Synthesis and characterization of polymeric emulsifiers containing reversible hydrophobes: poly(methacrylic acid-g-ethylene glycol)

A series of poly(methacrylic acid-g-ethylene glycol) copolymers of varying molecular architectures were synthesized in a custom-built semi-batch reactor by a free radical copolymerization of methacrylic acid with the macromonomer methoxy poly(ethylene glycol) methacrylate (MPEGMA). By virtue of intramolecular hydrogen bonding between the oligo(ethylene glycol) grafts and the poly(methacrylic acid) backbone, these polymers contain reversible hydrophobic segments, and may be used as reversible emulsifiers that allow emulsions to be broken and reformed. The copolymers were characterized using H-1 NMR to determine the polymer composition and gel permeation chromatography (GPC) to characterize the polymer molecular weight distribution. The GPC and NMR results were combined to estimate the number of grafts per chain for each of the polymer samples. The average number of grafts per chain was found to range from 0.3 to 18. As expected, for a constant initiator concentration, the average number of grafts per chain was found to increase as the amount of the MPEGMA in the reaction mixture was increased. In addition, for a constant MPEGMA content, the average number of grafts per chain decreased as the initiator concentration was increased. These studies provide important information about the relationship between the reaction conditions and the molecular architecture of the resulting reversible copolymeric emulsifiers. (C) 2000 Elsevier Science Ltd. All rights reserved.