Synthesis of poly(vinyl pyrrolidone) nanohydrogels by the template-assisted ionizing radiation

Poly(vinyl pyrrolidone), PVP nanohydrogels were successfully synthesized by a nanotemplate-assisted ionizing radiation method. Steady-state ionizing radiation (γ-ray) was used to generate the gel-forming chemical crosslinking bonds on polymer molecules confined in the highly ordered cylindrical capillary well structure of the nanoporous membrane. The inter-molecular separation of PVP molecules by the capillary well promoted the inter- and intra-molecular carbon-centered PVP radical recombination reaction only within the same capillary pore upon irradiation and produced the nano-sized hydrogels. It was observed that size of the synthesized PVP nanohydrogel particles was determined by the diameter of nanocapillary pore.     

Alkaline solid polymer electrolyte membranes based on structurally modified PVA/PVP with improved alkali stability

Novel alkaline solid polymer electrolyte membranes that can conduct anions (OH⁻) have been prepared from poly(vinyl alcohol)/poly(vinylpyrrolidone) (PVA/PVP) by blending and chemical cross-linking, followed by doping in aqueous KOH solution. The physicochemical properties of these membranes have been studied in detail by FTIR, TG, and SEM analyses. The ionic conductivity was found to be greatly dependent on the concentration of KOH and the interpenetrated PVP in the PVA matrix. A maximum conductivity of up to 0.53 S cm⁻¹ at room temperature was achieved for PVA/PVP in a mass ratio of 1:0.5 after doping in 8 m aqueous KOH solution. The membrane showed perfect alkaline stability without losing its integrity even upon exposure to 10 m KOH solution at up to 120 °C. Scanning electron micrographs revealed a highly ordered microvoid structure uniformly dispersed on the membrane surface with a pore size of ca. 200 nm after heat-curing, which imparted the membrane with good liquid electrolyte (KOH) retention ability. FTIR spectra showed that these high ionic conductivities may be attributed to the presence of excess free KOH in the polymer matrix in addition to KOH bound to the polymer. Almost constant, highly stable, ionic conductivity while maintaining mechanical integrity was retained at room temperature for more than one month.     

Wear resistant UHMWPE with high toughness by high temperature melting and subsequent radiation cross-linking

The goal of this study was to create wear resistant ultra high molecular weight polyethylene (UHMWPE) with improved strength and toughness. It was previously demonstrated that high temperature melting (HTM) of UHMWPE at 280-320 °C improved its toughness without detrimentally affecting its wear resistance. We hypothesized that radiation cross-linking after high temperature melting could further improve the wear resistance of UHMWPE, and the loss in toughness by radiation cross-linking could be compensated by the improved toughness achieved by the high temperature melting prior to irradiation. In this work, we demonstrated that irradiation after HTM generated UHMWPE with improved toughness compared to the irradiated UHMWPEs without HTM, partly due to the low cross-link density of irradiated HTM UHMWPE. At a given cross-link density, irradiated HTM UHMWPEs showed higher wear resistance than irradiated UHMWPE. Therefore, successive HTM and radiation cross-linking strategy is promising to create UHMWPE materials with low wear and improved mechanical properties for total joint implants.     

Synthesis of the combined inter- and intra-crosslinked nanohydrogels by e-beam ionizing radiation

Thermally collapsed poly(vinylpyrrolidone) (PVP) polymer radicals preferably undergo intra-crosslinking reactions producing a nanogel structure rather than a macro-gel that would be caused by inter-crosslinking reactions. In the radiolysis of PVP aqueous solutions, the predominance of the intra-crosslinking reactions was achieved at elevated temperatures up to 77 °C. The dominance of intra-crosslinking under these conditions was confirmed by the molecular weight measurements using asymmetric field flow fractionation (AFFF). A higher yield of C-centered free radicals along the PVP chain at higher electron beam pulse repetition rate (300 Hz) enhances the intra-crosslinking reactions. This represents, mainly, the intra-crosslinking of the radicals of collapsed PVP molecules, along with a minor contribution of inter-crosslinking of the polymer dimers formed by transient occupation by two molecules in the same hydrodynamic volume and the increased diffusivity at the higher temperature.     

