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MIT World Peace University

School of Polymer Engineering

The anisotropy of electrical conductivity has been studied in polypyrrole deposited on poly(ethylene oxide)-copper(II) chloride complex films deposited by the dip-coating technique. The preconditioning of these films has a strong influence on the anisotropy of conductivity and in many cases the conductivity is found to be higher in the perpendicular direction than parallel to the direction of pull. There is also a critical speed of the substrate used during dip coating at which the anisotropy is found to be a maximum. These various results have been explained on the basis of the morphology of the polypyrrole deposit which is influenced by the poly(ethylene oxide) complex and confirmed by deliberate modification of the same complex by blending it with other polymers. © 1995.

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Engineering and Technology

Thin Solid Films

Anisotropy of conductivity in polypyrrole deposited on crystalline poly(ethylene oxide)-copper(II) chloride complex and its blend

The changes in viscosity of epoxy–acrylate resins during the photocross‐linking process have been monitored continuously. The curing show change of shape and a distinct peak especially at high intensities. The intensity dependence of gel time follows a superlinear power law of the type tpαI−1.6 rather than the ½ power law. The dielectric relaxation studies on these photocross‐linked films having different compositions of epoxy and n‐butyl methacrylate reveal a particular composition range in which various dielectric parameters pass through critical values. These various findings have been explained on the basis of phase separation taking place during the UV curing process but at a submicron level leading to a very small domain size. © 1994 John Wiley &amp; Sons, Inc. Copyright © 1994 John Wiley &amp; Sons, Inc.

Journal of Applied Polymer Science

Continuous UV cure monitoring and dielectric properties of photocross‐linked epoxy–acrylate resins

The structure, development, morphology, and dielectric relaxation have been investigated in poly(vinyl chloride)–thermoplastic elastomer (copolyester–ether) blends having different compositions. The changes in the intensities of dielectric relaxation peaks for the β and γ processes with respect to blend composition have been found to be associated with corresponding changes in crystalline structure and morphology of the elastomeric component. The critical composition for observing such modification of properties is about 50% of poly(vinyl chloride) above which the blend becomes almost amorphous. © 1994 John Wiley &amp; Sons, Inc.<h2>&nbsp;</h2>

Structure and dielectric properties of poly(vinyl chloride) thermoplastic elastomer blends

Vapour phase polymerization of pyrrole on crystalline poly(ethylene oxide) (PEO) complexes gives ordered structure conforming to orthorhombic configuration with lattice parameters of&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mtext>a = 6.11</mtext><mtext>A</mtext><mtext>̊</mtext><mtext>, b = 7.19</mtext><mtext>A</mtext><mtext>̊</mtext><mtext>and</mtext><mtext>c = 16.31</mtext><mtext>A</mtext><mtext>̊</mtext></math>. The detailed analysis of these films has been carried out by wide angle X-ray diffraction and X-ray photoelectron spectroscopy. A strong influence of the crystalline substrate is seen in the molecular ordering of the polypyrrole grown on them which can be explained on the basis of lattice mismatch theory. The angular dependence of the C(1s) and N(1s) core level spectra together with their variation with polymerization time suggests a bulk-initiated growth rather than a surface one.

Synthetic Metals

Polypyrrole growth on crystalline PEO complexes: characterization by WAXD and XPS

Polycarbonate obtained by solid state polycondensation (SSP) crystallizes in an orthorhombic configuration with a = 12.1 A ̊, b = 10.1 A ̊ and c = 22.0 A ̊. Its morphology is of non-spherulitic lamellar type, while that of melt or solution crystallized commercial polycarbonate is distinctly spherulitic. These changes in crystalline structure and morphology can be explained, in the present case, on the basis of restricted mobility of the chains and the crystal growth in an extended chain configuration during the SSP step. © 1994.

Polymer

Structure and morphology of polycarbonate synthesized by solid state polycondensation

Conducting thermoplastic elastomer blends have been synthesised by deposition of polypyrrole in styrene–butadiene–styrene (SBS) block copolymers containing various amounts of ferric chloride (FeCl3). These blends have phasesegregated morphology with preferenatial deposition of polypyrrole in one of the domains as confirmed by structural investigations using optical microscopy, X‐ray diffraction and infrared spectroscopy. The electrical resistivity (ρ) for these blends shows a sharp transition in the region of 273 K and is sensitive to small mechanical deformations both in compressions and extension modes. The dependence of ρ on mechanical stress (P) follows a power law of the type ρ ∝ Pn, where n has a value between 3 and 4. These various findings have been explained on the basis of a phase‐segregated morphology having highly conducting domains separated by a semiconducting/insulating matrix, together with non‐linear conduction processes for charge transport in such heterogeneous materials. © 1994 Society of Chemical Industry

Polymer International

Structure and electrical properties of polypyrrole–thermoplastic elastomer blends

The “in situ” formation of cadmium sulphide in a polyethylene oxide matrix has been studied starting with its complex with cadmium chloride. It has been found that the complex crystallizes in orthorhombic configuration with lattice parameters of a = 8.42 Å, b = 15.39 Å and c = 18.49 Å, and that its morphology is spherulitic. At high concentrations (&gt;1:4 per monomer), the added salt gets excluded out of the spherulites and deposits in the interspherulitic regions. The cadmium sulphide formed from such a complex has mixed α and β phases and its crystallite/particle size depends on the initial concentration of the cadmium chloride.

Journal of Crystal Growth

Polymer induced crystallization III. PEO-CdCl2 and in situ formation of PEO-CdS composite

A high piezoresistive effect ( Δp po = 102 kg-1cm-2) has been observed in semiconducting polyvinylidene fluoride as well as polyphenylene sulfide composites containing metallic fillers. The nonlinear current-voltage characteristics conforming to the space charge limited conduction mechanism present at the interparticulate region can give rise to the observed high sensitivity of resistance to external pressure. The results predicted by this model have been confirmed by the experimental findings. © 1994.

Materials Letters

High piezoresistivity in conducting polymer composites

Growth of polypyrrole (PPy) on crystalline poly(ethylene oxide)-ferric chloride complexes has been investigated by X-ray diffraction, optical and scanning electron microscopy. PPy deposited on such crystalline substrates develops ordered structure conforming to orthorhombic configuration with lattice parameters of a=6.11, b=7.19 and c=16.31 A ̊, which has similarity to the substrate crystallites. Preferential nucleation of PPy is seen on these substrates especially when these are oriented into fibre form. No such order is observed when amorphous polymer substrates with FeCl3 are used for PPy deposition. The electrical conductivity σ depends on FeCl3 concentration c as a power law of the type σ∞c5 and has a minimum activation energy of 0.09 eV at a molar ratio of about 1:5. The various results are in keeping with the structured growth of PPy which is strongly influenced by the crystalline order in the substrate. © 1993.

Structure development and electrical properties of polypyrrole deposited on poly(ethylene oxide) complexes

The cure monitoring of cyanoacrylate resin using a dielectric technique shows that in addition to the usual fast anionic polymerization step, there may be a secondary process involved over longer time scales. Two peaks are distinctly observed in the isothermal curing curves, and from the position of these at various temperatures, the activation energies of 0.4 eV and 0.17 eV could be derived. In cured cyanoacrylate resin, three relaxations were observed, viz., α, β, and γ, occurring at 152°c, 87°c, and 47°c, respectively (for 1 KHz measuring frequency), with activation energies of 1.3 eV, 0.56 eV, and 0.4 eV, respectively. The various results have been explained on the basis of secondary bond formation through the nitrile group, for which some evidence could be obtained from the infrared absorption spectra.