Molecular Main Chain Research Articles

Application of triphenylphosphine organic compounds constructed with O, S, and Se in aluminum ion batteries

Due to their high reactivity and theoretical capacity, chalcogen elements have been favored and applied in many battery studies. However, the high surface charge density and high solubility of these elements as electrode materials have hindered their deeper exploration due to the shuttle effect. In this article, organic structural triphenylphosphine is used as a molecular main chain structure, and chalcogen elements O, S, and Se are introduced to combine with P as active sites. This approach not only takes advantage of the beneficial effects of the aromatic ring on the physical and chemical properties of the chalcogen element but also allows for the optimization of its advantages. By utilizing Triphenylphosphine selenide (TP-Se) as the cathode material in aluminum-ion batteries(AIBs), a high-performance Al-organic battery was fabricated, which exhibited a high initial capacity of 180.6 mAh g−1 and stable cycling for up to 1000 cycles. Based on density functional theory (DFT) calculations, TP-Se exhibits a smaller energy gap, which renders it favorable for chemical reactions. Moreover, the calculated results suggest that TP-Se tends to undergo redox reactions with AlCl2+. The molecular structure of triphenylphosphine and its combination with Se offers an enticing pathway for designing cathode materials in aluminum-organic batteries.

Synthesis and Characterization of a Self-Polycondensation Diazaphthalanone Monomer and Its Polymers from Polycondensation Reactions.

Polyether ketone (PEK) plastics are linear thermoplastic polymers connected by at least one ether bond and at least one ketone bond on the aryl group. The reason for their excellent heat resistance, rigidity, and mechanical strength is that their main molecular chain contains plenty of aromatic rings and polar carbonyl groups, and their molecular chain presents a large rigidity and strong intermolecular force. In addition, the main chain contains a considerable number of ether bonds, resulting in a certain toughness. However, polyether ketone materials have the disadvantage of poor solubility because of their excellent rigidity. To improve the solubility of polyether ketone, the preparation method of a novel nitrogenous heterocyclic polyaromatic ether monomer, 2-(4-chlorophenyl)-2,3-dihydrophthalazine-1,4-dione (CDD), was proposed, and its activity of polymerization was studied. The average molecular weight of the poly(aryl ether ketone) containing a nitrogenous heterocyclic polyaromatic ether group obtained by self-polycondensation of CDD was 4.181 × 103 kg/mol, and the yield was 90.5%. In order to further explore the activity of monomers, novel copolymerized poly(aryl ether ketone) (PBCD) containing a nitrogenous heterocyclic polyaromatic ether structure was prepared by ternary copolymerization with 4,4-difluorobenzophenone (DFBP) and bisphenol fluorene (BHPF) with high activity. The average molecular weight of PBCD was 72.793 × 103 kg/mol, the molecular weight distribution was 2.344, and the yield was 88.1%. Fourier transform infrared spectroscopy (FT-IR) and 1H NMR were used to confirm the structure of the obtained polymer. Through thermogravimetric analysis (TGA), the determined weight loss temperature of 5% under nitrogen was higher than 500 °C, indicating excellent thermal stability. Compared with the solubility of the binary copolymer containing fluorenyl poly(aryl ether ketone) (PBD), the polymer showed reasonable solubility in selective solvents such as chloroform and N,N-dimethylacetamide.

High-Voltage FDS of Thermally Aged XLPE Cable and Its Correlation with Physicochemical Properties.

