New Aspects of Impact Reactivity of Polynitro Compounds,Part III. Impact Sensitivity as a Function of the Imtermolecular Interactions

Published data of impact sensitivity of 33 polynitro compounds detected by sound were expressed as the drop energy, E_dr, required for 50 percent initiation probability. A logarithmic relationship has been found between the E_dr values and heats of fusion of the said compounds. The relationship has been found to be in accordance with the idea concerning the role of plastic deformations of crystal played in the initiation of energetic materials by impact and shock. An analogous application of heats of sublimation has not given convincing results.     

Inhibition of 12- and 15-lipoxygenase activities and protection of human and tilapia low density lipoprotein oxidation by I-Tiao-Gung (<Emphasis Type="Italic">Glycine tomentella</Emphasis>)

I-Tiao-Gung, Glycine tomentella, has been used extensively as a traditional herbal medicine to relieve physical pain, but its bioactivity has not been studied systematically. Ninety-five percent ethanol extracts of G. tomentella (GT-E) showed antioxidant activity in human plasma by prolonging the lag phase (+T_lag) of Cu²⁺-induced, LDL oxidation and were dose dependent. The+T_lag of LDL combined with 3.2 μg/mL GT-E was similar to that with 2.0 μM (ca. 0.5 μg/mL) Trolox. A similar inhibitory effect was found toward tilapia plasma LDL. In addition, GT-E inhibited tilapia thrombocyte (nucleated platelet), 5-, 12-, and 15-lipoxygenase (LOX). The IC₅₀ values were 0.43, 0.72, and 0.42 μg/mL, respectively, whereas the IC₅₀ values for nordihydroguaiaretic acid (NDGA) on 5-, 12-, and 15-LOX were 2.3, 1.6, and 1.7 μg/mL, respectively. The IC₅₀ value for cyclooxygenase-2 (COX-2) inhibition by GT-E was 42.0 μg/mL, whereas the IC₅₀ value by indomethacin as a positive control was 0.61 μg/mL. The prevention of LDL oxidation and the dual inhibition of LOX and COX-2 are indicative of the possible roles of I-Tiao-Gung in antiatherosclerosis and anti-inflammation.     

Molecular structure,crystallization behavior,and morphology of fractions obtained from an extrusion grade high-density polyethylene

An extrusion-grade of high density polyethylene (HOPE) (3 ethyl groups per 1000 carbons) has been divided into 16 fractions by preparative GPC and selective p-xylene extraction. The fractions, with molecular weights ranging from 900 to 1,000,000, have been studied by IR spectros-copy, DSC, WAXS, polarized microscopy, and small-angle light scattering (SALS), The average degree of chain branching (percent C₂H₅) is 0.5 percent for the part of the sample having a molecular weight lower than 10,000 and it decreases monotonically with increasing molecular weight, finally approaching 0.1 percent C2H5. A crystallinity depression with respect to linear PE equivalent to 20 percent/(percent C₂H₅) is recorded for all samples except for the very low molecular weight samples for which the crystallinity depression is much larger (30 to 35 percent/ (percent C₂H₅)). The unit cell volume increases with increasing percent C₂H₅, presumably due to the inclusion of ethyl groups in the crystals as interstitlals at 2gl kinks. The concentration of ethyl groups in the crystals (?_c) unanimously follows the relationship: ?_c(percent) = 0.32 + 0.25 log(percent C₂H₅) except for the low molecular weight fractions which have significantly lower values for ?_c. Our admittedly speculative explanation for this major discrepancy between high and low molecular weight samples is based on the idea that segments with ethyl groups close to chain ends have a greater difficulty in crystallizing than segments containing ethyl groups located at positions far from the chain ends. The fractions obtained from the extrusion-grade HDPE show a solidification temperature depression with respect to linear PE which can only be explained by the presence of chain branches in these samples. The depression is particularly pronounced for the low molecular weight samples as is expected from the data on molecular structure. Well-developed non-banded spherulites are observed in rapidly cooled (crystallized at about 35 K supercooling), low molecular weight samples (6,000 < M_w < 8,000)from the extrusion-grade HDPE in contrast to the axialites observed in linear PE of the same molecular weight and thermal treatment. This discrepancy in morphology has been related to the presence of ethyl groups in the extrusion grade HDPE fractions. Higher molecular weight samples (20,000 < M_w < 1,000,000)from the extrusion-grade HDPE and linear PE both display well-developed banded spherulites of similar nature as is expected due to the similarity in molecular structure of the two sets of sample.     

