Cryoscopy on sulfuric acid solutions of a heterocyclic polymer (BBB) and related compounds

Cryoscopic measurements have been carried out on solutions in sulfuric acid of a heterocyclic polymer, its monomers, and certain of its oligomers. The polymer, BBB, is prepared by the polycondensation of 1,4,5,8-naphthalenetetracarboxylic acid (NTC) with 3,3′-diaminobenzidine (DAB). The results show that the polymer, its oligomers and one of its monomers, DAB, are all extensively protonated in sulfuric acid, whereas its other monomer is not. The degree of protonation appears to be greater for the polymer than for its low molecular weight oligomers.     

Thermal–mechanical studies on a heterocyclic polymer (BBB). I. Tensile creep and recovery

Creep and recovery measurements have been used to study the thermal–mechanical properties of polybisbenzimidazobenzophenanthroline-dione (BBB) over the temperature interval 30–500°C (in vacuo). The creep measurements were augmented by x-ray diffraction, isothermal contraction, and solubility measurements. It is found that extensive intermolecular association giving a supramolecular structure with (nearly) planar polymeric repeat units stacked in a “graphite-like” array dominates the properties of BBB, and that this structure is maintained at temperatures as high as 500°C. The principal mode of creep gives rise to fully recoverable Andrade creep for which the strain depends on the cube-root of time.     

Kinetics of formation of polybisbenzimidazobenzophenanthroline-dione (BBB polymer)

The kinetics of the polycondensation of 3,3′-diaminobenzidine with 1,4,5,8-naphthalenetetracarboxylic acid (NTC) have been investigated. Polymerizations were carried out in solution in either polyphosphoric acid (PPA) or in PPA mixed with some sulfuric acid. The reaction is heterogeneous in PPA owing to partial solubility of NTC, whereas it is homogeneous in the mixed solvent. The rate of disappearance of NTC and of dicarboxylic endgroups on oligomers was followed as a function of time at several reaction temperatures. The results show that NTC is more reactive than oligomers, so that the principle of equal reactivity is not valid for the initial steps in the polycondensation reaction.     

Mechanical properties of heterocyclic polymer networks

Heterocyclic networds prepared by copolymerization of oligomeric epoxy rubber (ER) with different amounts of hexamethylene diisocyanate (HMDI) were characterized by room-temperature static Young's and bulk moduli, as well as by measurements of dynamic Young's modulus and linear thermal expansivity in the temperature interval 293–503 K. It was concluded that the major factor affecting thermoelastic properties of these networks is the relative content of three-arm, six-membered isocyanoureate rings which determine the apparent overall network density, and of two-arm, five-membered oxazolidone rings which act as a sort of internal diluent.     

Low temperature heat capacity of heterocyclic polymer networks

The predicted crossover to a fractal-like vibrational regime above 8–10 K was apparently proved by precise measurements of heat capacity of a series of cross-linked heterocyclic polymers.     

Ylide character and stability of heterocyclic benzenes

Optimizations are carried out on heterocyclic benzenes including oxabenzene ( 1_O ), thiabenzene ( 1_S ), selenabenzene ( 1_Se ), tellurabenzene ( 1_Te ), 1,1‐dihydropyridinium ( 2_N ), 1,1‐dihydrophosphinium ( 2_P ), 1,1‐dihydroarsinium ( 2_As ), and 1,1‐dihydrostybinium ( 2_Sb ), using HF and DFT methods with 6‐311++G* basis sets. These partly aromatic compounds have 6π‐electrons showing ylide character. Nonplanar boat conformers appear as global minima for 1_X . In contrast, planar conformers are the most stable in 2_X series. The inversion barrier energy of heteroatom in 1_O appears the least in 1_X structures. Ylide character increases in series 1_X and 2_X with the orders of 1_Te > 1_O > 1_Se > 1_S and 2_As > 2_N > 2_Sb > 2_P , respectively. Homodesmic studies show stability order for series 1_X to be 1_S > 1_Se > 1_Te > 1_O , whereas the order of stability for series 2_X is 2_As > 2_P > 2_Sb > 2_N . © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:412–417, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20443     

