Sorption and transport of carbon dioxide in a polyimide from 3,3′4,4′-biphenyltetracarboxylic dianhydride and 4,4′-diaminodiphenyl sulfone

CO₂ sorption and transport were investigated for the polyimide prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-diaminodiphenyl sulfone (DDS). The morphology of films did not change on annealing above the glass transition temperature and remained amorphous unlike the polyimide prepared from BPDA and 4,4′-oxydianilline (ODA). This seems to be due to the strong hindrance to rotation of the sulfonyl linkage. Sorption and transport data were analyzed according to the dual-mode model. Solubility, diffusion, and permeability coefficients at 20 atm and 80°C for BPDA-DDS polyimide were substantially equal between as-cast and annealed films and were 1.7, 2.2, and 3.7 times greater, respectively, than for the as-cast films of the BPDA-ODA polyimide. The higher solubility was due to larger values of the Henry's law solubility constant k_D, Langmuir capacity constant C, and the Langmuir affinity constant b. The sorption and transport properties were compared with those for amorphous glassy aromatic polymers including other polyimides. The relation of k, C, b, and the diffusion coefficients in the Henry's law population and the Langmuir population (D_D and D_H) with other properties of the polymers were discussed. Values D_D and D_H for BPDA-DDS polyimide were much larger than expected from the estimated free-volume fraction.     

Dynamic x-ray diffraction studies of high-density polyethylene

Dynamic x-ray diffraction is conducted to explore the structural origin of the α and β mechanical dispersions of a melt-crystallized high-density polyethylene. It is shown that the real component of the strain orientation coefficient for the crystal c axis C decreases with increasing frequency at a rate which decreases with decreasing temperature. Values of C for the c axis are positive, C for the a axis negative, and C for the b axis close to zero, suggesting that the predominant relaxation process is crystal rotation about the b axis. The activation energy found from Arrhenius plots of C corresponds to that of the α₁ mechanical dispersion. The dynamic birefringence in this region is dominated by the contribution from crystal orientation changes. At low temperatures, the imaginary component KC of the strain-optical coefficient of the crystal phase approaches zero, while KC of the amorphous phase exhibits a somewhat broad dispersion peak corresponding to the β birefringence dispersion. This suggests that the principal contribution to the β birefringence dispersion arises from the amorphous phase, probably owing to the amorphous orientation process. Contrary to the case of low-density polyethylene, the dynamic crystal lattice deformation and compliance functions reveal distinct frequency dispersions corresponding to the α₁ and α₂ mechanical processes. The α₁ lattice dispersion is thought to be associated with the α₁ crystal orientation dispersion, while the α₂ lattice dispersion is believed to be the inherent one arising from the onset of intracrystalline chain motions.     

Disproportionation-to-combination ratios for cyclohexyl-h11 and -d11 radicals in the gas phase as determined by the radiolysis of water vapor–cyclohexane mixtures

In the radiolysis of water vapor containing small concentrations of cyclohexane, the principal products which account for about 98% of all end products are found to be hydrogen, cyclohexene, and bicyclohexyl. Cyclohexene and bicyclohexyl yields were determined over a range of temperatures (70–200°C), total pressures (50–2400 torr), and total doses (0.15–2.0 Mrad). The disproportionation–combination ratio k/k for c-C₆H₁₁ radicals could be determined as 0.56 ± 0.01 from the ratio of cyclohexene to bicyclohexyl yield. By using c-C₆D₁₂, the ratio k/k for c-C₆D₁₁ radicals is found to be 0.38 ± 0.01. Comparison of the reactivity pattern of C₆H₁₁ and C₆D₁₁ radicals leads to (k)/(k)/(k/k) = 1.47 ± 0.02. The corresponding values for the reactions of c-C₆H₁₁ with c-C₆D₁₁ were also determined.     

Carbodications. I. The structures and energies of C4H isomers

At high levels of ab initio theory (6-31G*//4-31G), the most stable C₄H isomer is indicated to be the nonplanar cyclobutadiene dication ( 1a ); the planar form, 1b , is indicated to be 7.5 kcal/mol less stable. The second most stable C₄H isomer, the methylenecyclopropene dication, is indicated to prefer the perpendicular ( 2a ) over the planar ( 2b ) arrangement by 7 kcal/mol. The “anti van't Hoff” cyclo-(HB)₂C?CH₂ system ( 4 ), isoelectronic with 2 , also prefers the perpendicular conformation ( 4a ), and retains the C?C double bond. The linear butatriene dication ( 3 ) is the least stable C₄H species investigated. The perpendicular (D_2d) arrangement ( 3a ), permitting double allyl cationlike conjugation, is preferred over the planar D_2h form ( 3b ) by 26 kcal/mol. The heat of formation of the most stable form of C₄H, 1a , is estimated to be 623–640 kcal/mol. This species should be thermodynamically stable toward dissociation into smaller charged fragments.     

