High-temperature steam-treatment of PBI,PEEK, and PEKK polymers with H2O and D2O: A solid-state NMR study

Polyaryletherketones (PAEK) in blend systems with polybenzimidazoles (PBI) are of commercial interest due to their increased service temperature and reduction in abrasive wear against soft counterfaces when compared to PAEK alone. ASTM standard tensile specimens of PBI, polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) are immersed in stirred D₂O at room temperature, and additional samples are contacted with D₂O steam at temperatures of 150 and 315 °C. All samples are studied by TGA, IR, ¹³C CP/MAS, ¹H wideline, and ²H MAS NMR. Changes in the physical appearance of the samples and the extent of D₂O uptake are described. Different locations, mobilities, and types of water and protons in the polymers are identified and studied and it is proven that PBI contains the largest amounts of D₂O after exposure under all conditions. PEEK and PEKK only incorporate minimal amounts of D₂O even when steam-treated at 315 °C.     

The influence of processing conditions on the mechanical properties of poly(aryl-ether-ketone)/polybenzimidazole blends

Interest in developing high-performance blends for niche applications has grown significantly in efforts to meet ever-increasing harsh environment demands. In this work, four model poly(aryl-ether-ketone)/polybenzimidazole (PAEK/PBI) blends were chosen to study the influence of premixing methods, processing, and matrix polymers, on their mechanical properties. Among the model poly(ether ether ketone) (PEEK) and PBI blends, mechanical properties are greatly enhanced by melt premixing. The molding process mainly affects the matrix crystallinity, which in turn greatly influences fracture toughness of the blend. Poly(ether ketone ketone) (PEKK) and PBI blend exhibits a slightly lower tensile strength and fracture toughness than PEEK/PBI due to the differences in inherent properties of PEEK and PEKK matrices and their interfacial interaction with PBI. The processing−structure–property relationship of PAEK/PBI blends is established to help guide optimal design of high-performance polymer blends for structural applications. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48966.     

Polybenzimidazole (PBI) molecular weight and Mark‐Houwink equation

The molecular weight, and intrinsic viscosity of polybenzimidazole (PBI) and its phosphonylated derivatives are reported. The relationship between intrinsic viscosity [η] and weight average molecular weight (M_w) for PBI has been established in H₂SO₄ and DMF‐LiCl. The Mark Houwink constants K_w of 5.2 × 10^?3 mL/g, α of 0.92 for H₂SO₄ solvent systems and, K_w of 3.2 × 10^?2 mL/g, α of 0.754 for DMF‐LiCl solvent system have been determined at M_w < 65,000. The intrinsic viscosity of PBI determined by the Huggins–Kraemer method was compared with a single point method, and found that both methods fit well for PBI in relatively low concentration solvent system, giving ～ 99% accuracy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Tribological behavior of three‐dimensional braided carbon fiber reinforced polyetheretherketone composites

Three‐dimensional (3D) braided carbon fiber reinforced polyetheretherketone (denoted as CF_3D/PEEK) composites with various fiber volume fractions were prepared via hybrid woven plus vacuum heat‐pressing technology and their tribological behaviors against steel counterpart with different normal loads at dry sliding were investigated. Contrast tribological tests with different lubricants (deionized water and sea water) and counterparts made from different materials (epoxy resin, PEEK) were also conducted. The results showed that the incorporation of 3D braided carbon fiber can greatly improve the tribological properties of PEEK over a certain range of carbon fiber volume fraction (V_f) and an optimum fiber loading of ∼54% exists. The friction coefficient of the CF_3D/PEEK composites decreased from 0.195 to 0.173, while the specific wear rate increased from 1.48 × 10⁻⁷ to 1.78 × 10⁻⁷ mm³ Nm⁻¹ with the normal load increasing from 50 to 150 N. Abrasive mechanism was dominated when the composites sliding with GCr15 steel counterpart under dry and aqueous lubrication conditions. Deionized water and sea water lubricants both significantly reduced the wear of the CF_3D/PEEK composites. When sliding with neat PEEK counterpart, the CF_3D/PEEK composites possess lower friction coefficient than those against epoxy resin and GCr15 steel counterparts. In general, CF_3D/PEEK composites possess excellent tribological properties and comprehensive mechanical performance, which makes it become a potential candidate for special heat‐resisting tribological components. POLYM. COMPOS., 36:2174–2183, 2015. © 2014 Society of Plastics Engineers     

