Correlation between chain microstructure and activation energy in the pyrolysis of a high molecular weight isotactic polypropylene

Changes in chain microstructure during the pyrolysis of a high molecular weight isotactic polypropylene (iPP) have been tracked by means of FTIR, DSC and NMR techniques. For this purpose, preparative dynamic TGA experiments have been performed up to final temperatures between 200 degrees C and 420 degrees C. The evolutions of molecular weight, tacticity and both quality and content of chain-end double bonds have been analysed and correlated with the conversion-dependent Eact build-up, estimated from analytical TGA curves. The obtained results allows correlating the earliest low Eact values with the vanishing of chemical defective structures like carbonyls, as well as with the scission of some very few regular C-C bonds. The growing trend of the Eact, found from low to advanced pyrolysis stages, is associated to the collapse of the molecular weight and the decreasing of the isotacticity degree. The evolution towards shorter and more flexible chains is thought to underlie an increasingly energy demanding scission process. (c) 2015 Elsevier Ltd. All rights reserved.