Several diacetylene containing polyesters with thermochromic transitions at or around room temperature have been synthesized. Some of these polymers have been shown to be highly sensitive to body temperature, giving rise to either reversible or irreversible thermochromic changes, depending upon both the molecular structure and the processing conditions. By changing the structure and processing conditions, the thermochromic transition can be moved over a wide range of temperatures. Segmented polyurethanes using these diacetylene functionalized polyesters as soft segments and containing diacetylene groups in the hard segments have also been produced. Through a selective polymerization process, it is possible to selectively cross-polymerize the hard segment diacetylene groups or cross-polymerize both the hard and soft segments thereby making it possible to examine the effects of hard and soft segment crosslinking on mechanical properties.

The optical response of polyphosphazenes can be directly related to the π (out-of-plane) and π′ (in-plane) bonding interactions intrinsic to the electronic structure of these Materials. Altering this structure either by hydrogen bonding or absórbate effects, affects both the linear and nonlinear optical susceptibilities. In this paper, we have performed electronic structure calculations on the cyclic Molecules, P3N3 (NHCH3)6, P3N3(SCH3)6, P3N3 (OCH3)6 and P4N4 (NHCH3)8 as model systems for the polymer. Charge distribution arguments are discussed to explain the influence of a polarizing electric field on the π bonding systems, and are used to suggest methods to enhance their nonlinearities.

A large class of new layered semiconductors — lead iodide compounds — is of great interest because of possible optoelectronic applications due to pronounced excitonic effects. These compounds may be regarded as naturally grown semiconductor/insulator superlat-tices, with perovskite lead iodide (semiconductor) layers sandwiched by alkylammonium (insulator) layers. Exciton binding energies and oscillator strength in these structures are enhanced due to the so-called “dielectric confinement” caused by large difference between dielectric constants of adjoining layers. The binding energies, wave functions,& diamagnetic coefficient of excitons in these naturally grown superlattices are calculated with allowance for the image potential and the superlattice structure of the compounds. The localization of excitons in lead iodide layers causes also a strong dependence of a polariton spike in reflection spectra on the polarization of electromagnetic wave. The results obtained are in agreement with the experimental data.

Correlation effects on the band gap are studied to get the strength of electron interactions in conjugated polymers. In the presence of an additional electron or hole, the correlation induces a polarization cloud around the additional particle, which forms a polaron. For the excitation energy of a polaron, there is a competition between a loss of correlation energy in the ground state and a gain of polarization energy due to the scattering through the additional particle. The calculation has been done both for the Hubbard Model and long-range interactions. For polyacetylene, we obtain the on-site repulsion U = 4.4 eV and the nearest-neighbor interaction V = 0.8 eV. The polarization effect of Σ electrons and theoretical results on the effective interaction are discussed. The strength of effective interactions should depends on physical processes.

Two photon absorptions (TPA) in conjugated polymers with large bond alternation are reinterpreted. TPA to the 2Ag in long chains should be tiny due to cancellation effects, and therefore the observed strong, narrow TPA is to a higher even parity state. We also present the first theoretical evidence for bound biexcitons, and explain recent photoinduced absorption data.

Activated carbon fibers (ACFs) were heat-treated at temperatures above 2000°C to study both the effect of heat treatment on the order development in ACFs and the effect of granularity on the transport properties of granular materials in general. The electrical conductivity σ(T) and Magnetoresistance (MR) were measured as a function of temperature for ACFs Made of two different precursors and heat-treated at different temperatures. While the field dependence of the observed negative MR could be fit to the two-dimensional weak localization (2D WL) theory at each measurement temperature, σ(T) showed only a weak temperature dependence, inconsistent with the ln (T) dependence predicted by the same theory. Even More interesting is the observation of a negative MR, which is a quantum-Mechanical phenomenon, near room temperature. It is thought that the grain boundaries might be responsible for such deviations from the standard 2D WL theory.

The electrogeneration and electrodissolution of poly (SNS) have been improved by using aqueous acetonitrile solutions having a 1% (ν/ν) of water constant. Compact, adherent and thick films (until 0.4 Mg cm-2) were galvanostatically electrogenerated. The electrodeposited (oxidized) polymer is insoluble in 0.1 M L?CIO4 aqueous acetonitrile solution and solubilizes by cathodic reduction. Both, electrogeneration and electrodissolution, are faradaic processes. Those facts mimic electrodeposition and electroerosion of metals and their concomitant industrial applications. New technological possibilities using polymers in electrophotography, electroreprography, electropolishing, electro-erosion and electromachining are open through polymeric electrodissolution altogether to a new processible way, through the obtained solution, for the conducting polymers.

The evolution of the capacity to store electrical charges of electrogenerated polypyrrole and polythiophene films, as a function of the parameters of synthesis (electrical potential, solvent, Monomer concentration and temperature) was analyzed. The polymer production was followed by “ex situ” ultramicrogravimetry. The stored charge in each film was controlled by voltammetry and chronoamperometry, in the background electrolyte (in absence of Monomer). The charge storage ability was calculated from the ratio between stored charge and polymer mass adhered to the electrode. The charge storage ability of an electrogenerated film decreases several times when one of the parameters of synthesis: potential of polymerization, temperature, concentration of monomer or donor number of the solvent, increase. The change on the polymer property when the conditions of synthesis shift, points to a mixed polymerization-degradation process during polymer growth. The knowledge of those variations allows to optimize the conditions of synthesis to generate conducting polymers for specific batteries applications.