Effects of Binding Energy of Bioinspired Sacrificial Bond on Mechanical Performance of cis-1,4-Polyisoprene with Dual-crosslink

Although bioinspired sacrificial bonds have been demonstrated to be efficient in improving the mechanical properties of polymer materials, the effect of binding energy of a specific dynamic bond on the ultimate mechanical performance of a polymer network with dual-crosslink remains unclear. In this contribution, diamine and sulfur curing package are introduced simultaneously into a sulfonated cis-1,4-polyisoprene to create dually-crosslinked cis-1,4-polyisoprene network with sulfonate-aminium ionic bonds as the sacrificial bonds. Three diamines(primary, secondary and tertiary) with the same spacer between the two nitrogen atoms are used to create the ionic bonds with different binding energies. Although the binding energy of ionic bond does not affect the glass transition temperature of cis-1,4-polyisoprene(IR), it exerts definite influences on strain-induced crystallization and mechanical performance. The capabilities of diamine in dissipating energy, promoting strain-induced crystallization and enhancing the mechanical performance are in the same order of secondary diamine primary diamine tertiary diamine. The variations in mechanical performances are correlated to the binding energy of the ionic bond, which is determined by p Ka values.     

Theoretical Study of Substituent Effect in Aryl Group Migration in (<Emphasis Type="Italic">para</Emphasis>-C<Subscript>6</Subscript>H<Subscript>4</Subscript>X)Mn(CO)5 Complexes

In this study, we report substituent effect on aryl group migration in (para-C₆H₄X)Mn(CO)₅ complexes using mpw1pw91 quantum chemical calculations. These calculations reveal good linear relationships between barrier energy (ΔE), activation energy (ΔH^?), activation free energy (ΔG^?) values and rate constants with Hammett constants of X-substituents. The occupancy values of Mn–CO_cis and Mn–C(O)-(para-C₆H₄X) bonds in reactant, transition state and product were calculated by Natural bond orbital (NBO) method.     

Hydrogen-Bonding Interaction in a Complex of Amino Acid with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylformamide Studied by DFT Calculations

Theoretical studies on hydrogen-bonded complexes between amino acids (glycine, alanine and leucine) and N,N-dimethylformamide (DMF) in gas phase have been carried out using density functional theory (DFT) and ab initio calculations at the B3LYP/6-311++G** and MP2/6-311++G** theory levels. The structures, binding energy, stretching frequency and bond characteristics of the mentioned complexes were calculated. The NH₂ and COOH groups of amino acids form different types of hydrogen bonds with the DMF molecule, as well as alkyl side chains. High binding energy suggests multiple hydrogen bonds present in one complex. The nearly linear OH???O and NH???O contacts are stronger than a conventional hydrogen bond interaction with their H???O separation between 1.74 and 2.14 Å. The weaker CH???O H-bond is also discussed as being a crucial interaction in biological systems involving amino acids. The formation of this interaction results in a blue shift in the CH stretching frequency.     

Localization of Failures in Structural Order of <Emphasis Type="Italic">trans</Emphasis>-1,4-Butadiene Units in Interdefective Regions of a Butadiene-Nitrile Elastomer Matrix

The fractional free volume of chains passing and incorporated into the ordered structures of segments in trans-1,4-configuration in the copolymers of butadiene and acrylonitrile at different content of acrylonitrile units is calculated in order to determine the localization of order disturbances of butadiene trans-1,4-units. Amorphization of the structure occurs in the immediate vicinity of structural defects of acrylonitrilebutadiene rubbers formed by alternating acrylonitrile and trans-1,4-units of butadiene as well as cis-1,4-and 1,2-isomers of butadiene.     

Fabrication of <Emphasis Type="Italic">trans</Emphasis>-1,4-polyisoprene nanofibers by electrospinning and its crystallization behavior and mechanism

Trans-1,4-polyisoprene (TPI) nanofibers have been fabricated successfully through electrospinning technology. Through the control of electrospinning parameters, highly crystallized TPI fresh fibers composed mainly by β phase were produced. Morphology and diameter of TPI nanofibers can be controlled by adjusting the electrospinning conditions. The in situ observations of FTIR spectra revealed that the crystallinity of the TPI fibers decreased with aging. While for TPI nanofibers aging at 45 °C for 24 h, a decrease in crystallinity as well as β to α transformation was observed with aging and these changings happened in the first 50 h during aging. The mechanism for β-TPI formation during electrospinning process and the reduced crystallinity with aging were proposed.     

