Tailoring the Viscoelasticity of HEMA-Functionalized Styrene-Acrylate Copolymers Using Coagulants

Abstract

Coagulation is an important chemical process extensively used to harvest polymeric resins from natural or synthesized suspensions and emulsions. In this work, the coagulants were found effective to tune the viscoelasticity of poly(styrene-co-butyl acrylate) resins containing small amounts of hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA). Results showed that the viscoelasticity of the copolymers remarkably varied with the type of coagulant. For samples coagulated by H 2 SO 4 , the shear modulus G′ initially decreased and then rapidly increased with temperature. This observation suggested a cross-linking reaction during rheological measurement. Conversely, G′ continuously decreased with increased temperature and exhibited a higher solidlike plateau in the terminal zone for resins coagulated by metal salts with a higher charge/radius ratio. We demonstrated that the cross-linking reaction originated from the transesterification of the hydroxyl group with the ester group both from BA. Cations from the metal salts formed coordination bonds with HEMA hydroxyl during coagulation. These bonds shielded HEMA from transesterification reactions but resulted in physical networking among the copolymer chains.