Construction and characterization of bionanocomposites based on optically active poly(ester-imide) containg L-amino acids using nano-ZnO surface-coupled by γ-methacryloxypropyltrimethoxysilane

In this paper, we investigated the synthesis of an optically active poly(ester-imide) containing two aminoacid residues in the main chain. This macromolecule was synthesized by polycondensation of N,N- (pyromellitoyl)-bis-L-tyrosine dimethyl ester as a diphenolic monomer and a chiral trimellitic anhydride-derived diacid monomer containing L-methionine. The direct step-growth polymerization of this diacid with aromatic diol was carried out in a system of tosyl chloride (TsCl), pyridine (Py) and N,N-dimethylformamide (DMF) as a condensing agent. The obtained polymer has a useful level of thermal stability. Thereafter, the surface of zinc oxide nanoparticles (ZnO-NPs) was treated with a silane coupling agent, γ-methacryloxypropyltrimethoxysilane (KH570), which introduces functional groups on the surface of ZnO-NPs. Then, PEI/zinc oxide bionanocomposites (PEI/ZnO BNCs) containing 4, 8 and 12% of NPs were successfully prepared by an ultrasonic method as a simple and inexpensive route. In modified ZnO-NPs, the organic chains of KH570 can fulfill strict hindrance between inorganic NPs and prevent their aggregation. The obtained polymer BNCs were characterized by FT-IR, XRD, FE-SEM, TEM and TGA. The FT-IR spectroscopy indicated that the silane coupling agent was anchored on the surface of ZnO-NPs. Direct proof for the formation of the true polymer BNCs was provided by TEM investigation. Also, a morphology study of the synthesized polymer BNCs using FE-SEM analysis showed well-dispersed ZnO-NPs in the polymer matrix. TGA confirmed that the heat stability of the polymer BNCs was enhanced in the existence of modified nanostructure ZnO particles.