Understanding the structural origin of crystalline phase transformations in nepheline (NaAlSiO4)‐based glass‐ceramics

Nepheline (Na₆K₂Al₈Si₈O₃₂) is a rock‐forming tectosilicate mineral which is by far the most abundant of the feldspathoids. The crystallization in nepheline‐based glass‐ceramics proceeds through several polymorphic transformations — mainly orthorhombic, hexagonal, cubic — depending on their thermochemistry. However, the fundamental science governing these transformations is poorly understood. In this article, an attempt has been made to elucidate the structural drivers controlling these polymorphic transformations in nepheline‐based glass‐ceramics. Accordingly, two different sets of glasses (meta‐aluminous and per‐alkaline) have been designed in the system Na₂O–CaO–Al₂O₃–SiO₂ in the crystallization field of nepheline and synthesized by the melt‐quench technique. The detailed structural analysis of glasses has been performed by ²⁹Si, ²⁷Al, and ²³Na magic‐angle spinning — nuclear magnetic resonance (MAS NMR), and multiple‐quantum MAS NMR spectroscopy, while the crystalline phase transformations in these glasses have been studied under isothermal and non‐isothermal conditions using differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and MQMAS NMR. Results indicate that the sequence of polymorphic phase transformations in these glass‐ceramics is dictated by the compositional chemistry of the parent glasses and the local environments of different species in the glass structure; for example, the sodium environment in glasses became highly ordered with decreasing Na₂O/CaO ratio, thus favoring the formation of hexagonal nepheline, while the cubic polymorph was the stable phase in SiO₂–poor glass‐ceramics with (Na₂O+CaO)/Al₂O₃ > 1. The structural origins of these crystalline phase transformations have been discussed in the paper.     

Al2O3·2SiO2 powders synthesized via sol–gel as pure raw material in geopolymer preparation

Geopolymers are inorganic aluminosilicates mainly proposed as environmentally friendly building materials, which are obtained by alkali activation of natural minerals, calcined clay (e.g., metakaolin) and other aluminosilicate sources. The wide range of chemical and mineralogical compositions of these raw materials influences several properties of the obtained geopolymers. In the present work, pure Al₂O₃·2SiO₂ powders were synthesized via the sol–gel technique and proposed as pure aluminosilicate sources to prepare alkali activated geopolymers. Samples differing in the ratio between the SiO₂ precursor and the H₂O used in the sol–gel process were prepared, in order to study the effect of water content on the material structure and reactivity. The chemical structure of all the obtained Al₂O₃·2SiO₂ powders were characterized by Fourier transform infrared (FT‐IR) and solid‐state nuclear magnetic resonance (²⁷Al and ²⁹Si MAS NMR) spectroscopies and compared to that of a reference metakaolin. Moreover, material reactivity was evaluated by alkali activation of the samples. After 28 days of ageing, ²⁷Al and ²⁹Si MAS NMR and FT‐IR spectra ascertained the formation of a geopolymeric network in the activated samples. The results showed that lower water content allows obtaining a homogeneous Al‐rich geopolymer similar to that obtained, using metakaolin as raw material.     

