Thermal degradation kinetics and decomposition mechanism of two new aliphatic biodegradable polyesters poly(propylene glutarate) and poly(propylene suberate)

The synthesis, characterization and thermal behavior of two biodegradable aliphatic polyesters poly(propylene glutarate) (PPGlu) and poly(propylene suberate) (PPSub) derived from 1,3-propanediol and glutaric and suberic diacid, respectively, have been studied. These polyesters were characterized using several techniques. Thermal degradation of both polyesters was studied by determining theirs mass loss during heating. From the thermogravimetric curves it can be seen that PPSub present a relatively better thermostability than PPGlu since the maximum mass loss occurred at temperatures 411.2 and 409.1 °C, respectively. The activation energy (E) of degradation was calculated using the isoconversional methods proposed by Ozawa–Flynn–Wall (OFW) and Friedman. From the variation of E with increasing degree of conversion it was found that the polyester decomposition is taking place with a complex reaction mechanism with the participation of at least two different mechanisms. Two combinations of models, nth order and nth order with autocatalysis (Fn–Cn) as well as nth order with autocatalysis in both mechanisms (Cn–Cn) give the better results. Using pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) it is found from mass ions detection that the decomposition of both polymers takes place, mainly, through β-hydrogen bond scission and secondarily by α-hydrogen bond scission. At 410 °C CO2 is the main gas product of decomposition while allyl, diallyl, carboxylic acids, aldehydes and hydrocarbons are the main liquid products.