Thermal stability of poly(oxyalkylene)amine-grafted polypropylene copolymers

Abstract

The thermal and thermo-oxidative degradation of a family of amphiphilic copolymers consisting of a polypropylene (PP) backbone and several poly(oxyethylene) /poly(oxypropylene) (POE/POP) pendants were investigated by using a thermal gravimetric analysis (TGA). Their relative stability was correlated to the chemical structures with respect to the POE versus POP in pendants and the terminal functionalities. In comparing the starting amines, molecular weight (Mw) and the types of polymer backbone were the main controlling factors for thermal stability in nitrogen, while the terminal amine contributed most to the thermo-oxidative stability in air. In the amine-grafted PP copolymers, the functional groups including the tethered amine, quaternary amine and sodium salt complexes significantly stabilized the PP copolymers, particularly in oxidative condition. The following trends of relative stability in air were observed: PP- g-MA/EDA>PP- g-MA/DAP ≫ PP- g-MA/ED2001 ≫ PP- g-MA/M2070=PP- g-MA/D2000>ED2001>D2000=PEG2000>PPG2000; PP- g-MA/Na +>PP- g-MA. Under the condition of helium gas and at 550°C, the representative PP- g-MA/ED2001 copolymer was pyrolyzed into fragments of olefins/dienes from PP backbone as well as vinyl ethers from POE pendants, as observed by GC/mass spectroscopy. Reaction pathways for degradation and the controlling factors for the thermal and thermooxidative stability of these functionalized PP copolymers are discussed.