Universality in Branching Frequencies and Molecular Dimensions during Hyperbranched Polymer Formation: Step Polymerization of AB2 Type Monomer with Equal Reactivity

Hyperbranched polymer formation during step polymerization of AB₂ type monomer with equal reactivity of two B's is investigated theoretically, focusing the attention to the degree of branching (DB) and the mean square radius of gyration for the unperturbed chains, . It is found that the DB‐value at large degree of polymerization (P) limit, = 0.5 is unchanged during the whole course of polymerization. The average value of having the same P is invariant throughout the polymerization. The universal curve between and P agrees perfectly with that for the self‐condensing vinyl polymerization (SCVP), another method to synthesize hyperbranched polymers, when the reactivity ratio for SCVP, r_SCVP, is 2.589 that gives = 0.5. The power law, is found for large values of P.

     

An Efficient N‐Heterocyclic Carbene‐Ruthenium Complex: Application Towards the Synthesis of Polyesters and Polyamides

The ruthenium benzimidazolylidene‐based N‐heterocyclic carbene (NHC) complex 4 catalyzes the direct dehydrogenative condensation of primary alcohols into esters and primary alcohols in the presence of amines to the corresponding amides in high yields. This efficient new catalytic system shows a high selectivity towards the conversion of diols to polyesters and of a mixture of diols and diamines to polyamides. The only side product formed in this reaction is molecular hydrogen. Remarkable is the conversion of hydroxytelechelic polytetrahydrofuran ( = 1000 g mol⁻¹)—a polydispers starting material—into a hydrolytically degradable polyether with ester linkages ( = 32 600 g mol⁻¹) and, in the presence of aliphatic diamines, into a polyether with amide linkages in the back bone ( = 16 000 g mol⁻¹).

     

Transition‐Metal‐Free Synthesis of 1,3‐Butadiene‐Containing π‐Conjugated Polymers

This work describes the synthesis of π‐conjugated polymers possessing arylene and 1,3‐butadiene alternating units in the main chain by the reaction of α,β‐unsaturated ester/nitrile containing γ‐H with aromatic/heteroaromatic aldehyde compound. By using 4‐(4‐formylphenyl)‐2‐butylene acid ethyl ester as a model monomer, the different polymerization conditions, including catalyst, catalyst amount, and solvent, are optimized. The polymerization of 4‐(4‐formylphenyl)‐2‐butylene acid ethyl ester is carried out by refluxing in ethanol for 72 h with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as a catalyst to give a 1,3‐butadiene‐containing π‐conjugated polymer, poly(phenylene‐1,3‐butadiene), in 84.3% yield with and / (PDI) estimated as 6172 and 1.65, respectively. Based on this new methodology, a series of π‐conjugated polymers containing 1,3‐butadiene units with different substituents are obtained in high yields. A possible mechanism is proposed for the polymerization through a six‐membered ring transition state and then a 1,5‐H shift intermediate.

     

Controlled Polymerization of Protic Ionic Liquid Monomer by ARGET‐ATRP and TERP

The direct synthesis of structurally well‐defined protic polymeric ionic liquid (PIL) with controlled molecular weight and molecular weight distribution is examined using N,N‐diethyl‐N‐(2‐methacryloylethyl) ammonium bis(tri‐fluoromethylsulfonyl)imide (DEMH‐TFSI) as a monomer. Three polymerization methods, namely, atom transfer radical polymerization (ATRP), activators regenerated by electron transfer (ARGET)‐ATRP, and organotellurium‐mediated living radical polymerization (TERP) are employed in this study. While the polymerization by ATRP is slow and does not reach high monomer conversion that under ARGET‐ATRP and TERP proceeds smoothly and affords structurally well‐defined poly(DEMH‐TFSI)s. TERP is especially efficient for the control and poly(DEMH‐TFSI)s with low to high molecular weights ( = 49 100–392 500) and narrow molecular weight distributions (/ = 1.17–1.46) are obtained. These results represent the first example of synthesis of a structurally well‐defined protic, ammonium PIL by direct polymerization of the protic ionic liquid monomer. The polymerization of N,N‐diethyl‐N‐(2‐methacryloylethyl)‐N‐methylammonium bis(trifluoromethylsulfonyl)imide (DEMM‐TFSI), which possesses a quaternary ammonium salt, also proceeds in a highly controlled manner under TERP conditions. A diblock copolymer, polystyrene‐block‐poly(DEMH‐TFSI), is also successfully synthesized by TERP.

