Water-Soluble Polyurethane Resins as Emulsifiers in the Emulsion Polymerization of Styrene: The Effect of the Neutralization Degree of the Resin

Abstract

The emulsion polymerization of styrene in the presence of polyurethane resins (PUR-750 and PUR-2000) with a varying degree of neutralization (DN) was investigated. The PURs have carboxyl groups in their backbones, which are originated from 2,2-bis(hydroxymethyl)propionic acid (DMPA). Therefore, the PURs can form micelles or aggregates in the aqueous phase and can be water-soluble or water-dispersible according to the DN of the carboxyl groups. DN was varied by adding calculated amounts of NaOH with the same concentrations of all ingredients. The maximum rate of polymerization (Rp, max) became low at 100% DN and Rp, max increased as the DN increased or decreased. The average number of radicals per particle (n) was measured and it was observed that n varied according to DN having the same tendency as that of Rp, max. Additionally, it was found that the solubilization ability of the PUR aggregate was affected by DN. The effects of DN on Rp, max was explained by the hydrophobicity and electrosteric characteristics of the PUR aggregate.