Hyperbranched Structure Research Articles

A scalable and simple lignin-based polymer for ultra-efficient flocculation and sterilization

Current flocculation and sterilization are two separate steps that can cause environmental and economic problems. Lignin, an inedible industrial by-product, as raw material to prepare polymer that simultaneously realize flocculation and sterilization is of great significance for carbon neutral, sewage recycling, and economic benefit. However, the inherent defects of lignin such as heterogeneity, poor solubility and low reactivity cause difficulty in preparing and applying lignin-based polymers. Under this context, an energy-saving synergistic technology incorporating lignin refining and photoinitiated biphasic copolymerization system was pioneered, and an ultra-efficient dual-function lignin-based polymer with hyperbranched amphiphilic structure was successfully prepared, which contributed to 99.6% removal rate and distinguished sterilization effect for E. coli suspension at an ultra-low dose (4 mg/L and 10 mg/L, respectively). The purification mechanism indicated that the first flocculation was attributed to the synergy of charge attraction, bridging and sweeping, while the subsequent sterilization was achieved by blocking the metabolism and changing membrane permeability. The examination on various external influencing factors showed great adaptability of this lignin-based polymer to complex sewage environment with superiority over existing commercial products.

Hyperbranched ionic surfactants with polyether skeleton: Synthesis, properties and used as stabilizer for emulsion polymerization

A versatile strategy involves anionic ring-opening polymerization (AROP) and thiol-ene reaction was contributed for the construction of hyperbranched ionic surfactants. A series of hyperbranched surfactants composed of polyether skeleton and various ionic side groups such as anion, cation and zwitterion were synthesized and labeled as HPEanionic, HPEcationic and HPEzwitterionic, respectively. The chemical structures of all the intermediate and final products were verified by means of fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The surface and interfacial tension reduction performances of three obtained ionic surfactants were systematically investigated. And the results confirmed all the resultant surfactants could effectively reduce the surface and interfacial tension of the solution, and the CMC values were all determined approximately to 0.1 mg/mL. Meanwhile, three surfactants exhibit relatively low Krafft temperatures (below 6 ℃) and good wettability to oil-wetted surface. To further explore their promising applications, HPEanionic was proposed for use as a stabilizer in emulsion polymerization. Dynamic light scattering (DLS) measurements as well as transmission electron microscope (TEM) observation confirmed well-defined latex was obtained indeed. Moreover, as compared to latex synthesized by using the traditional small molecule compound surfactants, latex synthesized using HPEanionic as stabilizer exhibit improved tolerance to salinity. This beneficial result is probably caused by the special hyperbranched structure of HPEanionic, which contributes both electrostatic repulsion and steric hindrance drive force for the stabilization of latex particles.

Three-dimensional PdAuRu nanospines assemblies for oxygen reduction electrocatalysis

Tailoring morphology and composition of electrocatalysts has a substantial impact on catalytic properties for oxygen reduction reaction (ORR). In this work, trimetallic PdAuRu nanospine assemblies (PdAuRu NSAs) are fabricated via a simple one-step reduction route using DM-970 and KBr used as surfactant and structure directing agent, respectively. The hyperbranched structure has the characteristics of sufficient active sites, accessible transfer channels, and the excellent tolerance towards Ostwald ripening, migration and agglomeration of catalysts. Furthermore, the synergistic effect of Pd, Au and Ru atoms can alter the d-band energy of Pd, weaken the bond energy between the catalyst surface and the adsorbed species, thus changing the electronic structure and optimize the adsorption of oxygen on Pd. When explored for ORR in alkaline solution, the PdAuRu NSAs display superior catalytic activity and stability to commercial Pt/C. This synthesis tactic delivers a feasible route for the preparation of hyperbranched multi-metallic nanomaterials towards various electrocatalytic applications.

Modification of Cellulose Nanocrystals With 2-Carboxyethyl Acrylate in the Presence of Epoxy Resin for Enhancing its Adhesive Properties.