Disperse Composition of Titanium–Magnesium Catalyst Particles and <Emphasis Type="Italic">trans</Emphasis>-1,4-Polyisoprene Granules in Short-Time Polymerization

The disperse composition of trans-1,4-polyisoprene granules and supported titatium–magnesium catalyst particles in the ultrarapid polymerization of isoprene within 0.1–0.7 s is studied. It is shown that within this period the alteration of external and internal fragmentations occurs between two fractions of polymer granules that are formed by 0.1 s of polymerization and already contain significantly fragmented catalyst particles. The correlation between these processes and molecular mass characteristics of trans-1,4-polyisoprene is investigated. It is found that the external fragmentation is accompanied by a decrease in the average molecular masses of the polymer, while the internal fragmentation leads to formation of a higher molecular mass trans-1,4-polyisoprene. As a result, the fraction of polymer granules with a diameter of 7.5 μm is formed by 0.7 s of polymerization and replication to high conversions is developed on their basis.     

Comparative reactivity of substituted 1,3-and 1,4-thiasilinane <Emphasis Type="Italic">S</Emphasis>-oxides in the sila-Pummerer rearrangement and inversion of the thiocarbonyl group

The thermal sila-Pummerer rearrangement of diastereomeric 2,3,3-trimethyl-1,3-thiasilinane S-oxides was studied. Introduction of the methyl group in the 2 position of 3,3-trimethyl-3-thiasilinane S-oxide slows down the rearrangement. When heated in CCl₄, the trans isomer (2-Me_eq, SO_eq) converts into the cis isomer (2-Me_eq, SO_ax) which rapidly rearranges into 2,2,7-trimethyl-1,6,2-oxathiasilepane. On the contrary, the isomeric 2,4,4-trimethyl-1,4-thiasilinane S-oxide is thermally stable up to 160°C in DMSO. The inversion at the sulfur atom in 2,3,3-trimethyl-1,3-thiasilinane S-oxides and 2,4,4-trimethyl-1,4-thiasilinane S-oxides under the action of triethyloxonium tetrafluoroborate was studied. The trans isomer of 2,3,3-trimethyl-1,3-thiasilinane S-oxide (2-Me_eq, SO_eq) forms with Et₃O⁺BF ₄ ^? a salt which decomposes in two ways. The first involves recovery of the starting sulfoxide due to Sn2 substitution at the carbon atom of the ethoxy group, and the second, convertion into the cis isomer (2-Me_eq, SO_ax) which rearranges into 2,2,7-trimethyl-1,6,2-oxathiasilepane. Under the same conditions, the cis isomer of 2,3,3-trimethyl-1,3-thiasilinane S-oxide (2-Me_eq, SO_eq) decomposes to form siloxanes. trans-2,4,4-Trimethyl-4-thiasilinane S-oxide (2-Me_eq, SO_eq) under the action of Et₃O⁺BF ₄ ^? convers into the cis isomer (2-Me_eq, SO_ax). The B3LYP/6-311G(d,p) theoretical analysis showed that the thermal inversion at the sulfur atom in the compounds studied has a high energy barrier.     

Synthesis of tertiary amines containing <Emphasis Type="Italic">gem</Emphasis>-dichlorocyclopropane and cycloacetal fragments

Reactions of secondary amines containing gem-dichlorocyclopropane and cycloacetal fragments with allyl chloride, trans-1,3-dichloropropene, benzyl chloride, and chloromethyl-gem-dichlorocyclopropane were studied. The corresponding tertiary amines were obtained in 20–85% yield. Microwave radiation stimulates N-alkylation of the secondary amine containing the heterocyclic moiety. The structures of the tertiary amines prepared were studied. The configuration of the double bond in the trans-1,3-dichloropropene derivative is retained.     

Reactions of <Emphasis Type="Italic">N</Emphasis>-Allyl- and <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Diallyltrifluoromethanesulfonamides with Carboxylic Acid Amides under Oxidizing Conditions

Reactions of acetamide and benzamide with N-allyltrifluoromethanesulfonamide in the presence of t-BuOCl–NaI afforded exclusively 2,5-bis(chloromethyl)-1,4-bis(trifluoromethanesulfonyl)piperazine. Analogous reaction with N,N-diallyltrifluoromethanesulfonamide gave mixed halogenation product at only one C=C double bond of the substrate.     

