Thermal Degradation of Glutamate Polymers

Thermal properties of precipitated samples and films of poly-γ-benzyl-L-glutamate (PBG) and poly-L-glutamic acid (PGA) have been studied using TGA, DSC, and pyrolysis. The PBG film was identified as that described by McKinnon and Tobolsky as “form C” (“film A” of Uematsu et al.) using IR, dielectric relaxation, and DSC data. The PGA film is α-helical (IR) and was further characterized by dielectric relaxation measurements. With the exception of water loss at ∼110° from PGA, TGA and DSC measurements reveal only incomplete endotherms corresponding to decomposition. Volatile decomposition products were trapped and identified using combined GC/IR and GC/MS techniques. Identified products were as follows: from PGB–CO2, NH3, H2O, toluene, benzaldehyde, benzyl alcohol, and benzoic acid; from PGA–CO2, NH3, CH3OH, acetone, and H2O. Only minor differences were noted in GC traces of the total volatile decomposition products in air or in nitrogen streams. No evidence for retained solvent in cast films was obtained.