Chemiluminescence study of polymer oxidative stability

The application of the chemiluminescence technique to the study of polymer oxidative stability is discussed. For the initial stages of oxidation a sigmoidal change in the chemiluminescence intensity with time is justified when the experiment is performed isothermally at high oxygen pressure, whereas at low oxygen pressure and constant heating rate an exponential increase in the chemiluminescence intensity is expected. For advanced stages of oxidation depending on the ratio between the initial and equilibrium levels of hydroperoxides, the intensity of emitted light may either grow or decay until the equilibrium concentration of hydroperoxides is established. Two major parameters of an autocatalytic oxidation (induction time and oxidation rate) can be obtained by carrying out the experiment in an oxygen atmosphere at constant temperature. Alternatively, the extent of oxidation in a certain temperature region can be evaluated when a constant-heating-rate experiment is conducted under nitrogen.     

Fiber-in-tube solid-phase microextraction: a fibrous rigid-rod heterocyclic polymer as the extraction medium

A novel “fiber-in-tube” configuration has been applied to the extraction tube of solid phase microextraction (SPME), and the direct coupling of the extraction process to liquid chromatography (LC) has been accomplished for the analysis of n-butylphthalate in wastewater. By using this fiber-in-tube SPME/LC system the preconcentration factor for the phthalate was about 160 with 20 min extraction and no interference peak was observed in the chromatogram. The results also showed the potential applications of this fiber-in-tube SPME/LC for the analysis of sub-ppb level (i.e., lower than 1 ng/mL) of various organic analytes in aqueous sample matrix without a large solvent consumption during the preconcentration process.     

Fiber-in-tube solid-phase microextraction: a fibrous rigid-rod heterocyclic polymer as the extraction medium

A novel "fiber-in-tube" configuration has been applied to the extraction tube of solid phase microextraction (SPME), and the direct coupling of the extraction process to liquid chromatography (LC) has been accomplished for the analysis of n-butylphthalate in wastewater. By using this fiber-in-tube SPME/LC system the preconcentration factor for the phthalate was about 160 with 20 min extraction and no interference peak was observed in the chromatogram. The results also showed the potential applications of this fiber-in-tube SPME/LC for the analysis of sub-ppb level (i.e., lower than 1 ng/mL) of various organic analytes in aqueous sample matrix without a large solvent consumption during the preconcentration process.     

Polysiloxanes having aromatic heterocyclic units. I. Polydimethylsiloxane benzimidazole polymer

A polymer containing dimethylsiloxane units (35) and benzimidazole units (1) has been prepared by the condensation of 3,3′-diaminobenzidine and an α,ω-bis-(γ-carboxy-n-propyl) polydimethylsiloxane. The new polymer has some rubbery properties, but it decomposes catastrophically at 400°C.     

A generalized model for the stability of polymer colloids

A generalized model has been proposed to describe the stability of polymer colloids stabilized with ionic surfactants by accounting simultaneously for the interactions among three important physicochemical processes: colloidal interactions, surfactant adsorption equilibrium, and association equilibria of surface charge groups with counterions at the particle-liquid interface. A few Fuchs stability ratio values, determined experimentally for various salt types and concentrations through measurements of the doublet formation kinetics, are used to estimate the model parameters, such as the surfactant adsorption and counterion association parameters. With the estimated model parameters, the generalized model allows one to monitor the dynamics of surfactant partitioning between the particle surface and the disperse medium, to analyze the variation of surface charge density and potential as a function of the electrolyte type and concentration, and to predict the critical coagulant concentration for fast coagulation. Three fluorinated polymer colloids, stabilized by perfluoropolyether-based carboxylate surfactant, have been used to demonstrate the feasibility of the proposed colloidal stability model.     

