title: Study on the formation of the ketonic defects in the thermal degradation of ladder-type poly(p-phenylenes) by vibrational spectroscopy.
abstract: We have investigated the thermal degradation in air by Fourier transform infrared spectroscopy of a ladder-type copolymer containing fluorene units in the backbone (Me-LPF), to reveal the formation of the ketonic defects. As thermal treatment of Me-LPF film at 200 degrees C in air proceeds, a new group of complex absorption bands due to degradation products arises in the range between 1800 and 1600 cm(-1). The observed overlapping bands were separated and assigned by utilizing the second-derivative IR spectral analysis, which can narrow the peak width to one-third of the originals and thereby eases the analysis. The degraded products were assigned as fluorenone (1718 cm(-1)) and benzophenone (Ar-(C=O)-Ar) (1665 cm(-1)), formed by the oxidation of the backbone, and acylphenone (Ar-(C=O)-R) (1685 cm(-1)) from the side chain. The fluorenone was found to be the major component among the degraded products in the main chain, and the time and temperature dependence indicated that the oxidation is a kind of autocatalytic radical-chain process. The oxidation can reach a very high degree (approximately 30% for 6 h oxidation at 240 degrees C estimated by absorption of the alkyl). Our results suggest the possibility of the oxidation of the 9-bialkylfluorene sites. We propose that the degradation of the alkyl in the side chain can help the radicals to propagate in the chain reaction.
authors.affiliation: Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, Jilin University, 2699 Qianjin Avenue, Changchun 130012 People's Republic of China.
authors.forename: Linlin
authors.initials: L
authors.lastname: Liu
authors.forename: Song
authors.initials: S
authors.lastname: Qiu
authors.forename: Baoling
authors.initials: B
authors.lastname: Wang
authors.forename: Wu
authors.initials: W
authors.lastname: Zhang
authors.forename: Ping
authors.initials: P
authors.lastname: Lu
authors.forename: Zengqi
authors.initials: Z
authors.lastname: Xie
authors.forename: Muddasir
authors.initials: M
authors.lastname: Hanif
authors.forename: Yuguang
authors.initials: Y
authors.lastname: Ma
authors.forename: Jiacong
authors.initials: J
authors.lastname: Shen