The effect of annealing at 135° on the mechanical properties of injection molded high density polyethylene-polypropylene blends

The effect of annealing at 135°C for 5 hours on the tensile properties of mechanically mixed and then injection molded high density polyethylene (HDPE) and polypropylene (PP) blends has been investigated. Both the tangent elastic modulus and the tensile strength at yield exhibit a non-linear behavior versus blend composition with a minimum of properties typical for incompatible blends. Annealing substantially improves mechanical properties of pure components and blends (20 percent increase in the yield strength of pure components and blends and the modulus of pure components, and ～40 percent increase in the modulus of 50/50 blends) but the property behavior versus composition is still nonlinear. Scanning electron microscopy studies of fracture surfaces of blends seems to indicate some improvement in bonding between phases as a result of annealing, Both the elastic modulus and yield strength fit extremely well to the modified “rule of mixtures” equation in the general form: M_b = M_PEφ_PE + M_PPφ_PP + ΔM_PE/PPφ_PEφ_PP where M_b is the blend property, M_PE and M_PP are properties of pure PE and PP components, φ_PE and φ_PP are weight fractions of PE and PP, and ΔM_PE/PP is the interaction term being a measure of the deviation from simple additivity.     

The modification of secondary high molecular weight guayule rubber with metachloroperoxybenzoic acid

The epoxidation of secondary high molecular weight guayule rubber has been accomplished. The reaction is performed using metachloroperoxybenzoic acid as the epoxidation agent in various stoichiometric ratios including 5, 10, 20, and 50 mol %. The products were characterized by infrared spectroscopy, ¹H- and ¹³C-nuclear magnetic resonance (NMR), differential scanning calorimetry, and elemental analysis. ¹H-NMR is used quantitatively to calculate epoxidation levels that are compared to stoichiometry. DSC results record a linear relationship between percent epoxidation and T_g. © 1993 John Wiley & Sons, Inc.     

Effect of tensile strain,time, and temperature on gas transport in biaxially oriented polystyrene

The permeability and diffusion coefficients (P and D) for gases in a biaxially oriented polystyrene film have been found to increase when a specimen is stretched in simple tension and to decrease with time when the strain is held constant. These effects are attributed, respectively, to an increase in free volume with strain and to the continuous volume recovery (densification) at constant strain. The strain dependence, at small strains, of P and D for Ar, Kr, N₂, CO₂, and Xe at 1 atm pressure and 50°C indicates that the size distribution of free-volume elements is not distorted when a specimen is stretched. At a constant strain of 1.8 percent at 50°C, P and D for xenon decrease about 13.8 and 11.8 percent, respectively, per decade of time—two to threefold faster than for carbon dioxide. These results and those obtained with argon, whose molecular diameter is significantly smaller than that for xenon, suggest that the larger free-volume elements decrease in size faster than the smaller ones as volume recovery progresses.     

The importance of real-fluid behavior in predicting release rates resulting from high-pressure sour-gas pipeline ruptures

The real-fluid nonisentropic decompression model presented by Picard and Bishnoi (1988) has been used to evaluate the current practice of assuming perfect-gas behavior when predicting release rates from high-pressure sour-gas pipelines. It is shown that use of perfect-gas theory can result in the transient release rate being underestimated by 30 to 45 percent, and the total amount of fluid released, underestimated by 50 percent. Furthermore, perfect-gas theory cannot consider condensation effects; more than 35 percent of the H₂ S contained in a pipeline may be emitted as a liquid. Use of the popular “double exponential” model, as presented by Wilson (1979), will result in similar errors. However, if the model is modified slightly so that the initial mass of fluid in the pipeline is determined based on real-fluid theory, then a conservative estimate of the transient release rate may be obtained (i.e., the most rapid release of the fluid is predicted).     