Cellulose nanocrystals (CNCs) have unparalleled advantages in the preparation of nanocomposites for various applications. However, a major challenge associated with CNCs in nanocomposite preparation is the lack of compatibility with hydrophobic polymers. The hydrophobic modification of CNCs has attracted increasing interest in the modern era standing with long challenges and being environmentally friendly. Here, we synthesized CNCs by using cotton as raw material and then modified them with 2-carboxyethyl acrylate to improve their corresponding mechanical, adhesive, contact angle, and thermal properties. Different concentrations (1–5 wt%) of CNCs were used as modifiers to improve the interfacial adhesion between the reinforced CNCs and E-51 (Bisphenol A diglycidyl ether) epoxy resin system. CNCs offered a better modulus of elasticity, a lower coefficient of energy, and thermal expansion. Compared with the standard sample, the modified CNCs (MCNCs) showed high shear stress, high toughness, efficient degradation, thermal stability, and recycling due to the combined effect of the hyperbranched topological structure of epoxy with good compatibility. The native CNCs lost their hydrophilicity after modification with epoxy, and MCNCs showed good hydrophobic behavior (CA = 105 ± 2°). The findings of this study indicate that modification of CNCs with 2-carboxyethyl acrylate in the presence of epoxy resin and the enhancement of the features would further expand their applications to different sectors.

Synthesis of vegetable oil-based hyperbranched polyol via thiol-yne click reaction and their application in polyurethane

A novel bio-based hyperbranched polyol (HBP) with high functionality was prepared from grapeseed oil (GSO) through the following sequential steps: i) epoxidation, ii) propargylation and iii) thiol-yne click reaction. Structural analysis confirmed that the GSO-based HBP was synthesized successfully; and the hydroxyl value of the synthesized HBP was 612 mg KOH/g, which is close to that of commercialized HBP. Furthermore, the prepared HBP was employed as a crosslinker to fabricate bio polyurethane (PU) films via a two-step prepolymer polymerization. The successful synthesis of hyperbranched PUs was confirmed by Fourier transform infrared analysis. Moreover, according to the results of X-ray diffraction analysis, the crystallinity of the prepared hyperbranched PUs decreased because the crosslinked networks hindered the formation of crystalline structures. Based on the mechanical property analysis, it was confirmed that the tensile strength and elongation of PU using HBP reached 27 MPa and 2315%, respectively. From these results, it can be confirmed that the tensile strength and tensile elongation of the PUs significantly increased upon the introduction of a crosslinker with a hyperbranched structure.

Hierarchical Ni- and Co-based oxynitride nanoarrays with superior lithiophilicity for high-performance lithium metal anodes

Lithium metal has emerged as the most prospective candidate for the realization of improved battery systems. However, notorious Li dendrite formation and the huge volume effect during cycling critically impair the further practical deployment of Li metal batteries. Herein, we propose hierarchical Ni- and Co-based oxynitride (NiCoO2/CoO/Ni3N) nanoarrays with superior lithiophilicity on a three-dimensional nickel foam (NiCoON/NF) as a host for highly stable Li metal anodes. The uniform nitrogen-infused nanorod-on-nanosheet arrays present improved electrical conductivity and an increased concentration of active sites with oxygen vacancies to enhance the surface lithiophilicity, which effectively facilitates homogeneous Li nucleation/growth. Moreover, the hyperbranched structure can induce a homogeneous distribution of Li-ion flux, owing to the enlarged surface area, thereby providing sufficient space to store deposited lithium and relieve the volume expansion. Consequently, the NiCoON/NF host delivers a high Coulombic efficiency (98.4% over 600 cycles) at 1 mA cm-2 and an ultralong lifespan (> 2000 h) under a high capacity of 3 mAh cm-2. Remarkably, a Li@NiCoON/NF-LiFePO4 full battery also reveals impressive electrochemical performance. This work demonstrates new insights into safe rechargeable Li metal batteries.

Synthesis of Arylene Ether-Type Hyperbranched Poly(triphenylamine) for Lithium Battery Cathodes.

We synthesized a new poly(triphenylamine), having a hyperbranched structure, and employed it in lithium-ion batteries as an organic cathode material. Two types of monomers were prepared with hydroxyl groups and nitro leaving groups, activated by a trifluoromethyl substituent, and then polymerized via the nucleophilic aromatic substitution reaction. The reactivity of the monomers differed depending on the number of hydroxyl groups and the A2B type monomer with one hydroxyl group successfully produced poly(triphenylamine). Based on thermal, optical, and electrochemical analyses, a composite poly(triphenylamine) electrode was made. The electrochemical performance investigations confirmed that the lithium-ion batteries, fabricated with the poly(triphenylamine)-based cathodes, had reasonable specific capacity values and stable cycling performance, suggesting the potential of this hyperbranched polymer in cathode materials for lithium-ion batteries.

