Theoretical energies of representative carbon–carbon bonds

A bond-energy formula deduced by means of the Hellmann–Feynman theorem is applied to selected simple hydrocarbons. The required potentials at the nuclei are calculated with the help of large basis-set expansions including polarization functions. The carbon–carbon bond energy of ethane is evaluated at ～ 70 kcal mol^?1. The CC bond energies of ethane, ethylene, acetylene, benzene, and cyclopropane are approximately in a ratio of 1: 2.0: 3.0: 1.65 1.0. Limitations and possible improvements in future applications of this energy formula are discussed. © 1995 John Wiley & Sons, Inc.     

A Critical Evaluation of Bond Energy/ Group Contribution Methods of Calculating the Heat of Formation: Development of a New Generalized Scheme. Part I. Alkanes∗

Results of application of seven well-known bond energy/group contribution methods to the experimental data on heats of formation of 70 alkanes, including a few polymers, are reported. The earlier claims of accuracy of many of these schemes become untenable with the emergence of new data on nonanes and polymers, calling for more parameters to cope with the steric interaction energy in higher branched alkanes. A new general bond energy scheme is developed with low standard error of ±0.28 kcal/mole which is close to the experimental uncertainty. Heats of formation of some polyolefin structures are predicted for the experimental verification in the future. The energy terms of the new scheme are transferable to other non-hydrocarbon organic compounds for which a general scheme is under way.     

The equivalence of bond-energy schemes and the determination of resonance energies

 It is argued that the preservation of algebraic equivalence between the Allen and Laidler bond-energy schemes for nonconjugated alkenes logically determines that the Allen scheme should apply to a classical structure of a conjugated hydrocarbon exactly as it stands, i.e. no additional parameters are needed. Extending the requirement of equivalence to conjugated alkenes implies that, in the Laidler scheme, the bond energy of the pure single CC bond in a conjugated system is a combination of the bond-energies of the semiconjugated and normal CC single bonds: E(C_d—C_d)=2E(C_d—C)−E(C—C). This result is a deduction and is not an independent hypothesis. The equivalence of the two schemes for conjugated hydrocarbons is demonstrated numerically, by calculating the resonance energies of some selected molecules by both methods. Received: 5 December 1999 / Accepted: 5 March 2000 / Published online: 5 June 2000     

Bond Energy Scheme for Estimating Heats of Formation of Monomers and Polymers. VI. Sulfur Compounds

The bond energy scheme is extended to sulfur compounds and heats of formation and atomization energy terms derived from thermochemical data reviewed to 1977, for bonds of sulfur with carbon, hydrogen, halogens, and oxygen atoms. A precision of ± 1 kcal/mole was attainable for the covalent bonds of divalent sulfur in the lowest oxidation state S(± II). The higher valency states: S(IV) and S(VI) involve polar contributions depending upon the electrouegativity of the combining atom as well as (d^π -p^π) orbital promotion energies which are specific to the compound and transferable to other molecules only with a limited precision, no better than about ± 3 kcal/mole. The atomization energy terms (E_a ^25°C) of various bonds of sulfur a are found consistent with the experimental bond dissociation energies and bear a relationship with bond lengths and force constants as observed in the previous work. Heats of polymer-forming reactions and heats of formation of sulfur-containing monomers and polymers are estimated from the newly derived bond energy terms.     

Formation Mechanism of the First Carbon–Carbon Bond and the First Olefin in the Methanol Conversion into Hydrocarbons

The elementary reactions leading to the formation of the first carbon–carbon bond during early stages of the zeolite‐catalyzed methanol conversion into hydrocarbons were identified by combining kinetics, spectroscopy, and DFT calculations. The first intermediates containing a C?C bond are acetic acid and methyl acetate, which are formed through carbonylation of methanol or dimethyl ether even in presence of water. A series of acid‐catalyzed reactions including acetylation, decarboxylation, aldol condensation, and cracking convert those intermediates into a mixture of surface bounded hydrocarbons, the hydrocarbon pool, as well as into the first olefin leaving the catalyst. This carbonylation based mechanism has an energy barrier of 80 kJ mol^?1 for the formation of the first C?C bond, in line with a broad range of experiments, and significantly lower than the barriers associated with earlier proposed mechanisms.     

