Crosslinker Chemical Structure Research Articles

Introducing rigid-flexible integrated structure and constructing sacrificial bonds to achieve mechanically robust and malleable epoxy resin

Epoxy resin (EP) is usually brittle because of highly cross-linked chemical structure, so it is necessary to carry out research on toughening of epoxy resin. Here, a modified epoxy resin with enhanced mechanical toughness and strength was prepared using a novel modifier (PEA-BA), synthesized from polyetheramine D-400 (PEA) and benzoic acid (BA). Polyether chains that represent flexible structures, and aromatic rings representing rigid structures, were integrated together into the modifier to achieve simultaneous enhancement of the toughness and strength of the resulting epoxy resin. Moreover, the aromatic rings in PEA-BA formed π-π interactions with the aromatic rings in the EP network, further increasing the ductility of the modified epoxy resin. Research results demonstrated that the modified epoxy resin exhibited significantly improved elongation at break (increasing from 6.7% to 39.2%), as well as higher tensile strength (from 61.9MPa to 69.3MPa) and impact strength (from 25.3kJ·m-2 to 62.9kJ·m-2). Importantly, the glass transition temperature and thermal stability of the modified epoxy resin were not markedly reduced. The above properties indicated that PEA-BA achieved a favorable combination of high strength and ductility of epoxy resin, providing a new idea for toughening epoxy resin.

Covalently crosslinked poly(biphenyl dimethylamino benzene) membranes for high temperature proton exchange membrane fuel cells

The electrolyte membrane plays a pivotal role in high temperature proton exchange membrane fuel cells (HT-PEMFCs). Herein, we develops a new triarylmethane-backboned polymer, poly (biphenyl dimethylamino benzene) (PBDAB), synthesized through a facile one-step Friedel-Crafts reaction using biphenyl and 4-(dimethylamino) benzaldehyde as monomers. The presence of tertiary amine groups in PBDAB facilitates strong interactions with phosphoric acid (PA) molecules. To enhance the membrane's dimensional and mechanical stabilities, covalent crosslinking is performed via the Menshutkin reaction between the tertiary amine groups in PBDAB and chloromethyl groups in various crosslinkers. In order to study the influence of crosslinker chemical structure on the properties of PBDAB-based membranes, five different crosslinkers are employed, including small-molecule types such as 1,2-bis(2-chloroethoxy) ethane (BCE) and 1,4-bis(chloromethyl) benzene (BCB), siloxane type 3-chloropropyl (trimethoxy) silane (CTS), polymer types such as poly (vinylbenzyl chloride) (PVBC) and polyepichlorohydrin (PECH). Results reveal that the flexible and ether containing polymer crosslinker of PECH crosslinked membrane, denoted as CL-y%PECH, exhibits superior overall performance. When doped in an 85 wt% PA solution, the CL-5%PECH membrane achieves a PA uptake of 201%, resulting in an anhydrous proton conductivity of 0.064 S cm−1 at 180 °C and a mechanical strength of 7.2 MPa at room temperature. Using H2 and O2 as fed gases without humidification and backpressure, a single cell with abovementioned membrane attains a peak power density of 302 mW cm−2 at 160 °C. This work offers a kind of promising PBDAB based membranes for HT-PEMFC applications.

Mechanically Strong and Thermally Stable Chemical Cross-Linked Polyimide Aerogels for Thermal Insulator.

High-performance thermal insulating materials are highly desirable in several fields, especially for thermal insulation of buildings to reduce energy consumption. Owing to the remarkable thermal stability, high porosity, low density, and outstanding mechanical features, polyimide (PI) aerogels have attracted great attention. In this work, chemical cross-linked PI (CCPI) aerogels were fabricated via freeze-drying and thermal imidization, which possess outstanding mechanical properties, good thermal stability, and excellent thermal insulation characteristics. The chemically cross-linked structure can effectively inhibit shrinkage, while retaining the structural integrity, resulting in the lower density and lower shrinkage of the materials. In this paper, completely imidized and highly cross-linked polyimide aerogels were synthesized by using p-phenylenediamine (PDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and the cross-linker 2,3,6,7,14,15-hexaaminotriptycene (HMT). The CCPI aerogels with excellent properties, such as covalently cross-linked chemical structure, low density (0.069 g/cm3), low volume shrinkage (10%), high decomposition temperature (Td5% = 587 °C), and low thermal conductivity (25 mW m-1K-1) are in high demand in the field of thermal insulation. This work furnishes a new method for the development of polymer-based thermal insulation materials for various prospective applications.