Endohedral fullerene-noble gas clusters formed with high-energy bimolecular reactions of C (x = 60, 70; n = 1, 2, 3)

Results are reported for high-energy beam experiments which establish the formation of endohedral carbon cluster-noble gas compounds by bimolecular reactions of C (x = 60, 70; n = 1, 2, 3) with He and C with Ne. The ions were accelerated up to 8 ke V in a four-sector mass spectrometer and allowed to collide with the noble gas in a collision chamber at room temperatur. Product ions were monitored with a B/E = constant linked scan. Within the sensivity of the experiments, no carbon cluster-gas compounds were observed in the reactions of C with H₂, D₂, O₂, Ar, and SF₆, or of C with O₂. The observed fall in the cross-section for carbon cluster-noble gas compounds with increasing size of the noble gas, the observation of unimolecular loss of C₂ from mass-selected C_xHe⁺ ions, and the elimination of carbon fragments instead of He observed in the formation of the collision-induced C_xHeⁿ⁺ product ions are taken as evidence for endohedral compound formation. Results of ab initio molecular-orbital calculations for the perpendicular penetration of the plane of ionized benzene with He, Ne, and Ar indicate that sufficient kinetic energy should be available in the collisions with C to penetrate the C cage at the collision energies of the experiments.     

Ammonia chemical ionization mass spectrometry of alcohols: Structural,stereochemical, molecular-size and temperature effects

Ammonia chemical ionization (CI) mass spectra of various open-chain, cyclic and unsaturated C₅- to C₁₀-alcohols were obtained at source temperatures ranging from 60° to 250°C. The reactivity of the ammonia adduct ion MNH and its fragmentation channels are characteristic for substrate structure. Although strongly temperature-dependent, the spectra give nevertheless information on the OH-group environment as well as on the C-skeleton at any source temperature. Primary, secondary and tertiary alcohols as well as allylic and simple olefinic alcohols can be distinguished by their spectra, which show ammonium adduct ions [MNH₄]⁺, adduct dehydrogenation ions [MNH₄-H₂], ammonium substitution ions [MNH₄-H₂O]⁺ and [M-OH]⁺-ions as the main characteristic peaks. Moreover, konfigurational assignments of stereoisomeric alcohols are possible for larger substrate-size and source-temperature ranges than with isobutane CI mass spectrometry. Homologous M NH-ions show molecular-size control of fragmentation and linear MNH-ions are less stable than branched isomers due to incomplete energy randomization.     

Aromaticity of ionic structures: Investigation and application of NICS value and 4n + 2 rule

At DFT/B3LYP/6‐31G** theoretical level, C₆H and C (n = 0, ?2, and +2), C₆H and C (n = 0, ±2, ±4, and ±6), C₆H (n = 0–6), as well as C₆H₆‐A and C₆‐A (A = Be, B, N, O, Mg, Al, Si, S, and Fe) structures were investigated. Comparing NICS values of C₆H and C (n = 0, ?2, and +2), we discovered that C₆H, C₆H were antiaromatic, and C₆H₆, C₆, C, C had aromaticity with negative NICS values. According to research of C₆H and C (n = 0, ±2, ±4, ±6), C₆H (n = 0–6), we sustained that their σ and π orbit were different and the locations of electrons were difficult to confirm in ionic structures. Thus, neither 4n + 2 rule nor NICS values can precisely estimate the aromaticity of ionic structures. Besides, through WBI (NBO) research of C₆H₆‐A and C₆‐A (A = Be, B, N, O, Mg, Al, Si, S, and Fe) structures, we found that C₆H₆ was easy to accept electrons, contrarily, C₆ was prone to bestowing electrons. Moreover, C₆H₆ took the symmetrical carbon atoms form feeble interaction or bond, and C₆ used all carbon atoms to impact with other atom. C₆H₆ generated two contrapuntal single bonds with oxygen, sulfur, and nitrogen atoms, whereas C₆ molecule formed double bond with oxygen and nitrogen atoms, two conjoint single bonds with sulfur atom. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Conformation and dynamics of a self-avoiding sheet: Bond-fluctuation computer simulation