Synthesis,photophysics, structure‐tunable photoluminescence,and electrochemical properties of soluble poly(p‐phenylenevinylene)‐based polymers with adjacent 1,3,4‐oxadiazoles in the backbone

Three new poly(p‐phenylenevinylene)‐based polymers containing two 1,3,4‐oxadiazole moieties in the main chain per repeat unit were synthesized by Heck coupling. A single, double, or triple bond was introduced between the oxadiazoles to provide a means for modifying the polymer properties. The polymers were readily soluble in common organic solvents and showed T_g values lower than 50 °C. The color of the emissive light in both the solid state and the solution could be tuned by a change in the nature of the bond between the oxadiazole rings. The polymers emitted ultraviolet‐green light in solution with a photoluminescence (PL) emission maximum at 345–483 nm and blue‐green light at 458–542 nm in thin films. The PL quantum yields in solution were 0.36–0.43. The electrochemical properties are affected by the nature of the bond between the oxadiazoles as well. In polymers with a single bond between the oxadiazoles, a lower ionization potential was observed than in polymers with a double or triple bond. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3079–3090, 2005     

Macromolecular-chain rearrangement during synthesis of poly(N-phenylurethanes)

Poly(N-phenyliminocarbonates) capable of converting into poly(N-phenylurethanes) via thermal treatment at 300°C for 9 h through the Chapman mechanism were prepared via the polycondensation of bisphenols with plenyliminophosgene. The resulting polymers are soluble in chlorinated hydrocarbons and amide solvents. The polymers are characteristic by glass-transition and 10%-weight-loss temperatures during heating in air of 165–210 and 455–490°C, respectively.     

New force-field parameters for use in molecular simulations of s-triazine and cyanurate-containing systems. 1 — derivation and molecular structure synopsis

Cyanate ester resins are an emerging family of high performance polymers that are being studied for a variety of technological applications. The structure of the aromatic sym-triazine ring formed during cure of these polymers is investigated here by analysis of X-ray crystallographic data from a number of model compounds. The data show a preferred conformation of the ring structure with alternating internal bond angles of ca. 112° at nitrogen (C–N–C) and 128° at carbon (N–C–N). The C–N bond lengths are also shorter than those found in pyridine or pyrimidine, leading to a non-planar ring conformation. Force constants for the bond stretch, bend and torsional motions of the sym-triazine ring have also been calculated, using mopac, the semi-empirical quantum mechanics package.     

系列化合物C-H伸缩频率的自然杂化轨道研究

在计算C-H核自旋-自旋偶合常数的新公式及其与C-H伸缩频率之间的关系的基础上, 得出了计算C-H伸缩频率的新的一般关系式。并利用CNDO/2分子轨道和自然杂化轨道方法, 具体计算了三种不同系列化合物的原子净电荷和自然杂化轨道。给出了计算不同系列化合物C-H伸缩频率的良好线性关系式。结果表明, 碳氢化合物中的C-H伸缩频率主要由原子的轨道杂化作用所决定, 而对于含杂原子的取代碳氢化合物, C-H键的极性成为影响伸缩频率的重要因素。     

Bond Energy Scheme for Estimating Heats of Formation of Monomers and Polymers. VII. Nitrogen Compounds

The bond energy scheme is extended to nitrogen compounds by correlating experimental thermochemical data reviewed to 1980. Heats of formation and atomization energy terms are provided for bonds of nitrogen with other elements: H, C, O, N, S, and halogens. An overall precision of 3 kcal/mol was attainable at the best, which is rather low for chemical reaction kinetics purpose. This is attributable mainly to the intrinsically unpredictable bond energies of the nitrogen atom due to the “lone-pair” electrons participation in the valence bonding, rendering nitrogen bonds specific and less transferable. The nearest-neighbor interactions on nitrogen atom are also severe but predictable if sufficient energy terms are generated. The concept of ring strain in five-membered rings (about 5 × 2 kcal/mol in the background of thermochemical data) has been reviewed and amended by providing a special set of energy terms for the (C, O, N, S) -ring skeleton which is considered strain-free if the hydrogen atom is the only substituent. Heats of formation of some common molecular structures are predicted.

Heats of formation of nitrogen-containing polymers and heats of polymer-forming and polymer-modification reactions are estimated and compared with available calorimetric data.     

MBOHO calculations of C?H stretching frequencies in hydrocarbons and heterosubstituted hydrocarbons

Based on the generalized relationship for calculating the nuclear spin–spin coupling constants and the correlation of the bond stretching frequencies with the coupling constants, a novel generalized reationship, which includes the contributions of not only the hybrid orbitals, but also the net atomic charges, is introduced for calculation of the bond stretching frequencies and employed to elucidate the C? H stretching frequencies in hydrocarbons and heterosubstituted hydrocarbons on the basis of the MBOHO calculation employing the CNDO /2 approximation. By use of the obtained concrete realtionships, one can get different ν _CH value for the C? H bonds existing in different chemical environments, which is coincident with chemical intuition. The calculated numerical results show that for hydrocarbons the contribution of the net atomic charges can be neglected, but it is necessary for heterosubstituted hydrocarbons to include the contribution of the net atomic charges to the C? H stretching frequencies. The calculated C? H stretching frequencies are in good ageement with the experimental data, which shows its reasonableness. © 1994 John Wiley & Sons, Inc.     

