Hopping conduction in “pure” polypropylene

A recently developed theory of steady-state conduction in high-density polyethylene is applied to “pure” polypropylene (PP) in the temperature range 50–93°C. Morphological changes occur in PP, including a disordered-amorphous to monoclinic-amorphous transition between 50 and 80°C, where, with increasing temperature T, free volume increases, and decreases with decreasing amorphous fraction. The latter competing processes lead to large increases in hopping site separation, λ, in the transition region, followed either by saturation or a maximum in λ vs. T. We speculate that segmental and/or main chain molecular motions lower apparent activation energies, are “pinned“ by applied field, and impeded by dangling bonds in regions surrounding the surfaces of crystallites. Our analysis is semi-quantitative only, because the latter mechanisms have not been adequately quantified, and the relative contributions of each are unknown. Measurements were carried out on heated and cooled disordered-amorphous, and 106°C, 17-h annealed, 43% crystalline samples. Hopping distances, obtained from measured current vs. applied field characteristics, ranged from 1.2 to 5.2 nm. Apparent activation energies up to 1.80 eV were obtained from In (I/T) vs. (1/T) plots. Remarkable plateaus in the temperature range of the transition were observed in these plots, implying some carrier conduction with near zero activation energy. Possible explanations for the latter, and the electronic nature of the carriers are given. X-ray and density flotation measurements enabled crystallinity determinations. © 1994 John Wiley & Sons, Inc.     

On the concept of “Partitions” in the perturbation theory of n-electron systems

This paper deals with the perturbation theory of an n-electron Hamiltonian of the general form H = ∑ⁿ ?(i) + λ∑ⁿ g(i, j) = H (f, g; n). In comparison to the Brueckner–Goldstone diagrammatic perturbation theory, we adopt the more general standpoint of admitting, for the construction of an n-particle state, component states of 1, 2, 3, and more particles [O. Sinanoglu, Phys. Rev. 122 , 493 (1961) and C. D. H. Chisholm and A. Dalgarno, Proc. R. Soc. (London) Sec. A 292 , 264 (1966)]. We show that this leads to the concept of a “partition” of a perturbational eigenstate (or energy) of H. A “partition” is a natural decomposition which: (i) is finite; (ii) relates the eigenvalue problem of the system H = H (f, g; n) to those of certain subsystems H (f, g; n₁)(n₁ < n); (iii) uses “nonseparable” components. We domonstrate (under the preliminary assumption of “strict” nondegeneracy) the second-order energy to possess a “partition.” The components therein are second-order energies of two- and three-particle states. The proof uses an extension of Racah's concept of the fractional-parentage expansion.     

A general formulation of the “quantum chemical le Chatelier principle”

Regularities observed in the variations of calculated energy components, for example, those of electronic and nuclear repulsion energies in the analysis of conformational changes and in studies of the propagation of basis set errors in ab initio calculations, are found to be related to the variational principle and to the boundedness of energy expectation value functionals. These relations are analogous to the le Chatelier principle of equilibrium thermodynamics, and may be formulated as a general “compensation principle” for two sets of general parameters of the molecular total energy functional.     

The difluoroethylenes: A reconsideration of the “Cis effect”

Ab initio molecular orbital calculations have been carried out on all three isomers of difluoroethylene with geometry optimization. The calculations were done with a “double-zeta” basis set. After correction of the SCF energies for the effect of electron correlation, the 1,1-isomer is shown to be 8 kcal/mole lower in energy than the cis, which is 1 kcal/mole more stable than the trans. As the stabilization of the isomers increases, the distance between the fluorine atoms decreases: trans, 3.57 Å; cis, 2.77 Å; 1,1-isomer 2.20 Å. A simple explanation for these trends is based upon electrostatics and the small size and high electronegativity of the fluorine atom. As the fluorine atoms come closer together, the destabilization due to nuclear repulsions and electron repulsions is offset by the increased stabilizing electrons-nuclei attractions.     

