In situ fabrication of high performance polyimide/tyrosinemodified layered silicate nanocomposites
Several novel organic–inorganic hybrids consisting of high performance polyimide (PI) and organically modified montmorillonite (OMMT) with trifunctional swelling agent were successfully prepared by in situ polymerization technique. In this way, at first, OMMT was prepared by surface treatment of Cloisite Na+ with protonated form of bioactive L-tyrosine amino acid. Amine functional groups of this swelling agent formed an ionic bond with the negatively charged silicates, whereas the remaining acidic and phenolic functional groups are available for further interaction with PI chains. Then, organo-soluble PI with benzimidazole pendent group was prepared from pyromellitic dianhydride and 4-(3, 5-diaminophenyl)-benzimidazole in dry N,N-dimethylacetamide. PI/OMMT nanocomposites enclosing 1–10 wt.% of OMMT were successfully prepared by an in situ polymerization reaction through thermal imidization up to 300°C. Also, the relationship between the properties and OMMT content of the PI hybrid films were examined using Fourier-transform infrared spectroscopy, X-ray diffraction measurements and electronic microscopy (FE-SEM and TEM). The silicate layers in the polymer matrix were exfoliated as confirmed by XRD, FE-SEM and TEM techniques. The PI/OMMT films have good optical transparencies, and are almost colorless. The thermal stability of hybrids such as the decomposition temperature and weight residue at 800°C were also increased with increasing OMMT content.