Ab initio Study on Ionization Energies of 1-Methyl-hypoxanthine

Six low-lying tautomers of 1-methyl-hypoxanthine have been studied at the B3LYP/aug-cc-pVDZ level. Two tautomers N7H and N9H with the comparable energies are far more stable than the others. The vertical ionization energies of the tautomers calculated with ab initio electron propagator theory in the P3/aug-cc-pVDZ approximation are in agreement with the experimental data from photoelectron spectroscopy. According to the calculated relative energies and the comparison between the simulated and the experimental photoelectron spectra, it demonstrates that there are at least two tautomers of 1-methyl-hypoxanthine in the gas-phase experiments.     

Relative energy of organic compounds II. Halides, nitrogen, and sulfur compounds

The energies of the following types of compounds are characterized by their calculated relative enthalpies: alkyl, alkenyl, and aryl halides; carboxylic acid halides; carbonyl halides; amines; carboxylic acid amides; hydrazine derivatives; nitriles; heteroaromatic compounds; nitro-compounds; organic nitrites and nitrates; organic sulfides; thiols; disulfides; sulfoxides; sulfones; organic sulfites and sulfates; and selected inorganic compounds. Stabilization energy of pyrrol and thiophene has been estimated.     

Energetic analysis of 24 C20 isomers

Twenty-four individual geometric structures of the 20-carbon system are investigated using hybrid Hartree–Fock/density functional theory (DFT-B3LYP) in combination with the 6-31G and 6-311G* basis sets. These computations are carried out in order to evaluate the relative energies of the various C₂₀ isomers utilizing both geometry optimization and single-point energy calculations. The relative energies of the three most widely studied C₂₀ isomers (ring, bowl, and cage) are compared to the energies of other cyclic, bowl-like, and miscellaneous isomers. Although the ring and the bowl isomers are predicted to be the two most stable species, we have identified three to four additional cyclic structures that are predicted to be energetically competitive with the fullerene structure.     

Evaluation of the melt stabilization performance of hydroxytyrosol (3,4-dihydroxy-phenylethanol) in polypropylene

The use of hydroxytyrosol (3,4-dihydroxy-phenylethanol) as a potential alternative to synthetic compounds in the melt stabilization of polyolefins is considered. Hydroxytyrosol was found to play a role in enhancing the oxidative stability of olive oil, and a similar reduction in polyolefins’ thermo-oxidative degradation during processing is expectable. Rheological tests (melt flow index and viscosity vs. shear rate) showed the good antioxidant performance of hydroxytyrosol during polypropylene processing as was also demonstrated by the increase in apparent activation energies and oxidation induction parameters after addition to polypropylene (0.1 wt%). Results were compared to those obtained for a commercial synthetic phenolic antioxidant and for a natural compound widely used in polymer stabilization (α-tocopherol). The main conclusion of this work is the good performance of hydroxytyrosol in polypropylene stabilization during processing and consequently the possibility of its use in formulations with improved resistance to oxidative degradation.     

磷酸铝分子筛骨架结构及其稳定性的模拟计算

采用晶格能极小化技术模拟计算了块磷铝矿和１２种磷酸铝分子筛的骨架晶格，包括ＡｌＰＯ４－３１，ＡｌＰＯ４－１１，ＡｌＰＯ４－８，ＡｌＰＯ４－５，ＡｌＰＯ４－２０，ＡｌＰＯ４－１６，ＡｌＰＯ４－１７，ＡｌＰＯ４－３５，ＡｌＰＯ４－５２，ＡｌＰＯ４－１８和ＶＰＩ－５，预测了它们的几何构型和晶格能，讨论了计算晶格能和骨架结构间的关系，结果表明，随着骨架密度的增大，晶格能呈降低趋势，骨架的相对稳定性增强。     

Basis set effects on relative energies and HOMO–LUMO energy gaps of fullerene C36

Fifteen C₃₆ isomers were examined to determine the influence that the quality of basis sets has on the geometry parameters, the relative stability and HOMO–LUMO energy gaps of fullerene isomers calculated with density functional theory. It is worthwhile to note that the geometry parameters of all C₃₆ isomers are insensitive to basis sets. On the other hand, one set of d-type polarization functions plays an important role in evaluating relative stability and HOMO–LUMO energy gaps, while diffuse functions are not effective. To obtain reliable energies, at least a double-zeta plus polarization basis set is required, and a triple-zeta plus polarization basis set is suggested to lead to accurate energies at a reasonable computational cost.     

结构可控的功能化聚烯烃设计与合成

聚烯烃的功能化是聚烯烃研究领域的热点,设计和合成结构可控的功能化聚烯烃 是目前聚烯烃功能化的主要研究方向.本文首先对功能化聚烯烃进行结构上的归纳分类,然后针对不同结构的功能化聚烯烃,分别综述了其设计与合成方面近年来的研究进展,并展望了聚烯烃功能化研究的前景.     