     

Accurate,robust, and reliable calculations of Poisson–Boltzmann binding energies

Poisson–Boltzmann (PB) model is one of the most popular implicit solvent models in biophysical modeling and computation. The ability of providing accurate and reliable PB estimation of electrostatic solvation free energy, , and binding free energy, , is important to computational biophysics and biochemistry. In this work, we investigate the grid dependence of our PB solver (MIBPB) with solvent excluded surfaces for estimating both electrostatic solvation free energies and electrostatic binding free energies. It is found that the relative absolute error of obtained at the grid spacing of 1.0 Å compared to at 0.2 Å averaged over 153 molecules is less than 0.2%. Our results indicate that the use of grid spacing 0.6 Å ensures accuracy and reliability in calculation. In fact, the grid spacing of 1.1 Å appears to deliver adequate accuracy for high throughput screening. © 2017 Wiley Periodicals, Inc.     

Hyperbranched Polymers Formed Through Irreversible Step Polymerization of AB2‐Type Monomer with Substitution Effect in a Continuous Flow Stirred‐Tank Reactor (CSTR)

A new Monte Carlo simulation method is proposed for the step polymerization of AB₂‐type monomer conducted in a continuous flow stirred‐tank reactor (CSTR). The effect of the second B group reactivity, represented by the reactivity ratio r is investigated. The degree of branching (DB) at large degree of polymerization (P ) limit, DB_{P →∞} does not change with the mean residence time . The value of DB_{P →∞} becomes larger by increasing r and is larger than the corresponding batch polymerization. The weight fraction distribution at high molecular weight tail follows a power law , and a simple formula to predict the power exponent α is proposed. The relationship between the radius of gyration 〈s ²〉₀ and P does not change with , and large polymers obtained in a CSTR are much more compact than those formed in batch polymerization. CSTR is advantageous to synthesize compact HB polymers, especially with a smaller r‐value.     

Explicitly correlated variational estimates of the energy levels of negative hydrogen ion under spatial confinement

Comprehensive investigations on the structural modifications of negative hydrogen ion within an impenetrable spherical domain has been performed in the framework of Ritz variational method. Electron correlation plays a major role in the formation of H^– ion. The Hylleraas‐type basis set expansion of wave function considered here incorporates the effect of electron correlation in an explicit manner. Energy values of and 1sn states of H^– ion within confined domain have been calculated. Although the singly excited states do not exist for a “free” H^– ion, well converged energy values of such states have been found within a wide range of confinement radius. The thermodynamic pressure felt by the ion inside the sphere is also estimated. The general trend shows successive destabilization of the excited energy levels with increase of pressure. The contribution of angular correlation in the energy values have been estimated. Evolution of and energy levels of H^– ion as quasi‐bound states are being reported.     

Highly Ordered Structure Formation in RAFT‐Synthesized PtBOS‐b‐P4VP Diblock Copolymers

Linear poly(4‐tert‐butoxystyrene)‐b‐poly(4‐vinylpyridine) (PtBOS‐b‐P4VP) diblock copolymers are synthesized using reversible addition–fragmentation chain transfer polymerization. The self‐assembly of four different PtBOS‐b‐P4VP diblock copolymers is studied using small‐angle X‐ray scattering and transmission electron microscopy and a number of interesting observations are made. A tBOS₆₂‐b‐4VP₂₈ diblock copolymer with a weight fraction P4VP of 0.21 shows a disordered morphology of P4VP spheres with liquid‐like short‐range order despite an estimated value of of the order of 50. Increasing the length of the 4VP block to tBOS₆₂‐b‐4VP₁₉₉ results in a diblock copolymer with a weight fraction P4VP of 0.66. It forms a remarkably well‐ordered lamellar structure. Likewise, a tBOS₁₄₆‐b‐4VP₁₂₀ diblock copolymer with a weight fraction P4VP of 0.33 forms an extremely well‐ordered hexagonal structure of P4VP cylinders. Increasing the P4VP block of this block copolymer to tBOS₁₄₆‐b‐4VP₁₉₀ with a weight fraction P4VP of 0.44 results in a bicontinuous gyroid morphology despite the estimated strong segregation of . These results are discussed in terms of the architectural dissimilarity of the two monomers, characterized by the presence of the large side group of PtBOS, and the previously reported value of the interaction parameter, , for this polymer pair.

     

Hyperbranched Polymers Formed through Irreversible Step Polymerization of AB2‐Type Monomer in a Continuous Flow Stirred‐Tank Reactor (CSTR)

Hyperbranched polymers formed through step polymerization of AB₂‐type monomer with equal reactivity for both B groups in a continuous flow stirred‐tank reactor (CSTR) are investigated theoretically. The weight fraction distribution at high molecular weight tail follows a power law, W (P ) ∝ P ^−1/ξ for ξ ≤ 0.5 with , where is the mean residence time. The degree of branching (DB) at the large degree of polymerization (P ) limit is DB _{P →∞} = 0.6 irrespective of the ξ‐value, which is larger than the case for the corresponding batch polymerization that gives DB _{P →∞} = 0.5. The relationship between the radius of gyration 〈s ²〉₀ and P shows that the hyperbranched polymers formed in a CSTR are very compact, and the 〈s ²〉₀‐values for large polymers are even smaller than the smallest possible case for a batch reactor with DB _{P →∞} = 1. For large polymers, the power law 〈s ²〉₀∝P ^1/3 holds, which is 〈s ²〉₀∝P ^1/2 for batch polymerization.

