Synthesis, characterization, and evaluation as emulsifiers of amphiphilic-ionizable aromatic methacrylate ABC triblock terpolymers

Abstract

Four isomeric terpolymers based on benzyl methacrylate (BzMA, nonionic hydrophobic), 2-(dimethylamino)ethyl methacrylate (DMAEMA, ionizable hydrophilic), and methoxyhexa(ethylene glycol) methacrylate (HEGMA, nonionic hydrophilic) were synthesized using group transfer polymerization (GTP). The three of the terpolymers were the ABC block sequence isomers, ABC, ACB, and BAC, and the fourth was the statistical terpolymer. Their theoretical molecular weight was 5000 g mol-1, and the theoretical w/w composition was 33% from each monomer. The success of the synthesis was confirmed by gel permeation chromatography (GPC), which showed that the experimental molecular weights were in reasonable agreement with the theoretical ones and the polydispersity indices were low (in most cases <1.1), and by proton nuclear magnetic resonance (1H NMR) spectroscopy, which provided experimental compositions very close to the theoretical ones. All the terpolymers were characterized in aqueous solution by dynamic light scattering at room temperature to determine their hydrodynamic diameters and turbidimetry to determine their cloud points. The results indicated that the behavior of the terpolymers in aqueous solution was profoundly affected by the monomer distribution in the polymer chain. After polymer characterization, the above terpolymers were used as stabilizers at a 1% w/w polymer concentration to prepare xylene-water and diazinon (pesticide)-water emulsions. All emulsions formed were of the o/w type (no w/o emulsion was observed), probably due to the hydrophilic nature of the terpolymers (66% w/w composition in hydrophilic units). From emulsion droplet size measurements, it appeared that the emulsification efficiency of the terpolymers was also affected by the monomer distribution in the polymer chain with the most efficient terpolymer being the triblock with a BzMA midblock and the least efficient being the statistical terpolymer.