Synthesis of novel amphiphilic copolymers by acid-mediated free-radical polymerization and solution as well as particle stabilization properties

Abstract

Hydrophobically modified copolymers with different content of hydrophobic/hydrophilic segments can be synthesized by free radical copolymerization of acrylic acid (AA) with isobutene (IB) in the presence of strong Bronsted acids such as trifluoracetic acid (TFA). By variation of the comonomer ratio, the copolymer composition and its hydrophilic/hydrophobic properties can be adjusted. The copolymerization of AA and IB in the presence of TFA leads to copolymers which formally consist of periodic sequences of [IB-AA] X randomly interrupted by homo sequences of [AA] Y . This reflected from the linear dependence of the glass transition temperature with the [IB-AA] unit mole fraction while no direct correlation with the overall IB or AA mole fraction is given. The [IB-AA] sequences are relatively hydrophobic due to the IB unit, while [AA] sequences represent the hydrophilic part. Aqueous solutions of the periodic copolymers are characterized by specific and concentration dependent viscosities which are attributed to intermolecular association phenomena of alternating [IB-AA] X sequences. The copolymers have been shown to be potential stabilizers of titanium dioxide particle dispersions in water as has been established by electrokinetic sonic amplitude and sedimentation measurements. These data are again correlated with the periodic chain structure. A conformational model of [AA]y anchor segments as trains and [IB-AA] X loops and tails is proposed.