Lawrence W. Shacklette

Advances in polymer integrated optics

We report on advances in polymeric waveguide technologies developed worldwide for the telecom and datacom markets, and we describe in detail one such technology developed at AlliedSignal. Optical polymers are versatile materials that can be readily formed into planar single-mode, multimode, and microoptical waveguide structures ranging in dimensions from under a micrometer to several hundred micrometers. These materials can be thermoplastics, thermosets, or photopolymers, and the starting formulations are typically either polymers or oligomers in solution or liquid monomers. Transmission losses in polymers can be minimized, typically by halogenation, with state-of-the-art loss values being about 0.01 dB/cm at 840 nm and about 0.1 dB/cm at 1550 nm. A number of polymers have been shown to exhibit excellent environmental stability and have demonstrated capability in a variety of demanding applications. Waveguides can be formed by direct photolithography, reactive ion etching, laser ablation, molding, or embossing. Well-developed adhesion schemes permit the use of polymers on a wide range of rigid and flexible substrates. Integrated optical devices fabricated to date include numerous passive and active elements that achieve a variety of coupling, routing, filtering, and switching functions.

Electrical and optical properties of highly conducting charge-transfer complexes of poly(p-phenylene)

Abstract Electrical conductivity, Hall effectm and spectroscopic measurements have been made on AsF 5 -doped poly( p -phenylene). Doping increases the conductivity of the parent polymer by as much as 14 orders of magnitude to values as high as 5 × 10 4 S/m. Hall effect measurements indicate p-type conduction with a Hall mobility approaching 10 −4 m 2 /V s for doping levels between 0.24 and 0.42 moles of AsF 5 per mole of monomer. Doping with an electron donor, K, has increased the conductivity to about 10 3 S/m for a doping level of 0.57 moles of K per mole of monomer. Using this conductivity value, with the assumption of total charge transfer from the donor, suggests a drift mobility for electrons which is significantly less than that for holes. The assumption of an intercalant structure analogous to that of polyacetylene and graphite leads to the conclusion that the presently achieved AsF 5 -doping levels in poly( p -phenylene) correspond to a compound which is not wholly stage 1.

Structure and properties of polyaniline as modeled by single-crystal oligomers

A single‐crystal charge–transfer complex of a phenyl‐end‐capped tetramer of polyaniline has been synthesized and studied along with a similar dimer of polyaniline. Structural, optical, and electrochemical studies of these oligomers in various oxidation states provide detailed information which has been used to model the structure of polyaniline and its evolution during electronic doping. These studies of the polymer and its oligomers suggest that the emeraldine salt form of the polymer (50% doping per nitrogen) is a preferred low‐energy structure. The preference for this structure leads to phase segregation in doped compositions having average doping levels less than 50%.

The electronic and electrochemical properties of poly(phenylene vinylenes) and poly(thienylene vinylenes): An experimental and theoretical study

The electronic and electrochemical properties of poly(p‐phenylene vinylene), poly(thienylene vinylene), and their derivatives with electron donating moieties such as methyl, methoxy, and ethoxy are studied using the newly developed electrochemical potential spectroscopy (ECPS) and optical spectroscopy. It is shown that electrochemically derived band gaps agree well with band gap values obtained from optical measurements. Substitution with electron donating groups substantially lowers the ionization potentials and band gaps. A similar effect can be attributed to the incorporation of a vinylene linkage between rings of the polymer backbone. Our results imply that through a proper choice of substituents and backbone structure one can adjust the electrochemical potentials over a wide range as well as red shift the absorption edge of these polymers. In the case of the alkoxythienylene vinylenes the absorption edge is shifted through the visible range of the spectrum into the near infrared (NIR) yielding polyme...

