Thermal decomposition characteristics of poly(propylene carbonate) using TG/IR and Py-GC/MS techniques

The thermal decomposition behaviour of poly(propylene carbonate)s (PPC)s synthesized with varying molecular weights was studied at various pyrolysis temperatures by the combination of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetric analysis/infrared spectrometry (TG/IR) techniques. The pyrolysis products of PPCs with lower molecular weight of 26,900 and higher molecular weight of 144,600 at different pyrolysis temperatures were identified using Py-GC/MS. The dynamic decomposition was also explored with the TG/IR technique. The results showed that chain scission occurs at relatively lower temperature than for the unzipping reaction, and an increase in molecular weight can reduce the amount of the active terminal groups and restrict unzipping reaction to some extent. It was also observed that the backbone structure plays a great role in thermal decomposition behaviour of PPC. The same perfectly alternating structure leads to the same decomposition mechanism whereas unzipping needs a high activation energy and takes place at high decomposition temperature. The final pyrolysates are cyclic propylene carbonate, and 1,2 propanediol. Low molecular weight PPC undergoes a one-stage pyrolysis and high molecular weight PPC pyrolysis obeys two-step pyrolysis mechanism, viz. main chain random scission and unzipping. The thermal decomposition behaviour of PPC in the absence and presence of a metal complex catalyst was studied by TG/IR. It was further observed that the metal complex catalyst has little effect on the thermal decomposition of the PPC. The catalyst only slightly reduced the activation energy leading to the accelerated depolymerization reaction. (C) 2003 Elsevier Science Ltd. All rights reserved.