The conformation and dynamics of a self-avoiding sheet are analyzed by the bond-fluctuating Monte Carlo method. The mean-square displacement of the center of mass of the sheet and that of its center node (R) show asymptotic diffusive behavior. The segmental dynamics in short and long time regimes can be deduced from the motion of the center node described by the power law with μ ≃ 0.13 and ν ≃ ½, where C₁ and C₂ are fitting constants and t is the time. The radius of gyration, R_g, scales with the linear size, L_s, of the sheet as R_g ≃ N^γ with γ ≃ ½ and N = L, and this is consistent with the conformational analysis of open tethered membranes with excluded-volume constraints. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1041–1046, 2005     

Dipole,quadrupole, octupole,and dipole–octupole polarizabilities at real and imaginary frequencies for H,HE, and H2 and the dispersion-energy coefficients for interactions between them

We have calculated certain dynamic polarizabilities (for both real and imaginary frequencies) for H, He, and H₂ and the dispersion-energy coefficients for long-range interactions between them. We have done so in a sum-over-states formalism with explicitly electron-correlated wave functions to describe the states. To be precise, we have determined the dipole (α₁), quadrupole (α₂), and octupole (α₃) polarizabilities of H and He for real frequencies (ω) in a range between zero and the first electronic-transition frequency and for imaginary frequencies (iω) on a 32-point Gauss-Legendre grid running from zero to ?ω = 20 E_h, and for H₂, we have found the dipole (α), quadrupole (C), and dipole–octupole (E) polarizability tensors for the same real and imaginary frequencies. The dispersion-energy coefficients, obtained by combining the sum-over-states for-malism for the polarizabilities with analytic integration over ω, gave values of C₆, C₈, and C₁₀ for the atom–atom systems; C, C, C, C, and C for the atom–diatom systems; and C₆, C and C for the H₂? H₂ system. Nearly all the results are considered to be more reliable than those hitherto published and some have been obtained for the first time, e.g., C(iω), E(ω), and E(iω) for H₂ and C, C, and C for the H? H₂ system. © 1993 John Wiley & Sons, Inc.     

Theoretical predictions of the structures and electronic spectra of C60NH with comparisons with the isoelectronic molecules C60O and C60CH2

Intermediate neglect of differential overlap (INDO ) calculations were used to study two structures of C₆₀NH: one of C_2ν, geometry with a bridging NH across the bond between two fused six-membered rings in C₆₀ and the other of C_s geometry with a bridging NH across the bond between a five- and a six-membered ring. We calculated the most stable isomer of C₆₀NH to be of C_2ν, symmetry. It was found that the C_2ν isomer has a protonated aziridine structure with a bridging C? C bond length of 0.1520 nm. The electronic spectra of both isomers of C₆₀NH were calculated. Comparisons were made with the isoelectronic molecules C₆₀O and C₆₀CH₂, cases in which the calculated electronic spectra for the most stable isomers C₆₀O (C_2ν) and C₆₀CH₂ (C_2ν) are in good agreement with recent experimental results. © 1995 John Wiley & Sons, Inc.     

Structure and dissociation energy of weakly bound H (n = 5−8) complexes

The geometrical parameters, vibrational frequencies, and dissociation energies for H (n = 5–8) clusters have been investigated using high level ab initio quantum mechanical techniques with large basis sets. The highest level of theory employed in this study is TZ2P CCSD(T). The C₁ structure of H is predicted to be a global minimum, while the C_s structure of H is calculated to be a transition state. Harmonic vibrational frequencies are also determined at the DZP and TZ2P CCSD levels of theory. The dissociation energies, D_e, for H (n = 5–8) have been predicted using energy differences at each optimized geometry, and zero‐point vibrational energies (ZPVEs) are considered to compare with experimental values. The dissociation energies (D_o) have been predicted to be 1.69, 1.65, 1.65, and 1.46 kcal · mol for H, H, H (C₁ symmetry) and H, respectively, at the TZ2P CCSD(T) level of theory. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Critical behavior of brittle‐ductile transition of polymers