Solid‐state synthesis of highly conducting polyphenylene from crystalline oligomers

Paraphenylene oligomers (biphenyl, p‐terphenyl, p‐quaterphenyl, p‐quinquephenyl, p‐sexiphenyl) form electrically conducting complexes with AsF5. Prolonged exposure to AsF5 causes a polymerization of these p‐phenylene oligomers to give highly conducting charge‐transfer complexes of poly(p‐phenylene). Conductivities as high as 50 S/cm have been measured. Powders, thin films, and single crystals of p‐phenylene oligomers have been reacted with AsF5. The undoped oligomers and the doped, compensated, and annealed products have been investigated by means of x‐ray diffraction, and UV‐visible and IR transmission spectroscopy. The x‐ray diffraction studies give evidence for a change in lattice spacings to those characteristic of the crystalline polymer. The spectroscopic measurements during AsF5 doping reveal shifts in absorption bands in the UV and the IR to those characteristic of poly(p‐phenylene). Paraoligophenylenes have also been reacted with elemental potassium in THF solution with trace amounts of naphthale...

Conducting complexes of polyphenylene sulfides

Poly(p‐phenylene) sulfide, poly(m‐phenylene) sulfide, and the newly synthesized polymer poly(thio‐2,8‐dibenzothiophenediyl) have been treated with strong electron acceptors (AsF5, SbF5) to form conducting complexes with p‐type electronic conductivities up to 3 S/cm. Near IR to UV absorption spectra and temperature‐dependent conductivity measurements suggest a localization of charge carriers even at high doping levels. Elemental analysis and IR spectroscopy demonstrate that heavy exposure to AsF5 causes substantial changes in the backbone structure of these polymers. The dopant appears to predominantly induce the formation of carbon–carbon bonds bridging the sulfur linkages to form thiophene rings. This chemical modification enhances the conductivity of the complex and, in the case of poly(m‐phenylene), is shown to be an actual prerequisite for achieving high conductivity.

Theoretical studies on polyaniline

Theoretical predictions for various neutral and charged forms of polyaniline are presented and discussed. The MNDO semiempirical method is used to predict geometries which serve as input for valence effective Hamiltonian (VEH) calculations of the electronic band structure. The VEH calculations provide predictions for the band gaps, ionization potentials, electron affinities, and redox potentials for the various forms of polyaniline. Where possible, comparison is made to experiment with generally favorable results. The discussion emphasizes the electrochemistry of polyaniline and the structural evolution of the polymer during electrochemical oxidation and reduction.

Laser-fabricated low-loss single-mode raised-rib waveguiding devices in polymers

Organic polymeric materials offer a versatile medium for the creation of low-cost large-area optical guided-wave structures. In this work, we report on the use of a novel maskless laser-based microfabrication technique for the photochemical delineation of raised-rib single-mode waveguiding devices in polymers. This technology relies on accurate control of small refractive index differences (which is achieved by using intermiscible acrylate monomers), use of high-contrast photochemical response, as well as precise control of laser writing parameters. The devices reported here have cross-sectional dimensions and numerical apertures that match single-mode glass optical fibers. They exhibit very low losses of 0.03 dB/cm at 840 nm and exceptional thermal stability. We present the operational characteristics of bends, Y-branches, and directional couplers fabricated using this technology and compare these characteristics with those predicted from theory.

Polyaniline blends in thermoplastics

Abstract The doped form of polyaniline sold under the trade name, Versicon®, has been shown to provide sufficient thermal stability and dispersibility for compounding with thermoplastics such as PVC, PETG, and nylon 12 via conventional melt-processing techniques. The good performance of polyaniline in blends derives from its thermal stability and its dispersibility as fine sub-micron particles. Percolation curves follow a standard functional form, but the fit parameters and the maximum achievable conductivity are a strong function of processing history and of the choice of matrix polymer.

The Evolution of Structure During The Alkali Metal Doping of Polyacetylene and Poly(p-Phenylene)

Abstract The progression of phases which evolve during the alkali metal doping of polyacetylene and poly(p-phenylene) is examined using newly developed structure concepts, crystal packing analysis, and diffraction and electrochemical data. At least for alkali metals larger than Li+, at dopant concentrations above a few percent the alkali metal ions aggregate in columns within the host polymer lattice. Structural variations result for polyacetylene both from the degree these columns are filled and the chain-to-column ratio. More limited phase variation results for poly(p-phenylene), where 2,3, and 4 chain/column structures are observed, but the metal-metal spacing within the columns is fixed. Structural models are presented for the 2 chain/column complex of poly(p-phenylene) and the 3 chain/column complexes of K and Rb doped trans polyacetylene.