On thermal stability of polydiphenylenesulfophthalide lithium salt

Abstract

Thermolysis of polytriarylcarbinol (PTAC-Li) (lithium salt of polydiphenylenesulfophthalide (PDSP)) was studied in the temperature range from 100 to 500 °С by thermogravimetric analysis (TG) and IR and electronic spectroscopy to check the available data on the higher thermal stability of PDSP salts over the initial polymer. The mass losses detected by the TG method in the polymer salt at 80—150 and 240—350 °С are mainly caused by the desorption of weakly and strongly bound water. According to the calculations in the B3LYP/6-311+G(d,p) approximation, the С—ОН and C—SO₃^-Li⁺ bonds are weakest in the carbinol model for PTAC-Li (D(C—O) ~ D(C—S) ~ 72 kcal mol^–1). The thermolysis of PDSP is accompanied by SO₂ evolution, whereas hydroxy and sulfo groups detached from PTAC-Li macromolecules remain in the thermolyzate. Phenol fragments and an inorganic phase, the final form of which is lithium sulfate, are formed in this process. An analysis of the IR and UV spectra of the thermolyzates of PTAC-Li and PDSP confirmed that fluorenyl fragments are predominantly formed upon the thermolysis of these polymers. The data obtained do not confirm a higher stability of PTAC-Li compared to that of PDSP.