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Silicon-containing oligomeric poly(amides) with phthalimidyl-amide side groups: synthesis, characterization and thermal studies

Oligomeric poly(amide)s (PAs) were synthesized from monomeric diacids, which were obtained from phthalic anhydride and the amino acid glycine, l-alanine, l-phenylalanine, l-valine, l-leucine, l-isoleucine and p-aminobenzoic acid. The phthalimidyl acids (IA-1 to IA-7) reacted with 5-amino-isophthalic acid in order to obtain the monomeric diacids (1-7). Furthermore, the monomeric diacid 8 was obtained by direct reaction between phthalic anhydride and 5-amino-isophthalic acid. The isophthalic acid derivatives were reacted with bis(4-aminophenyl)diphenylsilane in order to obtain the PAs. Monomers and polymers were characterized by infrared and 1H-, 13C- and 29Si-NMR spectroscopy, elemental analysis and, when necessary, optical rotation. The results were in agreement with the proposed structures. The yields were generally good, but the η inh values were low, indicating that the polymers were of oligomeric nature, namely, a chain of moderate molecular weight. The polymers were soluble in polar aprotic solvents and some of them were soluble in m-cresol and tetrahydrofuran. The glass transition temperatures (T g) values were obtained by differential scanning calorimetry, showing, in general, a decrease in value when the volume of the side chain of the amino acid moiety was increased. The thermal stability of the polymers was determined by dynamic thermogravimetry, showing good values of thermal decomposition temperatures (TDT), especially for those with aromatic residue in the amino acid, and for PA without amino acid. For PAs in which the side chain of the amino acid was larger, the TDT values were lower, probably due to the lack of symmetry and the length of the side chain, both of which have influence on the thermal stability.