Thermai treatment of cold-formed poly(vinyl chloride)

Cold-drawing poly(vinyl chloride) at 24°C increased the yield strength by 25 percent, modulus by 50 percent, and the ultimate strength by 100 percent. The onset of thermal shrinkage was reduced from 80°C (T_g) to 45°C. This thermal instability can be a significant disadvantage of cold-forming for many applications. It is shown in this study that subsequent thermal treatment at 70°C (T < T_g) re-establishes a shrinkage onset temperature of 80°C without reducing property levels. The structural changes associated with both orientation and thermal treatment were investigated using DSC, X-ray diffraction and birefringence. Cold-drawing produces molecular alignment as measured by birefringence and X-ray. Thermal treatment of unstretched samples, as well as stretched samples under constraint and stretched samples unconstrained, always leads to a small reduction in free volume as revealed by a measured increase in enthalpy at T_g. However, this free volume change, produces a thermally-stable oriented structure only when the samples are treated under constraint. Thermal treatment does not stabilize unconstrained samples. Rather it causes almost complete molecular relaxation and a reduction of physical property levels.     

Compatibility and physical properties of a new polyester blend

The compatible nature of a new polyester blend, polybutylene-terephthalate (PBT) and a copolyester of bisphenol-A-neopentyl glycol-terephthalate (CP-350), has been inferred from the single T_g by DSC and dynamic mechanical studies. Compatibility is further confirmed from the progressive melting point depression of PBT, and the increasingly coarse and open spherulitic morphology of the blends as the weight percent of CP-350 increases. At and above 40 weight percent of CP-350, crystallization of PBT is impeded by the presence of high concentrations of CP-350 which results in a low degree of PBT crystallinity (0-8 percent) in such blends. The melt viscosity as a function of blend composition shows a good fit to the Hayashida model.     

Fatigue crack propagation in poly(methyl methacrylate): Effect of molecular weight and internal plasticization

In spite of the importance of fatigue behavior in engineering plastics, relatively few fundamental studies have been made of the effects of polymer structure, molecular weight, composition, and morphology on fatigue crack propagation (FCP). As, part of a broad program for the study of such effects, the role of molecular weight and internal plasticization has been studied in poly(methyl methacrylate) (PMMA) which had been specially prepared and characterized with respect to molecular weight, dynamic mechanical behavior, and, in some cases, stress-strain response. As expected, values of fracture toughness, K_c, varied considerably as the molecular weight was rai ed, from 0.7 MPa, √m at M _v = 1.0 × 10⁵ to 1.1 at M_v, = 4.8 × 10⁶. However, a specific effect of fatigue was noted: over the same range of K_c, values of FCP rate decreased by two orders of magnitude as molecular weight was; increased. It is proposed that this high sensitivity is due to differences in the degree of chain disentanglement effected by the cyclic loading, with consequent differences in the strength of the craze preceding the crack. With PMMA plasticized internally with a low level (10 percent) of n-butyl acrylate (nBA), the FCP rate and K_c, were similar to those of controls, with very high rates shown. At higher nBA levels (up to 30 percent), the sensitivity of FCP rate to stress intensity factor range decreased considerably, K_c, increased by 30 percent and the pre-exponential constant in the growth rate law increased. Plasticization weakens the polymer but at high degrees leads to enough hysteretic heating to induce local creep and crack blunting.     

Miscibility in poly(vinyl chloride)/chlorinated poly(vinyl chloride) blends,and blends of different chlorinated poly(vinyl chlorides)

Blends of poly(vinyl chloride) with chlorinated poly(vinyl chloride) (PVC), and blends of different chlorinated poly(vinyl chlorides) (CPVC) provide an opportunity to examine systematically the effect that small changes in chemical structure have on polymer-polymer miscibility. Phase diagrams of PVC/CPVC blends have been determined for CPVC's containing 62 to 38 percent chlorine. The characteristics of binary blends of CPVC's of different chlorine contents have also been examined using differential calorimetry (DSC) and transmission electron microscopy. Their mutual solubility has been found to be very sensitive to their differences in mole percent CCl₂ groups and degree of chlorination. In metastable binary blends of CPVC's possessing single glass transition temperatures (T_g) the rate of phase separation, as followed by DSC, was found to be relatively slow at temperatures 45 to 65° above the T_g of the blend.     

Miscibility of blends of epoxidized natural rubber and poly(ethylene-co-acrylic acid)

The blends of epoxidized natural rubber (50 mol %) (ENR) and poly(ethylene-co-acrylic acid) (PEA) (6 wt %) are demonstrated to be partially miscible up to 50% by weight of PEA and completely miscible beyond this proportion. The miscibility has been confirmed by a DSC study which exhibits a single second-order transition (T_g) for the 30 : 70 and 50 : 50 (ENR : PEA) blends. For the 70 : 30 (ENR : PEA) blend, the T_g's shift toward an intermediate value but do not merge to form a single T_g, making the blend partially miscible. The miscibility has been assigned to the esterification reaction between – OH groups formed in situ during melt blending of ENR and – COOH groups of PEA. The occurrence of such reactions have been confirmed by UV and IR spectroscopic studies. The existence of a single phase of the blends beyond 50 wt % of PEA has been shown by SEM studies. © 1995 John Wiley & Sons, Inc.     