We report that the brittle‐ductile transition of polymers induced by temperature exhibits critical behavior. When t close to 0, the critical surface to surface interparticle distance (ID_c) follows the scaling law: ID_c ∝ t^?v, where t = 1 ? T/T (T and T are the test temperature and brittle‐ductile transition temperature of matrix polymer, respectively) and v = 2/D. It is clear that the scaling exponent v only depends on dimension (D). For 2, 3, and 4 dimension, v = 1, 2/3, and 1/2 respectively. The result indicates that the ID_c follows the same scaling law as that of the correlation length (ξ), when t approach to zero. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 766–769, 2008     

Symmetry breaking and its influence on the correlation energy for CF and CF ions

We have studied symmetry breaking in three open-shell systems: CF (D_2d and C_2v) and CF (D_3h) molecular ions. These different Hartree–Fock solutions are employed as starting points to calculate the correlation energy of these ions with perturbative, configuration interaction, and density functional methods. When symmetry-broken or symmetry-adapted wave functions are used, the correlation energy obtained with each method changes the order of stability of CF for a determined symmetry. Density functional methods produce higher correlation energies although they do not alter the order of stability of Hartree–Fock calculations. The behavior of correlation energy with different methods and the characteristics of the symmetry of wave functions are compared. A study of appearance energies for three different channels of the decomposition reaction of ionized carbon tetrafluoride are considered by using different methods with symmetry-broken or symmetry-adapted wave functions to calculate correlation energies. © 1994 John Wiley & Sons, Inc.     

Determination of thermodynamic properties of macroporous glycidyl methacrylate‐based copolymers by inverse gas chromatography

Macroporous crosslinked poly(glycidyl methacrylate‐co‐ethylene glycol dimethacrylate) (PGME) was synthesized by suspension copolymerization and modified by ring‐opening reaction of the pendant epoxy groups with ethylene diamine (EDA). Inverse gas chromatography (IGC) at infinite dilution was applied to determine the thermodynamic interactions of PGME and modified copolymer, PGME‐en. The specific surface areas of the initial and modified copolymer samples were determined by the BET method, from low‐temperature nitrogen adsorption isotherms. The specific retention volumes, V, of 10 organic compounds of different chemical nature and polarity (nonpolar, donor, or acceptor) were determined in the temperature range 333–413 K. The weight fraction activity coefficients of test sorbates, , and Flory–Huggins interaction parameters, , were calculated and discussed in terms of interactions of sorbates with PGME and PGME‐en. Also, the partial molar free energy, , partial molar heat of mixing, , sorption molar free energy, ΔG, sorption enthalpy ΔH, and sorption entropy, ΔS, were calculated. Glass transitions in PGME and PGME‐en, determined from IGC data, were observed in the temperature range 373–393 K and 363–373 K, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2524–2533, 2005     

Poly(ionic liquid)s as new materials for CO2 absorption

A series of imidazolium‐based ionic liquid monomers and their corresponding polymers (poly(ionic liquid)s) were synthesized, and their CO₂ sorption was studied. The poly(ionic liquid)s had enhanced CO₂ sorption capacities and fast sorption/desorption rates compared with room temperature ionic liquids. The effects of the chemical structures, including the types of anion, cation, and backbone of the poly(ionic liquid)s on their CO₂ sorption have been discussed. In contrast to room temperature ionic liquids, the polymer with PF anions had the highest CO₂‐sorption capacity, while those with BF or Tf₂N^? anions had the same capacities. The CO₂ sorption and desorption of the polymers were fast and reversible, and the sorption was selective over H₂, N_2, and O₂. The measured Henry's constants of P[VBBI][BF₄] and P[MABI][BF₄] were 26.0 bar and 37.7 bar, which were lower than those of similar room temperature ionic liquids. The preliminary study of the mechanism indicated that the CO₂ sorption of the polymer particles was more absorption (the bulk) but less adsorption (the surface). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5477–5489, 2005     

Structures of three crystal modifications of poly(3,3-dimethyloxacyclobutane)

Three crystal modifications of poly(3,3-dimethyloxacyclobutane) [? CH₂C(CH₃)₂CH₂O? ]_n were found and their structures were analyzed by x-ray diffraction. Modification I is obtained only under tension and disappears on relaxing the tension. From the fiber period of 4.83 Å, the molecular structure seems to be planar zigzag. In modification II, two chains in T₃GT₃? conformation pass through a monoclinic cell with parameters a = 8.93 Å, b = 7.48 Å, c (fiber axis) = 8.35 Å, β = 97.9°, and the space group P2₁/c-C. In modification III, two (T₂G₂)₂ chains pass through an orthorhombic cell with parameters a = 15.60 Å, b = 5.74 Å, c (fiber axis) = 6.51 Å, and the space group, C222₁–D. Molecular conformations of the three crystal modifications correspond to those of polyoxacyclobutane.     

