Intrinsic birefringence of nylon 6

Different values are reported in the literature for the intrinsic birefringence of the crystalline (Δn) and the amorphous (Δn) phases in nylon 6. Mostly, these values have either been determined by extrapolation (and then it is assumed that Δn = Δn) or calculated theoretically. In this study, intrinsic birefringence values Δn and Δn for nylon 6 were determined using the Samuels two-phase model which correlates sonic modulus with structural parameters. Three series of fiber samples were used: (1) isotropic samples of different degrees of crystallinity for estimation of E and E moduli at two temperatures. The following modulus values were obtained: 1.62 × 10⁹ and 6.66 × 10⁹ N/m² for 28.5°C, and 1.81 × 10⁹ and 6.71 × 10⁹ N/m² for ?20°C; (2) anisotropic, amorphous fiber samples for estimation of Δn = 0.076 and E = 1.63 × 10⁹ N/m² at 28.5°C; (3) semicrystalline samples of various draw ratios for estimations of Δn = 0.089 and Δn = 0.078. All measurements were carried out with carefully dried samples to avoid erroneous results caused by moisture.     

Electrochemical synthesis and properties of poly(3‐methylthiophene): Novel synthesis of poly(3‐methylthiophene) with pentachlorostannate and hexachloroantimonate

Poly(3‐methylthiophene) (P3‐MeT) doped with different anions were prepared electrochemically in the presence of tetraalkylammonium salts. The new poly(3‐methylthiophene) SnCl and SbCl (P3‐MeT SnCl₅ and P3‐MeT SbCl₆) were prepared electrochemically using tetra‐n‐butylammonium pentachlorostannate and tetra‐n‐butylammonium hexachloroantimonate as the supporting electrolytes. The effect of current density, salt concentration, reaction temperature, and the nature of solvents on the polymer yield and polymer conductivities have been investigated. Cyclic voltammetry of poly(3‐methylthiophene) has been examined at platinum electrode in 1,2‐dichloroethane medium containing n‐Bu₄NSnCl₅, Bu₄NSbCl₆, and Bu₄NClO₄ as the supporting electrolytes in the range of −1.0 to 1.7 V versus SCE in the presence and absence of 3‐methylthiophene. Electrical conductivity, magnetic susceptibility measurements, and structural determination by elemental analysis and infrared studies were also made. Scanning electron microscopy revealed a globular, branched, fibrous and a spongy, fibrous morphology of poly(3‐methylthiophene) SnCl, ClO, and SbCl, respectively. The thermal analysis of the polymers was also investigated. Possible causes for the observed lower conductivity of these polymers have also been discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 91–102, 1999     

Inverse gas chromatography of poly(vinylisobutyl ethers) and polymer-solute thermodynamic interactions

Gas chromatography (GC) retention behavior of atactic and isotactic poly(vinylisobutyl ether) stationary phases has been studied in the temperature range 30–90°C using 16 solutes which include various alkanes, alkylbenzenes, and chlorinated aliphatic hydrocarbons. The bulk sorption equilibrium retention data have been employed to derive various thermodynamic quantities at infinite dilution of solutes in the polymers, viz., χ, χ^*, χ_H, χ_S, X₁₂, δH_S, h . Their dependence on temperature, polymer structure, and chemical nature of solutes has been discussed.     

Elektrochemisches Verhalten von N-Aryl-Δ2-pyrazolinen. VIII. Zusammenhänge zwischen dem anodischen und kathodischen Verhalten und den Absorptions- und Fluoreszenz-eigenschaften von N-Aryl-Δ2-pyrazolinen

Electrochemical Behavior of N-Aryl-Δ²-pyrazolines. VIII. Relationships between the Anodic and Cathodic Behaviour and the Absorption and Fluorescence Properties of N-Aryl-Δ²-pyrazolines The anodic and cathodic half-wave potentials in acetonitrile and dimethylformamide (DMF) and the absorption and fluorescence spectra in DMF and cyclohexane of 61 N-aryl-Δ²-pyrazolines have been measured. The following correlation has been found between the difference of the half-wave potentials E–E of the first oxidation and reduction steps and the fluorescence maximum in DMF, h · ν: This confirms the charge-transfer character of the corresponding spectroscopical transition. The deviations of some compounds from this correlation are due to differences in the electrochemical behaviour as, e.g., the cathodic elimination of halogen from halogen substituted pyrazolines or the intramolecular hydrogen bond in 1, 5-diaryl-3-o-hydroxyphenyl-Δ²-pyrazolines.     