     

Spin–orbit effects on magnetically induced current densities in the () clusters

This study reports the spin–orbit effects on the aromaticity of the , , , , , and anionic clusters via the magnetically induced current‐density method. All‐electron density functional theory (DFT) calculations were carried out using the four‐component Dirac‐Coulomb (DC) hamiltonian, including scalar and spin–orbit relativistic effects. The magnetic index of aromaticity was calculated by numerical integration over the current flow between two atoms in the pentagonal ring. These values were compared to the spin‐free values (spin–orbit coupling switched off), in order to assess the spin–orbit effect on aromaticity. It was found that in the heavy anions, and , there is a significant influence of the spin–orbit coupling. © 2018 Wiley Periodicals, Inc.     

Individually Addressable Thermo‐ and Redox‐Responsive Block Copolymers by Combining Anionic Polymerization and RAFT Protocols

A novel diblock copolymer consisting of poly(vinylferrocene) (PVFc) and poly(N,N‐diethylacrylamide) (PDEA) is synthesized via a combination of anionic and RAFT polymerization. The use of a novel route to hydroxyl‐end‐functionalized metallopolymers in anionic polymerization and subsequent esterification with a RAFT agent leads to a PVFc macro‐CTA ( = 3800 g mol⁻¹; Đ = 1.17). RAFT polymerization with DEA affords block copolymers as evidenced by ¹H NMR spectroscopy as well as size exclusion chromatography (6400 ≤ ≤ 33700 g mol⁻¹; 1.31 ≤ Đ 1.28). Self‐assembly of the amphiphilic block copolymers in aqueous solution leads to micelles as shown via TEM. Importantly, the distinct thermo‐responsive and redox‐responsive character of the blocks is probed via dynamic light scattering and found to be individually and repeatedly addressable.

     

The Trifluoromethyl Anion: Evidence for [K(crypt‐222)]+

[K(crypt‐222)]⁺ ( 1 ) and [K(crypt‐222)]⁺ ( 3 ) are isostructural, displaying nearly identical unit cell parameters. The two structures are similar to the extent that the previously reported [K(crypt‐222)]⁺ model can be refined against the new data for [K(crypt‐222)]⁺ , with extra electron density being observed from the fourth fluorine atom of the . In agreement with experimental observations, theoretical calculations suggest that deprotonated [K(crypt‐222)]⁺ is highly unstable even at as low as 195 K. The previously considered 1:1 CHF ₃ clathrate of deprotonated [K(crypt‐222)]⁺ (crystallographically indistinguishable from 1 ) is ruled out on the basis of all available data.     

Ritz variational method for the high‐lying nonautoionizing doubly excited 1,3Fe states of two‐electron atoms

Energy eigenvalues of nonautoionizing doubly excited states originating from 2pnf ( ) configuration of two‐electron atoms have been calculated by expanding the basis set in explicitly correlated Hylleraas coordinates under the framework of Ritz variational method. A detailed discussion on the evaluation of correlated basis integrals is given. The energy eigenvalues of a number of these doubly excited states are being reported for the first time especially for the high lying states. The effective quantum numbers ( ) for the states mentioned above have been calculated by using the theory of quantum defect.     

Highly Active ppm Level Organic Copper Catalyzed Photo‐Induced ICAR ATRP of Methyl Methacrylate

A novel photo‐induced homogeneous atom transfer radical polymerization (ATRP) system is constructed using an organic copper salt (Cu(SC(S)N(C₂H₅)₂)₂) as a photo‐induced catalyst at 30 °C. Herein, N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) is used as a ligand, ethyl 2‐bromophenylacetate (EBPA) as an ATRP initiator, and (2,4,6‐trimethylbenzoyl) diphenylphosphine oxide (TPO) as a photo‐induced radical initiator to establish an ICAR (initiators for continuous activator regeneration) ATRP using methyl methacrylate (MMA) as a modal monomer. The effect of the concentration of the organic copper on the polymerization is investigated in detail. It is found that well‐controlled polymerization can be obtained even with the amount of (Cu(SC(S)N(C₂H₅)₂)₂ decreasing to a 1.56 ppm level, with the molecular weight of the resultant polymers increasing linearly with monomer conversion while maintaining a narrow molecular weight distribution (/ < 1.3).

