THE EFFECT OF THE MONOMER SEQUENCE DISTRIBUTION ON THE PHOTOOXIDATION OF STYRENE ACRYLONITRILE COPOLYMERS

Infrared spectroscopy was used to study the photooxidation of styrene-acrylonitrile (SAN) copolymer samples that were exposed to ultraviolet radiation having a minimum wavelength of 290 nm. Peaks at 1952 cm-1, 1881 cm-1, 912 cm-1 and 549 cm-1 were found to have negative intensity values in the difference spectrum of photooxidized SAN. While the peaks at 1881 cm-1 and 912 cm-1 had previously been assigned to the SAS triad structure, the peaks at 1952 cm-1 and 549 cm-1 were assigned to the monad, dyad or triad structures of the styrene repeat unit. Furthermore, it had previously been established that the photooxidation of SAN occurs exclusively at the styrene repeat units within the copolymer structure. It was therefore concluded that the microstructure sequence which participates in the photooxidation of SAN is the triad SAS. More specifically, the styrene repeat units within the SAS triad structure undergo photooxidation when SAN is exposed to ultraviolet radiation.