Polycondensation Of Dianhydride Research Articles

Thermal induced structural rearrangement of cardo-copolybenzoxazole membranes for enhanced gas transport properties

We have successfully designed amendable polybenzoxazole materials with enhanced gas transport properties via incorporation of cardo moiety into thermally rearrangeable polymer chains. A series of cardo-copoly(hydroxyimide) have been synthesized by polycondensation of dianhydride with various molar ratios of two different ortho-functional diamine sources: 3,3′-dihydroxybenzidine (non-cardo) and 9,9-bis(3-amino-4-hydroxyphenyl)fluorene (cardo). The effect of cardo-containing diamine composition in the range of 5–50mol% on the structural and gas transport properties of the copolybenzoxazole membranes have been systematically investigated in the present work. It is found that the incorporation of cardo group has increased the gas permeability significantly. Thermally rearranged copolybenzoxazole membrane with the addition of 10mol% of cardo moiety has shown the largest enhancement in gas permeability. An increment of 3 times in CO2 permeability has been achieved as compared to the CO2 permeability in the non-cardo counterparts. The excellent features of the cardo-copolybenzoxazole shows a promising approach for the future cavity engineering in the field of high performance materials.

Layer-by-layer self-assembly of polyimide precursor/layered double hydroxide ultrathin films

The layer-by-layer (LBL) self-assembly has been extensively used as a simple and effective method for the preparation of polyelectrolyte multilayer films. In this work, we utilized this unique method to prepare polyimide precursor/layered double hydroxide (LDH) ultrathin films. Well-crystallized Co–Al–CO 3 LDH and subsequent anion exchanged Co–Al–NO 3 LDH were prepared and characterized by scanning electron microscopy and X-ray diffraction (XRD). By vigorous shaking of the as-prepared Co–Al–NO 3 LDH, positively charged and exfoliated LDH nanosheets were obtained. Atomic force microscopy and XRD investigations indicated the delamination of LDH nanosheets. The precursor of polyimide, poly(amic acid) tertiary amine salt (PAS) was prepared by the polycondensation of dianhydride and diamine, and subsequent amine salt formation. By using the LBL method, heterogeneous ultrathin films of PAS and LDH were prepared. The formation of the ordered nanostructured assemblies was confirmed by the progressive enhancement of UV absorbance and the XRD results.

Pervaporative studies using polyimide‐filled PDMS membrane

AbstractThe application of pervaporation (PV) to the removal of volatile organic from aqueous solutions has become very interesting in the last few years. It is caused by the increasing level of compounds, such as petrochemical solvents (benzene, toluene, and xylenes) or chlorinated solvents (trichloroethylene or tetrachloroethylene), which are polluting the natural environment. In this work, effects of polyimide (PI) (prepared by direct polycondensation of dianhydride and diamine followed by thermal cyclization of polyamic acid) filler on PV properties of poly(dimethyl siloxane) (PDMS) have been studied. PDMS membrane filled with PI was used for the separation of benzene (Bz) and toluene (Tol) from the diluted aqueous solution and the results were compared with the neat PDMS membrane of similar thickness. The PDMS‐PI membrane showed normalized flux (J′) upto 1.2 kg μm/m2h for Bz and 1.48 kg μm/m2h for Tol and selectivity of organics varies from 7.3 to 3.2 for Bz and 8.9 to 2.8 for Tol with increasing concentration of organics. Concentration of PI filler in PDMS varied 5–25% w/w. PI filler increases thermal as well as mechanical stability of filled PDMS membranes. PDMS membrane filled with 25% PI was chosen for the pervaporation studies. The membranes were characterized by FTIR, thermogravimetric analyser and scanning electron microscopy. The mechanical strength of PDMS filled with 25% w/w PI (SPI‐25) membrane was found to be 2.7 MPa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Metallized polyimide films: Metallization and mechanism of the process

The formation of metallized polyimide films in situ, namely, the alkaline hydrolysis of film surfaces, chelation of the modified surface with metal ions, and their chemical reduction giving rise to a metal layer, has been investigated. Initial polyimide films are cast from reaction solutions on a glass substrate. The solutions are prepared through the polycondensation of dianhydride of tricyclo[4.2.2.02.5dec-7-ene-3,4,9,10-tetracarboxylic acid and 4,41-diaminodiphenyl oxide in N-methyl-2-pyrrolidone at 160°C. It has been shown that alkaline water-alcohol solutions are optimal media for the hydrolysis of the film surface. The maximal exchange of alkali metal ions is achieved through formation of a more stable metal-ligand complex of poly(amido acid), with the chelation rate depending on the nature of a metal. The metal reduction proceeds rapidly; however, the mechanism of this process depends on the pH of a medium. The annealing of metallized films results in the imidization of poly(amido acid) and in the growth of metal grains on the material surface to yield a metal layer with good optical properties and high conductivity.