     

Electron‐density delocalization in many‐electron atoms confined by penetrable walls: A Hartree–Fock study

The electronic structure of several many‐electron atoms, confined within a penetrable spherical box, was studied using the Hartree–Fock (HF) method, coupling the Roothaan's approach with a new basis set to solve the corresponding one‐electron equations. The resulting HF wave‐function was employed to evaluate the Shannon entropy, , in configuration space. Confinements imposed by impenetrable walls induce decrements on when the confinement radius, R_c, is reduced and the electron‐density is localized. For confinements commanded by penetrable walls, exhibits an entirely different behavior, because when an atom starts to be confined, delivers values less than those observed for the free system, in the same way that the results presented by impenetrable walls. However, from a confinement radius, shows increments, and precisely in these regions, the spatial restrictions spread to the electron density. Thus, from results presented in this work, the Shannon entropy can be used as a tool to measure the electron density delocalization for many‐electron atoms, as the hydrogen atom confined in similar conditions.     

Ugi Reactions with CO2: Access to Functionalized Polyurethanes,Polycarbonates, Polyamides,and Polyhydantoins

A novel strategy for the incorporation of carbon dioxide into polymers is introduced. For this purpose, the Ugi five‐component condensation (Ugi‐5CC) of an alcohol, CO₂, an amine, an aldehyde, and an isocyanide is used to obtain step‐growth monomers. Polymerization via thiol‐ene reaction or polycondensation with diphenyl carbonate gives diversely substituted polyurethanes or alternating polyurethane‐polycarbonates, respectively. Furthermore, the application of 1,12‐diaminododecane and 1,6‐diisocyanohexane as bifunctional components in the Ugi‐5CC directly results in the corresponding polyamide bearing methyl carbamate side chains ( = 19 850 g mol⁻¹). The latter polymer is further converted into the corresponding polyhydantoin in a highly straightforward fashion.

     

Nuclear quantum effects induce metallization of dense solid molecular hydrogen

We present an accurate computational study of the electronic structure and lattice dynamics of solid molecular hydrogen at high pressure. The band‐gap energies of the , Pc, and structures at pressures of 250, 300, and 350 GPa are calculated using the diffusion quantum Monte Carlo (DMC) method. The atomic configurations are obtained from ab initio path‐integral molecular dynamics (PIMD) simulations at 300 K and 300 GPa to investigate the impact of zero‐point energy and temperature‐induced motion of the protons including anharmonic effects. We find that finite temperature and nuclear quantum effects reduce the band‐gaps substantially, leading to metallization of the and Pc phases via band overlap; the effect on the band‐gap of the structure is less pronounced. Our combined DMC‐PIMD simulations predict that there are no excitonic or quasiparticle energy gaps for the and Pc phases at 300 GPa and 300 K. Our results also indicate a strong correlation between the band‐gap energy and vibron modes. This strong coupling induces a band‐gap reduction of more than 2.46 eV in high‐pressure solid molecular hydrogen. Comparing our DMC‐PIMD with experimental results available, we conclude that none of the structures proposed is a good candidate for phases III and IV of solid hydrogen. © 2017 Wiley Periodicals, Inc.     

General build up of basis and matrix in the diagonalization approach. Determination of Kramers configuration state functions

Algorithms to build the basis and matrix representation to obtain the Kramers configuration space functions (KCSFs) via diagonalization will be formally generalized to an arbitrary number of unpaired (open shell) fermions. Effective build up of the matrix representation will be outlined (including threading and graphical processing unit parallelism) to subsequently obtain the KCSFs via calling external/numerical library routines for diagonalization. The effective build up of the matrix representation relays on a binary tree search algorithm to allow evaluation the action on a given basis vector. The binary tree search avoids the treatment of zero matrix elements which leads to an exponential acceleration. The implementation ( basis creation, matrix representation, and matrix diagonalization) will be done in an all in core and all at once manner, hence the available core memory sets the physical limits in practical applications. Memory limitations, sparsity of the matrix, general case of n fermions in m spinors, and the application of KCSFs will be put into further perspective.     

Correlating Boron–Hydrogen Stretching Frequencies with Boron–Hydrogen Bond Lengths in Closoboranes: An Approach Using DFT Calculations

Using harmonic and anharmonic DFT calculations, we have established a general correlation between B–H stretching frequencies and B–H bond lengths valid for the closoboranes (x = 6 – 12), substituted closoboranes B₁₂H_{12 –} (with X = F, Cl, Br and n = 1 – 3 and 9 – 12) and the carboranes and , suggesting that this correlation is also applicable to other similar species. It appears that the average B–H stretching frequency observed around 2500 cm⁻¹ shift by about −100 cm⁻¹ if the average B–H bond length increases by 1 pm. In contrast to , the B–H bond in closoboranes is practically covalent and the correlation evidenced between its stretching frequency and its length proves to be similar to the one observed for the C–H bond.