Infrared spectra and compositional analysis of styrene/2-ethylhexyl acrylate copolymers

Compositional analysis of a series of free-radical emulsion polymerized styrene/2-ethylhexyl acrylate copolymers following close to random polymerization statistics was accomplished by elemental analysis, UV and IR. A satisfactory agreement was obtained between the three independent techniques. IR calibration curves were constructed based on sequence-independent infrared absorption bands determined by plotting peak intensities against the number fraction of each of the possible monad, dyad and triad structures in the copolymers. The intensities of the skeletal ring breathing vibration of styrene units at 1602 cm(-1) as well as the C-O stretching vibration of the saturated ester group of 2-ethylhexyl acrylate units at 1158 cm(-1) were shown to be representative of the copolymer composition, whereas the position and shape of the carbonyl stretching band at 1730 cm(-1) were shown to depend on both the composition and the monomer sequence distribution. A calibration curve not requiring the use of an internal thickness band was obtained by plotting the ratio of absorbances of the 1602 cm(-1) and the 1158 cm(-1) peaks as a function of the mole ratio of the corresponding monomers in the copolymer.