Electron paramagnetic resonance of ultraviolet-irradiated polyolefins

If films of polyolefins are ultraviolet-irradiated at liquid nitrogen temperature, alkyl radicals which can be examined by EPR are produced. No EPR spectra are observed from polyolefins irradiated at room temperature in air. Ultraviolet irradiation of polyolefins containing small alkyl side chains generally produces radicals corresponding to the pendant group or methyl radicals if the side chains contain a methyl branch. For some polymers the radical species could not be identified with certainty. Stabilization studies indicate that an optimum concentration of ultraviolet stabilizer is necessary for maximum stabilization of polyolefins. Preliminary results of EPR studies of the ultraviolet irradiation of various polyolefins are given, and some possible radical species are discussed.     

聚烯烃的化学接枝改性

综述了化学接枝改性聚烯烃的三种方法，即溶液法，熔融法及固定相法，并讨论了接枝单体的选择，接枝机理和接枝物的性能表征。     

Polar-Functionalized,Crosslinkable, Self-Healing,and Photoresponsive Polyolefins

The nonpolar nature of polyolefins is one of their biggest limitations. Now, an efficient route to generate polar-functionalized, crosslinkable, self-healing, photoresponsive polyolefins with thermoplastic, elastomeric, and thermosetting properties is reported. Tunable amounts of carboxylic acid and a cyclic comonomer are installed onto polyolefins by palladium-catalyzed terpolymerization reactions. The incorporated carboxylic acid unit can alter the surface properties of polyolefins. The subsequently introduced Fe³⁺/citric acid combination induces dynamic crosslinking and enables self-healing. Under UV light irradiation, citric acid reduces Fe³⁺ to Fe²⁺ and decreases the crosslinking density. The Fe²⁺ moiety can be easily oxidized back to Fe³⁺, making the process reversible at the expense of citric acid. The incorporated cyclic comonomer modulates the crystallinity of polyolefins, provides elastic properties, and installs carbon–carbon double bonds for sulfur-induced vulcanization.     

Photoconduction in polyolefins and in poly(ethylene–carbon monoxide)

The ultraviolet photoconductivity of high-density polyethylene, polypropylene, and poly(ethylene–carbon monoxide) has been studied in the range 360–180 nm. The response of the polyolefins is similar to that found in low-density polyethylene both in spectral distribution and in time behavior, with hole injection setting in at 3.7 eV. There is evidence also of electron injection in polypropylene at 4.5 eV and higher energies. A copolymer containing 0.5% CO is similar except that the hole threshold is at 4.2 eV, but a 1% CO copolymer shows marked differences, with electron injection being dominant. It is suggested that the change is due to a shift in the Fermi level rather than direct excitation of electrons from carbonyl groups, but some inconsistencies remain in this model.     

Quantum-chemical analysis of the mechanism of action of sterically hindered amines in photostabilization of polyolefins

A quantum-chemical study was made of the reaction of sterically hindered amines with the degradation products of polyolefins. The reactivity indices of these compounds and the formation energies of their reaction products were calculated by the semiempirical CNDO/2 and MINDO/3 methods. The mechanism of the photostabilizing action of sterically hindered amines was substantiated theoretically. The criteria by means of which it is possible to determine their relative reactivities were established, and the role of the substituent was determined. The results are compared with experimental data on the photostabilizing effectiveness of these compounds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 594–597, September–October, 1989.     

Commercialization of metallocene produced polyolefins in Japan

A recent trend in the Japanese polyolefin industry is reviewed focusing on the commercialization of metallocene produced polyolefins. The potential applications of these polyolefins will also be described.     

Polar‐Functionalized,Crosslinkable, Self‐Healing,and Photoresponsive Polyolefins

The nonpolar nature of polyolefins is one of their biggest limitations. Now, an efficient route to generate polar‐functionalized, crosslinkable, self‐healing, photoresponsive polyolefins with thermoplastic, elastomeric, and thermosetting properties is reported. Tunable amounts of carboxylic acid and a cyclic comonomer are installed onto polyolefins by palladium‐catalyzed terpolymerization reactions. The incorporated carboxylic acid unit can alter the surface properties of polyolefins. The subsequently introduced Fe³⁺/citric acid combination induces dynamic crosslinking and enables self‐healing. Under UV light irradiation, citric acid reduces Fe³⁺ to Fe²⁺ and decreases the crosslinking density. The Fe²⁺ moiety can be easily oxidized back to Fe³⁺, making the process reversible at the expense of citric acid. The incorporated cyclic comonomer modulates the crystallinity of polyolefins, provides elastic properties, and installs carbon–carbon double bonds for sulfur‐induced vulcanization.     

反应性聚烯烃的分子设计、催化聚合及应用

通用高分子材料高性能化研究的一个主要内容是聚烯烃(聚乙烯和聚丙烯)的高性能化和功能化.但是,由于聚烯烃大分子的化学惰性,其化学(分子)改性和物理(材料)改性都存在很大困难.近年来,烯烃聚合催化剂技术不断进步,烯烃聚合理论研究持续深入,从而为通过分子设计手段以可控方式在聚烯烃中引入化学活泼基团而制备结构明确和组成均匀的反应性聚烯烃奠定了基础.本文从反应性聚烯烃的分子设计、催化聚合以及其在聚烯烃高性能化研究中的应用等几个方面综述了近年来反应性聚烯烃领域的研究进展,并对此领域今后的研究发展方向提出了建议.     

