Aqueous dispersion of polyurethane ionomers from hexamethylene diisocyanate and trimellitic anhydride

Polyurethane (PU) ionomers were prepared from trimellitic anhydride (TMA), poly(tetramethylene adipate) glycol (PTAd), and hexamethylene diisocyanate (HDI) in acetone. Upon neutralizing the carboxylic groups with a tertiary amine (TEA), and adding water to PU ionomer solution, followed by removing the acetone, stable aqueous PU dispersions were obtained.Effects of interionic molecular weight and nonionic hydrophilic segment, viz. monofunctional ethylene-propylene oxide ether on particle, size, emulsion viscosity, mechanical, and viscoelastic properties of the emulsion cast films were examined.     

Studies on cross-linkable copolyimides

Some new flexible and cross-linkable copolyimides containing rubbery unsaturated aliphatic chain moiety (CPLA) were prepared by low temperature polycondensation betweenm-phenylene diamine,bis- 3(4 carboxy phthalimido) benzene, and liquid, bis [2-(4 piperazinyl) ethyl aminocarbonyl] poly-(butadiene-co-acrylonitrile) (ATBN) in (DMAC) solution. The effect of rubbery aliphatic moiety in these copolyimides on the polymer properties has been reported. A comparative study on the properties of these copolyimides (CPLA) with the mixture of ATBN and a low molecular-weight cross-linkable copolyimide possessing the same molecular structure as the aromatic moiety of CPLA polymers has been made.     

Recovery of thermal and mechanical properties after thermal treatment in a polyester-based polyurethane

Solution casted films of segmented polyurethanes based on poly (ethylene adipate) glycol, 4,4diphenylmethanediisocyanate, and 1,4 butanediol were studied by thermal-mechanical methods including differential scanning calorimetry and mechanical hysteresis. Data demonstrate that, following thermal treatment at 70 °C for 15 min, these polymers show time-dependent thermal and mechanical properties. In fact, because 70 °C is a temperature greater than the melting point of soft segments (about 42 °C), the soft-segment crystals are melted and their crystallization is time dependent. The results are explained in terms of phase separation. In particular, the sample with better phase separation has a faster and larger recovery.     

Dielectric relaxation in polymer solids Part 2: Application of the new model to polyurethane systems

Measurements of the complex permittivity of crosslinked polyurethanes at different temperatures in the frequency range 1–10⁵ Hz are discussed with respect to shape of relaxation curves. Using a new model (published in preceding paper) the shape parameters are related to small and large scale interaction.     

A two-ply artificial blood vessel of polyurethane and poly(L-lactide)

A biodegradable microporous small-caliber vascular prosthesis has been developed that consists of two layers. The inner layer has been made highly antithrombogenic by cross-linking of a mixture of linoleic acid and an aliphatic polyetherurethane with dicumylperoxide. Microporosity was introduced by adding sodiumfluoride crystals of about 5 m in diameter prior to cross-linking and leaching them out afterwards.The outer ply has been constructed by precipitating a (95/5) physical mixture of polyesterurethane and poly(L-lactide) from solution in the presence of sugar crystals with dimensions in the range 30–90 m which were removed by exposing the graft to water.The two-ply grafts were tested in vivo by replacing 1 cm of the abdominal aorta of rats. All the grafts remained patent at least up to 1 year and did not exhibit any aneurismal formation. The inner layer was covered with endothelial cells and several layers of smooth muscle cells.     

Preparation of muscovite with ultrahigh specific surface area by chemical cleavage

The specific surface area of a muscovite sample increases drastically after exposure to a LiNO₃ solution, e.g., from 3.4 m²/g, corresponding to platelets of ca. 200 silicate layers, to 295 m²/g (platelets of ca. 2–3 silicate layers) after treatment at 180°C under atmospheric pressure for 46 h. The efficiency of the cleavage process decreases with decreasing temperature (down to 50°C). The LiNO₃/H₂O weight ratio is also very important: at 130°C and a reaction time of 46 h, for instance, a value in the range of 1.7–1.8 leads to the highest specific surfaces. The cleaved products have the form of strong papers that disperse readily in water. During the cleaving procedure, not only the particle thickness, but also the diameter decreases. There is no evidence of damage or partial dissolution of the silicate structure after cleavage, by IR spectroscopy and yield. The use of LiCl also leads to an increase in specific surface area, but the effect is weaker than in the case of LiNO₃. Treatment with some other alkaline and alkaline earth nitrates and chlorides did not increase the specific surface area of muscovite significantly.     

