Isam M. Arafa

Two-Dimensional Texture of Intrinsic Conductive Poly(styrene-co-maleanilic Acid) Grafted with Polyaniline: Formation and Conductivity

Intrinsically conducting polyaniline is grafted onto a preformed poly(styrene-co-maleanilic acid) copolymer backbone via chemical oxidative coupling of aniline in acidified chloroform/water emulsion. The structure and textural morphology of the grafted poly(S-co-MA-g-PANI) are examined by different spectroscopic, thermal, powder X-ray diffraction and scanning electron microscopic techniques. The d.c. electrical conductivity of the grafted emeraldine base of the obtained materials displays a d.c. conductivity of the order of 10−7 – 10−9 Scm−1, which is ∼2 orders of magnitude greater than that of the reported PANI-EB homopolymer. This enhancement in d.c. conductivity is explained in terms of microstructure-electronic conductivity relationship.

SYNTHESIS AND CHARACTERIZATION OF DIAMINECARBOSILAZANE-CONTAINING POLYMERS

ABSTRACT A series of diaminecarbosilazane-containing polymers of the general formula [-SiPh2-NH-R-NH-]n, (R is 1,2-ethane, 1,3-propane, 1,4-butane, 1,6-hexamethylene and 1,4-phenylene) has been prepared by polycondensation of dichlorodiphenylsilane with the corresponding aliphatic and aromatic diamines in the presence of a weak base. These carbosilazane polymers were characterized by elemental analysis, thermogravimetric analysis (TGA), infrared (FT-IR), 1H NMR and electronic(UV-vis) spectroscopy. The average molecular weight and n value of these polymers were found to range from 6000 to 9500 and 20 to 37, respectively.

Formation, Characterization and Electrical Conductivity of Polycarbosilazane-Cu(II), -Ni(II) and -Cr(III) Chloride Metallopolymers

A series of transition metal-polycarbosilazane complexes have been prepared by the reaction of poly(N,N′-bis(dimethylsilyl)ethylenediamine), [–Si(CH3)2NHCH2CH2NH–]n, with Cu(II), Ni(II), and Cr(III) chloride. The resulting complexes were characterized by infrared (FT-IR) and UV-visible spectroscopy, magnetic susceptibility measurements, thermogravimetric analysis (TGA), and powder X-ray diffraction (XRD). The average chain-chain spacing in these materials were estimated from XRD data and found to be 6.88, 7.91, 7.09, and 6.33 Å in metal-free, Cu(II)-, Ni(II)-, and Cr(III)-containing polycarbosilazanes, respectively. DC electrical conductivity measurements showed that all these metal-polycarbosilazane complexes exhibit semiconductor behavior while the metal-free matrix is an insulator.

Dielectric spectroscopy of polycarbosilazane-based CuCl2 metallopolymers

ABSTRACT A series of poly (carbosilazane-CuCl2) metallopolymers was prepared by the reaction of varying amounts (5% to 30%) of anhydrous CuCl2 with polycarbosilazane, [–(CH3)2SiNH(CH2)2NH–]n, matrix in tetrahydrofuran under continuous sonication. Dielectric measurements were performed at room temperature (25°C) in the frequency range 1 Hz to 106 Hz. It was found that the ac conductivity increases with increasing the CuCl2 up to 16% and then starts to dramatically decrease. The results reveal that all the dielectric parameters such as ac impedance, dielectric permittivity, and electric modulus behave similar to that observed in ac conductivity. (i.e., maximum or minimum depends on the considered dielectric parameter). It is suggested that at low concentration of metal content, all the CuCl2 is uniformly bound to the backbone of the polymer chains, where the conduction mechanism in the system is by electrons jumping (carrier hopping between the chains), whereas at high metal content the coordination capacity of the backbone is exceeded and CuCl2 is present as molecular clusters that lead to an increase in the interaction distances, and make hopping between chains more difficult, and hence, resulting in a reduction of conductivity.

Crystalline Amphiphilic (Maleanilic acid-ran-styrene) Copolymers: Structural and Kinetic Properties

Abstract A series of amphiphilic (maleanilic acid-ran-styrene) copolymers composed of hydrophobic and hydrophilic moieties were prepared by radical copolymerization using different molar feed ratios of maleanilic acid and styrene. The obtained copolymers were structurally examined by FT-IR, TGA, XRD, and SEM. The weight average molecular weight (Mw) was determined by light scattering method in DMSO and found to lie in the range of 20,000–334,000 g/mol depending upon the molar feed ratio of the maleanilic acid and styrene monomers. The reactivity ratios and Q-e scheme values for the copolymerization process showed a random arrangement of repeating units. The corresponding activation energies for the degradation process (E a,d ) for maleanilic acid and styrene fractions in the copolymer were determined from the TGA data and found to be 57.1 and 89.5 kJ/mol, respectively. The SEM and XRD data show that these copolymers exhibit a rigid rock-like texture with different degree of percent crystallinity. The hydrophilic moiety (–COOH) in these copolymers was found to play a crucial role in determining their crystallinity and textural morphology. The implication of the presence of the hydrophobic and hydrophilic groups in close proximity is discussed.