Semi‐rigid polyesters analysed using the “strong‐fragile” concept

Semi‐rigid polyesters from diphenyl dicarbonic acid and some branched propyl and butyl spacers have been investigated using Differential Scanning Calorimetry. From Δc_p at Tg and the determination of the fragility index m, we studied the “strong‐fragile” behaviour of these materials. All the samples appear thermodynamically “strong” and “kinetically” fragile. A comparison of these results with those obtained from glass‐forming liquids leading to linear polymers ‐ such as PET, PCT, PEN or poly‐methyl (α‐n‐alkyl) acrylates ‐ shows that a modification of the polymer rigidity leads to change the fragility index m and the Δc_p at the glass transition.     

Molecular weight distributions in radiation-induced polymerization. VII. γ-ray-induced polymerization of “wet” styrene in the solid state

In the present paper kinetic and molecular weight distribution results are reported for the γ-ray-initiated polymerization of styrene in the solid state. “In-source” polymerization over the temperature range ?35°C to ?55°C and post-polymerization at ?35°C have been investigated for “wet” styrene samples (water concentration ≈ 10^?3 mole/l.). An interesting feature of the solid-state polymerization of styrene is the bimodal nature of the molecular weight distribution. On a qualitative basis the results resemble those obtained previously for the polymerization of rigorously dried (“dry”) styrene. However, there are noticeable differences on a quantitative basis resulting from the considerable difference in the water content between wet and dry samples. On the basis of these studies, the kinetic and molecular weight distribution data have been interpreted as being indicative of polymerization occurring simultaneously via free-radical and cationic mechanisms.     

“Proton Sponges” and the Geometry of Hydrogen Bonds: Aromatic Nitrogen Bases with Exceptional Basicities

Certain aromatic diamines (the “proton sponges”) are found to have exceptionally high basicity constants: this is due to spatial interaction of the basic centers, which are in close proximity. The two factors which are most important in causing this effect are, on the one hand, the extreme steric strain in these systems and the destabilizing effect of the overlap of the nitrogen lone pairs of the neutral diamines and, on the other, the strong N?H?N hydrogen bonds which are formed on monoprotonation and which lead to a considerable relaxation of the steric strain. By the systematic variation of the structures of such aromatic diamines we have been able to study these effects as a function of steric factors, in particular of the geometry and the bond length of the N?H?N hydrogen bonds, by means of X-ray structural analysis. The hydrophobic shielding of the basic centers and the N?H?N hydrogen bonds, which was characteristic of the “proton sponge” compounds studied previously, is indeed responsible for the extremely low rate of protonation and deprotonation of these compounds; however, it apparently has no influence on their high thermodynamic basicity. The recent synthesis and basicity determination of a new type of “proton sponge” with no hydrophobic shielding whatever show that not only very strong but also kinetically active bases are accessible using the “proton sponge” concept. Their unusual properties, which are discussed here as the result of steric interactions between two basic centers, provide examples of the fact that cooperative steric interactions of reactive structural elements can lead to properties which cannot be derived from an isolated consideration of the various functional groups. Such “proximity effects” are certainly of general importance in chemistry and biochemistry; the study of their structure-function relationships is worthy of closer consideration.     

Dynamic mechanical thermal and infrared analyses of polyacrylonitrile “electrografted” onto a metal

Polyacrylonitrile (PAN) films have been “grafted” onto copper electrodes by cathodic polarization and analyzed by infrared spectroscopy and dynamic mechanical thermal analysis (DMTA). The dynamic mechanical response shows two or three transitions depending on the film thickness and the potential deposition. The viscoelastic properties of “ungrafted” PAN films, e.g., solvent cast films of commercially available PAN, are deeply different from those of “electrografted” films. The experimental data support that “ungrafted” chains are paracrystalline in contrast to the “grafted” ones which are essentially amorphous. Moreover, the irreversible transformation of the “grafted” PAN chains observed beyond 225°C is confirmed by Fourier transform infrared (FTIR) analysis and ascribed to an intramolecular cyclization of PAN into polyimine. This reaction occurs rapidly and at a comparatively low temperature with respect to “ungrafted” PAN, which suggests that the “grafted” chain configuration might be predominantly isotactic. The isotacticity and the amorphous structure appear to decrease as the thickness of the PAN film is increased. Literature data and the herein reported observations would suggest a dependence of the amorphous structure of PAN on the chain isotacticity. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 543–553, 1998     