Influence of zirconium crosslinker chemical structure and polymer choice on the performance of crosslinked fracturing fluids

AbstractCommonly used borate crosslinkers produce weak fracturing fluids at high temperature, high pressure, high salinity, and low pH conditions. Accordingly, zirconium crosslinkers were developed to address these shortcomings. Zirconium crosslinking chemistry is complicated and depends on many factors such as pH, ionic strength, ligand type, ligand order, and ligand to metal ratio. This work evaluated the rheological performance of four commercial zirconium crosslinkers with a polysaccharide and a polyacrylamide. The tested crosslinkers are manufactured with similar zirconium content but differ in ligand type and ligand order, producing different crosslinker chemical structures. The rheological performance was assessed using an HPHT rheometer at 93–204°C for 1.5 h. Shear tolerance performance was evaluated under shear rates of 40 s−1–1000 s−1. The results showed substantial variation in crosslinking performance due to the differences in the crosslinker chemical structure and type of polymer used. Zirconium lactate and propylene glycol crosslinker exhibited the greatest enhancement in shear and thermal stability with the polysaccharide‐based fracturing fluid. Remarkably, the same crosslinker performed the least with the polyacrylamide‐based fracturing fluid. However, Zirconium triethanolamine and lactate demonstrated considerable improvements in shear and thermal stability with the polyacrylamide‐based system. The work unravelled the influence of the zirconium crosslinker ligand type and ligand order on the rheological properties of both tested polymers. The performance evaluation showed that shear resistance, crosslinking delay, and thermal stability could be improved by utilizing the appropriate crosslinkers. The enhancements ultimately reduce additional additives required, prevent screenouts, and save cost during field treatments.

Design of Hydrolytically Degradable Polyethylene Glycol Crosslinkers for Facile Control of Hydrogel Degradation.

Hydrogels, whose degradability can be controlled while also preserving cell viability or biomolecule stability, are in demand. Degradable polyethylene glycol crosslinkers are hydrolytically designed for use in hydrogels. Degradation is controlled by crosslinker chemical structure, such as introducing local hydrophobicity, steric hindrance, or electron-withdrawing moieties near a degradable ester moiety.Hydrogels made using these crosslinkers have gelation times from 1 to 22 min, storage moduli from 3 to 10 kPa, mesh sizes from 10 to 13 nm, and degradation times from 18 h to 16 d. However, when reaction conditions are modified to achieve similar gelation time, hydrogels have similar initial properties but preserve the wide range of degradation times. All crosslinkers support high cell viability upon hydrogel encapsulation or exposure to leachables and degradation products. This innovation in controlling degradation can help realize the hydrogels' potential for drug delivery or as matrices for cell encapsulation and transplantation.

Studying Crosslinker Chemical Structure Effect on the Tuning Properties of HTPB‐Based Polyurethane

AbstractHydroxyl terminated polybutadiene based polyurethanes with various crosslinker compounds have been prepared to investigate the effect of crosslinker content and structure on polyurethanes mechanical properties. Three various crosslinkers have been used in this study, including trimethylolpropane, triethanolamine, and boron trifluoride triethanolamine complex. The results established that increasing crosslinker content increased the polyurethane strength. Moreover, boron trifluoride triethanolamine complex showed better ability in making network polyurethanes. The tensile test revealed that using boron trifluoride triethanolamine complex as crosslinker led to increasing chemical crosslinking bonds in comparison to two other crosslinkers via catalyzing side reaction like chain coupling. Swelling test and dynamical‐mechanical analysis confirmed this result, too.

