Disorder Effects in “Plastic” and Highly Conducting Compounds of Poly(aniline)

Numerical methods of molecular dynamics have been combined to measurements of X-ray and neutron scattering in order to obtain a realistic view of structural and dynamical disorder properties of conducting compounds of so called “plastdoped” poly(aniline)s. This combination allowed us to propose for the whole family of these compounds one generic model of a layered structure in which exist statistical fluctuations of the electronic density along the stacking direction of alternating molecular layers. The most part of the dynamics in the 10⁻¹³–10⁻⁹ s time range concerns the motions of protons borne by the flexible tails of doping counter-ions contained in the structure. We found that the molecular dynamics is characterized by both broad time and spatial distributions. These experimental facts coupled to those obtained with electrical conductivity measurements indicate that the high mobility of the counter-ion sublattice seems to be a prerequisite to promote a global metal like electronic behaviour of the polymer films.     

Relaxing nonequilibrated polymers in thin films at temperatures slightly above the glass transition

We have studied the dewetting process of thin polystyrene films on nonwettable substrates in the viscoelastic regime slightly above the glass transition temperature. The evolution of the shape of the dewetting rim for varying film thickness, molecular weights and dewetting temperatures allowed us to determine the relaxation rates of residual stresses, which originated from nonequilibrated polymer chain conformations formed during film preparation by spin‐coating. For long chain polymers, we found rates notably faster than the longest bulk relaxation processes, highly independent of molecular weight and temperature. Our study demonstrates that dewetting is a powerful tool for sensitive characterization of nonequilibrium properties of thin polymer films. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 515–523     

Supramolecularly organized systems based on transition metal complexes with schiff's bases. Photo- and electrochemical activity

In the present paper we report about the last advances concerning the structure and properties of electrochromic photosensitive metallopolymers based on the complexes of Pt, Pd, Ni, Co, Cu with Schiff's bases. The criteria of selection of the object for the synthesis of new polymers with one-dimensional, reversible, controlled photo- and electroinduced charge transfer was determined. A model for the polymer structure was proposed. The ohmic resistance in the direction parallel and perpendicular to the microelectrode surface of gold-coated α-Al₂O₃ differs as 1: 10⁶-10⁹ depending on the polymer and film thickness. A qualitative model of the processes of light energy accumulation was proposed.     

Substituent effects of phosphonate groups electronic repartition of π-conjugated ferrocene analogues of stilbene

The synthesis of para-substituted ferrocene analogues of stilbene was performed by using the Heck reaction, starting from vinylferrocene. The variation of the electronic density of these compounds with the electronic withdrawing strength of the substituents was studied using ¹³C NMR spectroscopy, absorption spectra and cyclic voltammetry. The correlation of Hammett constants with the redox properties of the substituted compounds using Nagy's method allowed us to revisit the determination of the Hammett constants of diethyl phosphonate ester and phosphonic acid substituents. Our measurements were in agreement with the literature except for the diethyl phosphonate group.     

11B Nuclear magnetic resonance study of the reactivity of borane tetrahydrofuran with representative dithianes,diazolidines, thiazolidines,benzothiazolines and benzothiazoles

The reaction of borane tetrahydrofuran with the title compounds led by ring opening to the synthesis of new borolidine heterocycles. ¹¹B NMR not only allowed the observation of borane adducts of dithianes, diazolidines, thiazolidines, benzothiazolidines and benzothioles, but even provides useful information concerning their stereochemistry.     

Vibrational dynamics and hydrogen bond properties of β-CD nanosponges: an FTIR-ATR, Raman and solid-state NMR spectroscopic study

Cyclodextrin nanosponges (CDNS) are cross-linked polymers with remarkable inclusion/release properties. CDNS show swelling capability and a hydrophilicity/hydrophobicity balance that can be dramatically modified by the type and quantity of cross-linking agents. Here, we focus our attention on samples of β-cyclodextrin nanosponges (β-CDNS) obtained by reacting β-cyclodextrin (β-CD) with the cross-linking agent carbonyldiimidazole at different β-CD:cross-linking agent molar ratio. The vibrational properties of CDNS thus synthesized have been investigated by Fourier transform infrared spectroscopy in attenuated total reflectance geometry and Raman spectroscopy in the dry state at room temperature. The quantitative analysis of the O–H stretching region (3,000–3,800 cm^?1) allowed us to obtain structural information on the role played by primary and secondary OH groups in the hydrogen bond network of the polymer. Also, the contribution of interstitial and intracavity crystallization water molecules is reported. Solid-state NMR spectroscopy is used to study the molecular mobility of the polymer by measuring the ¹H spin–lattice relaxation time in the rotating frame (T_1ρ). The T_1ρ values obtained for the polymer β-CDNS are compared with free β-CD. The observed relaxation parameters point out that the ester formation occurs mainly at the primary OH groups of CDs, also supporting the interpretation of vibrational spectra.     