Modified MXene-doped conductive organosilicon elastomer with high-stretchable, toughness, and self-healable for strain sensors

Polymers/nanomaterials conductive elastomers based on reversible interactions are of great significance in the application of resistive sensors because they repair themselves after mechanical injury, just like living things. The electronic devices developed with such materials will be more stable and reliable. Herein, we innovatively used ring opening polymerization (ROP) of sulfur-containing five membered rings to endow organosilicon supermolecule and MXene with hyperbranched structure which had terminal carboxyl groups. Subsequently, organosilicon conductive elastomer (PDMS@MXene) crosslinked by hydrogen bonds and metal–ligand bonds was prepared. The fully disconnected PDMS@MXene could recover 91.7% of its original mechanical properties after spontaneous repair. The well-organized composite had high stretchability and excellent tensile strength, which enhanced its application prospects in soft robots, motion monitoring and other fields. This novel design idea and simple preparation process will provide a reference for the development of self-healable conductive elastomer in the future.

A high bonding performance and antibacterial soybean meal adhesive with Maillard reaction based cross-linked structure

Environmentally friendly soybean meal-based (SM) adhesive has been developed to replace harmful formaldehyde-based adhesives in the wood-based panel industry. But, the extensive application of SM adhesives is limited by several deficiencies, including high brittleness, poor coating ability, and poor antibacterial/mildew resistance, etc. In this study, a new SM adhesive has been designed by constructing a hyperbranched cross-linked structure via the Maillard reaction instead of traditional epoxide-based crosslinking structure. Specifically, the hyperbranched poly(ethylenimine)-functionalized carboxymethyl chitosan was synthesized via a one-step procedure using carboxymethyl chitosan and polyethyleneimine , and then mixed with soybean meal and a crosslinker (2,3-butanedione) to develop a wood adhesive. The dry and wet shear strength of plywood bonded by the obtained adhesive was 55% and 357% higher than those of the original SM adhesive, respectively, which were attributed to the formation of Maillard reaction-based crosslinked structure and improvement of adhesive toughness. The corresponding wood failure percentage was increased to 70% compared to pure SM adhesive. Notably, the prepared adhesive exhibited mildew resistance for 240 h and had a uniform coating ability on the wood surface. Construction Maillard reaction based crosslinking structure has potential application in the enhancement of other bio-adhesives and protein-based hydrogels.

Thiolated Polyethyleneimine-Based Polymer Sponge for Selective Removal of Hg2+ from Aqueous Solution.

Polymer sponges with molecular recognition provide a facile approach to water purification and industrial separation with easy operation. Herein, a thiolated polyethyleneimine (PEI)-based polymer sponge was prepared through cryo-polymerization of PEI, followed by grafting of PEI and then post-modification of the amine functionalities present within the hyperbranched structure with methyl mercaptoacetate, which afford high density of thiol functional groups on the surface of the sponge. The developed sponge was characterized by scanning electron microscopy and element analysis, and the adsorption kinetic and isotherm studies were conducted in detail. The sponge presents a remarkable maximum adsorption capacity of 2899.7 mg/g, which can be attributed to its high density of thiol functionalities. The sponge also shows excellent selectivity toward Hg2+ against other metal ions and natural organic matter, indicating its great potential in removing mercury from real water bodies. In addition, the sponge can be chemically regenerated and exhibits good reusability, which decreases the economic and environmental impacts. Hence, the high removal efficiency, high selectivity toward mercury, and good reusability of the sponge material highlight it as a promising sorbent for mercury removal in water pollution treatment.

Preparation and Characterisation of Polyurethane Acrylate-Based Titanium Dioxide Pigment for Blue Light-Curable Ink.