The N1s ESCA Spectrum of Protonated 1,8-Bis-(Dimethylamino) Naphthalene (“proton sponge”)

The ESCA spectrum of protonated 1,8-bis-(dimethylamino) naphthalene (“proton sponge”) (I) has been recorded in the region of N1s binding energies. The results indicate that IH⁺ possesses an unsymmetrical N? H…?N hydrogen bridge.     

A test of the new “integrated MO + MM” (IMOMM) method for the conformational energy of ethane and n-butane

Test calculations of the newly developed “Integrated Molecular Orbital + Molecular Mechanics” (IMOMM) method were performed for the optimized equilibrium and transition structures and energies of ethane and n-butane. In this method, the total energy of a large molecular system is expressed as a sum of the MO energy of the small “model” system and a modified MM energy of the “real” system, and full geometry optimization is carried out using the gradient of this total energy. Various schemes of partition of the system into the MO part and the MM part, including some not intended in the original design of the method, were examined and compared with the pure ab initio MO and the pure MM results. In most reasonable partition schemes, the IMOMM method can reproduce the pure ab initio and the pure MM geometries and energies quite well. © 1996 John Wiley & Sons, Inc.     

Knots “Choke Off” Polymers upon Stretching

Long polymer chains inevitably get tangled into knots. Like macroscopic ropes, polymer chains are substantially weakened by knots and the rupture point is always located at the “entry” or “exit” of the knot. However, these phenomena are only poorly understood at a molecular level. Here we show that when a knotted polyethylene chain is tightened, most of the stress energy is stored in torsions around the curved part of the chain. The torsions act as “work funnels” that effectively localize mechanical stress in the immediate vicinity of the knot. As a result, the knot “chokes” the chain at its entry or exit, thus leading to bond rupture at much lower forces than those needed to break a linear, unknotted chain. Our work not only explains the weakening of the polymer chain and the position of the rupture point, but more generally demonstrates that chemical bonds do not have to be extensively stretched to be broken.     

Investigations of the reactivity of “kick‐started” oxetanes in photoinitiated cationic polymerization

The ability of certain alkyl substituted epoxides to accelerate the photoinitiated cationic ring‐opening polymerizations of oxetane monomers by substantially reducing or eliminating the induction period altogether has been termed by us “kick‐starting.” In this communication, the rates of photopolymerization of several model “kick‐started” oxetane systems were quantified and compared with the analogous biscycloaliphatic epoxide monomer, 3,4‐epoxycyclohexylmethyl 3′,4′‐epoxycyclohexanecarboxylate (ERL). It has been found that the “kick‐started” systems undergo photopolymerization at rates that are at least two‐fold faster than ERL. These results suggest that “kick‐started” oxetanes could replace ERL in many applications in which high speed ultraviolet induced crosslinking photopolymerizations are carried out. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 586–593     

Quino[7,8-h]quinoline,a New Type of “Proton Sponge”

So far, “proton sponges” have been defined as bis(dialkylamino)arenes whose dialkylamino groups are in close spatial proximity.^[1] The unusual basicity of these compounds is ascribed to the destabilizing overlap of the lone electron pairs on the nitrogen atoms, to the formation of especially strong hydrogen bonds in the monoprotonated diamines, and to the hydrophobic shielding of these hydrogen bonds. In order to differentiate and assess the relative importance of these factors, we were interested in quino[7,8-h]quinoline 1 , whose nitrogen atoms exhibit a mutual orientation similar to that in 1,8-bis(dimethylamino)naphthalene 2 (“proton sponge”). In contrast to 2 , however, 1 lacks the hydrophobic shielding of the hydrogen bonds of its monoprotonated derivative. This shielding is considered to be responsible for the low rates of proton transfer, which make the “proton sponges” reported so far unsuitable as auxiliary bases in chemical reactions.     

