Thermal decomposition mechanism investigation of hyperbranched polyglycerols by TGA-FTIR-GC/MS techniques and ReaxFF reactive molecular dynamics simulations

Abstract

Molecular structure of hyperbranched polyglycerols (hbPGs) strongly affected the thermal stability as the critical heat transfer medium to maintain thermal homeostasis during working of heat engine. Here, thermogravimetric analysis (TGA)-fourier-transform infrared spectroscopy (FTIR)-gas chromatography (GC)-mass spectroscopy (MS) and reactive force-field (ReaxFF) techniques were utilized to identify major thermal decomposition products and explore the molecular mechanism. TGA-FTIR-GC/MS results showed that the major products were CO, CO2, water molecules and C3 organic moieties. To perform ReaxFF molecular dynamic simulation, timestep-dependent images revealed that C3 molecules were mainly originated from glycerol units and hydroxyl groups played an essential role in catalyzing thermal decomposition. To examine our hypothesis, different methoxylation levels of hbPGs were prepared, and TGA analysis of these methoxylated hbPGs polymers clearly corroborated that lower percentage of hydroxyl groups in the hbPGs can significantly increase maximum peak temperature from ∼400 °C to ∼460 °C. Our investigation clearly provided the molecular mechanism of hbPGs thermal decomposition and identified a potential way to improve thermal stability of hbPGs.