Polyimides having pendant hydroxy and acetoxy groups. I. Synthesis of polyimides from pyromellitimide and bisepoxides

Polyimides having pendant hydroxy groups were prepared by addition of pyromellitimide with bisepoxides. Tertiary amines and quaternary ammonium halides were effective as a catalyst. The polyimides were soluble in dichloroacetic acid and had inherent viscosities in the range 0.16–0.19 dl/g. Thermogravimetric analysis showed that a rapid weight loss of the polymers occurred at about 400°C. The pendant hydroxy groups were easily acetylated by treating the polymers with a mixture of acetic anhydride and pyridine. The acetylated polyimides were soluble in dimethylformamide, dimethylacetamide, and dioxane and melted at 120–150°C.     

The fusion of highly crystalline poly(vinyl chloride)

Low molecular weight PVC polymers of known degree of crystallinity (44% by x-ray diffraction), prepared in the presence of the chain-transfer agents n-butyraldehyde and n-butyl mercaptan, are examined by differential scanning calorimetry in order to ascertain temperatures and heats of fusion. Initial thermal scans are accompanied by large endotherms and appreciable weight losses due to the lability of the terminal groups originating from the chain-transfer agents. However, further successive scans result in approximately invariant endotherms attributable to crystalline fusion. The maximum melting point, about 265°C, exceeds the value for commercial PVC, about 210°C, but is lower than a value deduced for a hypothetical completely syndiotactic polymer, about 400°C. The average heat of fusion ΔH_u is 1180 ± 90 cal/mole, and the resultant entropy of fusion is 1.1 cal/deg/bond. The present ΔH_u value differs significantly from previously reported values of 660–785 and 2700 cal/mole, based on melting point depression theory, but appears to be concordant with known heats for a series of vinyl polymers.     

Synthesis and characterization of 9,10‐diphenylanthracene‐based blue light emitting materials

A new series of conjugated polymers having diphenylanthracene vinylene biphenylene and diphenylanthracene vinylene terphenylene in the main chain and fluorene pendant group, were synthesized by nickel catalized Yamamoto coupling and palladium catalized Suzuki coupling. The obtained polymers showed good solubility in the common organic solvent and number average molecular weights of 14,000–9500 with a polydispersity indexes ranging from 1.7 to 2.1. Both polymers possess excellent thermal stability with glass transition temperatures of 123–127 °C and the onset decomposition temperatures of 420–400 °C. The obtained polymers showed blue emission (λ_max = 461 for PFPA and λ_max = 455 nm for PFPAME) in PL spectra, specially, PFPAME containing diphenylanthracene vinylene terphenylenevinylene showed the consistent emission in the solution and film. The double‐layered device with an ITO/PEDOT/PFPAME/LiF/Al structure has a turn‐on voltage of about 5.8 V, maximum brightness of 152 cd/m² and an electroluminescent efficiency of 0.143 lm/W, and stable blue EL emission that is not altered by increased voltage. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5908–5916, 2009     

New high temperature polymers. VI. Ordered heterocycle copolymers

A new class of linear, thermostable polymers is reported. The compositions are ordered heterocycle copolymers in which two different heterocycles alternate regularly along the polymer chain. Examples of combinations studied are: oxadiazole–benzimidazole, oxadiazole–pyromellitimide, and thiazole–pyromellitimide. The heterocycle copolymers, or alternatively, the corresponding precursor polymers, were prepared by condensing preformed di-or tetrafunctional blocks which contain one type of heterocycle with a second di- or tetrafunctional monomer under such conditions that no rearrangement of bonds occurred. The polymers are characterized in general by neither melting nor decomposing below 500°C. when heated in an inert atmosphere at a rate of about 10°C./min. Some of the copolymers are readily soluble in organic solvents; many, however, are soluble only in solvents such as concentrated sulfuric acid. In the case of the more intractable polymers, soluble precursor polymers can usually be prepared. In such precursor polymers only one of the heterocycles is preformed; the second heterocycle is formed by post-treatment after the polymer has been fabricated into an end product. All of the polymers yielded self-supporting films, some having very high strength; films of several of the polymers were hot-drawable. Drawn film of an ordered oxadiazoleimide copolymer was shown to be well oriented and moderately crystalline.     