Molecular aggregation of poly(γ-phenacyl L-glutamate) in N,N-dimethylformamide

Summary Gel formation and the melting of solutions of poly (-phenacyl L-glutamate) in DMP were investigated up to 40 wt% of polymer concentration. Two thermally reversible transitions were observed around 24°C and 55°C. The transition temperatures were almost independent of the concentration. The transition at 24°C was considered to be due to the collapse of the order in side-chain structures. The transition from gel into Isotropie or cholesteric liquid-crystal phase occured in the 50–60°C range, above which the gel rigidity and an X-ray reflection of about 40 A suggesting a complex phase disappeared.     

Water sorption in cross-linked poly(vinyl alcohol) networks

Poly(vinyl alcohol) (PVA) networks of different cross-linking densities were prepared by reaction with hexamethylene diisocyanate in solution and casting. The dynamic-mechanical properties of PVA films have been investigated in the temperature range of −150 to +150 °C. Two relaxations processes labeled α and β in order of decreasing temperature were observed. The α-relaxation shifts to lower temperature and the average molecular weight between cross-links decreases with increasing cross-linking density. Isothermal sorption from vapor and liquid water allowed determination of the Flory-Huggins interaction parameter between water and the polymer chain segments, which decreased with the water activity in the hydrogel and increased with the cross-linking density as a consequence of the hydrophobic character of the cross-linking agent. The water diffusion coefficients, D, in the networks obtained by means of dynamic sorption experiments increased with increasing water activity. This behavior is interpreted in terms of plasticization of the polymer by water molecules.     

Investigation of nanostructures and properties of sulfonated poly(arylenethioethersulfone) copolymer as proton conducting materials by small angle neutron scattering

Sulfonated poly(arylenethioethersulfone) copolymer (SPTES-50), a promising candidate material for proton exchange membrane fuel cell (PEMFC), exhibited excellent thermal stability, high proton conductivity (135 mS/cm at 85 °C, 85% relative humidity), and electrochemical property. Small angle neutron scattering (SANS) of fully hydrated SPTES-50 membranes revealed the presence of embedded spherical nanodomains containing ionic group and water within the polymer membranes. The polydispersity of the nanoscale structure limited scattering contrast between the polymer backbone and sulfonated groups, and precluded analysis of intermediate and large scattering vectors in terms of the polymer-water interface structure. Inter-cluster correlations associated with the large extent of water absorption in the fully hydrated SPTES-50 membranes were accounted by Percus-Yevick liquid-like ordering of polydispersed hard sphere model with Schulz polydispersity approximation. Approximation of their low q upturn with an exponential decay results in a decay of −3 at 25 °C accounted for inter-cluster correlations which changed to a decay of −1.1 at 55 °C and 77 °C. This indicated a change in morphology upon increase of temperature such as to fractal morphology or an interconnected cylindrical network. The scattering patterns don't exhibit any further changes within examined range of q when the temperature increased from 55 °C to 77 °C. The number density of ionic clusters remained approximately constant (∼1.1818 × 10¹⁷ cm³), which indicated that additional water adsorbed by the polymer at the elevated temperature did not result in substantial coalescence of the clusters. Transmission electron microscopy (TEM) observation of the silver exchanged SPTES-50 membranes exhibited aggregates of Ag⁺ embedded within the dry membranes which can be approximated by isolated spheres.     

New highly proton-conducting membrane poly(vinylpyrrolidone)(PVP) modified poly(vinyl alcohol)/2-acrylamido-2-methyl-1-propanesulfonic acid (PVA-PAMPS) for low temperature direct methanol fuel cells (DMFCs)