Studies on polybenzimidazole/poly (4‐vinylpyridine) blends and their proton conductivity after doping with acid

In the present work, polybenzimidazole (PBI) and poly(4‐vinylpyridine) (P4VP) were chosen because they form miscible blends and both materials are suitable for acid doping as a matrix, which can eventually be used as proton conductor. The miscibility and inter‐polymer interactions were studied by infrared (IR) spectroscopy and differential scanning calorimetry (DSC). DSC and IR results suggest that PBI blended with P4VP exhibits good miscibility due to the strong hydrogen bonds formed between PBI's NH groups and P4VP's N: groups. The glass transition temperatures of the blends can be fitted to the Fox equation very well. The blends were also studied by thermogravimetry. Their thermal stability is slightly higher than that of P4VP, but is still lower than that of PBI. Temperature‐dependent conductivity of acid‐doped PBI/P4VP blends was studied. As the temperature increases, the conductivity of PBI/P4VP doped with H₃PO₄ increases. The temperature‐dependent conductivity of the blends follows a simple Arrhenius relationship when the P4VP content is low (less than 15%), while a non‐Arrhenius behaviour of the conductivity of the blends becomes more and more significant with increasing P4VP content. This means that the proton transport in the blends is controlled by both a hopping mechanism and the segmental motion of the polymer. The contribution of these two mechanisms depends on the P4VP content. Copyright © 2003 Society of Chemical Industry     

Polymerization of cyclic monomers. VII. Synthesis and radical polymerization of 1,3‐bis[(1‐alkoxycarbonyl‐2‐vinylcyclopropane‐1‐yl)carboxy]benzenes

1,3‐Bis[(1‐alkoxycarbonyl‐2‐vinylcyclopropane‐1‐yl)carboxy]benzenes 1 [RO: CH₃O (a), C₂H₅O (b)] were synthesized by the esterification of the corresponding 1‐alkoxycarbonyl‐2‐vinylcyclopropane‐1‐carboxylic acids with resorcinol. The structure of the new vinylcyclopropanes was confirmed by elemental analysis and infrared (IR), ¹H nuclear magnetic resonance (¹H‐NMR), and ¹³C nuclear magnetic resonance (¹³C‐NMR) spectroscopy. The radical polymerization of difunctional 2‐vinyl‐cyclopropanes in bulk with 2,2′‐azoisobutyronitrile (AIBN) results in hard, transparent, crosslinked polymers. During the bulk polymerization of the crystalline bis[(1‐methoxycarbonyl‐2‐vinylcyclopropane‐1‐yl)carboxy]benzene 1a, an expansion in volume of about 1% took place. The radical solution polymerization of 1a resulted in a soluble polymer with pendant 2‐vinylcyclopropane groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1775–1782, 1999     

A H2SO4 Loaded Polybenzimidazole (PBI) Membrane for High Temperature PEMFC

Sulfuric acid loaded polybenzimidazole (PBI) membranes were prepared with loading levels up to 10.58 (acid molecule per repeat unit of PBI) and characterized with Fourier transform infrared spectroscopy. Ionic conductivity of the PBI–H₂SO₄ membrane was found greater than that of the PBI–H₃PO₄ membrane. Through plane conductivity of a PBI–H₂SO₄ membrane with loading level 9.65 was >0.2 S cm^–1 at 150 °C. However, the conductivity of PBI–H₂SO₄ membrane increased greatly with increasing relative humidity. Membrane electrode assemblies using PBI–H₂SO₄ membrane exhibited better power density performances with pre‐humidified H₂ and air than that with none‐humidified gases. Polymer electrolyte membrane fuel cells with PBI–H₂SO₄ membrane in a single cell fixture demonstrated a peak power density >0.35 W cm^–2 with H₂ and air.     

Electrocopolymerization kinetics of a binary mixture of 3‐chloroaniline 2‐amino‐4‐phenylthiazole and characterization of the obtained block copolymer films

Electrocopolymerization of a binary mixture of 3‐chloroaniline and 2‐amino‐4‐phenylthiazole on platinum electrode in acid medium was carried out under different reaction conditions such as temperature, current density, hydrochloric acid, and monomer concentrations with duration time. The initial rate of the electrocopolymerization reaction on platinum electrode is small and the rate law is R_p = K₂ [D]^1.29[HCl]^0.97[M]^1.94. The apparent activation energy is found to be 38.87 kJ/mol. The obtained copolymer film is characterized by ¹H‐NMR, elemental analysis, GPC IR, UV‐visible, and cyclic voltammetry and compared with those of the two homopolymers. The mechanism of the electrocopolymerization reaction is also discussed and the monomer reactivity ratio (r₁and r₂) is calculated. The thermogravimetric analysis (TGA) is used to confirm the proposed structure and determination of the number of water molecules in the polymeric chain unit. X‐ray and scanning electron microscopic analysis are used to investigate the surface morphology. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2076–2087, 2005     