Modellrechnungen zum Gegenioneneinfluß auf die kationische Polymerisation; Der Zerfall der gemischten Halogenoantimonate SbCl5Br− und SbClBr

Model Calculations on the Counterion Effect in the Cationic Polymerization; Decay of the Mixed Halogenoantimonates SbCl₅Br⁻ and SbClBr The decay of the halogenoantimonates SbCl₅Br⁻ and SbClBr according to SbCl₅Br⁻ → SbCl₅ + Br⁻ resp. SbCl₄Br + Cl⁻ and SbClBr → SbBr₅ + Cl⁻ resp. SbClBr₄ + Br⁻ has been investigated by the quantum-chemical CNDO/2 method including geometry optimization. The calculations show that the dissociation of the Sb Cl bond needs more energy (7,8 kcal/mol) than the dissociation of the Sb Br bond. Dissociation of the complex anions is facilitated with increasing Br content.     

Transformation products of antioxidants: The role in stabilization mechanisms

Antioxidants acting in polymers by chain-breaking and hydroperoxide decomposing mechanisms are chemically transformed during the stabilization process as a consequence of trapping radicals R^?, RO^? or RO and/or reactivity with hydroperoxides. New chemical compounds with typical structures characteristic of the starting stabilizer are formed stepwise in the polymer mass. Most of these transformation products participate actively in consecutive steps of polymer degradation. Finally observed phenomena depend on the concentration of individual transformation products. Generally, autocooperative effects with starting stabilizers take place. Important data regarding properties of transformation products have been summarized.     

Mechanical properties of polyethylene/ethylene vinyl acetate filled with calcium carbonate

The tensile behavior of polyethylene/ethylene vinyl acetate (PE/EVA) polymer blends filled with calcium carbonate (CaCO₃) was studied using tensile and viscoelastic tests. The relations between tensile properties (modulus, strength, etc) of oriented and unoriented PE/EVA-CaCO₃, and void volume of polymer/CaCO₃ interface, PE/EVA blend ratio, and CaCO₃ content were investigated. The results indicated that the tensile strength and elongation of PE/EVA-CaCO₃ decreased with CaCO₃ content and PE blend ratio for unoriented PE/EVA-CaCO₃ systems. In the case of oriented samples, the relative modulus (E/E, where E and E are the modulus of oriented composites and the modulus of oriented matrix, respectively) of PE/EVA-CaCO₃ is larger than that of PE/CaCO₃ by increasing the EVA content relative to PE and CaCO₃. The value of E/E can be simply expressed as the function of void volume and CaCO₃ modulus to polymer matrix modulus.     

Effect of sub-Tg annealing on CO2 sorption in polycarbonate

High pressure CO₂ sorption data in polycarbonate (PC) are reported as a function of temperature and thermal history. The bulk physical structural changes produced by annealing at 125 and 135°C were monitored by density and thermal property changes. The sorption data are analyzed by the dual sorption model which assumes the sorption isotherm to consist of Henry's law and Langmuir sorption terms; The Langmuir capacity term C of PC can be grossly correlated with the reported volumetric parameters of the polymer. This excess volume interpretation of C has found support in the good correlation between C and the corresponding enthalpy relaxation from parallel Differential Thermal Analysis of the samples. Density measurements provide gross evidence of the free volume interpretation of C. The experimental uncertainties in the data compromise a more critical test of the relationship between C and the density of annealed samples.     

Nonlinear programming methods to determine surface free energy components of polymers using harmonic mean approximation

The dispersion and polar surface free energy components, γ and γ, and the critical surface free energy, γ_c, of polymers were determined from contact angle data by the application of a nonlinear programming method using harmonic mean approximation. The surface free energy components of the probe liquids, γ and γ, which reflect the conditions of the maximized interaction parameter, Φ, were also simultaneously determined by this method.     

Preparation and solid‐state nuclear magnetic resonance characterization a styrene/butadiene/acrylonitrile (ABS)/poly(vinyl chloride) (PVC)/gypsum ternary system

Polymer blends were prepared to obtain a new material with specific characteristics. To prepare a miscible polymer blend, it is necessary to evaluate the chemical structure and molecular dynamics of all polymers involved and to thereby establish a structure–property relationship for these materials. In this work, ternary blends for application in plates chromatography were formed with styrene/butadiene/acrylinotrile (ABS), poly(vinyl chloride) (PVC), and gypsum, and were studied by solid‐state carbon‐13 nuclear magnetic resonance (¹³C NMR). Magic‐angle spinning (MAS), cross‐polarization magic‐angle spinning (CPMAS), variable contact time (VCT), and proton spin‐lattice relation time in the rotating frame (Tρ) were the techniques used to evaluate the miscibility, homogeneity, and compatibility of polymer blends at the molecular level. From the values of Tρ, it was verified that ABS/PVC/gypsum formed good polymer blends with some specific physical interaction at the molecular level. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 293–296, 2003     

