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

The effect of molecular weight on the thermal degradation of poly(epsilon-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 degrees 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) = 10,000 g/mol) PCL (PCL(10k)) decomposed in a three-step mechanism. The evolved gases detected by FT-IR spectroscopy were identified as epsilon-caprolactone, 5-hexenoic acid, CO(2), and methyl pentanoate and traces of H(2)O. 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, CO(2), H(2)O, 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 CO(2), CO, H(2)O, and short-chain carboxylic acids.