Herein, a polyurethane acrylate-based TiO2 (PU-TiO2) was fabricated using a two-step method. First, a polyurethane prepolymer was prepared. Second, PU-TiO2 was prepared using amino-modified TiO2 (A-TiO2). The best synthesis process of the polyurethane prepolymer was when the reaction temperature was 80 °C, the reaction time was 3 h and the R-value of the polyurethane acrylate was 2. Next, the influence of the A-TiO2 content on the structure and performance of PU-TiO2 was examined. The analysis of the rheological properties of the PU-TiO2 ink indicated that its viscosity gradually increased as the A-TiO2 content increased. The tensile performance of film improved because of the presence of A-TiO2. The photo-polymerisation and photo-rheological performance indicated that the PU-TiO2 structure changed from a hyperbranched structure with TiO2 as the core to a segmented structure, as the A-TiO2 content was 3%.

Design, synthesis, flame retardancy and dielectric properties of novel aromatic hyperbranched benzoxazine

Two kinds of novel aromatic hyperbranched benzoxazines (HBs), HB-Tppa1 and HB-Tppa2, were designed and prepared by using 1,1,1-tris(4-hydroxyphenyl)ethane (THPE), p-phenylenediamine (PPA), paraformaldehyde and phenol through two different synthetic routes via Mannich condensation reaction. Fourier transform infrared (FTIR) and nuclear magnetic resonance (1H and 13C NMR) spectroscopy were employed to characterize the featured structures of these (HB-Tppa)s. HB-Tppa1 exhibits greater molecular weight than HB-Tppa2, owing to a priority of forming the hyperbranched structure for preparing HB-Tppa1 without adding capped phenol in the first step. The greater reaction enthalpy (ΔH) value of HB-Tppa1 has been provided by differential scanning calorimeter (DSC), indicating that the mass fraction of benzoxazine rings in HB-Tppa1 is higher than that of HB-Tppa2. The thermal and flame retardancy properties of poly(HB-Tppa1) superior to poly(HB-Tppa2) are affected by these mentioned factors. Besides the high glass transition temperature (Tg, ≥ 320 °C), the low total heat release (THR) and heat release capacity (HRC) values of poly(HB-Tppa)s in the range of 5.4–11.7 kJ/g and 41.5–50.5 J/(g K), respectively, suggest that they are potential nonignitable materials. Moreover, the poly(HB-Tppa)s exhibit low dielectric constants (2.27 ≥ k ≥ 2.15) in the high-frequency range of 2 to 18 GHz, which may perform well in next-generation integrated circuits.

Interaction of polyamidoamine dendrimers and amphiphylic dendrons with lipid membranes

Polyamidoamine (PAMAM) dendrimers and amphiphilic dendrons are one of the types of nanomaterials characterized by a hyperbranched structure of polymer branches. In the case of dendrimers, the dendrons are covalently linked at the central focal point. In the case of amphiphilic dendrons, dendrons are non-covalently linked by hydrophobic interactions, forming micellar structures. These nanoparticles are widely used in biology and medicine as contrast agents, carriers of drugs and genetic material. Their use in scientific practice requires an understanding of the basic mechanisms of their interaction with membranes – the main obstacle to the entry of dendrimers into the cell. This review discusses the regularities of the interaction of dendrimers and amphiphilic dendrons with lipid membranes. Various models of dendrimer-membrane interactions are described as the basis for the penetration of dendrimers and amphiphilic nanoparticles into cells. Keywords: polyamidoamine dendrimers, amphiphilic dendrons, lipid membranes, cells, antitumor therapeutics, antibacterial agents, diagnostics, genetic therapy.

Bioinspired Multifunctional Cellulose Nanofibril-Based In Situ Liquid Wound Dressing for Multiple Synergistic Therapy of the Postoperative Infected Wound.

A smart in situ-formed wound dressing with excellent antibacterial ability against drug-resistance bacterial, antitumor, and biofilm-eliminating activities to promote effective wound closure is highly desirable in therapeutic and clinical applications. Herein, we designed and developed a multifunctional; shape-adaptable; and pH, temperature, and near-infrared radiation (NIR) multiple responsive cellulose nanofibril (CNF)-based in situ liquid wound dressing, using a pH-sensitive CNF grafted with terminated amino hyperbranched polyamines (HBP-NH2) as a substrate, along with poly(N-isopropylacrylamide) and indocyanine green (ICG) loaded as the temperature and NIR on/off switches, respectively. The 3D nanocage network structure of CNF and the nanocavities in the hyperbranched structure of HBP-NH2 endow the dressing with a high loading capacity for active drugs (doxorubicin and ICG) simultaneously. Moreover, the responsiveness of the dressing to multiple stimuli enables controllable and efficient drug release to the wound area. The bioinspired dressing demonstrates excellent antibacterial activity against common bacteria and methicillin-resistant Staphylococcus aureus, antitumor activity against A375 tumor cells, and biofilm-eliminating capability. In addition, the developed dressing synergistically combines multiple therapeutic strategies for effective wound healing, specifically photothermal therapy, photodynamic therapy, and chemotherapy. The design provides an ideal clinical intervention strategy for irregular tumor postoperative infected wounds.