On the variable dissolution kinetics of zinc ferrite in acid media

Different magnetic fractions of narrow-sized industrial residues of zinc ferrite [(Zn_1-x, Fe)FeO₄, x ≤ 0.4] have been leached with 1 mol/L H₂SO₄ at temperatures ranging from 348 to 368 K. Fractions with excess iron, which exhibit higher magnetic susceptibility, are found to dissolve faster. It is believed that the lattice substitution of Zn by Fe²⁺ in the more magnetic ferrite fractions creates crystal defects and renders the ferrite more chemically reactive. An interfacial electrochemical reaction mechanism has been advanced to account for the effects of solid state composi tion and solution composition on the variation of the dissolution kinetics of zinc ferrite. Finally, the practical implications of these findings on the industrial leaching of zinc ferrite are briefly addressed.     

Surface free energy analysis of polymers and its relation to surface composition

The dispersion force component of surface free energy, γ, and the nondispersive interaction free energy between solid and water, I, were determined by the two-liquid contact-angle method, i.e., by the measurement of contact angles of water drops on plain solids in hydrocarbon, for commercialy available organic polymers such as nylons, halogenated vinyl polymers, polyesters, etc. A method to estimate the I values from the knowledge of the polymer composition is also proposed, on the basis of the assumption of the spherical monomer unit and the sum of interactions between functional groups and water molecules at the surface.     

Forced oscillations in continuous flow stirred tank reactors with nonlinear step growth polymerization

The self-step growth polymerization of RA_f monomers in homogeneous, continuous flow stirred tank reactors (HCSTRs) is simulated under conditions of periodic feed concentration (with frequency ω and amplitude α). By having periodic operation, the polydispersity index of the polymer is found to increase by about 35% over the values at steady state. Periodic operation of HCSTRs is found to lead to gelation only for certain values of the frequency and the dimensionless residence time τ^*. Gelling envelopes have been obtained to give conditions under which HCSTRs should be operated. These envelopes can be described in terms of two critical dimensionless residence times, τ and τ such that nongelling operation is always ensured when τ^* < τ. For τ^* > τ, periodic operation always leads to gelation, and HCSTRs cannot be used. For τ < τ^* < τ, the gelling behavior is found to depend on the functionality f, amplitude α, and the dimensionless residence time τ^*.     

Viscoelasticity of some engineering plastics analyzed with the modified stress-optical rule

The complex Young's modulus, E*(ω), and the complex strain-optical coefficient, O*(ω), of poly(ether sulfone) (PES), polysulfone (PSF), and polyethermide (PEI), were measured over the frequency range 1 to 130 Hz. The data were analyzed with a modified stress-optical rule: The Young's modulus was decomposed into two complex functions, E(ω) and E(ω); the modified stress-optical coefficient, C_R and C_G, associated with the rubber (R) and glass (G) components, respectively, were determined. The results for six polymers, including polystyrene, poly(α-methyl styrene), and bisphenol A polycarbonate were compared with each other. One of the coefficients, C_R, equivalent to the stress-optical coefficient in melts, mainly depended on the way in which phenyl groups were connected to the chain. The other, C_G, was in the range of 20 to 40 Brewsters, and did not strongly depend on the details of polymer structure. The component function, E(ω), which was located in the glassy region and originated from the high glassy modulus, was almost the same in shape when plotted against ω with double logarithmic scales. The R component, E(ω), located at the long time end of the glass-to-rubber transition zone, was slightly sensitive to the molecular structure of polymers.     

Determination of crystallinity ratio and some physicochemical properties of poly(4‐methyl‐1‐pentene)

It was determined that the thermal stability of poly(4‐methyl‐1‐pentene) (P4MP) was maintained up to 424°C in an inert atmosphere by thermogravimetric analysis. The retention diagrams of ethyl acetate, tert‐butyl acetate, and benzene on P4MP were plotted at temperatures between 30 and 280°C by inverse gas chromatography (IGC) technique. Melting temperature of the polymer was determined as 230 and 239.5°C by IGC and differential scanning calorimetry (DSC), respectively. The percent crystallinity of P4MP was obtained from the retention diagrams at temperatures below melting point. The percent crystallinity obtained by IGC is in good agreement with the ones obtained by DSC. Then, specific retention volume, V, weight fraction activity coefficient, Ω, Flory‐Huggins polymer‐solvent interaction parameter, χ, equation‐of‐state polymer‐solvent interaction parameter, χ, and effective exchange energy parameter, X_eff of octane, nonane, decane, undecane, dodecane, tridecane, n‐butyl acetate, isobutyl acetate, isoamyl acetate with P4MP, were determined between 240 and 280°C by IGC. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Liquid–solid mass transfer for cocurrent gas–liquid upflow through solid foam packings