Improved Prediction of Young's Modulus of Fluorine‐Containing Glasses Using MAS‐NMR Structural Data

The model developed by Makishima and Mackenzie (M–M) may yield reasonable estimates for the E‐modulus of a range of glasses. In the M–M model the bonding enthalpy and packing densities present in the compounds that form the glass are taken as input for the calculation. This study shows that a more accurate estimate can be obtained by incorporating in the model structural information from MAS‐NMR data. Specifically, we have determined by means of the impulse excitation technique (IET) the E‐modulus for ionomer glasses with composition 4.5SiO₂–3Al₂O₃–1.5P₂O₅–3MO–2MF₂, where M denotes the alkaline earth metal (M = Mg, Ca, Sr, or Ba). The MAS‐NMR structural analysis shows that substitution of calcium by barium or strontium results in a disrupted network, whereas magnesium leads to a more packed network. In this study we will show how a higher coordination state of the aluminum as determined by ²⁷Al MAS‐NMR can be taken into account in the model. This leads to rather small corrections of the estimates for these particular glasses. In contrast, the ¹⁹F MAS‐NMR study shows the presence of Al–F–M(n) or Al–F and Si–F–M(n) types of environment in the glass network. Al–F and Si–F bonds are not accounted for in the E‐modulus estimate by the M–M model. We will show how by incorporating the new bonding of F with Al and Si a significantly improved estimate of the E‐modulus is obtained compared with the original model.     

Polyethylene‐block‐poly(ε‐caprolactone) diblock copolymers: synthesis and compatibility

A strategy is introduced for the synthesis of polyethylene‐block‐poly(ε‐caprolactone) block copolymers by a combination of coordination polymerization and ring‐opening polymerization. First, end‐hydroxylated polyethylene (PE‐OH) was prepared with a one‐step process through ethylene/3‐buten‐1‐ol copolymerization catalyzed by a vanadium(III) complex bearing a bidentate [N,O] ligand ([PhN?C(CH₃)CHC(Ph)O]VCl₂(THF)₂). The PE‐OH was then used as macroinitiator for ring‐opening polymerization of ε‐caprolactone, leading to the desired nonpolar/polar diblock copolymers. The block structure was confirmed by spectral analysis using ¹H NMR, gel permeation chromatography and differential scanning calorimetry. The unusual topologies of the model copolymers will establish a fundamental understanding for structure–property correlations, e.g. compatibilization, of polymer blends and surface and interface modification of other polymers. © 2014 Society of Chemical Industry     

Thermal history driven molecular structure transitions in alumino‐borosilicate glass

The glass network structure governs various thermos‐physical properties such as viscosity, thermal, and electrical conductivities, and crystallization kinetics. We investigated the effect of temperature on structural changes in a Na₂O‐CaO‐Al₂O₃‐SiO₂‐B₂O₃ glass system using ²⁷Al MAS NMR spectroscopy. Around the glass transition temperature, most of aluminate structures exist as AlO₄, acting as a glass former. When the temperature is above the melt crystallization temperature, the AlO₄ structure is drastically decreased and glass structures are mainly composed of AlO₅ and AlO₆, acting as glass modifiers. Thermodynamic assessment based on Gibbs energy minimization was used to confirm the dependency of aluminate structure's amphoteric characteristic on temperature by calculating the site fraction of aluminate molecular structures at different temperatures. Temperature‐induced aluminate structural variation can also influence silicate and borate structural changes, which have been confirmed by the ²⁹Si and ¹¹B NMR spectra.     

