ANALYSIS OF PHOTODEGRADATION MECHANISM OF ALIPHATIC AND AROMATIC POLYESTERS USING FT-IR-ATR, GPC, AND DMA

Photodegradation of poly(butylene succinate) (PBSU), random copolymer of poly(butylene succinate adipate) (Co-PBSU . AD), and poly(ethylene terephthalate) (PET) with ultraviolet(UV) irradiation of wavelength 31 2 nm was investigated with FT-IR-ATR, GPC, and DMA. The results of GPC measurement showed that M(n) and M(w) decreased remarkably for PBSU a nd Co-PBSU . AD, but they were almost unchanged for PET on UV irradiat ion. DMA measurements showed the cleavage of main chains for PBSU and Co-PBSU . AD and the formation of three-dimensional net-works for PET. In FT-IR-ATR spectra of PBSU and Co-PBSU . AD, the intensities of ban ds at 2947 cm(-1) (-C-H), 1713 cm(-1) (C=O of ester), and 1154 cm(-1) (C-O-C) decreased, and new bands at 3480 cm(-1) (O-H), 3000 cm(-1) (=C -H), 2964 cm(-1) (-CH3), and 1699 cm(-1) (C=O of COOH) were observed. In the case of PET, the intensities of bands at 1713 cm(-1) (C=O of es ter) and 1098 cm(-1) (C-O-C) decreased, and new bands at 3480 cm(-1) ( O-H), 2650 cm(-1) (-C-H of aldehyde), 1760 cm(-1) (C=O of aldehyde), a nd 1688 cm(-1) (C=O of COOH) were observed. These results indicate tha t photodegradation of PBSU and Co-PBSU . AD undergoes mainly by the me chanism of Norrish II type which causes the cleavage of main chains to give CH2=CH-, -COOH, and -COCH3 end goups. On the other hand, photode gradation of PET undergoes mainly by the mechanism of photo-Fries rear rangement to form three-dimensional net-works in the primary photolysi s process and subsequently, photooxidation reactions occur, resulting in the cleavage of main chains to give -CHO and -COOH end groups, and radicals which form the three-dimensional net-works.