This paper aims to investigate the influence of thermal aging on a crosslinked polyethylene (XLPE) cable, and the relationships between the macroscopical high-voltage dielectric and the microscopical physicochemical properties are also elucidated. To better simulate thermal aging under working condition, the medium-voltage-level cable is subjected to accelerated inner thermal aging for different aging times. Then, high-voltage frequency domain spectroscopy (FDS) (cable sample) and analyses of microscopic physical and chemical properties (sampling from the cable), including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and elongation at the break (EAB), are conducted at different cable aging stages. The dielectric test results show that after a certain aging time, the high-voltage FDS curves of the cable have layered characteristics, and this phenomenon is more obvious as the aging degree increases. Moreover, the slope and the integral of the high-voltage FDS curves rise with aging time. The mechanism is deduced by the physicochemical results that thermo-oxidative aging results in increasing polar groups and dislocation defects in the crystal region, which leads to the above phenomenon. On the one hand, the appearance of polar groups increases the density of the dipole. On the other hand, the destruction of the crystal region increases the probability and amplitude of dipole reversal. In addition, the breaking of molecular bonds and the increase in the amorphous phase also reduce the rigidity of the XLPE molecular main chain. The above factors lead to obvious delamination and larger dielectric parameters of the thermally aged cable. Finally, according to the experimental results, an on-site diagnosis method of cable insulation thermal aging based on high-voltage FDS is discussed.

Effect of main chain modification during reversion on strain‐induced crystallization of polyisoprene rubbers

AbstractThe effect of main chain modification during reversion on strain‐induced crystallization (SIC) of unfilled natural rubber (NR) and synthetic polyisoprene rubber (IR) cured with a conventional vulcanization system has been investigated. To eliminate the interference of crosslink density, vulcanizates were prepared using different amounts of curatives, chosen to give mainly monosulfidic or carbon–carbon crosslinks, having similar crosslink densities to the conventional compound at different states of reversion. Crystallinity was characterized by the degree of stress softening, and the contents of trans‐methine were qualitatively and quantitatively analyzed by Fourier transform infrared spectroscopy. It was found that crosslink density exerts much greater influence on crystallinity than crosslink structure. At the same crosslink density, SIC of NR vulcanizates after reversion is lower than that of samples cured with tetramethylthiuram disulfide or dicumyl peroxid to the optimum cure state, which might be attributed to molecular main chain modification during reversion. NR was found to have better reversion resistance than IR.

Research on Aging Dielectric Properties and Physical Testing of Electric Vehicle Insulating Silicone Rubber under First Principles

Aiming at the aging problem of insulating silicone rubber for new energy vehicles, this paper studies the equations of the aging of silicone rubber and its dielectric properties based on first-principles calculations. First, through the analysis of the microscopic mechanism of silicone rubber aging, the equations of the aging of silicone rubber and the rupture of the molecular main chain is obtained. Then the equations of silicone rubber molecular length and dielectric constant are solved by density functional theory. Ultimate, a molecular chain scission model of silicone rubber was built, and the micro-dielectric relationship was extended to the macroscopic level. The equation of the norm molecular length of silicone rubber and the dielectric constant is obtained. It provides an important theoretical basis for the aging detection of insulating silicone rubber for new energy vehicles based on electromagnetic waves.

Preparation, performance and structure-properties relationship of poly (lactic acid)/modified saponite nanocomposites based on thiol-ene click chemistry

ABSTRACT Saponite (SA)-mercaptopropyl polyhedral oligomeric silsesquioxane (POSS-SH) grafted poly (L-lactic acid) (SA-POSS-PLLA) was synthesized by thiol-ene click chemistry. SA-POSS-PLLA was characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. When 0.3 wt% SA-POSS-PLLA was used as a modifier in poly (lactic acid) (PLA), the impact strength and elongation at break of PLA/SA-POSS-PLLA nanocomposites were increased by 1.73 times and 4.25 times compared with pure PLA, respectively. The differential scanning calorimeter analysis showed that the crystallinity of PLA/SA-POSS-PLLA nanocomposites was increased from 7.74% to 30.32%. The addition of SA-POSS-PLLA increased the crystallization rate of PLA and significantly reduced the grain size of PLA, which also was proved by polarization optical microscopy analysis. Rheonaut technology for simultaneous rheometry and FTIR demonstrated that the reason why the addition of SA-POSS-PLLA nanoparticles accelerated the crystallization rate of PLA was that SA-POSS-PLLA nanoparticles promoted the adjustment of C-O-C structure and -CH3 group in the main molecular chain of PLA.