The structure and stability of the acetylene dication

The dication C₂H has been investigated by ab initio molecular orbital theory. It is found to have a linear (D_∞h), structure with a triplet (³σ^?_g) ground state. Deprotonation to C₂H⁺ is exothermic by 9.8 kcal/mol, but this process is hindered by a large barrier of 65 kcal/mol.     

Dipole,quadrupole, octupole,and dipole–dipole–quandrupole polarizabilities and second hyperpolarizabilities at real and imaginary frequencies for helium in the 23S state: Dispersion-energy coefficients for interactions between He(23S) and H(12S), He(11S), He(23S), or H2(X1∑g+)

We have determined the dynamic dipole (α₁), quadrupole (α₂), octupole (α₃), and dipole–dipole–quadrupole (B) polarizabilities and the second hyperpolarizability tensor (γ) for the helium atom in its lowest triplet state (2³S). We have done so for both real and imaginary frequencies: in the former case, for a range of frequencies (ω) between zero and the first electronic-transition frequency, and in the latter case for a 32-point Gauss–Legendre grid running from zero to ?ω = 20 E_h. We have also determined the dispersion-energy coefficients C₆, C₈, and C₁₀ for the systems H(1²S)? He(2³S), He(1¹S)? He(2³S), and He(2³S)? He(2³S) and the C, C, C, C, and C coefficients for the interaction He(2³S)? H₂(X¹∑). Our values of the higher-order multipolar polarizabilities and of γ for the 2³S state of helium are, we believe, the first to be published. © 1993 John Wiley & Sons, Inc.     

Novel thermoplastic elastomers. III. Synthesis,characterization, and properties of star‐block copolymers of poly(indene‐b‐isobutylene) arms emanating from cyclosiloxane cores

Novel thermoplastic elastomers (TPEs) consisting of poly(isobutylene‐b‐indene) (PIB‐b‐PInd) arms radiating from hexamethylcyclohexasiloxane (D) cores were prepared, characterized, and their properties investigated. The syntheses of these star‐blocks involved the linking by hydrosilation of PInd‐b‐PIB CH₂ CHCH₂ prearms to D. The prearms were obtained by initiating the living polymerization of Ind by the cumyl chloride (CumCl)/TiCl₄ or cumyl methoxide (CumOMe)/TiCl₄ systems, continuing by the sequential block copolymerization of IB, and concluding the synthesis by end quenching with allyltrimethylsilane (ATMS). Dedicated experiments were carried out to develop conditions for the various synthesis steps. Select mechanical, thermal, and rheological properties of TPE star‐blocks having 5–18 PInd‐b‐PIB arms have been investigated. Because of the high T_g of the glassy PInd segment (T_g,PInd = 170–220°C), these TPEs maintained their strength at higher temperatures than those of similar polystyrene‐based star blocks. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 279–290, 2000     

The decomposition kinetics of chemically activated methyl-d1-methylsilane-d2 and ethylsilane-d3

The decomposition kinetics of chemically activated methyl-d₁-methylsilane-d₂ (DMS-d) and ethylsilane-d₃ (ES-d) from the Si-D and C-H insertion reactions of CH₂ (¹A₁) with methylsilane-d₃ have been studied. The total rate constants for decomposition of chemically activated DMS-d₃ and ES-d₃ have been measured. The individual rate constants for molecular elimination of CH₃D, CH₂D₂, and D₂ from DMS-d and for molecular elimination of CH₃CH₂D and D₂ from ES-d have been measured. All of the above rate constants exhibit the expected kinetic isotope effect when compared to those found previously in the undeuterated system. RRKM theory calculations of the rate constants for the expected C-Si and Si-D bond rupture processes, based on energetics and activated comple× models deduced previously for the undeuterated system, were carried out. In the case of DMS-d the RRKM theory calculations of rate constants for the bond rupture processes combined with experimental rate constants for the molecular elimination processes gave a total rate constant for decomposition in agreement with the measured value. The results of a high-pressure study of the CH₃D/CH₂D₂ ratio from chemically activated DMS-d₃ decomposition were consistent with complete randomization of internal energy up to a pressure of 4 atmospheres (lifetime of ～1.7 × 10^×11 sec). This is not an unexpected result in light of earlier work.