N-Type Self-Doped Hyperbranched Conjugated Polyelectrolyte as Electron Transport Layer for Efficient Nonfullerene Organic Solar Cells.

The electron transport layer (ETL) exerts a dramatic influence on the power conversion efficiency (PCE) of the nonfullerene organic solar cells (NOSCs). Currently, the majority of the organic ETLs possess a relatively poor conductivity, which is not conducive to carrier transport and collection. Herein, we design and develop a novel hyperbranched conjugated polyelectrolyte (CPE) based on n-type perylene diimide (PDI) as the center core and quaternary ammonium salt as the side polar groups. The lone pair electrons of the nitrogen atoms can transfer to the electron deficient PDI core and endow the molecule with an efficient n-type self-doping effect. Moreover, the hyperbranched structure makes the molecule functionalized with more side polar groups, favoring forming more dipoles and stronger dipole moments. Therefore, the CPE PTPAPDINO possesses a high conductivity and can notably decrease the work function (WF) of the electrode, contributing to the carrier transport and collection of the device. The NOSC with PTPAPDINO as ETL delivers an excellent PCE of 15.62%, which is even superior to the device using the classical PDINO ETL. Moreover, the PCE can retain 82.6% of the optimal device when the thickness has been increased to 28 nm. These results manifest that it is a feasible strategy to design an n-type self-doping hyperbranched CPE as efficient ETL, and PTPAPDINO is a promising alternative ETL for high performance NOSCs.

Gas permselectivity of hyperbranched polybenzoxazole – silica hybrid membranes treated at different thermal protocols

Hyperbranched polybenzoxazole (HBPBO) – silica hybrids were treated at different thermal protocols and their gas permselectivity were studied. Inter-chain distance and free volume of pristine HBPBO were enlarged with increasing treated temperature. Gas permeability and diffusivity of the HBPBO were considerably increased with increasing treated temperature, which was resulted from increased fractional free volume due to enlarged inter-chain distance. Gas permeability of the HBPBO was further increased by the hybridization with silica, mainly owing to the increased gas diffusivity. This fact indicated additional free volume holes were formed at the HBPBO matrix – silica interfaces. It was worth noting the HBPBO – silica hybrids had a prominent CO2/CH4 permselectivity which exceeded the upper bound, and the CO2/CH4 permselectivity was enhanced with increasing treated temperature. The notable CO2/CH4 permselectivity of the HBPBO – silica hybrids would be achieved by the synergistic effect of characteristic hyperbranched molecular structure, thermal treatment, and hybridization with silica.

Enhanced high‐temperature resistance and magnetic property of SiFeC nanocomposites containing a small amount of boron

AbstractIn this paper, the boron‐modified polyferrocenylcarbosilanes (namely HBPFCS‐Bs) with hyperbranched structure, as single‐source‐precursors, were successfully prepared by using 9‐borabicyclo [3, 3, 1] nonane (9‐BBN) and polyferrocenylcarbosilanes (HBPFCSs) as starting materials. The obtained HBPFCS‐Bs were characterized using Fourier transform infrared spectroscopy (FT‐IR), nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC), providing that the boron element can be introduced into the HBPFCS chains by the hydroboration (B‐H/C = C) reaction. Then, the structural evolution of HBPFCS‐Bs and the boron‐containing SiFeC ceramics at different temperatures (1100–1500°C) was further investigated by thermogravimetric analysis, X‐ray diffraction, energy dispersive spectroscopy, scanning electron microscope, and transmission electron microscopy. The results show that the incorporation of a small amount of boron (1 wt%) into precursors significantly improves the properties of the final ceramics, including the significant increase of the ceramic yield, enhanced high‐temperature resistance, as well as the higher ceramic densification. Finally, the saturation magnetization of the HBPFCS‐Bs‐derived ceramics was also enhanced by the introduction of boron.