Effects of ultrasound, freeze-thaw pretreatments and drying methods on structure and functional properties of pectin during the processing of okra

Although, okra has features of high moisture content, rich nutrients, and pectin, it has extremely short shelf life, so deteriorate easily. Simple drying can prolong okra's shelf life but takes considerable time and is not cost-effective. Therefore, suitable pretreatments are usually employed to improve the drying efficiency and reduce the costs. This study showed that ultrasound (US) and freeze-thawing (FT) pretreatments, as well as three drying methods including vacuum pulsed drying (VPD), vacuum freeze-drying (VFD) and hot air drying (HD) have effects on structure and functional characteristics of okra pectin. The results indicated that drying methods affected differently the structure and chain conformation of the pectin molecular main chain. The thermal drying processes reduced molecular weight and increased viscosity, oxidation resistance, thermal stability, cohesion, and resilience. Particularly, the VPD pectin samples had lower molecular weight, higher antioxidant activity, better retention of the homogalacturonan (HG) main chain, thermal stability, emulsification activity, cohesiveness, resilience and weaker hardness and gel strength. The pretreatments had little effect on molecular weight, improved the antioxidant activity and emulsification activity of samples, and increased the viscosity of cold processed samples. US pretreatment retained pectin molecular chains, and FT pretreatment aggravated molecular chain debranching. In summary, VPD and US/FT pretreatments are beneficial to the development and utilization of pectin products.

Effect of crosslinked structure on the chemical degradation of EPDM rubber in an acidic environment

The degradation of peroxide-cured EPDM and sulfur-cured EPDM in an acid solution (12.5 ppm H2SO4+1.8 ppm HF) was investigated, and it was found that the degradation of the two in an acid solution was different. The degradation degree of the sulfur curing system is lower than that of the peroxide curing system. During the aging process, the molecular main chain of the peroxide-cured EPDM was broken, resulting in a double bond and C=O structure. When there is a coagent TAIC in the peroxide curing system, the presence of TAIC delays the degradation time of the EPDM molecular backbone, and the hydrolysis reaction of the TAIC crosslinking point occurs preferentially, which makes the stability of EPDM improved. In addition, regardless of the presence or absence of TAIC, the peroxide-cured EPDM undergoes a crosslinking reaction in the later stage of aging, resulting in an ether-crosslinked structure, thereby improving the damaged crosslinking network. Unlike the degradation of the peroxide curing system, the breakage of the molecular backbone does not occur in the sulfur-cured EPDM, but only an internal crosslinking reaction of the curing precursor occurs, resulting in a crosslinked network dominated by polysulfide bonds, thereby increasing the crosslinking density of the EPDM during the aging process.

Synthesis and characterization of SPDSCD and its flame retardant application on epoxy resins

In this study, a flame retardant agent, 2,4,8,10-tetraoxo-3,9-diphosphospiro[5.5]undecane spirophosphate-4,4-diaminopair benzene disulfone-1,3,5-himetriazine (SPDSCD), is synthesized through a direct polycondensation reaction. SPDSCD is a chemically expanded phosphorus-containing flame retardant in epoxy resins (EP). The molecular structure of SPDSCD and thermal stability are characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and thermogravimetric analysis, and EP/SPDSCD composites were investigated in detail. These properties are associated with the phosphorus-containing spiro structure on the main molecular chain which can promote condensation polymerization into carbon during pyrolysis, the new nitrogen-containing carbon source, and the triazine structure. SPDSCD shows good thermal stability and low flammability, the weight loss from 500 to 800 °C was only 6.1 wt%, and the residual mass at 800 °C was 48.9 wt%. With the addition of SPDSCD, the flame retardant quality of the composites was gradually enhanced, the carbon residue becomes denser, which isolates heat transfer and inhibits the volatilization of flue gas. The addition of 20 wt% SPDSCD in the EP sample was associated with a limited oxygen index (LOI) value of 26% and a vertical burning V-0 rating. Cone calorimeter test shows that the peak heat release rate is reduced by 75%; the heat release rate curve enters the heat release platform area with a value lower than the first peak, TSP is reduced by 24%, the ac-CO2Y value reduced by 25.6%, indicating that SPDSCD/EP produced less CO2, which obviously prevented the combustion of volatile gas. SPDSCD exerted a charring and barrier effect in the condensation phase. Using basic characterization and flame retardancy testing, this work determined that SPDSCD has good flame retardancy when added to EP.