Stored energy of cold work in polystyrene

The energy stored in polystyrene after plastic deformation is measured by the differential scanning calorimetry (DSC) technique. Similar to metals, the stored energy increases with plastic straining, first rapidly, and then more slowly, and finally the stored energy seems to approach a saturation value (about 1 cal/gram). By comparing to the plastic work done, the fraction stored ranges from 30 percent after 10 percent compression to 10 percent after 60 percent compression. The fraction is about twice as large as that of copper. The release of stored energy has two distinct parts, one below T_g and the other above T_g. Most of the strain recovery seems to accompany the second part. By using the Kissinger plot, the second part has an activation energy, of 142 kcal/mole which is about 10 percent larger than that of compressive strain recovery.     

Anionic ring opening polymerization of 1-phenyl-1-vinyl-1-silacyclopent-3-ene

Summary Poly(1-phenyl-1-vinyl-1-sila-cis-pent-3-ene) (I) has been prepared by the anionic ring opening polymerization of 1-phenyl-1-vinyl-1-silacyclopent-3-ene (II) co-catalyzed by n-butyllithium and hexamethylphosphoramide (HMPA) in THF at-78°C. I has been characterized by ¹H, ¹³C and ²⁹Si NMR as well as by IR and UV spectroscopy. The molecular weight distribution of I has been determined by gel permeation chromatography (GPC), its thermal stability by thermogravimetric analysis (TGA) and its glass transition temperature (T_g) by differential scanning calorimetry (DSC). Thermal degradation of I in an inert atmosphere gives a twenty-seven percent char yield.     

Gas permeabilities of cellulose nitrate/poly(ethylene glycol) blend membranes

The permeability (P) of cellulose nitrate (CN)/poly(ethylene glycol) (PEG) blend membranes for N₂, O₂, and CO₂ has been measured as a function of film composition. The system CN/PEG-300 showed excellent miscibility, and films of the composition from 100/0 to 50/50 could be used for permeability measurements. P for each gas has been found to be almost constant or rather slightly lowered up to ca. 20 wt % PEG-300 content and then increased appreciably with increasing fraction of PEG. The increment of permeability was most remarkable for CO₂, and hence the permselectivity for CO₂ was considerably enhanced. Such a behavior of P has been found to be attributable to the plasticizing effect of PEG molecule lowering the glass transition temperature of the blend polymers. The effect of the molecular weight of PEG and that of closed voids generated in glassy blend membranes fabricated from acetone cast on gas permeabilities have been also discussed.     

New Aspects of Impact Reactivity of Polynitro Compounds,Part II. Impact Sensitivity as “the First Reaction” of Polynitro Arenes

The impact reactivity (“the first reaction”) of 22 polynitro arenes was expressed as the drop energy, E_dr, required for 50 percent initiation probability. Relationships have been found between the E_dr values and heats of fusion, on the one hand, and ¹³C NMR chemical shifts of carbon atoms in reaction centers, on the other hand. On the basis of the said relationships it was stated that the impact reactivity of polynitro arene molecules depends on the electronic configuration within their reaction centers and on the intensity of their intermolecular interactions in the molecular crystals. The relationships found make it possible to specify this reaction center which is illustrated by the molecules of 1,5‐dinitronaphthalene and 3,3′‐dimethyl‐2,2′,4,4′,6,6′‐hexanitrodiphenyl sulfide.     

