Molecular Weight Dependence of the Thermal Degradation of Poly(ε-caprolactone): A Thermogravimetric Differential Thermal Fourier Transform Infrared Spectroscopy Study

Abstract

The effect of molecular weight on the thermal degradation of poly(ε-caprolactone) (PCL) was investigated by thermogravimetric analysis in combination with differential thermal analysis and Fourier transform infrared spectroscopy (TGA/DTA/FT-IR). The measurements were made in the temperature range 40–720 °C and it was found that PCL undergoes completely different degradation processes in nitrogen and oxygen atmosphere. Thus, in nitrogen atmosphere low molecular weight (M_n = 10000 g/mol) PCL (PCL^10k) decomposed in a three-step mechanism. The evolved gases detected by FT-IR spectroscopy were identified as ε-caprolactone, 5-hexenoic acid, CO₂, and methyl pentanoate and traces of H₂O. In the case of high molecular weight (M_n = 80 000 g/mol) PCL (PCL^80k) only a two-step degradation was observed. By FT-IR spectroscopy 5-hexenoic acid, CO₂, H₂O, and methyl pentanoate were detected as decomposition products. In an oxygen environment, similar degradation products were detected for the different molecular-weight PCLs. The recorded FT-IR spectra of the evolved gases were identified as CO₂, CO, H₂O, and short-chain carboxylic acids.