Synthesis and structural characterization of novel chiral nanostructured poly(esterimide)s containing different natural amino acids and 4,4′-thiobis(2-tert-butyl-5-methylphenol) linkages
Pyromellitic dianhydride (benzene-1,2,4,5-tetracarboxylic dianhydride) (1) was reacted with several amino acids in acetic acid and the resulting imide-acid [N,N′-(pyromellitoyl)-bis-L-amino acid diacid] (4a–4d) was obtained in high yield. The direct polycondensation reaction of these diacids with 4,4′-thiobis(2-tert-butyl-5-methylphenol) (5) was carried out in a system of tosyl chloride(TsCl), pyridine, and N,N-dimethyl formamide (DMF) to give a series of novel optically active poly(esterimide)s. Step-growth polymerization was carried out by varying the time of heating and the molar ratio of TsCl/diacid, and the optimum conditions were achieved. These new chiral polymers were characterized with respect to chemical structure and purity by means of specific rotation experiments, FTIR, 1H-NMR, X-ray diffraction, elemental, and thermogravimetric analysis (TGA) field emission scanning electron microscopy (FE-SEM) techniques. These polymers are readily soluble in many polar organic solvents like DMF, N,N-dimethyl acetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, and protic solvents such as sulfuric acid. TGA showed that the 10% weight loss temperature in a nitrogen atmosphere was more than 390°C; therefore, these new chiral polymers have useful levels of thermal stability associated with good solubility. Furthermore, study of the surface morphology of the obtained polymers by FE-SEM showed that each polymers exhibit nanostructure morphology.