Synthesis and characterization of acrylate monomers used in the “Hydrophobic Alkali Swellable Emulsion (HASE)” synthesis.

Synthetic associative acrylic monomers functionalized by oxo alcohol based hydrophobic group have been synthetized and then used in “Hydrophobic Alkali Swellable Emulsion (HASE)”. One of the features of use these associative acrylic monomers resides in that once added into the aqueous phase containing a latex and possessing an alkaline nature, they lead to a phenomenon of increased viscosity over a wide range of shearing gradients without adding a neutralization agent. This constitutes a major asset compared to the conventional HASE polymers, which thickened a medium after adding a neutralization agent to it; such an addition has not possible in the emulsion as it has, as it might increase its viscosity to a level that would make it unworkable [1]. Higher thickening efficiency is achieved by the self-associating properties of the attached hydrophobic groups to the polymer backbone. The importance of HASE polymers is due to the great market demand since they are used in a wide range of industrial applications such as viscosizers, paint formulations, cosmetics, cleaning products and coatings paper [2]. The synthesis of the associative monomers has been carried out by an esterification reaction. The reagents used are methacrylic acid, an ethoxylated alcohol and sulfuric acid to catalyze the reaction. Because the properties of the HASE polymers are certainly related to the structure and composition, several associative acrylic monomers can be synthetized changing the ethoxylated alcohol structure (i.e. number of ethoxy groups, length of alkyl chain, linear or branched chain). The characterization of associative monomers has been performed by acid-base titration and IR spectroscopy for structural information. Another aim of the present work, as mentioned above, is to use these associative monomers synthetized in HASE polymers formulation. An example of the polymeric structure is reported in Figure 1. Figure 1 – Molecular structure of a hydrophobically modified alkali-soluble emulsion polymer. x, y, z are structural parameters. n is the number of poly(ethylene oxide). HASE polymers have been synthetized by emulsion polymerization. In particular, have been synthetize HASE with higher molecular weight, low residual solid and with a correct value of polydispersity index. To characterize the HASE polymers have been performed rheological tests to analyze the increasing of viscosity