A new type of chemically cross-linked polymer blend membranes consisting of poly(vinyl alcohol) (PVA), 2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS) and poly(vinylpyrrolidone) (PVP) have been prepared and evaluated as proton conducting polymer electrolytes. The proton conductivity (σ) of the membranes was investigated as a function of cross-linking time, blending composition, water content and ion exchange capacity (IEC). Membranes were also characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), and the differential scanning calorimetry (DSC). Membrane swelling decreased with cross-linking time, accompanied by an improvement in mechanical properties and a small decrease in proton conductivity due to the reduced water absorption. The membranes attained 0.088 S cm⁻¹ of the proton conductivity and 1.63 mequiv g⁻¹ of IEC at 25±2 °C for a polymer composition PVA-PAMPS-PVP being 1:1:0.5 in mass, and a methanol permeability of 6.1×10⁻⁷ cm² s⁻¹, which showed a comparable proton conductivity to Nafion 117, but only one third of Nafion 117 methanol permeability under the same measuring conditions. The membranes displayed a relatively high oxidative durability without weight loss of the membranes (e.g. 100 h in 3% H₂O₂ solution and 20 h in 10% H₂O₂ solution at 60 °C). PVP, as a modifier, was found to play a crucial role in improving the above membrane performances.     

Thermally reversible cross-links in a healable polymer: Estimating the quantity,rate of formation,and effect on viscosity

The conversion behavior of 2MEP4FS, a polymer with thermally reversible Diels–Alder cross-links, is modeled. A processing method is developed to create small, homogeneous prepolymer samples. The glass transition temperature of the prepolymer is estimated using temperature modulated differential scanning calorimetry and equated with the conversion of the polymer. Comparing the measured energy with the literature and computational estimates, the fully cured polymer appears to have a large portion of its moieties unreacted. An autocatalytic model is considered to approximate the reaction rate of 2MEP4FS as a function of conversion and temperature. Outside of the fitted temperature range, the model underpredicts the reaction rates at room temperature and 100 °C. Manual mixing of the monomers is determined to be inadequate to obtain a maximum level of cross-linking. Viscosity measurements made at room temperature and elevated temperatures are correlated with the conversion of the prepolymer.     

Regime II–III transition in isotactic polybutene-1 tetragonal crystal growth

The lateral growth rate and growth shape morphology of isotactic polybutene-1 tetragonal crystals were investigated for crystallization from the melt at temperatures of 68–101 °C. The growth rate of tetragonal crystals shows supercooling dependence derived from the nucleation theory, and a regime II–III transition is observed at temperatures of 77–82.2 °C. The morphology of single crystals is rounded below temperatures of 77–85 °C, while the growth shape has a faceted morphology at a higher crystallization temperature of 100 °C. The kinetic roughening transition occurs between 77 and 85 °C. The regime II growth mode is observed above 82.2 °C and proceeds by multiple nucleation on the faceted growth front, while the regime III growth mode is observed below 77 °C and proceeds by rough surface growth on the kinetically roughened growth front. The observed regime II–III transition can therefore be explained by the morphology transition of crystal growth shape.     

Temperature dependence of rheological properties of poly(methyl methacrylate) filled with silica nanoparticles

Creep-recovery experiments up to the steady state were performed on neat poly (methyl methacrylate) and on composites filled with 2.1 vol.% silica nanoparticles in order to get information on the long retardation times that occur due to polymer-particle interactions. The temperature dependence of the elasticity was investigated, varying the temperatures between 170 °C and 200 °C. For the neat polymer it was found that it behaves thermorheologically simple, whereas the composite exhibits a thermorheological complexity. An interpretation of these findings can be given, if the corresponding retardation spectra are regarded. The interactions between the polymer molecules and the particle surface is reflected by a particular maximum at longer retardation times, which exhibits a different temperature dependence compared to the spectra of the unfilled polymer matrix. This thermorheological complex behaviour is not seen in the usual dynamic-mechanical measurements down to angular frequencies of ω = 10⁻² s⁻¹. If the frequency range of the dynamic moduli is extended, however, by making use of the retardation spectra, a thermorheological complexity can be found, too. These results demonstrate that appropriate experimental time windows have to be applied to obtain a comprehensive picture of the rheological behaviour of nano particle-filled polymer melts.     