Solvothermal synthesis and crystal structure of a 1d coordination polymer: [Ni(1,4-BDC)(N-MIM)<Subscript>2</Subscript>]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (1,4-BDC = 1,4-benzenedicarboxylic acid,N-MIM = <Emphasis Type="Italic">N</Emphasis>-methylimidazole)

A new metal-organic coordination polymer, namely [Ni(1,4-BDC)(N-MIM)₂] _n (I) (1,4-BDC = 1,4-benzenedicarboxylic acid and N-MIM = N-methylimidazole), has been synthesized under solvothermal conditions by using N-MIM as solvent and characterized by elemental analysis, IR, and X-ray single-crystal diffraction. The X-ray diffraction analysis reveals that I crystallizes in the monoclinic system, space group C2/c. The 1,4-BDC ligand adopts a bis(bidentate) chelating mode to connect two adjacent Ni(II) centers to form a one-dimensional (1D) zigzag chain. The adjacent chains are further linked through hydrogen bonds and π-π stacking interactions, forming a three-dimensional (3D) supramolecular framework. The unit cell parameters for I: a = 17.250(10), b = 7.214(4), c = 16.506(7)Å, β = 125.53(4)°, V = 1671.6(15)ų, Z = 4.     

Activated sterically strained C=N bond in <Emphasis Type="Italic">N</Emphasis>-substituted <Emphasis Type="Italic">p</Emphasis>-quinone mono- and diimines: XV. Synthesis,structure, and reactions with alcohols of <Emphasis Type="Italic">N</Emphasis>-carbamoyl-1,4-benzoquinone imines

The reaction of 4-aminophenols with N-nitrourea or with sodium cyanate in acetic acid gave the corresponding 4-ureidophenols which were oxidized to N-carbamoyl-1,4-benzoquinone imines, substituted N-(4-oxocyclohexa-2,5-dien-1-ylidene)ureas. N-(2,6-Dimethyl-4-oxocyclohexa-2,5-dien-1-ylidene)urea possessing activated sterically strained C=N bond reacted with alcohols to afford N-(1-alkoxy-2,6-dimethyl-4-oxocyclohexa-2,5-dienyl)ureas.     

<Emphasis Type="Italic">Ab initio</Emphasis> calculation of nitrogen oxide dimer structure and its anion-radical

A comparative quantum chemical analysis has been made for the most stable dimer of nitrogen oxide with the structure cis-ONNO in a singlet state ¹A₁ by ab initio method of SCF MO LCAO, allowing for electron correlation according to Meller-Plesset perturbation theory of the second order (MP2), and density functional technique (DFT). The computations by MP2 method show anion-radical (ONNO)^? to have a strong bond between nitrogen atoms (N-N 1.44 Å) in contrast to molecular weakly bound cis-dimer with equilibrium distance N-N 2.23 Å. Molecular orbital structure of the dimer and its anions was examined that made it possible to suggest a reason of preferable stabilization of nitrogen oxide dimer in the cis-form. Calculated high affinity to electron (E_a = ?1.55-?1.69 eV) for the molecular dimer ONNO (¹A₁) explains an intense strengthening of N-N bond in anion-radical and confirms the experimental data on a possibility of surface anion-π-radical formation on electron donor centers. The DFT computations indicate that this technique poorly reproduces the experimental geometry and electron structure of the cis-dimer ONNO having predicted a triplet ground state with the equilibrium distance N-N ≈2 Å instead of a singlet one with N-N 2.26 Å. The comparison between MP2 and DFT calculations for complex dimer ONNO with copper cation reveals the energy state of the complex (Cu-O₂N₂)⁺ corresponding to stabilization of anion-π-radical (N₂O₂)^? {term-³A₂, Cu(d)⁹-(ONNO)^?1} to be highly overestimated by DFT.     

Formation of solvate structures by the <Emphasis Type="Italic">ortho</Emphasis>-, <Emphasis Type="Italic">meta</Emphasis>-, and <Emphasis Type="Italic">para</Emphasis>-isomers of hydroxybenzoic acid in supercritical fluid