Effect of substituting CaO with BaO on the viscosity and structure of CaO‐BaO‐SiO2‐MgO‐Al2O3 slags

In this study, the effect of CaO and BaO substitution on the viscosity and structure of CaO‐BaO‐SiO₂‐MgO‐Al₂O₃ slags was investigated. The results showed that the viscosity increased with an increase in the BaO substitution concentration, which was correlated to an increase in the degree of polymerization (DOP) of the slag structural units as the activation energy increased from 207.9 to 263.8 kJ/mol for viscous flow. Deconvolution and area integration of the Raman spectrum of the slag revealed that the ratio of Q³/Q² (Qⁱ, i is the number of O⁰ in a [SiO₄]‐tetrahedral unit) increased and NBO/Si (nonbridging oxygen per unit silicon atom) decreased with higher BaO content. It was also observed from the ²⁷Al magic angles pinning nuclear magnetic resonance (²⁷Al MAS‐NMR) spectrum that the relative proportion of Al^IV increased, while that of Al^V decreased because of the decrease in the percentage of nonbridging oxygen (O^?), indicating the polymerization of the slag. O_1s X‐ray photoelectron spectroscopy (XPS) was also carried out to semi‐quantitatively analyze the various types of oxygen anions present in the slag. The XPS results correlated well with the results obtained from the analysis of the Raman and ²⁷Al MAS‐NMR spectra of the slags and its viscous behavior.     

Preparation of organo‐soluble poly[(2,2′‐m‐phenylene)‐5,5′‐bibenzimidazole] with high yield by homogeneous nitration reaction

To prepare organo‐soluble poly[(2,2,′‐m‐phenylene)‐5,5′‐bibenzimidazole] (PBI) with high yield, a homogeneous nitration of PBI was attempted. Nitro‐substituted PBI (NO₂‐PBI) was synthesized through the homogeneous reaction of the PBI powder with nitric acid in sulfuric acid. The degree of substitution (DS) of this NO₂‐PBI is higher than that of the NO₂‐PBI prepared through the heterogeneous reaction of the PBI fiber. The viscosity of the NO₂‐PBI prepared through the homogeneous reaction decreased with increasing amount of nitric acid added. The DS of the NO₂‐PBI reached the maximum value of 2. The substitution efficiency of nitro groups decreased as the amount of nitric acid added increased. When a small quantity of nitric acid was added, the substitution of the sulfonic acid group was confirmed as well as that of the nitro group. The solubility of the NO₂‐PBI depended strongly on the DS. The NO₂‐PBI having the DS of about 2 was completely soluble in dimethylacetamide and almost soluble in N‐methylpyrrolidone. At an elevated temperature, it was also soluble in other polar aprotic solvents such as dimethylformamide and dimethylsulfoxide. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 438–445, 2000     

Synthesis,Crystal Structure,and Thermal Behaviors of 3‐Nitro‐1,5‐bis(4,4′‐dimethylazide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP)

The energetic material, 3‐nitro‐1,5‐bis(4,4′‐dimethyl azide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP), was firstly synthesized by means of Click Chemistry using 1,5‐diazido‐3‐nitrazapentane as main material. The structure of NDTAP was confirmed by IR, ¹H NMR, and ¹³C NMR spectroscopy; mass spectrometry, and elemental analysis. The crystal structure of NDTAP was determined by X‐ray diffraction. It belongs to monoclinic system, space group C2/c with crystal parameters a=1.7285(8) nm, b=0.6061(3) nm, c=1.6712(8) nm, β=104.846(8)°, V=1.6924(13) nm³, Z=8, μ=0.109 mm⁻¹, F(000)=752, and D_c=1.422 g cm⁻³. The thermal behavior and non‐isothermal decomposition kinetics of NDTAP were studied with DSC and TG‐DTG methods. The self‐accelerating decomposition temperature and critical temperature of thermal explosion are 195.5 and 208.2 °C, respectively. NDTAP presents good thermal stability and is insensitive.     