Molecular dynamics of a smectic liquid-crystalline side-chain polymer. The dielectric properties of aligned and nonaligned material studied over a wide range of frequency and temperature

The dielectric relaxation behavior of a nonaligned and an aligned liquid-crystalline (LC) polymer are reported for the ranges 10^?3.5 to 10⁵ Hz and 274–363 K. Multiple processes (δ and α) are observed that follow a Vogel equation for the temperature dependence related to the apparent glass transition temperature. The occurrence of these processes and the variation in their relaxation strengths as sample alignment is changed is interpreted in terms of a molecular theory for the dielectric behavior of a LC polymer that involves the director order parameter S_d, the mesophase order parameter S, the dipole moment components of the mesogenic head groups, and their associated relaxation functions.     

Induction and measurement of glassy-state relaxations by vapor sorption techniques

Recent gravimetric studies of the sorption of organic vapors by poly(vinyl chloride) and polystyrene powders have demonstrated several features which promise to be generally useful in studying the structure and properties of the glassy state. The uptake of vapor can be significantly altered by prior thermal or vapor treatment of the polymer, apparently reflecting changes in the microvoid content or free volume of the polymer. Fickian sorption in sufficiently fine powders proceeds to equilibrium in a few minutes. Upon exposure of a polymer powder to an appreciable pressure of vapor, both a rapid Fickian sorption and a slower, relaxation-controlled sorption are observed. Superposition of these processes leads to widely varied sorption kinetics; a model comprising Fickian diffusion and first-order relaxation terms accurately describes the data and allows estimation of equilibrium and rate constants for both processes. After prolonged exposure, removal of a swelling vapor induces a slow reconsolidation of the polymer structure; this deswelling relaxation can be monitored by the decreasing amounts of vapor sorbed in repeated brief exposures to low vapor pressures, and can also be described by a first-order relaxation model. In this regard, the penetrant vapor serves as a molecular probe, monitoring glassy-state relaxation occurring in the absence of penetrant. The same, presumably true equilibrium is ultimately reached both by swelling from a low free-volume state and by consolidation from a preswollen state of high free volume. The rates of both swelling and consolidation relaxations appear to be retarded by the presence of low concentrations of vapor in the polymer, suggesting that vapor molecules may preempt some of the free volume required for relaxation.     

An unexpected synthesis of 7-azidofurazano[3,4-b]tetrazolopyrazine

In the course of our program focused on the preparation of high-nitrogen content heterocyclic compounds, we wish to report an original synthesis of the tricyclic 7-azidofurazano[3,4-b]tetrazolopyrazine via an unprecedented reaction between 2,6-dimethoxy-3,5-dinitropyrazine and hydrazine hydrate. This compound was identified by an X-ray diffraction analysis. Further studies of its structure by ¹⁵N and ¹³C NMR spectroscopy were carried out in different solvents. This allowed us to observe a noteworthy equilibrium involving three forms resulting from the reversible opening of a tetrazole ring.     

Biodegradable starburst carbon chain polymer-protein and lysine dendrite conjugates: adjustment of immune properties,DNA bonding and delivery

In the past decade, the development of gene therapy technology has focused on the design of new nonviral carriers for gene delivery. Proteins modified with polyethyleneimine^[1] or polylysine^[2] as well as dendrites^[3] have shown to be perspective carriers for DNA targeted delivery. The usage of protein conjugates as carriers of biologically active compounds will depend on the adjustment of their immune properties. To investigate this we have prepared starburst carbon chain polymer/protein conjugates containing low molecular weight biologically active compounds, salsolinol and bradykinin, in the polymer moieties and studied their immune properties. We have shown that chemical structure of the polymer moiety determines the conjugate biodegradation as well as their immune properties. The starburst poly(N-vinylimidazole) transferring poly(N-vinylimidazole) and polylysine 3G lysine dendrite conjugates have been prepared. The study of their ability to bind DNA and to guarantee its targeted delivery have shown that they are perspective DNA carriers.     

The structure of plasma-polymerized toluene: A solid-state 13C-NMR study of isotopically labeled polymers

A detailed magic angle spinning ¹³C-NMR investigation of the intractable polymer prepared by plasma polymerization of toluene and isotopically labeled toluene led to a proposed model for the structure of the polymer and suggested some of the likely processes that occur in the gas phase leading to film formation. From the ¹³C spectra four resolved resonances permitted the determination of the contribution of nonprotonated and protonated unsaturated as well as methyl and other aliphatic carbons to the polymer structure. Specific ¹³C isotopic labeling of the methyl and phenyl C-1 toluene carbons in the injected liquid vapor allowed the destination of these carbons in the deposited polymer to be traced. The dominant structure is derived primarily from two precursors: benzyl radical and toluene itself. The ¹³C data further requires a net saturation of ca. 30% of the toluene double bonds and a net displacement of hydrogen by carbon on ca. 20% of the toluene ring carbons.     