This article presents the liquid–solid mass transfer characteristics for cocurrent upflow operated gas–liquid solid foam packings. Aluminum foam was used with 10, 20, and 40 pores per linear inch (PPI), coated with 5 wt % Pd on γ‐alumina. The effects of gas velocity (u_g = 0.1?0.8 m m s^?1) and liquid velocity (u_l = 0.02 and 0.04 m m s^?1) are studied using the Pd/Bi catalyzed oxidation of glucose. The volumetric liquid–solid mass transfer coefficient, k_lsa_ls, is approximately the same for 10 PPI and 20 PPI solid foams, ranging from 2 × 10^?2 to 9 × 10^?2 m m s^?1. For 40 PPI solid foam, somewhat lower values for k_lsa_ls were found, ranging from 6 × 10^?3 to 4 × 10^?2 m m s^?1. The intrinsic liquid–solid mass transfer coefficient, k_ls, increases with increasing liquid velocity and was found to be proportional to u. Initially, k_ls decreases with increasing gas velocity and after reaching a minimum value increases with increasing gas velocity. The values for k_ls range from 5.5 × 10^?6 to 8 × 10^?4 m m s^?1, which is in the same range as found for random packings and corrugated sheet packings. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Swelling of superabsorbents polymers in an aqueous medium

The polymers studied are superabsorbents materials. They were synthesized by inverse suspension polymerisation of acrylic acid. The polymers studied, X10 and X5, are different in their degree of ionisation. In fact, our objective was to increase the amount of water that may be stored by the polymer. In this article, we investigated not only the effect of temperature and pH on the satured water absorbency of polymers X10 and X5, but also various swelling behaviours of polymer X10 in different saline solutions. The results show that for temperature ranging from 10 to 90°C, the effect of temperature on the satured water absorbency is rather limited when the superabsorbent is swelled by distilled water. Further, water absorbency of X10 and X5 is strongly affected by the pH value. The results also indicate that saline solutions can weaken the swelling abilities of the polymer X10. Water absorbency of polymer X10 in aqueous chloride salt solutions has the following order: Na⁺ = K⁺= NH > Ca²⁺ = Mg²⁺ all through the range of investigated concentration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Molecular weight and molecular weight distribution from dynamic measurements of polymer melts

A method for determining the molecular weight distribution (MWD) of a polymer melt has been developed using the dynamic elastic modulus (G'), plateau modulus (G), and zero shear complex viscosity (η). The cumulative MWD was found to be proportional to a plot of (G'/G)^0.5 vs. measurement frequency (ω). Frequency (ω) was found to be inversely proportional to (MW)^3.4, as expected. Results were scaled to absolute values using the empirical relationship η ∝ (M?_w)^3.4, where M?_w is the weight-average MW. M?_w, M?_n (number-average MW) and M?_w/M?_n calculated from melt measurements were found to agree with size exclusion chromatography usually well within 10 percent for broad and bimodal distribution samples. M?_w/M?_n tended to be approximately 20 percent higher for narrow distribution samples (M?_w/M?_n < 1.2) because we did not account for a finite distribution of relaxation times from a collection of monodisperse polymer chains. We also did not account for the plasticizing effect of short chains mixed with long ones which caused peak positions to be closer together for Theological vs, size exclusive chromatography (SEC) determinations of MW for bimodal distribution blends.     

Influence of solvent and molecular weight on thickness and surface topography of spin-coated polymer films

The influence of polymer molecular weight, molecular weight distribution, and polymer-solvent interactions on the thickness and topography of spin-coated polymer films was examined. For films prepared from dilute solutions, highly volatile solvents or fair or “poor” solvents for the polymer adversely affect film surfaces causing nonuniformities (waves) to appear. However, if the concentration of these solutions is increased to approximately the concentration at which entanglements are formed, nearly uniform films are produced even if the solvent employed is highly volatile, such as dichloromethane. When toluene is employed as the solvent, which has a relatively low volatility and therefore forms nearly flat film surfaces, films prepared from dilute solution were found to have thicknesses, h, proportional to η Ω^?0.49 for polystyrene and η Ω^?0.49 for poly(methylmethacrylate) where η_o is the zero-shear rate solution viscosity and Ω is the rotational speed at which the films were prepared. These results suggest that the exponents associated with η_o and Ω may be nearly independent of the type of polymer used as long as flat films are produced. Finally, the molecular weight parameter most important in controlling final film thickness for films made from dilute solutions is M_v, the viscosity-average molecular weight.