both systems could be achieved when grafted polymer of both phases was obtained. This required an intimate contact between the components of the hybrid system. Because alkyd resins are very hydrophobic materials, this could be achieved by miniemulsion polymerization. In miniemulsion polymerization almost the entire polymerization process occurs in the dispersed droplets, where the alkyd resin and the acrylic monomers were located. Nevertheless, the practical implementation of hybrid miniemulsion polymerization has been jeopardized by the relatively low limiting conversion often observed in these systems. The combined role of the glass effect and the entrapment of the monomer because phase separation as well as the formation of inactive radicals upon propagation of the monomeric radicals with the vinyl groups of the resin have been proposed as reasons for the limiting conversion. The deeper knowledge of the kinetics should help to determine the cause of the limiting conversion and therefore, find ways to overcome it. In this work, the kinetics of miniemulsion polymerization used to synthesize high solids waterborne acrylic-alkyd nanocomposites was studied. It was found that the use of redox initiators during the synthesis of the hybrid alkyd-acrylic latex could improve monomer conversion. However, the concentration of residual monomer was still unacceptable for industrial requirements and the performance of post-polymerization was also analyzed. The obtained results suggested that the main mechanism responsible of limiting conversion was chain transfer to alkyd, which forms a rather unreactive radical stabilized by the conjugation of the double bond. Moreover, polymer microstructure, which in turn affected particle morphology, was modified during synthesis and during post-polymerization, the modification being stronger when hydrophobic oxygen-centered radicals were used.