Influencing mechanism of phenyl thioether group in the main molecular chain on high frequency electrical properties of the modified polyimide films

Polyimides (PIs) and their nanocomposites may render quite high dielectric loss under high frequency (HF) electrical stresses, which will significantly affect the insulation properties and operating lifetime of the equipment when the composite materials are used in the high-voltage and large-capacity power electronics transformers (HFPTs). In this paper, the phenyl thioether groups of various molar ratios were introduced into the diamine residue as to prepare modified PI films via alternating copolymerization method. Frequency-domain dielectric spectrum and high frequency surface discharge were adopted to study the HF electrical properties. The results indicated that with the increase of the phenyl thioether content, the dielectric loss factor firstly decreased and thereafter rose up again, while the lowest arrived at 9.29 × 10–4 for a PI film incorporating 40% phenyl thioether content, which case also presented the longest endurance lifetime against surface discharge tests at 15 kHz. Based the UV–vis tests on the charge transfer complexation, further analysis verified that for the 40% molar content of phenyl thioether in the PI molecule, it was the weak charge transfer characteristics that resulted in the smallest stacking structure of the ordered molecular chain in the film, which led to the weakest lossy polarization under the HF alternating electric field and manifested the minimal dielectric loss factor accordingly. The proposed research presents a feasible technological approach to regulate HF electrical properties of the modified PI films.

Properties of a novel carboxymethyl chitosan derived from silkworm pupa.

In this study, a carboxymethyl chitosan derived from silkworm pupa (SP-carboxymethyl chitosan) was prepared. The physical characteristics of the SP chitin, chitosan, and carboxymethyl chitosan were analyzed. The scanning electron microscopy results showed that the surfaces of the samples from SP were more uneven, with more surface fractures compared with those of the reference substance (RS). Thermal analysis, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy analysis showed that the main molecular chain structures of SP samples and RSs had no substantial differences. However, the crystallinity and thermal decomposition temperature of the SP samples were lower compared with those of the RSs. All of these results provide a theoretical basis for the development of applications for the SP-carboxymethyl chitosan.

Structure, thermal stability, electrochemical behaviors, and mechanical properties of organosoluble polyimide with pyrimidine ring in the main chain

ABSTRACTA novel organosoluble polyimide (PI) with pyrimidine ring in the main chain was synthesized by chemical and thermal imidization, respectively, from 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride and 2,4‐diamino‐6‐chloropyrimidine as raw materials and its molecular structure, solubility, UV–visible absorption characteristic, crystallinity, thermal stability, electrochemical behaviors, and mechanical properties were also studied. It was found that the introduction of pyrimidine ring in the main chain could increase the solubility of PI in polar aprotic solvents at room temperature and 60 °C, respectively, because of its molecular main chain with asymmetric structure and two polar N atoms in pyrimidine ring. Furthermore, PI had strong optical absorption peak intensity, excellent thermal stability, good redox reversibility, especially outstanding mechanical properties, which were conductive to its potential applications in adhesives, polyelectrolyte, separation membrane, and so on. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43680.

