Structure of Styrene/Acrylic Acid Copolymer in Aqueous Solution Determined by Fourier Transform Infrared Spectroscopy

Abstract

A random styrene/acrylic acid copolymer has been examined by Fourier transform infrared spectroscopy with the use of the attenuated total reflectance (ATR) technique, in a study of the conformational structure in aqueous solution. The presence of a base in the aqueous solution leads to ionization of the acrylic acid segments and to conformational changes. The ionization is demonstrated by the appearance of asymmetric and symmetric C-O stretching bands of the COO− ion at 1547 and 1407 cm−1. Our results show that the water molecules are coordinated to the COO− ion through the positively charged cations. The acrylic segments of the copolymer are exposed to the aqueous solvent, whereas styrene is surrounded by acrylates. The molecular interactions of the copolymer in the two-phase water and benzyl alcohol system are determined. In the benzyl alcohol phase, the copolymer forms a coil-type structure, with the acrylic acid segments exposed to the aqueous phase. With time, the cations diffuse into the benzyl alcohol phase and cause ionization of the acrylic acid units, resulting in formation of the COO− ions.