Anemotactic response threshold of the Indian meal moth,Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), to its sex pheromone

The effect of different concentrations of the sex pheromone (Z,E)-9,12-tetradecadien-1-ol acetate on the upwind anemotactic behavior of the malePlodia interpunctella (Hübner) was measured at 23 ± 1 ° C and 34 ± 1 ° C. The stimulus-response regression lines were analyzed by a new procedure that accounts both for control responses in the absence of pheromone and also for peak responses below 100% in the presence of concentrations considerably above the normal physiological levels. From the regression line for each temperature, the upwind anemotactic thresholds were calculated to be 1.34 × 10⁶ molecules/cm³ at 23 ° C and 1.65 × 10⁴ molecules/cm³ at 34 ° C, similar to other thresholds reported in the literature. Since departures from the two lines occurred at the highest concentrations tested, near 10⁸ molecules/cm³, the upwind anemotactic behavior may change qualitatively above an altered-behavior threshold that is about two orders of magnitude higher than the upwind anemotactic threshold. The lower response at 23 ° C suggests that cool temperatures inhibit flight in response to pheromonal stimulation.Mention of a commercial or proprietary product in this paper does not constitute an endorsement of that product by the USDA.     

Effect of heat-treatment and hydrostatic loading upon the poro-elastic properties of a mortar

This contribution aims at identifying experimentally the poro-elastic properties of a cement-based material under different levels of confining pressure, and after a heat-treatment up to 400 °C. The model material used is a normalized mortar, with a (W/C) ratio of 0.5. After a given heating/cooling cycle, drained bulk modulus K_b, solid matrix bulk modulus K_s and Biot's coefficient b are measured at different confining pressure levels (with a maximum of 25 MPa).Results show that under drained conditions, mortar stress-strain relationship evolves with increasing heat-treatment temperature from linear elastic with brittle failure (up to 105 °C heat treatment) to plastic and ductile (from 200 °C and above). Plastification testifies of material degradation under gradual confining pressure. At the microstructure scale, this is attributed to thermal damage after heat treatment above 105 °C, which consists mainly in various micro-cracking. This leads to easier failure of solid skeleton bridges (or trabecules), and to pore network collapse. Concomitantly to this, at given confining pressure P_c, secant drained bulk modulus K_b decreases monotonously, for heat-treatment temperatures above 105 °C. On the opposite, at given heat-treatment temperature above 105 °C, secant drained bulk modulus K_b increases when confining pressure is increased. This testifies of a solid matrix rigidification in the elastic domain, and it is attributed to increased skeleton compactness linked with pore network collapse. This is directly attributable to heat treatment followed by confinement.At given confining pressure P_c, matrix bulk modulus K_s and Biot's coefficient b increase with heat-treatment temperature above 105 °C. The increase in b means that mortar becomes less and less cohesive and more and more of a granular nature. Moreover, Biot's coefficient b and solid matrix bulk modulus K_s are independent of confining pressure P_c for intact mortar, whereas they decrease for heat-treated mortars when P_c increases. From literature analysis alone, it was quite unexpected that after heat treatment, K_s should vary under confinement. This is interpreted as the closure, under confining pressure, of micro-void connections and of micro-cracks created by heat-treatment. Therefore, increasing confinement induces more and more occluded pores in the solid matrix, whereby K_s diminishes.     

Proton exchange membrane bearing entangled structure: Sulfonated poly(ether ether ketone)/bismaleimide hyperbranch

Physical cross-linking of sulfonated poly(ether ether ketones) sPEEKs with hyper-branched bismaleimide oligomer (modified bismaleimide, mBMI) leads to densely packed polymer. Different curing conditions on the two sPEEK samples containing Bismaleimide (BMI) monomer and modified Bismaleimide oligomers (mBMI) mole ratios of 70:30 (mBMI(30)) and 2:98 (mBMI(98)) are present. As the amount of BMI monomer increases, the branched structure and their degree of entanglement with sPEEK polymer matrix also increase. More rigid and more compact membrane is found in the case of mBMI(30). In contrast, relatively loose entangled network is found for mBMI(98) sample where the mBMI unit remains far apart and mostly un-connected, until high concentration of mBMI(98) is present. The branched structure and their degree of entanglement with sPEEK polymer matrix increases with longer curing time. The results shows physical cross-linking with highly branched mBMI is effective in reducing water uptake, lower methanol permabiity with reduced sPEEK membrane swelling. Except for heavily entangled sample (sPEEK/mBMI(30)) annealed for 20 h, all membranes displayed fair proton conductivity above 10⁻² S/cm at room temperature. Methanol permeability is also substantially reduced to 1.39 × 10⁻⁷ cm²/s for sPEEK/15% mBMI(98). The DMFC single cell assembled by the sPEEK/20% mBMI(98) membrane (59 μm thickness) displayed the highest OCV of 839 mV with a power density reaching 30 mW/cm² at 60 °C. This value is higher than that using sPEEK membrane alone.     