Curing Kinetics and Thermal Properties of Aromatic Multifunctional Epoxy Resins

In order to investigate the relationship between the chemical structure of multifunctional epoxy resins and their properties, two tetrafunctional epoxies with different aromatic rings content in the molecular main chain, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl ether (4,4'-TGDDE) and N,N,N',N'-tetraglycidyl-2,2-bis[4-(4-aminophenoxy)phenyl]propane (TGBAPP), were cured with 4,4'-diaminodiphenyl ether (4,4'-DDE) and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), respectively. Then four amine curing systems (TGBAPP/BAPP, TGBAPP/4,4'-DDE, 4,4'-TGDDE/BAPP and 4,4'-TGDDE/4,4'-DDE) were obtained. Additionally, the 4,4'-TGDDE and another TGDDE with m-glycidyl amino, named N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl ether (3,4'-TGDDE) were cured with methyl nadic anhydride (MNA). Then the anhydride curing systems (4,4'-TGDDE/MNA and 3,4'-TGDDE/MNA) were prepared. The curing kinetics and thermal properties of these systems were studied in detail. The results indicated that the anhydride curing systems exhibited higher curing reactivity than the amine curing systems, and the resins cured with the anhydride showed better thermal properties. Moreover, introducing more aromatic rings into the backbone would decrease the curing reactivity but enhance the thermal property of the multifunctional epoxy resins. And the tetrafunctional epoxy with p-glycidy amino groups had higher curing reactivity than the epoxy with p-glycidy amino groups, and the thermal property of the front epoxy was better.

Thermal degradation kinetics and mechanism of epoxidized natural rubber

Abstract Thermal resistance is one of the most dominative properties for polymer materials. Thermal degradation mechanisms of epoxidized natural rubber (ENR) and NR are studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The results show that, the introduction of epoxy groups into the NR molecular main chain leads to a remarkable change in the degradation mechanism. The thermal stability of ENR is worse than that of NR. For the first thermooxidative degradation stage, the thermal decomposition mechanism of ENR is similar to that of NR, which corresponds to a mechanism involving one-dimensional diffusion. For the second stage, the thermal decomposition mechanism of ENR is a three-dimensional diffusion, which is more complex than that of NR. Kinetic analysis showed that activation energy (Eα), activation entropy (ΔH) and activation Gibbs energy (ΔG) values are all positive, indicating that the thermooxidative degradation process of ENR is non-spontaneous.

Thermal Stabilities and Mechanical Properties of Two Tetra-Functional Epoxy Resins

To study the relationship between the molecular main chain structure and the properties of amine based tetra-functional epoxy resins, especially for the thermal stabilities and the mechanical properties, N,N,N',N'-Tetraglycidyl-2,2-Bis[4-(4-aminophenoxy)phenyl]propane (TGBAPP) and N,N,N',N'-Tetraglycidyl-4,4'-diamino diphenyl ether (TGDDE) were cured with Methyl nadic anhydride (MNA). The thermal behavior of the cured epoxy resins were studied with the thermo-gravimetric analysis (TGA), and the glass transition temperature (Tg) were determined with the Dynamic Mechanical Analysis (DMA). Additionally, the mechanical properties of them were tested. The results indicated that the cured epoxy resin based on TGBAPP had better thermal stabilities and toughness.

Time dependent density functional study of the absorption spectra of 1,3-benzoxazole and three substituted benzoxazole in gas phase and liquid phase

Time dependent density functional (TD-DFT) calculations were performed on 1,3-benzoxazole and substituted benzoxazoles using the B3LYP functional and the 6-31+G(d) basis sets. The geometry of the S0 and S1 singlet ground and excited states were optimized in gas phase, toluene and methanol using B3LYP/6-31+G(d) y CIS/6-31+G(d) methods, respectively, and the vertical π → π* absorption largest wavelength transitions were determined. Several global molecular descriptors were considered such as the hardness, chemical potential, electronegativity and the dipole moment for each molecule and was determined the influence that has, about the values of these descriptors, the alteration of the main molecular chain of an initial structure (1,3 not substituted Benzoxazole). Generally, the predicted spectra are in agreement with the experimental data.