Characterization of p-hydroxybenzoic acid methylester physi- and chemiadsorbates on silica by IR and UV-spectroscopy

Physiadsorbates and chemiadsorbates of p-hydroxybenzoic acid methylester (pHBAME) on colloidal and porous silicas were studied by IR and UV spectroscopy. In the IR spectra of self-supporting discs of the adsorbates, typical features were detected which allow differentiation between the physi- and the chemiadsorbed state: a strong absorption band at 1417 cm^–1 characterizes the chemiabsorbate. Dehydration by annealing and rehydration of the adsorbates proceeded also in a different way, indicated by absorption bands both in the carbonyl group and in the ring vibration frequency range. In the UV spectra the absorption maximum of the chemiadsorbate occured at 250 nm and that of the physiadsorbate at 255.5 nm (from cyclohexane suspensions of the adsorbates).Dedicated to Prof. Dr. Paul Heinz List on the occasion of his 65^th birthday.     

Studies of thermally stimulated current in polypropylene/calcium carbonate/surfactant systems

Thermally stimulated polarization (TSP) and depolarization (TSD) experiments have been performed with two grades of polypropylene and some respective CaCO₃-filled composites containing small amounts of nonionic surfactant (0–2 wt%). The effects of electrode blocking, electrode materials on the thermally stimulated currents, and reproducibility of the measurements have been studied. The effect of water vapor adsorbed from the ambient air on the AC dielectric properties and on the thermally stimulated polarization behavior has been determined.The addition of either CaCO₃ or surfactant to PP decreases the intensity of the _c depolarization current peak in the pre-melting region, while the presence of both components increases the current. Partial discharges are present in poly propylene/CaCO₃ composites under high voltages if neither water vapor nor a coherent surfactant layer is present at the matrix/filler interface.A short literature survey is presented on the TSC studies of polyolefins and their composites, and various mechanisms responsible for the observed changes are discussed, including interfacial polarization, trap redistribution through nucleation, and oriented adsorption.     

Scattering function and the dynamics of phase separation in polymer mixtures under shear flow

The phenomenological mean-field theory describing concentration fluctuations and spinodal decomposition of binary mixtures of long flexible macromolecules is generalized to mixtures under steady shear flow. This shear flow leads to a partial orientation and stretching of the coils, as well as to an anisotropic deformation of concentration fluctuations. Generalizing the approach of Onuki and Kawasaki, we obtain the collective scattering function describing these concentration fluctuations in the mixture under shear flow. Both the steady-state situation in the one-phase region and the initial stages of spinodal decomposition for concentrations inside of the spinodal curve are considered.Contributed paper delivered at the Tagung der Deutschen Physikalischen Gesellschaft, Fachausschuß Polymerphysik, Berlin, March 30–April 3, 1987.     

Growth of polyethylene single crystals from the melt: change in lateral habit and regime I–II transition

Using the technique of extraction, single crystals have been obtained from polyethylene fractions isothermally crystallized from the melt at atmospheric pressure. It has been found that the lateral habit of single crystals changes in the vicinity of the transition temperature of growth regime (regime I–II): lenticular shape elongated in the direction of theb axis (type A) in the range of regime I and truncated lozenge with curved edges of {200} and {110} growth faces (type B) in that of regime II. The transition of lateral habit causes a drastic change in the width of {110} growth faces; {110} growth faces are well developed in type B crystals while they cannot be observed and must be very small in type-A crystals. It has been shown that the growth regime of the small {110} growth face of type-A crystals must be in regime I; hence the regime I–II transition can be explained as the result of this change in lateral habit (width of the {110} growth face).     

