Silicon-containing oligomeric poly(imido-amides) with amino moieties. Synthesis, characterization and thermal studies

Abstract

Silicon-containing oligomeric poly(imido-amides) (PIAs) were synthesized from dicarboxylic imido-acids containing a Si atom, which were obtained from dianhydrides and the amino acids glycine, L-alanine, L-phenylalanine, L-valine, L-leucine, L-isoleucine and p-aminobenzoic acid (I–III-(a–g)), were polymerized with the diamine bis(4-aminophenyl)diphenylsilane. Monomeric dicarboxylic imido-acids and PIAs were characterized by IR and ¹H, ¹³C and ²⁹Si NMR spectroscopy and, when necessary, optical rotation, and the results were in agreement with the proposed structures. The yields were very good, greater than 90%, but the η_inh values were low, indicating that PIAs were of oligomeric nature, especially those derived from dicarboxylic imido-acids with aromatic groups bonded to the Si central atom. PIAs were soluble in polar aprotic solvents, and also in other organic solvents like m-cresol, tetrahydrofuran, and several in CHCl₃ and acetone, due to the inclusion of Si atoms and amino acidic residues in the main chain. The glass transition temperature (T_g) values were obtained by DSC, and showed a tendency in the sense that when the side chain of the amino acidic residue is increased, the T_g values decrease, as the higher volume of the side chain implies a higher chain separation and consequently a higher free rotation of them. PIAs including glycine or p-aminobenzoic acid residues, without side groups, showed higher T_g values due to an increase of the molecular rigidity. The thermal stability was determined by dynamic thermogravimetry showing that almost all PIAs were thermally stable, with TDT_10% values greater than 400 °C. The most stable PIAs were those including the p-aminobenzoic residue in the main chain. The groups, methyl or phenyl, bonded to the Si atom of the carboxylic imide-acids residue did not show an important influence. The UV-vis transparency was studied showing that the increase of the aromatic content decreases the UV-vis transparency. PIAs derived from carboxylic imide-acids containing only phenyl groups bonded to the Si atom, were non-transparent.