Sodium metabisulphite initiated aqueous polymerisation of methyl methacrylate

Sodium metabisulphite (Na₂S₂O₅) has been found to initiate the aqueous polymerisation of methyl methacrylate (MMA) at 35°C in phosphate buffer solutions of pH 6.85 and a constant ionic strength (μ) of the media in an inert atmosphere of pure nitrogen. The reaction has a well defined induction period which is a function of the concentrations of the initiator, of the monomer and also of temperature. The polymerisation is signalled by the sudden appearance of a haze at the end of the induction period in a given run, and the polymer separates out as a coarse precipitate during the progress of the polymerisation reactions. When the conversion is over 50 per cent complete, the polymerisation media looks like a thick curd if the monomer concentration is relatively high. The rate of polymerisation is found to decrease with conversion or time in a given run, and the initial rate (v_p), obtained by extrapolating the linear yield/time versus time curves to zero time, keeping the conversion below 10 percent, is found as where (I) = initiator concentration in the range, (0.26 to 3.94) × 10^?3 (mol dm^?3), and (M) = monomer concentration in the range 0.019 to 0.141 (mol dm^?3). At high initiator concentrations, the rate of polymerisation is found to decrease. In a given run, the viscosity average molecular weights (M _v) of the polymers is found to increase quickly with a conversion of up to 25 to 30 percent, and then slowly with the further increase in conversion. (M_v) however is found to decrease with the increase of the initiator concentrations at a given conversion but increases with the increase of the monomer concentrations. Hydroquinone inhibits the polymerisation reactions, whereas air is found to increase the induction period, but later enhances the polymerisation rate in the same run. It has been shown that the bisulphite addition reaction of MMA is not important under the experimental conditions, and the polymerisation occurs by the free radical mechanism. The rate constant (k₂) of the reaction, has been estimated from the analytical data as, k₂ = 14.62 × 10^?2 (dm³ mol^?1 s^?1) at 35°C.     

The kinetics of the in situ polymerization of glycidyl methacrylate in wood using dynamic mechanical measurements

The in situ polymerization of glycidyl methacrylate in wood, in the presence of uranyl nitrate, (UN), and/or 2,2′-azo-bis-isobutyronitrile, (AIBN), has been investigated in the temperature range 55°-72°C. The course of the polymerization reaction was followed by measurement of tan 5 in an automated Rheovibron viscoelastometer. The kinetics, studied by applying the Guggenheim method to the data, showed the polymerization to be first order whether catalyzed by UN or initiated by AIBN. The activation energy (E_α) for AIBN-initiated polymerization was 121 kJ/mol, and was unaffected by varying monomer concentration in acetone. On the other hand, E_α for the UN-catalyzed polymerization was found to be 59.1 and 73.5 kJ/mol respectively for the neat and 50 percent monomer concentration reaction mixture. The enhancement in E_α is attributed to the complexatton of the dioxouranium (VI) ion in the presence of solvent acetone, with consequent reduction in catalytic activity.     

Effect of concentration on apparent viscosity of a globular protein solution

The viscosity of a globular protein solution as a function of concentration was studied with a cone and plate viscometef (Ferranti-Shirley Viscometer System) using, β-lactoglobulin as a model. An aqueous buffer solution (pH 7, ionic strength 0.04) containing up to 40 percent protein was subjected to rates of shear between 800 and 17,000 sec^?1. Specific viscosity of β-lactoglobulin up to 10 weight percent was proportional to the weight concentration of protein in solution such that: η_s = η₀ [ 1+0.8 (weight percent concentration)] where η₀ and η_s are viscosity coefficients for the pure solvent and the solution, respectively. For 3-40 weight percent, a linear relation of shear rate and shear stress was observed at high shear rates. Linearity began at 3500, 4300, 6800, and 7000 see^?1 for 10, 20, 30 and 40 weight percent concentrations respectively. The apparent viscosity was lower below these critical shear rates.     

Molecular transport of n‐alkanes into PU/PBMA interpenetrating polymer network systems

The methylene diisocyanate (MDI) and toluene diisocyanate (TDI) based polyurethane/polybutyl methacrylate (PU/PBMA‐50/50) interpenetrating polymer network (IPN) membranes have been prepared. The molecular migration of n‐alkane penetrants such as hexane, heptane, octane, nonane, and decane through PU/PBMA (50/50) membranes has been studied at 25, 40, and 60°C using a weight gain method. From the sorption results, diffusion (D) and permeation (P) coefficients of n‐alkane penetrants have been calculated. Molecular migration depends on membrane‐solvent interactions, size of the penetrants, temperature, and availability of free volume within the membrane matrix. Attempts have been made to estimate the parameters of an empirical equation and these data suggest that molecular transport follows Fickian mode. From a study of temperature dependence of transport parameters, activation energy for diffusion (E_D) and permeation (E_P) have been estimated from the Arrhenius relation. Furthermore, sorption results have been interpreted in terms of enthalpy (ΔH) and entropy (ΔS) of sorption. The liquid concentration profiles have been computed using Fick's equation with appropriate initial and boundary conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 739–746, 2003