SiOC Ceramic Foams through Melt Foaming of a Methylsilicone Preceramic Polymer

A process for the production of SiOC ceramic foams has been for the first time developed through melt foaming of a siloxane preceramic polymer with the help of a blowing agent, followed by pyrolysis under an inert atmosphere. The raw material consisted of a methylsilicone resin, a catalyst (which accelerated the cross-linking reaction of the silicone resin) and a blowing agent (which generated gas above 210°C). Methylsilicone resin foams were obtained through controlling the melt viscosity around 210°C, temperature where the blowing agent started to decompose, by varying the initial molecular weight of the preceramic polymer and the amount of the catalyst. The obtained SiOC ceramic foams exhibited excellent oxidation stability up to 1000°C, as shown by thermal gravimetric analysis (TGA). As expected, the mechanical properties of the SiOC ceramic foams varied as a function of their bulk density, possessing a flexural strength up to 5.5 MPa and a compression strength up to 4.5 MPa. The main steps in the process, namely foaming and pyrolysis, were analyzed in detail. The viscosity change was analyzed as a function of temperature by the dynamic shear measurement method. The pyrolysis process of foams was analyzed by TGA coupled with infrared spectroscopy (IR).     

Effect of sintering temperature on the microstructure and mechanical properties of ZrO2-3 mol%Y2O3 sol–gel films

The microstructural evolution and mechanical properties of ZrO₂-3 mol%Y₂O₃ films were investigated as a function of the sintering temperature in the range from 100 °C to 1500 °C, using a battery of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and nanoindentation. It was found that the crystallization occurs at temperatures close to 300 °C. A gradual increase in the grain and crystallite sizes is observed as the sintering temperature increases up to 1000 °C, and above this sintering temperature the tendency changes abruptly with a rapid increase in these values. Although Young's modulus of the coatings did not change with sintering temperature, a slight decrease was observed in the hardness values above 1000 °C which is attributed to microstructure coarsening. Finally, a slight degradation of the films occurs above 1300 °C, which is due to the occurrence of a process of grain spheroidization.     

Hydrogen balance for catalytic pyrolysis of atmospheric residue

The catalytic pyrolysis of atmospheric residue over the commercial catalytic pyrolysis process catalyst (Al₂O₃/Fe₂O₃/Na₂O (46.3, 0.27 and 0.04 wt.%, respectively)) was investigated in a confined fluidized bed reactor. The yield of light olefins was above 37 wt.% at reaction temperature above 600 °C and it reached a maximum of 47 wt.% at 660 °C. The main components in light olefins were ethylene and propylene, and those in liquid samples were aromatics. The main components in light alkanes were propane and i-butane at low reaction temperature (600 °C), and those were methane and ethane at high reaction temperature (700 °C). The hydrogen content of light olefins was about 14.27 wt.%, that of light alkanes was above 18.5 wt.%, that of gasoline was below 12.5 wt.%, and that of diesel was below 7.8 wt.%. The percentage of the hydrogen in light alkanes to total hydrogen was above 29% and that in light olefins was above 40%. The effective utilization ratio of hydrogen decreased from 66.60% at 600 °C to 61.44% at 700 °C.     

Morphology of sulfonated polyarylenethioethersulfone random copolymer series as proton exchange fuel cells membranes by small angle neutron scattering