The solvate structures formed by the ortho-, meta-, and para-isomers of hydroxybenzoic acid (o-HBA, m-HBA, and p-HBA) with a polar co-solvent (methanol at a concentration of 0.030 and 0.035 mole fractions) in supercritical carbon dioxide at a constant density of 0.7 g/cm³ and temperatures of 318 and 328 K have been studied by the classic molecular dynamics. It has been determined that a stable hydrogen-bonded complex with the co-solvent forms via the hydrogen of the carboxyl group for all isomers. The probability of this complex existence is high at all temperatures and concentrations. In the o-HBA molecule, the other functional groups are engaged in the intramolecular hydrogen bond, but not involved in interactions with methanol. It has been found that m-HBA and p-HBA can be involved in hydrogen bonds with methanol via hydroxyl hydrogen and oxygen atoms; they are characterized by the presence of one more co-solvent molecule (rarely, two molecules) in their solvation shell and intermittent formations/breakages of hydrogen bonds via other functional groups. These bonds are far less stable, and their formation is sensitive to change of temperature and co-solvent concentration. It has been concluded that the degree of selective solvation of m-HBA and p-HBA by co-solvent molecules is approximately the same, but the rate of structural rearrangements in the nearest environment of m-HBA is higher than that of p-HBA.     

Chemistry of Acyl(imidoyl)ketenes: IX. Synthesis and Thermolysis of 3-Aroyl-8-chloro-1,2-dihydro-4<Emphasis Type="Italic">H</Emphasis>-pyrrolo[2,1-<Emphasis Type="Italic">c</Emphasis>][1,4]benzoxazine-1,2,4-triones

Reactions of 3-Z-aroylmethylene-6-chloro-3,4-dihydro-2H-1,4-benzoxazine-2-ones with oxalyl chloride afford 3-aroyl-8-chloro-1,2-dihydro-4H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones and Z-3-(2-aryl-2-chlorovinyl)-6-chloro-2H-1,4-benzoxazine-2-ones. Aroyl(imidoyl)ketenes generated by decarbonylation of pyrrolobenzoxazinetriones undergo dimerization through [4+2]-cycloaddition to form 4-aroyl-3-aroyloxy-2-(2-oxo-2H-1,4-benzoxazin-3-yl)-1H, 5H-pyrido[2,1-c][1,4]benzoxazine-1,5-diones.     

Synthesis and structure of 1-(buta-1,3-dien-2-yl)pyrazoles and their behavior in Diels-Alder reactions

A convenient procedure has been developed for the synthesis of cis-and trans-isomeric 1-(buta-1,3-dien-1-yl)-1H-pyrazoles by reaction of the corresponding pyrazoles with β-methylacrolein diethyl acetal and subsequent 1,4-cleavage of the nucleophilic substitution products. The behavior of the title compounds in Diels-Alder reactions with maleic anhydride has been studied. According to the ¹H NMR data, 1-(buta-1,3-dien-1-yl)-1H-pyrazole is a mixture of cis and trans isomers. Butadienylpyrazoles having methyl groups in the pyrazole ring do not react with maleic anhydride.     

Potential function of the internal rotation of a methacrolein molecule in the ground (<Emphasis Type="Italic">S</Emphasis> <Subscript>0</Subscript>) electronic state

The structural parameters of s-trans- and s-cis-isomers of a methacrolein molecule in the ground (S₀) electronic state are determined by means of MP2 method with the cc-pVTZ basis set. Kinematic factor F(φ) is expanded in a Fourier series. The potential function of internal rotation (PFIR) of methacrolein in this state is built using experimental frequencies of transitions of the torsional vibration of both isomers, obtained from an analysis of the vibrational structure of the high-resolution UV spectrum with allowance for the geometry and difference between the energy (ΔH) of the isomers. It is shown that the V_n parameters of the potential function of internal rotation of the molecule, built using the frequencies of the transition of the torsional vibrations of s-trans- and s-cis-isomers of the methacrolein molecule, determined from vibrational structure of the high-resolution UV spectrum and the FTIR spectrum, are close.     

Stereochemistry of dihydroxylation of <Emphasis Type="Italic">N</Emphasis>-arylbicyclo[2.2.1]-hept-5-ene-<Emphasis Type="Italic">endo</Emphasis>- and -<Emphasis Type="Italic">exo</Emphasis>-2,3-dicarboximides

Stereochemistry of the oxidation of N-arylbicyclo[2.2.1]hept-5-ene-endo-and-exo-2,3-dicarboximides at the double bond with peroxyacetic acid generated in situ in the presence of sulfuric acid and with an anhydrous dioxane solution of peroxyacetic acid was studied. In both cases, the reaction was stereospecific, regardless of the substituent in the N-aryl group and configuration of the imide ring, but the reaction direction depended on the presence of water in the system. In the first case, the corresponding trans-5,6-dihydroxy derivatives were formed, while in the second, exo-5,6-epoxy derivatives. The oxidation of N-arylbicyclo[2.2.1]-hept-5-ene-endo-and-exo-2,3-dicarboximides with a solution of potassium permanganate in aqueous acetone gave the corresponding N-aryl-cis-5,6-dihydroxybicyclo[2.2.1]heptane-endo-and-exo-2,3-dicarboximides. The exo,cis,exo and exo,cis,endo configurations of the synthesized compounds were determined by ¹H NMR spectroscopy.     