Flame-Retardant multifunctional epoxy resin with high performances

High-performance and multifunctional epoxy resins (EPs) are of great use in the booming electric & electronic and 5G fields, however their fabrication shows huge challenges. Herein, through a facile strategy by simply incorporating a functional molecule DPI (phosphaphenanthrene polyethylenimine), which possessed a unique structure with hyperbranched polyethyleneimine as flexible inner core and phosphaphenanthrene groups as rigid outer shell, a high-performance and multifunctional epoxy resin was successfully fabricated. The hyperbranched rigid-flexible structure of DPI endowed the resultant thermoset EP-DPI with superb mechanical performance and high glass transition temperature, for which, at a low DPI content (≤4 wt%), EP-DPI exhibited 160%, 40%, and 31% improvement in impact toughness, tensile strength, and flexural strength compared with neat EP. At the same time, the good compatibility between DPI and the EP matrix enabled EP-DPI to be highly transparent, and the aromatic phosphorus structure endowed EP-DPI with excellent UV-shielding effect in the UV-A band. The dielectric performance of EP-DPI was enhanced due to the unique structure of DPI and its interaction with the EP matrix. Furthermore, the phosphaphenanthrene groups endowed EP-DPI with excellent anti-ignition, self-extinguishing, and low heat release during combustion. This work opens up a new strategy for developing novel high-performance and multifunctional EPs with potential versatile applications.

Sustainable Hyperbranched Functional Materials via Green Polymerization of Readily Accessible Levoglucosenone‐Derived Monomers

The homopolymerization in basic conditions of the recently reported bis(γ-lactone), 2H-HBO-HBO, is herein described for the first time. The solvent-free polymerization of this pentafunctional levoglucosenone (LGO) derivative affords fully renewable poly(vinyl-ether lactone) copolymers with a highly hyperbranched structure. This investigation stems from the polycondensation trials between 2H-HBO-HBO and di(methyl carbonate) isosorbide (DCI) that fails to give the anticipated polycarbonates. Such unexpected behavior is ascribed to the higher reactivity of the 2H-HBO-HBO hydroxy groups toward its α,β-conjugated endocyclic C═C, rather than the DCI methylcarbonate moieties. The different mechanistic scenarios involved in 2H-HBO-HBO homopolymerization are addressed and a possible structure of poly(2H-HBO-HBO) is suggested. Furthermore, the readily accessible (S)-γ-hydroxymethyl-α,β-butenolide (HBO) is also polymerized for the first time at a relatively large scale, without any prior modification, resulting in a new hyperbranched polymer with an environmental factor (E factor) ≈0. These new HBO-based polymers have a great potential for industrial-scale production due to their interesting properties and easy preparation via a low-cost, green, and efficient process.

Improving the comprehensive properties of PBO fibres/cyanate ester composites using a hyperbranched fluorine and epoxy containing PBO precursor

Hyperbranched fluorine and epoxy containing PBO precursor (epoxy-preFHBPBO) was synthesized and utilized as interface compatibilizer to synchronously improve the mechanical and dielectric properties of poly(p-phenylene-2, 6-benzobisoxazole) (PBO) fibres reinforced bisphenol A dicyanate ester (BADCy) resins (PBO fibres/FHBPBO-co-BADCy) laminated composites. 1H NMR, 13C NMR, and FTIR analyses confirmed the successful preparation of epoxy-preFHBPBO. The introduction of hyperbranched structure and fluorine groups significantly improved the mechanical properties and wave-transparent performance. Compared with PBO fibres/BADCy, the flexural strength and interlaminar shear strength of PBO fibres/FHBPBO-co-BADCy composites with 7 wt% epoxy-preFHBPBO were respectively enhanced to 634.9 and 46.9 MPa, increased by 8.1% and 27.8%. The corresponding dielectric constant and dielectric loss were 2.65 and 0.003, respectively, lower than those of PBO fibres/BADCy (3.06 and 0.006) composites. Meanwhile, the corresponding volume resistivity and breakdown strength were 4.93 × 1015 Ω•cm and 25.38 kV/mm, higher than PBO fibres/BADCy resins composites (2.2 × 1015 Ω•cm and 17.69 kV/mm).