Effect of photoinitiator on photopolymerization of inorganic–organic hybrid polymers (ORMOCER®)

Inorganic–organic hybrid polymers have been developed and tested for evaluation in optical and electrical applications. Although hybrid inorganic–organic polymers can be synthesized by sol–gel chemistry at first, the physical properties of hybrid inorganic–organic polymers are changed during thin film-making processes, that is, photocuring and thermal curing. To investigate the effect of photoinitiator on the material properties during processing, a model system containing methacrylic groups as organically polymerizable units was selected. The conversion of CC double bond of methacrylic groups depending on some kinds of photoinitiator quantities was characterized by Fourier transform infrared spectroscopy. It was confirmed to correlate the degree of CC double bond conversion with the refractive indices. Thermodynamically, the enthalpy of the photopolymerization of hybrid polymer was investigated by UV–DSC. UV–DSC spectra showed the exothermic nature of photopolymerization of ORMOCER® to be in dependence of photoinitiator quantities. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1979–1986, 2004     

Direct synthesis of polyaromatic chains of tribenzopentaphene copolymers through cyclodehydrogenation of their poly‐tetraphenylbenzene precursors

Three polyaromatic‐based polymers are reported to contain co‐monomers of trapezoidal tribenzopentaphene (TBP) polycyclic aromatic hydrocarbons. The synthetic strategy consists of initially making highly soluble tetraphenylbenzene copolymers 4a–c , followed by a cyclodehydrogenation/aromatization reaction to obtain target polymers 5a–c . The polymers were characterized by gel permeation chromatography, FT‐IR, UV‐vis, emission, ¹H‐, and ¹³C‐nuclear magnetic resonance spectroscopy. The target polymers 5a–c reveal emission spectra in the range of 430–480 nm; thus, qualifying them to act as blue emitters. Investigation of the polymers optical properties and their correlation with density functional theory calculations suggest a distorted TBP core from planarity caused by the introduction of a dodecyl group at its wide edge. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3565–3572     

Rigid-Rod benzobisthiazole polymers with reactive fluorene moieties: Synthesis and characterization

High purity 2,7-fluorenedicarboxylic acid chloride was synthesized in a multistep reaction scheme from 2,7-dibromofluorene. Subsequent polycondensation in polyphosphoric acid of 2,5-diamino-1,4-benzenedithiol dihydrochloride with terephthaloyl chloride and 2,7-fluorenedicarboxylic acid chloride led to rigid-rod benzobisthiazole polymers with reactive fluorene moieties. The proportion of fluorene in the resultant polymers was controlled through reaction stoichiometry. Soluble polymers with intrinsic viscosities as high as 33.7 dL/g (methanesulfonic acid, 30°C) were obtained if the polymerization temperature was not allowed to exceed 165°C. Insoluble, presumably crosslinked polymers were obtained at higher temperature (190–200°C). Thermal characterization of the polymers by differential thermal analysis and thermal gravimetric analysis/mass spectroscopy did not disclose any thermal transition to 450°C. Onset of weight loss in air did not occur until over 550°C.     

Electroinitiated polymerization of vinylic monomers in polar systems. III. Polymerization of acrylates and methacrylates in alcohol solutions

Methyl, ethyl, and n-butyl acrylates and methacrylates are polymerized by electroinitiation in methanol–, ethanol–, and n-propanol–electrolyte mixtures in which the monomers are soluble whereas the polymers obtained are insoluble. The technique of changing the polarity of the electrodes described earlier was used. The relationships between molecular weights and polymer yields as function of current density, initial monomer concentration and dielectric constant of the solvent are described. A kinetic scheme for the initiation, propagation, and termination is given.     

Synthesis of novel polyaryl(ether–ketones) with tert-butyl pendent groups

Linear polyaryl(ether ketones) containing tert-butyl pendent groups were prepared from aromatic hydrocarbons and aromatic diacid chlorides, both classes of monomers containing tert-butyl pendent groups. The polymers were prepared in high yield and high molecular weight by low-temperature precipitation polycondensation in 1,2-dichloroethane. The presence of meta-oriented moieties and bulky pendent groups played a beneficial role with regard to solubility, while the thermal transitions and thermal resistance were not greatly impaired relative to conventional all para-oriented polyaryl(ether–ketones). The current polyaryl(ether–ketones) showed glass transition temperatures in the range 170–240°C and decomposition temperatures, as measured by TGA, of about 500°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1251–1256, 1998