Investigating the degradation of thermoplastics by thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR)

Abstract

Themogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) has been used to study the thermal degradation of three types of synthetic thermoplastics: Poly(arylene ether)s containing an acenaphthylene moiety, poly(arylene ether ketone)s prepared as analogues of the commercial polymer poly(ether ether ketone) (PEEK), and aromatic polyimides synthesized by a single-step solution polymerization. TG-FTIR was found to be useful in providing important structural information about the poly(arylene ether)s and polyimides, which was not apparent through conventional NMR or FTIR techniques. Spectra obtained using air as a purge for insoluble and soluble poly(arylene ether)s 1 revealed that residual sulfur remained in both polymers after preparation through a reaction with Lawesson's reagent. Comparison of TGMN-FTIR results of new poly(arylene ether ketone)s 2 with previously reported data on degradation studies of PEEK obtained with TG-mass spectrometry (TG-MS) showed that both polymers had similar degradation patterns, with phenol being a major degradation product. TG-FTIR studies on polyimides 3 and 4 synthesized by one-step solution polymerization demonstrated that it was possible to determine the imidization degree by monitoring the intensity of the water absorption band at 1795 cm−1 as a function of the TG temperature during a weight-loss occurring near 300 °C. The FTIR spectra of both polyimides studied in this work showed that carbon monoxide was a significant degradation product. Other degradation products detected for polyimide 3 were ammonia, isocyanic acid and phenyl isocyanate. FTIR peaks consistent with hydrogen cyanide also appeared for polyimide 3.