Basis set effects on the stability of the Cl2O3 isomers using B3P86 and B3LYP methods of density functional theory

Four Cl₂O₃ isomers have been calculated using density functional theory with B3P86 and B3LYP functionals and various basis sets. The energy hypersurfaces of Cl₂O₃ are very flat and the relative energies of the isomers which have hypervalent characters such as ClOCl(O)O and ClClO₃ are strongly dependent on the basis sets. The stability for Cl₂O₃ isomers are in the order of (1)ClOOOCl(C_s), (2)ClOOOCl(C₂), (3)ClClO₃ and (4)ClOCl(O)O with ClOCl(O)O being most stable. We suggest that at least the cc-pV6Z(-ghi) basis set for Cl and the cc-pVTZ basis set for O are required to obtain reliable relative stabilities of Cl₂O₃ isomers with hypervalent characters.     

Pyrolysis of mixed polyolefins in a fluidised-bed reactor and on a pyro-GC/MS to yield aliphatic waxes

Polyolefins (PE, PP and PS) were pyrolysed in a fluidised-bed reactor on kilogram scale at 510°C. Pyrolysis products were analysed with GC, GC/MS and other methods. It was shown that valuable products, mostly aliphatic waxes, are received from polyolefins. It was also investigated if mixtures of different polyolefins (PE, PP, PS) interact with each other in fluidised bed pyrolysis yielding different pyrolysis products than received from the pure, individual polyolefins. The same polymer mixtures were also analysed using a pyro-GC/MS-device.     

Global weathering of aromatic engineering thermoplastics

The rates of gloss loss and color shift for 24 aromatic engineering thermoplastics at nine exposure sites world-wide have been compared relative to a commercial Miami exposure site. The scatter among individual samples was large, but on average, light dose alone was enough to account for almost all of the rate differences among the various sites for these materials. Temperature, humidity, rainfall, and acid rain seemed to play minor roles for most samples. Samples containing no particulate pigment had more erratic gloss loss and showed some dependency on the amount of rainfall. The overall “cleanliness” of the samples seemed to be an important factor in gloss retention, and washing protocols during the exposure period and before readings were important variables in cases of slow erosion and/or no particulate pigment. Microbial growth (fungus) was observed on Miami samples after 12–18 months of exposure, but none was seen at any other site.

Relative to Miami defined as 1.0, the average rates of color shift and gloss loss were approximately 0.67 in the northern U.S., 0.8 in the central U.S., and 1.15 in the U.S. desert southwest. Southern Europe was nearly as harsh as Miami, while Northern Europe was comparable to the northern U.S. Northern Europe was found to be somewhat harsher than expected while the northern U.S. was slightly less harsh than expected based on light dose or temperature-weighted light dose. These conclusions apply only to aromatic engineering plastics and should not be assumed to hold for other kinds of materials, such as polyolefins or coatings, without experimental verification.     

A review on the development of liquid chromatography systems for polyolefins

Polyolefins are the most widely produced synthetic polymer commodity and are found in countless applications ranging from bottles, packaging films to bullet-proof jackets, etc. Such widely different applications rely on high variability in the physical properties of polyolefins, which is a result of variations in microstructure, chemical composition and molar mass. Though polyolefins contain only carbon (C) and hydrogen (H) atoms, the microstructures of polyolefins are extremely variable, differing in the nature of the monomers (e.g. ethylene versus propylene), the degree of branching, chemical composition in the case of copolymers and finally their molar masses. Production, research and development of polyolefins require the analysis of polyolefin samples in terms of all these parameters. Development of efficient and robust analytical techniques based on the interactive LC is reviewed. The needed computational/theoretical studies to understand the retention mechanism in the newly developed chromatography systems are discussed.     

Ab initio Calculation of Intermolecular Dispersion Energy and Induction Energy of Nitramide Dimer

The dispersion energies, induction energies and their exchange counterparts (exchange-dispersion and exchange-induction energies) between two interacting nitramide molecules at several separations are derived based upon symmetry-adapted perturbation theory (SAPT). The results show that (1) the effect of intramonomer electron correlation on dispersion energies and induction energies for nitramide dimer system is remarkable especially in the region near the van der Waals minimum distance (0.42 nm). (2) At smaller separations the dispersion energies and the induction energies are largely quenched by their exchange counterparts, and this case in induction interaction is much more remarkable than in dispersion interaction. (3) Since at shorter distances there exists the strong short-range interaction due to electron transfer which quickly decays and even disappears at larger separations, the two different R-dependency formulae of induction energies were found: one is ca. R^-12.7 at short distances, and the other ca. R^-7.0 at large separations. The latter R-dependency is similar to that (ca.R^-7.2) of dispersion. (4) In the case of strong polar interaction existing in nitramide dimer, the “true“ induction correlation terms of higher order than ^1Eind^(22) may be important.