Synthesis of isotactic polystyrene-block-polyethylene by the combination of sequential monomer addition and hydrogenation of 1,4-<Emphasis Type="Italic">trans</Emphasis>-polybutadiene block

Herein, we demonstrate the synthesis of a well-defined diblock copolymer consisting of isotactic polystyrene (iPS) and linear polyethylene, isotactic polystyrene-block-polyethylene (iPS-b-PE), by the combination of sequential monomer addition and hydrogenation. Isospecific living polymerization of styrene and living trans-1,4-polymerization of 1,3-butadiene were catalyzed by 1,4-dithiabutandiyl-2,2′-bis(6-cumenyl-4-methylphenoxy) titanium dichloride (complex 1) activated by triisobutyl aluminum modified methylaluminoxane (MMAO) at room temperature to provide highly isotactic polystyrene (iPS) and 1,4-trans-polybutadiene (1,4-trans-PBD) with narrow molecular weight distribution. Furthermore, the iPS-b-1,4-trans-PBD was synthesized via sequential monomer addition in the presence of complex 1 and MMAO. The hydrogenation of the 1,4-trans-PBD block was promoted by RuCl₂(PPh₃)₃ used as a catalyst to produce iPS-b-PE.     

Blinded predictions of standard binding free energies: lessons learned from the SAMPL6 challenge

In the context of the SAMPL6 challenges, series of blinded predictions of standard binding free energies were made with the SOMD software for a dataset of 27 host–guest systems featuring two octa-acids hosts (OA and TEMOA) and a cucurbituril ring (CB8) host. Three different models were used, ModelA computes the free energy of binding based on a double annihilation technique; ModelB additionally takes into account long-range dispersion and standard state corrections; ModelC additionally introduces an empirical correction term derived from a regression analysis of SAMPL5 predictions previously made with SOMD. The performance of each model was evaluated with two different setups; buffer explicitly matches the ionic strength from the binding assays, whereas no-buffer merely neutralizes the host–guest net charge with counter-ions. ModelC/no-buffer shows the lowest mean-unsigned error for the overall dataset (MUE 1.29?<?1.39?<?1.50 kcal mol^?1, 95% CI), while explicit modelling of the buffer improves significantly results for the CB8 host only. Correlation with experimental data ranges from excellent for the host TEMOA (R² 0.91?<?0.94?<?0.96), to poor for CB8 (R² 0.04?<?0.12?<?0.23). Further investigations indicate a pronounced dependence of the binding free energies on the modelled ionic strength, and variable reproducibility of the binding free energies between different simulation packages.     

Phase transition temperature controllable poly(acrylamide-<Emphasis Type="Italic">co</Emphasis>-acrylic acid) nanocomposite physical hydrogels with high strength

Poly(acrylamide-co-acrylic acid) nanocomposite physical (P(AAm-co-AAc)NCP) hydrogels have been prepared through the in situ free radical solution polymerization based on a “single network, dual cross-linkings” strategy. The P(AAm-co-AAc) NCP hydrogels are composed of nanobrushes of P(AAm-co-AAc) chains grafted on the surface of vinylhybrid silica nanoparticles (VSNPs). In the hydrogel system, the VSNPs act as the “analogous chemical cross-linking points” once the hydrogen bonds formed between the P(AAm-co-AAc) chains of the nanobrushes, thus leading to the fabrication of high-strength P(AAm-co-AAc) NCP hydrogels. Compared with conventional thermosensitive P(AAm-co-AAc) hydrogels, the P(AAm-co-AAc) NCP hydrogels have a broader range of phase transition temperature, which can be adjusted by altering the monomer ratio, the VSNPs concentration, the addition of urea and N,N-dimethylacrylamide (DMAAm). At the same time, the mechanical properties of the P(AAm-co-AAc) NCP hydrogels have been improved significantly by the introduction of VSNPs. Furthermore, both the phase transition and the tensile strength of the P(AAm-co-AAc) NCP hydrogels are largely influenced when Fe³⁺ ions are introduced as the ionic crosslinkers into the hydrogel networks.