Alkyl Chain Cross-Linked Sulfobutylated Lignosulfonate: A Highly Efficient Dispersant for Carbendazim Suspension Concentrate

A new family of highly water-soluble alkyl chain cross-linked sulfobutylated lignosulfonates (AASLSs) with a three-dimensional network structure and naked alkyl sulfonic acid groups were readily prepared by using 1,4-butane sultone (BS) and C6H12Br2 by a one step reaction in water, which simultaneously improved the sulfonation degree and molecular weight. GPC, 1H NMR, FTIR and functional group content tests confirmed their cross-linked chemical structure and efficient nucleophilic substitution reaction mechanism. Furthermore, the dispersion properties of AASLSs in a carbendazim suspension concentrate (SC) system were investigated. AASLS4 with high molecular weights (Mw) and moderate sulfonation degrees showed suspensibility of 99% in 45% carbendazim SC after hot storage at 50 °C for 14 days. Meanwhile, AASLS4 also showed smaller SC particle size and better rheological performance than commercial lignosulfonate. The adsorption isotherms and ζ-potential of AASLSs on carbendazim SC particles were studied to ...

Hollow polyphosphazene microspheres with cross-linked chemical structure: synthesis, formation mechanism and applications

Hollow polyphosphazene microspheres with highly cross-linked chemical structures were prepared by a template-induced assembly mechanism. The hollow microspheres display good stability towards Au nanoparticles.

Characterization and Chemical Stability of Anion Exchange Membranes Cross-Linked with Polar Electron-Donating Linkers

The effect of the cross-linker chemical structure on the properties and chemical stability of anion exchange membrane is the focus of this study. Two different cross-linkers were investigated, one with linear hexyl chain between crosslinking sites, and the other, ether in the center of the alkyl linker. These two cross-linkers have a fundamental difference in their polarity and hydrophilicity. The ether-containing cross-linker is more polar and therefore will improve membrane's water uptake and conductivity. Swelling and conductivity measurements were performed at various temperatures for both types of samples. While water uptake and conductivity were found to be higher for the ether-based cross-linker, degradation measurements indicated that the membrane that is cross-linked with electron-rich linker degraded in hydroxide faster than the alkyl linker at temperature of 60°C.

Semi-degradable poly(β-amino ester) networks with temporally controlled enhancement of mechanical properties

Biodegradable polymers are clinically used in numerous biomedical applications, and classically show a loss of mechanical properties within weeks of implantation. This work demonstrates a new class of semi-degradable polymers that show an increase in mechanical properties through degradation via a controlled shift in a thermal transition. Semi-degradable polymer networks, poly(β-amino ester)-co-methyl methacrylate, were formed from a low glass transition temperature crosslinker, poly(β-amino ester), and high glass transition temperature monomer, methyl methacrylate, which degraded in a manner dependent upon the crosslinker chemical structure. In vitro and in vivo degradation revealed changes in mechanical behavior due to the degradation of the crosslinker from the polymer network. This novel polymer system demonstrates a strategy to temporally control the mechanical behavior of polymers and to enhance the initial performance of smart biomedical devices.

Robust Microsieves with Excellent Solvent Resistance: Cross-Linkage of Perforated Polymer Films with Honeycomb Structure.

Polymeric microsieves with uniform and tunable pores were fabricated with the breath-figure method and sequent vulcanization procedure using commercially available block copolymer polystyrene-b-polyisoprene-b-polystyrene. Uniform pore size and small film thickness endow the microsieves with high size selectivity and low operation pressure, while the cross-linked chemical structure gives them good mechanical properties and excellent chemical and thermal stability. These microsieves are able to separate particles in various media, including corrosive solvents, hot water, and organic solvents. The process reported in this communication is a simple and inexpensive method for the preparation of high-performance microsieves.

Effect of Crosslinker Chemical Structure and Monomer Compositions on Adsorption of Uranium (VI) Ions Based on Reactive Crosslinked Acrylamidoxime Acrylic Acid Resins

Adsorption capacities of uranyl ions using crosslinked acrylamidoxime acrylic acid (Am/AA) resins composed from acrylonitrile (AN), acrylic acid (AA), having different molar ratios were determined. The AN/AA molar ratios were 80/20, 50/50 crosslinked with 10% N,N′-methylenebisacrylamide (MBA) and divinylbenzene (DVB). Polymerization was occurred in the presence of potassium persulfate and sodium metabisulfite as redox initiator. Reaction of synthesized resins with hydroxyl amine in basic media yield polyacryl acrylamidoxime acrylic acid (Am/AA). The chemical structure of the AN/AA and Am/AA resins, before and after loaded with uranyl ions and after elution, was confirmed by FTIR analysis. The effect of ions sorption on the morphologies of the prepared resins was examined by scanning electron microscope (SEM). Effects of pH, time of loading, type of acid, molar ratio, and type of crosslinker were investigated. Elution of adsorbed ions on resins was investigated by different eluents. The elution efficiency was determined.