The problem of intrinsic birefringence and chain conformation in polycarbonate from bisphenol-A

The PC-monomer is found to be a good example for elucidating the problems engendered by more complex monomers when the orientation behavior is investigated. The discrepancies found in the literature regarding the intrinsic birefringence can be fully resolved with the following assumptions:The carbonyl-unit is neither in the trans nor in the cis configuration, and the absorption band at 1364 cm^–1 is a mixture of in-phase and out-of-phase symmetric bending vibrations of the isopropyl methyl-groups. Planar and helical chain conformations are found which are thought to build up the amorphous phase. It is demonstrated that the crystal structure as known from literature can be realized by the planar conformations.Dedicated to Prof. E. W. Fischer on the occasion of his 60^th birthday     

The effect of carrier solution on the particle size distribution of inorganic colloids measured by steric field-flow fractionation

The number average and the weight average particle diameters for suspended inorganic colloids found by the new technique of steric field-flow fractionation may be successfully used provided that the most suitable carrier solution is selected, in order to minimize the coagulation and adhesion phenomena.In the present work polydisperse, irregular colloidal particles of FePO₄·2H₂O (strengite) were studied. The average particle diameters were found to vary with the electrolyte concentration in the suspending medium. A strong variation of the number and weight average particle diameters was also observed with the quantity of the surfactant added to aquatic medium in order to increase colloidal stability. The influence of the electrokinetic charge of the FePO₄·2H₂O particles in relation to the surface charge of the material of the column employed, on the particle size measured was investigated. The proper carrier solution for minimizing coagulation and adhesion phenomena in the FePO₄·2H₂O colloidal particles was found to contain either 1.5% (v/v) detergent FL-70 and 0.1 MKNO₃ or 0.5% (v/v) detergent FL-70 and 0.033 MNa₂SO₄.     

Thermal and electrical studies of some polychelates

Polychelates of Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) with 4,4′-dihydroxy-3,3′-diacetylbiphenyl-dithioxamide (DDBDO) have been prepared. Their structures were determined by visible reflectance spectroscopy and magnetic measurements in conjunction with thermogravimetric and IR measurements. Elemental analysis indicates a 1∶1 metal-ligand stoichiometry and the association of water molecules with the central metal. The decomposition temperature of the chelates is in the order Ni(II)>Fe(II)>Co(II)>Mn(II)>Cu(II). Thermal activation energies (E _a ), calculated with the help of Freeman-Carroll and Sharp-Wentworth methods, are in agreement with each other. The polychelates were found to be semiconductive, and the activation energy obtained from semiconducting behavior follows the order Co(II)>Ni(II)>Fe(II)>Cu(II)>Mn(II). The probable structure, such as six coordinated octahedral for Mn(II) and Fe(II) polychelates and four coordinated square planar for Co(II), Ni(II), and Cu(II) polychelates, have been suggested.     

Charge-transfer interaction of some pyridinium salts with hen egg-white lysozyme

The charge-transfer interaction of pyridinium salts with lysozyme and L-tryptophan has been investigated by visible absorption, circular dichroism and fluorescence spectroscopy. Four quaternized and substituted pyridinium salts were used as electron acceptors. L-tryptophan was used as a model compound of electron donor for the purpose of the comparison with lysozyme. The binding constants obtained from absorption and circular dichroism spectra were 2.0–13 M^–1 and the sequence of the magnitude was found as EPCl(1-ethylpyridinium chloride) < MPCl(1-methylpyridinium chloride) < MNCl(1-methylnicotinamide chloride) < MNMCl(1-methyl-3-carbomethoxypyridinium chloride), which could be explained by the electron affinity of the pyridinium salt. The fluorescence spectra of lysozyme and L-tryptophan in the absence and presence of pyridinium salts were interpreted by Stern-Volmer plot. The static constants thus determined were in agreement with the binding constants obtained by other methods.     