Novel polyethylene‐b‐polyurethane‐b‐polyethylene triblock copolymers: Facile synthesis and application

A series of novel polyethylene‐b‐polyurethane‐b‐polyethylene (EUE) triblock copolymers is successfully prepared through a facile route combining the thiol‐ene chemistry, addition polymerization, and coupling reaction. The resulting EUE triblock copolymers are characterized by Nuclear magnetic resonance (¹H NMR), Fourier transform‐infrared spectra (FT‐IR), High temperature gel permeation chromatography (HT‐GPC), Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), and Transmission electron microscopy (TEM). In addition, the EUE triblock copolymers have been evaluated as compatibilizers in the polymer blends of thermoplastic polyurethane elastomer (TPU) and high‐density polyethylene (HDPE). The SEM results show that the compatibility of immiscible blends is enhanced greatly after the addition of EUE triblock copolymers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42967.     

Proton Conducting Membranes Based on Poly(2,2′‐imidazole‐5,5′‐bibenzimidazole)

Poly(2,2′‐imidazole‐5,5′‐bibenzimidazole) (PBI‐imi) was synthesized via the polycondensation between 3,3′,4,4′‐tetraaminobiphenyl and 4,5‐imidazole‐dicarboxylic acid. Effects of the reaction conditions on the intrinsic viscosity of the synthesized polymers were studied. The results show that the molecular weight of the polymers increases with increasing monomer concentration and reaction time, and then levels off. With higher reaction temperature, the molecular weight of the polymer is higher. With the additional imidazole group in the backbone, PBI‐imi shows improved phosphoric acid doping ability, as well as a little higher proton conductivity when compared with widely used poly[2,2′‐(m‐phenylene)‐5,5′‐bibenzimidazole] (PBI‐ph).Whereas, PBI‐imi and PBI‐ph have the similar chemical oxidation stability. PBI‐imi/3.0 H₃PO₄ composite membranes exhibit a proton conductivity as high as 10^–4 S cm^–1 at 150 °C under anhydrous condition. The temperature dependence of proton conductivity of acid doped PBI‐imi can be modeled by an Arrhenius equation.     

The dispersants effect on physical properties of long‐lasting luminescent polypropylene

Two series of blends, O‐PP₁₅ and O‐PP₃₅, were prepared by mixing polypropylene (PP), luminescent powders (SrAl₂O₄: Eu²⁺, Dy³⁺) of 15 and 35 μm average particle diameter, and hydrophobic dispersant at about 190°C in the Brabender mixer. The effect of amounts and diameter of luminescent powders on the physical properties of PP material were discussed herein. The luminescence and afterglow time tests indicated that the initial luminescence of all blends increased with the luminescent powders amounts. O‐PP₃₅ blends showed lower afterglow luminance than O‐PP₁₅ blends at low luminescent powder amounts. The melting and crystallization temperatures of the blends appeared at 152–168°C and 87–103°C, respectively. The blends displayed peaks attributable to a α crystal structure at 2θ = 18°–19°. The β crystal structure was only evident from its characteristic 2θ peak at 15°–16° in the WAXD pattern of the O‐PP₃₅ blends with high luminescent powder amounts. All of the blends had lower tensile strengths. However, the improvement in the luminescent powder distribution was evident from the SEM images after adding hydrophobic dispersant. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Prediction of the creep of heterogeneous polymer blends: Rubber‐toughened polypropylene/poly(styrene‐co‐acrylonitrile)

A previously proposed predictive format for elastic, storage and loss moduli is extended for the time‐dependent compliance D_b(t) of polymer blends. The format employs a two‐parameter equivalent box model (EBM) and the data on the phase continuity of components in blends obtained by using modified general equations of the percolation theory. As input data, the compliances D₁(t) and D₂(t) and the critical volume fractions V_1cr and V_2cr (delimiting the interval of phase co‐continuity in blends) of components are sufficient. To describe the effect of time on D₁(t), D₂(t) and D_b(t) within the linear stress‐strain region, a routinely used empirical equation was found suitable. Applicability of the proposed format is demonstrated on rubbertoughened polypropylene/poly(styrene‐co‐acrylonitrile) blends consisting of components with markedly different viscoelastic properties. The proposed predictive format fits fairly well the creep behavior of blends over the interval 0.1‐10,000 minutes.