Effect of Crosslinker Chemical Structure and Monomer Compositions on Adsorption of Uranium (VI) Ions Based on Reactive Crosslinked Acrylamidoxime Acrylic Acid Resins

Adsorption capacities of uranyl ions using crosslinked acrylamidoxime acrylic acid (Am/AA) resins composed from acrylonitrile (AN), acrylic acid (AA), having different molar ratios were determined. The AN/AA molar ratios were, 80/20,50/50,20/80, crosslinked with 10% N,N′-methylenebisacrylamide (MBA) and divinylbenzene (DVB). Polymerization occurred in the presence of potassium persulfate and sodium metabisulfite as redox initiator. Acrylonitrile acrylic acid resins (AN/AA) were converted to acrylamidoxime acrylic acid (Am/AA) by reaction with hydroxylamine solution. The chemical structure of the AN/AA and Am/AA resins, before and after loaded with uranyl ions and after elution, was confirmed by FTIR analysis. The effect of ions sorption on the morphologies of the prepared resins was examined by scanning electron microscope (SEM). Effect of pH, time of loading, type of acid, molar ratio, and type of crosslinker were investigated. Elution of adsorbed ions on resins was investigated by different eluents. The elution efficiency was determined.

Liquid crystalline epoxy resin modified cyanate ester for high performance electronic packaging

A high performance modified cyanate ester (CE) resin system with significantly improved toughness, water resistance and dimensional stability was developed by copolymerizing CE resin with liquid crystalline epoxy resin (LCE) for electronic packaging. Four LCE/CE resins with different contents of LCE were prepared to systemically evaluate the effect of the content of LCE on the key properties of the modified system such as mechanical, dielectric and thermal properties as well as water resistance. Results reveal that the addition of LCE to CE can not only decrease the curing temperature of CE, but also significantly improve the integrated properties including mechanical and dielectric properties, thermal resistance as well as water resistance of cured resin. For example, compared with the whole exothermic peak of CE, that of LCE10/CE significantly shifts toward low temperature with a gap of about 15°C. On the other hand, the impact strength of cured LCE10/CE resin (22 kJ/m2) is about 2.1 times of that of CE resin; while the water absorption of the former is only 81.2% of that of the latter. In addition, cured LCE/CE resins also exhibit lower and more stable dielectric loss than CE resin over the whole frequency range from 10 to 106 Hz. All these improvements in macro-performance by the addition of LCE to CE resin are not only ascribed to the cross-linked chemical structure, but also attributed to the rigid structure of liquid crystalline resin. The outstanding integrated properties of LCE/CE resins suggest great potential to be applied in the field of high performance electronic packaging.

Investigations of the hydrophobic and scratch resistance behavior of polystyrene films deposited on bell metal using RF-PACVD process

Polystyrene films are deposited on bell metal substrates using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) process. The deposition of polystyrene film is carried out at working pressure of 1.6×10−1mbar and in the RF power range of 20–110W. The hydrophobic and mechanical behaviors of the polystyrene films are studied as a function of RF power. The chemical compositions and surface chemistry of the polystyrene films are investigated using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It is revealed that enhanced cross-linked chemical structure and higher loss of oxygen by peroxy polystyryl radical with increasing RF power results in the formation of polystyrene films with more hydrophobic and scratch resistance behavior. However, extensive destruction of cross-linked chemical structure due to high energetic ion bombardment tends to decrease the hydrophobic and scratch resistance behavior of the polystyrene film deposited at RF power of 110W. Atomic force microscopy (AFM) images show quite uniform and crack free surfaces of the polystyrene films having rms roughness in the range of 0.35–0.87nm. Attempts are made to correlate the characterization results with the parameters that are used for thin film depositions.