Ultrasonic measurements and other allied parameters of praseodymium and neodymium palmitates in mixed organic solvents

Ultrasonic measurements on praseodymium and neodymium palmitates were made in a mixture of 60% benzene and 40% dimethyl sulfoxide (V/V), to determine the critical micelle concentration (CMC), soap-solvent interaction, and various acoustic and thermodynamic parameters. The values of the CMC increase with the increase in the size of the cation in the soap molecules. The ultrasonic velocity, specific acoustic impedance, apparent molar compressibility, apparent molar volume and relative association increase while the adiabatic compressibility, intermolecular free length, solvation number, molar sound velocity and available volume decrease with increasing soap concentration.     

Changes in electrokinetic properties of natural rubber latex after surface chemical modifications

High-ammonia latex concentrate prepared from doubly-concentrifuged fieldHevea latex was exhaustively dialyzed to remove any residual water-soluble non-rubber constituents. The specially purified latex was then treated with specific chemical reagents to modify the surface ionogenic groupings originally present on the latex particle surface. The electrophoretic mobility of the modified latexes was investigated as a function of pH. The change in electrokinetic properties of the surface-modified latex was explained in terms of chemical modification to the ionogenic groups of the adsorbed layer of proteins and long chain fatty acid soaps on the latex particle surface, the negative charges of which are primarily responsible for the colloidal stability of the latex. For comparison direct extraction of the long-chain fatty acid soaps from the specially purified latex by solvent was also carried out. Present results indicate that the number of carboxyl groups from the adsorbed long-chain fatty acid soaps plays a major role in the stabilization of the latex concentrate. In comparison the contribution of negative charges from the adsorbed proteins towards the stability of the latex is of less importance.     

Mechanisms and micromechanics of fatigue crack propagation in glassy thermoplastics

An iterative approach is used to estimate, from interference optics measurements, the variation of refractive index and, hence, extension ratio along the length of a craze at the tip of a fatigue crack. The finite element method is used to compute craze surface stress distributions which are found to be similar to those obtained for static loading. High extension ratios, in the range 6 to 8 for retarded fatigue crack growth in poly(vinylchloride), are attained in the craze fibrils at the crack tip before crack jump occurs. The craze thickens primarily by surface drawing during the early stages of its growth but in the later stages the fibril creep mechanism predominates. The critical fibril extension ratio is not reached in a single cycle, as in normal fatigue crack propagation, and crack jump does not occur until, typically, after several hundreds of cycles during which the fibrils accumulate considerable damage.Presented in part at the 7th Int. Conference Deformation, Yield and Fracture of Polymers, Cambridge, UK, 11–14 April 1988.     

CPS LG 313 Phenylalkanol — adsorbates on silica as types of immobilized drugs 1. Chemiadsorption on activated silica surfaces

The chemiadsorption of phenylalkanols onto a porous silica support (d _pore 10 nm) viaSi-O-C bonds was studied. The silica support was activated prior to the alcohol adsorption by annealing or by the introduction ofSi-Cl groups. Different reaction conditions were applied, namely time, temperature, solvent and drug-support ratio. The yield of chemiadsorption was dependent on both the reaction conditions and the structure of the alcohols. Long alkyl chains, especially those with an alcohol OH-group positioned in the vicinity of bulky substituents, reduce the yield considerably. Using chlorinated silica, a reasonable yield of chemiadsorption can be obtained even at relatively low reaction temperatures.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occassion of his 60th birthday.     

X-ray scattering study of molecular order in a liquid crystal-side group polysiloxane

The molecular structure of a polysiloxane with phenyl benzoate mesogenic side groups was investigated in an x-ray scattering study in the partially crystalline, smectic and nematic phase, and in the melt. In the crystalline phase polymer molecules have the form of straight ribbons with a double-comb-conformation. A bilayer structure is built up by regular stacking. Layers are the dominating structure element not only in the crystalline and smectic phase, but also in the nematic phase, and even in the isotropic melt. Layers are planar in the smectic phase and curved in the nematic phase, with an asymmetric distribution of the normal vectors about the director. In the isotropic melt there is evidence for the occurrence of clusters with layer-like short-range order.