Gas phase hydrodechlorination of CCl 4 over Pd–Cu and Pd–Fe bimetallic catalysts supported on an AlF 3 matrix

Two bimetallic catalytic systems composed of Pd–Cu and Pd–Fe supported over AlF3 were prepared by the sol–gel method and characterised by BET, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (P-XRD). Analysis of the XPS and P-XRD data showed that the surface of these bimetallic catalysts may be described as Pd0–CuI and Pd0–FeIII hydroxides. The gas phase hydrodechlorination reaction (HDC) of CCl4 over these bimetallic catalysts showed that the presence of CuOH and Fe(OH)3 altered their catalytic activity, selectivity and product distribution compared to their monometallic Pd/AlF3 analogue. The bimetallic catalysts showed a very high selectivity for the formation of C1-products (CHCl3, CH2Cl2 and CH3Cl) in contrast with the tendency shown by the monometallic Pd/AlF3 analogue of forming coupled C2–C5 products. Interestingly, the pore-controlled version of the Pd–Fe*/AlF3 catalyst showed a greater efficiency favouring the formation of CHCl3 and CH2Cl2 compared with its Pd–Fe/AlF3 analogue which predominantly favoured the formation of CH3Cl. The effect of temperature, in the range of 458–513 K, and time on stream on the catalytic performance of the bimetallic catalysts in terms of percentage conversion, reaction rate and product distribution are discussed.

Formation, Characterization, and Stability of Novel Aluminocarbosilazane Macromolecules

Abstract A novel class of polycarbosilazaneċAlCl3 macromolecules (AlCSZ) with a Si/Al molar ratio of 1 : 1, 2 : 1, and 3 : 1 were prepared by a two‐step reaction, formation of H2NCH2CH2NH2ċAlCl3 adducts followed by condensation of H2NCH2CH2NH2 with (CH3)2SiCl2 in an aprotic solvent containing triethylamine base. The resulting AlCSZ materials were examined by elemental analysis, infrared spectroscopy (FT‐IR), mass spectrometry (MS), and powder x‐ray diffraction (XRD). The average polycarbosilazane chain–chain distances in the aluminum‐free polycarbosilazane and these AlCSZ macromolecules were estimated from the XRD data and found to be 5.94, 6.75, 6.88, and 7.19 Å, respectively. This demonstrates that AlCl3 is incorporated between the polycarbosilzane chains and has caused chain–chain expansion. The thermal properties of these AlCSZs were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). They are air stable white solids but decompose in water forming the corresponding dimethylsiloxane, ethylenediamine, and aluminum oxide.

Hydrodechlorination of (CH3)3SiCHCl2 over Pd, Ni, Co and Fe supported on AlF3

AbstractGas phase hydrodechlorination (HDC) process of Me3SiCHCl 2 was studied in a flow reactor at 200 ∘C using a 2% metal loading (w/w) of four different monometallic catalysts (Pd/AlF 3, Ni/AlF 3,Co/AlF 3 and Fe/AlF 3). The catalysts were prepared by sol-gel method and structurally examined by BET method, FT-IR and XPS techniques. The XPS technique showed that Ni II, Fe III and Co III exist as oxides. The major products in the HDC process of Me 3SiCHCl 2 were identified by GC and GC-MS and found to include Me 3SiCH 2Cl, Me 3SiCl, and Me 4Si. The effect of these catalysts on the quantitative conversion, selectivity and conversion rates are reported. Graphical AbstractGas phase hydrodechlorination process of Me3SiCHCl2 was studied in a flow reactor at 200°C using a 2% metal loading (w/w) of four different monometallic catalysts (Pd/AlF3, Ni/AlF3, Co/AlF3 and Fe/AlF3). The XPS technique showed that NiII, FeIII and CoIII exist as oxides. The major products in the process of Me3SiCHCl2 were identified to include Me3SiCH2Cl, Me3SiCl, and Me4Si

Mossbauer Spectroscopy Study of Macromolecular Complexes of Polycarbosilazane Coordinated with Fe(II), Fe(III) and Mixed Valence Fe(II-III) Chlorides

A series of iron-polyethylenediaminecarbosilazane (PEDCSZ-Fe) macromolecular chloride macromolecular complexes were prepared by the reaction of Fe(II), Fe(III), and mixed valence Fe(II-III) chlorides with polyethylenediaminecarbosilazane matrix in toluene under inert atmosphere. The mixed valence macromolecular complexes composed of three different ratios of Fe(II)/Fe(III) (1:2, 1:1, and 2:1). Mössbauer spectra were recorded for the samples at room temperature. The spectra of the PEDCSZ-Fe(II) and PEDCSZ-Fe(III) macromolecular complexes showed pure paramagnetic phase, whereas, the spectra for the mixed valence PEDCSZ-Fe(II-III) showed both magnetic and paramagnetic splitting. The magnetic splitting is so broad such that it was fitted with three magnetic sextets and one quadrupole doublet. The relative intensity of the magnetic phase was the highest for the PEDCSZ-Fe(II-III) with 1:1 ratio. The magnetic phase could be attributed to an iron oxide phase (Fe3O4 or FeOOH phase) in a fine powder form as it is clear from the Mössbauer parameters. The XRD patterns of the PEDCSZ-Fe(II-III) with 1:1 ratio contained additional diffraction peaks similar to those observed for Fe3O4 in a fine particle form.