Pentapnictogen heterocyclic monoanions: Structure,stability, and aromaticity

Inorganic planar ring-shape molecules with 4n + 2 π electrons are always the focus of experimental synthesis and theoretical research due to their potential aromaticity and stability. In this work, the whole series of five-membered heterocycle monoanions X _nY_5-n⁻ (X, Y = group 15 elements; n = 1-4) were thoroughly investigated by means of density functional theory calculations. They all have large formation energies and HOMO-LUMO gap energies, suggesting the potential thermodynamic and kinetic stability. Their aromaticities are comparable to that of typical aromatic hydrocarbons. Their thermal stabilities were firmly established by the ab initio molecular dynamics simulations. As most of them are predicted for the first time, their various spectra were simulated for experimental characterization. Furthermore, we demonstrate that these five-membered cyclic anions can be employed as η⁵-ligand to construct novel all-inorganic metallocenes, which may serve as the building blocks of low-dimensional nanomaterials.     

Effects of polymer solutions on colloid stability

Some theoretical properties of a semidilute polymer solution (in a good solvent) near a repulsive wall (no adsorption) are discussed. (i) Near a single wall, the existence of a depletion layer (where the concentration is strongly reduced) with thickness equal to the correlation length ξ(c) is predicted. Scaling laws are obtained for the concentration c_s at the first layer as a function of the bulk concentration c, and for the concentration profile c(z) at distance z from the wall. (ii) When two parallel walls are separated by a slab of polymer solution (thickness d), there is an attractive interaction between the plates. The range of the attraction is ca. 3ξ(c) and can be varied by suitable choice of concentration. It may lead to destabilization of certain colloidal systems.     

The effect of γ-irradiation and polymer composition on the stability of PLG polymer and microspheres

The effects of lactide:glycolide ratio and γ-irradiation on the stability characteristics of poly(d,l-lactide-co-glycolide) (dl-PLG) co-polymer and microspheres were studied. Samples containing 50:50, 65:35, 75:25, 85:15 and 95:5 lactide:glycolide were studied as both the raw polymer and microspheres. The samples were characterised and degradation was monitored using a variety of spectroscopic, chromatographic, thermal and particle analysis techniques. The lactide:glycolide ratio was shown to be an important parameter in controlling the degradation of PLG co-polymer, especially in the microspheres, and the raw polymer samples were observed to be less stable than the microspheres. γ-Irradiation was shown to reduce the molecular weight of the PLG samples without significantly affecting the polydispersity, suggesting a random chain scission degradation mechanism. The detrimental effects of γ-irradiation were shown to continue on storage of the samples for 4 weeks in the solid state at ambient and accelerated conditions.     

When tethered chains meet free ones; the stability of polymer wetting films on polymer brushes

We present a combined experimental and theoretical self-consistent field (SCF) investigation of the wetting behavior of a polystyrene melt (composed of chains with degree of polymerization P) on top of a polystyrene brush (composed of chains with length N) grafted onto a silica surface. The control variables are the grafting density σ of the brush chains and the length of mobile chains P. Experiments show in agreement with the theory that there is a window of complete wetting. Both at very low and at high grafting densities the system remains partial wet. At large degree of polymerization P, there is a difference between the experimental and theoretical results. Theory predicts partial wetting only, whereas the window of complete wetting persists in the experiments even when P >> N. This difference is attributed to the double-well structure of the disjoining pressure as revealed by the SCF theory. With this type of disjoining pressure it is conceivable that a metastable zero contact angle remains present for very long times.     

Thermal stability and flammability of silicone polymer composites

Silicone polymer composites filled with mica, glass frit, ferric oxide and/or a combination of these were developed as part of a ceramifiable polymer range for electrical power cables and other high temperature applications. This paper reports on the thermal stability of polymer composites as determined by thermogravimetric techniques, thermal conductivity and heat release rate as measured by cone calorimetry. The effects of fillers on thermal stability and flammability of silicone polymer are investigated. Of the fillers studied, mica and ferric oxide were found to have a stabilising effect on the thermal stability of silicone polymer. Additionally, mica and ferric oxide were found to lower heat release rates during combustion, but only mica was found to increase time to ignition.     

Thermal stability of polymer compositions with modified alumina

Thermal stability and combustibility of polymer compositions: foam plastic (trade mark PEN-I) based on an epoxide novolak block copolymer, and poly(methyl methacrylate, containing modified alumina of various dispersion as a filler, were investigated.