Synthesis and evaluation of novel anionic polymeric surfactants based on polybenzoxazines

A novel platform of anionic polymeric surfactants, poly(4HBA-oca(-)Na(+)), poly(4HBA-dea(-)Na(+)), and poly(4HBA-doa(-)Na(+)), has been synthesized by polymerizing benzoxazine monomers that are synthesized by reacting an aliphatic amine of variable chain length (C8, C10 and C12), with 4-hydroxybenzoic acid and paraformaldehyde. The structures of the monomers and polymeric surfactants are confirmed by NMR and FTIR. The ring-opening polymerization and thermal behavior of the benzoxazine monomers are studied by DSC and TGA. Size exclusion chromatography (SEC) coupled with Viscotek triple detection technique is used to characterize the molecular weight distribution of polybenzoxazine surfactants. The surfactants have low MW, varying from 2200 to 6000, and are fairly polydisperse. The influence of the structure on the surface activity is investigated by measuring the surface tension of aqueous solutions of the polymeric surfactants using the Wilhelmy plate method. The tensiometry results indicate that the adsorption at the air/water interface is similar for the octylamine, decylamine and dodecylamine-based surfactants. Increasing the alkyl chain length from C8 to C12 does not significantly affect the surface tension at the critical micelle concentration (γcmc), while the critical micelle concentration (cmc) gradually increases due to increasing hydrophobic effect. These polymeric surfactants give cmc values ranging from 0.12 g/L to 0.17 g/L, comparable to other polymeric surfactants reported in the literature. The influences of salt addition on the surface tension at the critical micelle concentration (γcmc) for these surfactants are studied. Theminimum values of the γcmc are observed around 1 wt% NaCl for the polybenzoxazine surfactant solution.