Poly(esters) Containing Two Silicon Atoms and Aminoacidic Residues in the Main Chain: Synthesis, Characterization and Thermal Studies

Abstract

Poly(esters) (PEs) derived from the reaction between bis(imido acids) containing Si as central atom and an aminoacidic residue, and a Si-containing diphenol, were synthesized according to the procedure described by Higashi. PEs were characterized by spectroscopic methods including 29Si NMR and the results were in agreement with the proposed structures. PEs were soluble in aprotic polar solvents and also in other common organic solvents such as tetrahydrofuran, acetone or CHCl3, which was attributed to the presence of aliphatic residues in the main chain provided by the amino acids, with the exception of those PEs which include p-aminobenzoic acid moieties. The PEs showed inherent viscosity values, indicative in some case of oligomeric species. Almost all the PEs showed good thermal stability, the most stable being those that include p-aminobenzoic acid as aminocidic residue due to the presence of a new p-aromatic ring in the main chain. Also it was possible to see that when the aromatic content was increased in the bis(imido acid) portion, the thermal decomposition temperature values also increased, especially when the values are compared with those PEs only with methyl groups bonded to the Si atoms. The Tg values were determined by DSC technique and those PEs with high aromatic content showed the highest Tg values due to the rigidity of the polymeric chain. On the other hand, when the size of the aliphatic side chains provided by the aminoacidic residues increased, the Tg values decreased due to the higher separation of the polymeric chains and consequently the higher free volume between them. The same tendency was observed as a function of the groups bonded to the Si atom of the bis(imido acids). PEs showed low UV–vis transparence due mainly to the high aromatic content, which favors the absorption.