CHAIN HETEROGENEITY AND LUMINESCENCE OF POLY(ETHYLENE-TEREPHTHALATE)

Poly(ethylene terephthalate) films and polycrystalline powder of terephthalic acid (TPA) were found to exhibit the same fluorescent properties. The nature of the optically active centers in TPA and PET was established. The TPA molecules exhibit no intrinsic fluorescence. The fluorescence spectra of TPA powders depend on the degree and method of purification, which suggests the emitting centers to be associated with the presence of impurities. On the basis of the published data on the presence of various side products of TPA synthesis in the powdered acid, the optically active centers responsible for the emission in the 360 - 440 nm region were identified as trace amounts of dicarboxystilbene, and those responsible for the emission in the 320 - 380 nm region, were identified as trace amounts of dicarboxydiphenyl. The corresonding optically active centers in PET were interpreted as molecular chain defects, formed as a result of the participation of the above dicarboxy compounds in the polymeriozation reaction. The concentration of the defects in the molecular chain is insignificant, and is manifested to a significant extent only in the fluorescence spectra.