The Synthesis of Associative Copolymers with Both Amphoteric and Hydrophobic Groups and the Effect of the Degree of Association on the Instability of Emulsions

The acrylamide (AM)/methacryloyl ethyl sulfobetaine (SPE)/behenyl polyoxyethylene ether methacrylate (BEM) terpolymer (PASB) was synthesized by soap-free emulsion polymerization. Four types of PASBs were synthesized by adjusting the moles of AM and BEM with constant total moles of monomers. The synthesized copolymers were characterized by Fourier-transform infrared spectroscopy, thermogravimetry, molecular weight, and viscosity. By measuring the microscopic morphology and backscattered light intensity of the emulsions, the instability process of the emulsions prepared by PASBs was investigated in detail. The main instability processes of the emulsions prepared from PASBs within 45 min were flocculation and coalescence. The intermolecular association of copolymer PASBs was dominated by the behenyl functional groups on the molecular chains. The stability of the emulsions, which were prepared from isoviscosity aqueous solutions controlled by the concentration of the associative copolymers, was increased with the degree of association of copolymers. The hydrophobic association between the copolymer molecules can further slow down the flocculation and coalescence of the emulsion droplets on the basis of the same aqueous solution viscosity, which is one of the reasons for improving the stability of the emulsion.