Thermal stability and thermal decomposition study of hindered amine light stabilizers

The thermal decomposition of hindered amine light stabilizers for polyolefins based on bis(2,2,6,6-tetramethyl-4-piperidinyl) terephthalate (I), bis(2,2,6,6-tetramethyl-4-piperidinyl) o-phthalate (II) and 2,2,6,6-tetramethyl-4-piperidinyl stearate (III) has been studied using TG, DSC as well as FTIR of solid and GC/MS of high boiling decomposition products. The onset of weight loss in TG increases in the series: III < II < I. Ester cleavage by the β-elimination mechanism, scission of C–N bonds of the piperidine ring and aminolysis of the ester group have been shown to account for the formation of the decomposition products in the temperature range of 200–350 °C. The aminolysis reaction depresses the thermal stability of the studied compounds, in addition to the scission of the ester and C–N bonds. The yield of the products of aminolysis is higher from (I) and (II) compared to that from (III). The mass spectra of decomposition products and the decomposition scheme of the compounds under study are discussed.