Sulfonated polyarylenethioethersulfone (SPTES) copolymers with high proton conductivity (100-215 mS/cm at 65 °C, 85% relative humidity) are promising potential proton exchange membrane (PEM) for fuel cells. Small angle neutron scattering (SANS) of the hydrated SPTES copolymer membranes at 25 °C exhibit a nanostructure which can be approximated by correlated polydisperse spherical aggregates containing water molecules with liquid-like ordering (Percus Yevick approximation) and large scale water pockets. The ionic domain radius and the volume packing density of the aggregates present in the hydrated SPTES copolymer membranes at 25 °C increased with increasing degree of sulfonation. SPTES-80 with highest degree of sulfonation (71.6%) showed a Guinier plateau at the very low q range (q < 1 × 10⁻⁴ 1/Å) indicating presence of isolated large scale morphology (R_g = 1.3 ± 0.18 micron). The radius of spherical ionic aggregates present in the hydrated SPTES-50 and SPTES-60 copolymer membranes increased with increasing temperature to 55 °C, but the large scale morphology changed to a fractal network. Further increase of the sulfonation degree to 63.3% and 71.6% (SPTES-70 and SPTES-80) resulted in a substantial morphology change of the spherical aggregates to an irregular bicontinuous hydrophobic/hydrophilic morphology for the hydrated SPTES-70 and SPTES-80 copolymer membranes at 55 °C. Presence of ionic maxima followed by a power law decay of −4 for SPTES-70 and SPTES-80 copolymer membranes was attributed to the bicontinuous phase morphology at high degree of sulfonation and elevated temperature (55 °C). The disruption of the larger scale fractal morphology was characterized by significant decrease in the intermediate scattering intensity. Hydrophobic and hydrophilic domains were separated distinctly by sulfonic groups at the interface showing as power law decay of −4 for all hydrated SPTES copolymers.     

Photo-mediated copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) “click” reactions for forming polymer networks as shape memory materials

The formation of polymer networks polymerized with the Copper (I) – catalyzed azide – alkyne cycloaddition (CuAAC) click reaction is described along with their accompanying utilization as shape memory polymers. Due to the click nature of the reaction and the synthetic accessibility of azide and alkyne functional-monomers, the polymer architecture was readily controlled through monomer design to manipulate crosslink density, ability for further functionalization, and the glass transition temperature (55–114 °C). Free strain recovery is used to quantify the shape memory properties of a model CuAAC network resulting in excellent shape fixity and recovery of 99%. The step growth nature of this polymerization results in homogenous network formation with narrow glass transitions ranges having half widths of the transition close to 15 °C for these materials resulting in shape recovery sharpness of 3.9%/°C in a model system comparable to similarly crosslinked chain growth polymers. Utilization of the CuAAC reaction to form shape memory materials opens a range of possibilities and behaviors that are not readily achieved in other shape memory materials such as (meth) acrylates, thiol-ene, thiol-Michael, and poly(caprolactone) based shape memory materials.     

Calorimetric study of fluorinated methacrylic and vinyl polymer blends: part 2: correlation between miscibility, chemical structure and χ12 interaction parameter in binary systems

The miscibility of poly(methylmethacrylate) (PMMA) and (trifluoroethyl methacrylic ester-MMA) copolymers (MMA-MATRIFE) with poly(vinylidene fluoride) (PVDF) and VDF copolymers was studied by differential scanning calorimetry (DSC) as a function of the fluorinated copolymer crystallinity and fluoroalkyl methacrylic ester content in the methacrylic copolymer. Miscibility limits were found identical whatever be the blend preparation technique, although solution mixing induced some polymer fractionation, thus giving slightly higher blend glass transition temperature. The miscibility domain widths are reduced when using MMA-MATRIFE copolymers as compared to PMMA-containing blends and miscibility limits are dependent on the MATRIFE content in the methacrylic copolymer. Moreover, PVDF or VDF copolymer melting enthalpy decrease is associated to a partial dissolution of the semi-crystalline polymer in PMMA or MMA-MATRIFE copolymer above the total miscibility limit. The evolution of dynamic moduli as a function of blends composition confirms the miscibility limits determined by DSC. The Flory-Huggins interaction parameters were determined through the melting point depression analysis and compared to correlate the intensity of inter- or intra-molecular interactions between the polymers to the postulated ‘acidity’ of hydrogen atoms in various VDF-containing polymers. The interaction parameter χ₁₂ increases with the fluoroalkyl methacrylic ester content, corresponding to a prevalence of intra-molecular on inter-molecular interactions in these blends. Similarly, PVDF offers higher χ₁₂ values as compared to VDF-TFE or particularly to VDF-TrFE copolymers. These results highlight the importance of the nature of fluorinated polymers and of the inter- or intra-molecular character of dipolar interactions on both, copolymer miscibility and interaction parameter values.