Analysis of Photodegradation Mechanism of Aliphatic and Aromatic Polyesters Using FT-IR-ATR, GPC, and DMA

Abstract

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 312 nm was investigated with FT-IR-ATR, GPC, and DMA. The results of GPC measurement showed that Mn and Mw decreased remarkably for PBSU and Co-PBSU •AD, but they were almost unchanged for PET on UV irradiation. 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 bands at 2947 cm-1 (-C-H), 1713 cm-1 (C=0 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=0 of ester) 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=0 of aldehyde), and 1688 cm-1 (C = Oof COOH) were observed. These results indicate that photodegradation of PBSU and Co-PBSU•AD undergoes mainly by the mechanism of Norrish II type which causes the cleavage of main chains to give CH2 = CH-, -COOH, and -COCH3 end goups. On the other hand, photodegradation of PET undergoes mainly by the mechanism of photo-Fries rearrangement to form three-dimensional net-works in the primary photolysis 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. © 1995, The Society of Polymer Science, Japan. All rights reserved.