Nuclear magnetic resonance of rapidly rotated elastomers

The NMR line narrowing effect by high speed rotation of the specimen at the magic angle is observed in several elastomers at room temperature. The ¹H and ¹⁹F chemical shifts thus revealed permit the investigation of the monomer ratio and conformational structure in copolymers. Using a weak collision relaxation model, we explain the possibility of line narrowing in elastomers by the existence of slow inter-chain motion; the observed limiting line-width is attributed to rapid segmental motion. Our experiences allow us to determine these two correlation times for elastomers under investigation. This procedure is also applied to viscous polymer solutions.     

Thermally induced low-temperature relaxation of plastic deformation in glassy organic polymers and silicate glasses

A deep analogy between the processes of low-temperature thermally induced relaxation of plastic deformation in amorphous polymers and inorganic glasses is observed. The results of the calculation of the activation energy and activation volume of this relaxation process in terms of the excited state model satisfactorily agree with the experimental data obtained for both epoxy polymer systems and sheet silicate glasses. This evidence allows us to conclude that the initial stage of macroscopic plastic deformation in glassy systems involves small critical displacements of excited atoms (groups of atoms) that are provided by local rearrangements of neighboring particles (entropy fluctuations). In the vicinity of the yield point, the number of excited atoms per unit volume induced by the action of mechanical stresses appears to be quite sufficient (10²⁶–10²⁷ m^?3) for promotion of a marked plastic deformation of glasses and preservation of appreciable amounts of internal energy.     

Photochemical aspects in anthracene-containing cationic polyurethanes

The synthesis, characterization and photochemical properties of a new polyurethane cationomer (PUC-AN) with anthracene chromophore groups attached on the quaternary ammonium units is reported and compared to those of a model compound (AN) carrying the same moiety. PUC-AN synthesis implied the quaternization reaction with 9-chloromethylanthracene of the tertiary amine of one precursor polymer based on poly(tetramethylene oxide) diol of 2000 average molecular weight, tolylene-2,4-diisocyanate (as 2,4- and 2,6-TDI, 80:20 v/v isomers mixture), N-methyldiethanol amine and terephthalaldehyd-bis(3-hydroxymethylphenylimine) in a molar ratio of 1:3:1:1. The fluorescence spectra of the anthracene structure indicates that the synthesized compounds present different shifts in solution and in the solid state, their photochemical behavior being influenced by monomer and excimer emission. The photophysical investigations revealed that such structures can function as fluorescent chemosensors for transitional metals, showing a fluorescence quenching in the presence of different metal ions (, Fe³⁺, Cu²⁺). The quenching mechanisms for PUC-AN and the corresponding model compound (AN) are assigned to electron transfer and/or energy transfer processes of Dexter type.     

From Peptide Nucleic Acids to Supramolecular Structures of Nucleic Acid Derivatives

Nucleic acids play a pivotal role in life processes. The endeavours to shed light on the essential properties of these intriguing building blocks led us to the synthesis of different analogues and the investigation of their properties. First various peptide nucleic acid monomers and oligomers have been synthesized, using an Fmoc/acyl protecting group strategy, and their properties studied. The serendipitous discovery of a side reaction of coupling agents led us to the elaboration of a peptide sequencing method. The capricious behaviour of guanine derivatives spurred the determination of their substitution pattern using ¹³C, ¹⁵N NMR, and mass spectrometric methods. The properties of guanines initiated the logical transition to the study of supramolecular systems composed of purine analogues. Thus, xanthine and uracil derivatives have been obtained and their supramolecular self-assembly properties scrutinized in gas, solid, and liquid states and at solid-liquid interfaces.     

Branched polyphenylenes and phenylene dendrimers: NMR and optical studies

Two branched polyphenylenes with 1,3,5-triphenylbenzene as branching centers were synthesized together with a family of phenylene cyclotrimers as model compounds. On the basis of the NMR analysis, specifically ¹H NMR, ¹³C NMR and 2D heteronuclear correlation experiments (HSQC and HMBC) of model compounds, the huge number of overlapping signals in the polymer spectra are attributed to aromatic protons and carbon atoms of the branched phenylene structure. The comparison with absorption spectra of linear model compounds clearly shows that the polymer optical properties depend on the length of the segments between the branching cores. This result strongly supports the proposed NMR assignment proving that the combination of the two techniques is a powerful tool for unveiling complex branched structures.