Effects of carboxyl groups dissociation and dielectric constant on particle size of polyurethane dispersions

Aqueous polyurethane (PU) dispersions were prepared by pre-polymer mixing and the neutralization emulsification method. PU dispersions were electrostatically stabilized with carboxyl groups incorporated into their particles, which were neutralized by triethylamine (TEA). The reaction parameters were molecular weight of polyol, amount of chain extender, TEA/dimcthylolpropionic acid mole ratio, and the dielectric constant of the dispersion medium. The average particle sizes ranged between 27 and 415 nm. Owing to an enlargement of the stabilization site, the particle size decreased as the concentration of carboxyl groups and the degree of neutralization increased.