Effects of freezing on the condensed state structure of chitin in alkaline solution

Chitin powder was soaked in concentrated sodium hydroxide solution (45%, w/w), and freezed at −18/−35 °C for further modification (the ratio of chitin and sodium hydroxide solution was 1:10, w/v). The degree of deacetylation (DDA) was determined by acid–base titration while the structural changes of the regenerated chitin after alkali-freezing treatment were investigated by X-ray diffraction (XRD), infrared spectroscopy (IR) and differential scanning calorimetry (DSC). The results showed that the formation and growth of ice crystal during the slowly freezing process could break the intra- and inter-molecular hydrogen bonds, disorganize the ordered molecular structure, destruct the compact crystal structure and decline the crystallinity. However, such structural damage was unstable and reversible. Nevertheless, the study explained that the alkali-freezing treatment was beneficial for further modification of chitin, which could significantly promote its solubility and accelerate the chemical reaction rate, while it could also keep its main molecular chains completely.

Hydrodynamic, optical, and electrooptical properties of macromolecules of third-generation cylindrical dendrimers in chloroform and dichloroacetic acid

Acrylic polymers containing side dendrons of the third generation based on L-aspartic acid have been studied via the methods of molecular hydrodynamics, dynamic and static light-scattering, optics, and electrooptics. There are marked differences in hydrodynamic and optical properties of the macromolecules under study and previously examined polymers with side dendrons of first and second generations. In the range of degrees of polymerization from 10 to 40, these macromolecules possess an extremely low shape asymmetry. Experiments demonstrate the predominant orientation of end side dendrons along the main molecular chain. In chloroform solutions, the orientation of macromolecules in hydrodynamic and electric fields occurs according to the large-scale mechanism. In dichloroacetic acid, the hydrodynamic dimensions of macromolecules decrease, an effect that is accompanied by an increase in the kinetic flexibility of polymer chains.

Newly synthesized polybenzoxazole derivative with an adjacent hydroxyphenyl ring for optical sensing

AbstractA photoluminescent polymer with a 2‐(2′‐hydroxyphenyl)benzoxazole unit in the molecular main chain was synthesized through the deprotection reaction of a precursor polymer. The amorphous, conjugated polymer emitted green light, both in solution and as a solid, with a fluorescence emission maximum at 518 nm from an excited keto tautomer because of excited‐state intramolecular proton transfer. The polymer showed different fluorescence emission spectra in solvents with different polarities because of intramolecular hydrogen‐bond interruption. The intramolecular hydrogen‐bond‐induced emission change was successfully used as a sensitive sensing signal for metal cations as expected, the polymer acting as a fluorescence‐based chemosensor. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1397–1403, 2005

Fabrication of a gold pattern with a nanoscale edge by using heptanethiol self-assembled monolayers and a metastable helium beam

By exposure to a metastable helium beam, latent images of the patterns were formed in the heptanethiol (HT) self-assembled monolayer (SAM) resists on Au(1 1 1) films, and then the patterns were transferred to the underlying gold films by wet chemical etching. Negative patterns, as well as positive patterns with lower doses, were fabricated with higher exposures to a metastable-atom beam. The smallest width of edge, ∼40 nm, among alkanethiol SAM resists was achieved in the condition of negative pattern formation. According to the metastable-atom-stimulated desorption (MSD) measurement of alkanethiol SAMs on Au(1 1 1), the SAMs were damaged under the irradiation of metastable-atom beam losing either H atoms or CH 3 groups. Thus, the highly concentrated energy deposition by a metastable-atom beam, which induced crosslinking of the main molecular chain in the SAM resists and increased the resistance to etching, could lead to the negative pattern formation at higher doses.