Synthesis of Amphiphilic Poly(acrylic acid)-b-poly(n-butyl acrylate-co-acrylic acid) Block Copolymers with Various Microstructures via RAFT Polymerization in Water/Ethanol Heterogeneous Media

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Abstract

The batch copolymerization of n-butyl acrylate (50 mol %) and acrylic acid (50 mol %)—two monomers with close reactivity but with very different water solubility—was performed under RAFT (reversible addition–fragmentation chain transfer) control, in heterogeneous conditions in water or water/ethanol mixtures. The polymerizations were conducted in the presence of poly(acrylic acid) end-capped with a trithiocarbonate reactive group, serving as a control agent, a precursor for the in situ synthesis of amphiphilic block copolymers and a stabilizer for the formed particles. Good control over the polymerization and stable colloidal suspensions were achieved under such conditions. The kinetic study demonstrated that the polymerization rates of each monomer varied upon a change of the water/ethanol volumetric ratios and of the overall comonomer concentrations. The compositional microstructure of the copolymers was characterized by NMR analysis and by potentiometric titration. This work demonstrates that the distribution of the comonomer units in a copolymer formed under heterogeneous conditions can be controlled by the solubility of the monomers in the medium, hence leading to various types of compositional gradient structures.

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