A target‐group‐change couple with mass defect filtering strategy to identify the metabolites of “Dogel ebs” in rats plasma,urine and bile

“Dogel ebs” was known as Sophora flavescens Ait., a classical traditional Chinese Mongolian herbal medicine, which had the effects on damp‐heat dysentery, scrofula, and syndrome of accumulated dampness toxicity. Although the chemical constituents have been clarified by our previous studies, the metabolic transformation of “Dogel ebs” in vivo was still unclear. To explore the mechanism of “Dogel ebs,” the metabolites in plasma, bile, and urine samples were investigated. A fast positive and negative ion switching technology was used for the simultaneous determination of flavonoids and alkaloids in “Dogel ebs” in a single run. And a target‐group‐change coupled with mass defect filtering strategy was utilized to analyze the collected data. 89 parent compounds and 82 metabolites were characterized by high‐performance liquid chromatography with quadrupole exactive Orbitrap mass spectrometry. Both phase I and phase II metabolites were observed and the metabolic pathways involved in oxidation, demethylation, acetylation, and glucuronidation. 69 metabolites of “Dogel ebs,” including three hydroxyls bonding xanthohumol, formononetin‐7‐O‐glucuronide, 2′‐hydroxyl‐isoxanthohumol decarboxylation metabolite, oxysophocarpine dehydrogen, 9α‐hydroxysophoramine‐O‐glucuronide, etc. were reported for the first time.     

Low-temperature modification of dienic polymers via the “Ene” reaction with 4-substituted-1,2,4-triazoline-3,5-diones

4-Substituted-1,2,4-triazoline-3,5-diones have been used to synthesize a series of new polydienes by the “ene” reaction at ambient temperatures. The extent of chemical conversion can be varied widely and up to 93% of the diene-repeating units of the parent polymer chain undergo reaction. Yields of the new polymers based on the reactant range from 90 to 95% at room temperature; their physical properties range from secondary crosslinking effects or elasticity at low degrees of conversion to rigid, amorphous polymers with high softening points at high degrees of conversion. The new polymers show a predictable correlation between the extent of conversion and the softening point. A similar correlation exists between the polarity of the new polymers and the extent of conversion. Polydienes with conversions to the extent of 45% or greater are soluble in aqueous solutions of sodium hydroxide and those with conversions of 60% or greater are soluble in aqueous sodium bicarbonate. Thus, in general, the new polymers (1) have higher T_g, (2) become increasingly polar, hence are soluble in polar solvents, and (3) possess a reasonably acidic proton, hence form salts. Bistriazolinediones result in room temperature crosslinking. A kinetic study with model compounds suggests that the rate of the reaction can be varied, depending on the electronic nature of the 4-substituent.     

Photo‐initiated thiol–ene “click” hydrogels from RAFT‐synthesized poly(N‐isopropylacrylamide)

Despite the efficiency and robustness of the widely used copper‐catalyzed 1,3‐dipolar cycloaddition reaction, the use of copper as a catalyst is often not attractive, particularly for materials intended for biological systems. The use of photo‐initiated thiol‐ene as an alternative “click” reaction to synthesize “model networks” is investigated here. Poly(N‐isopropylacrylamide) precursors were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and were designed to have trithiocarbonate moieties as end groups. This structure design provides opportunity for subsequent end‐group modifications in preparation for thiol‐ene “click.” Two reaction routes have been proposed and studied to yield thiol and ene moieties. The advantages and disadvantages of each reaction path were investigated to propose a simple but efficient route to prepare copper‐free “click” hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4626–4636     

On the possibility of using organic phosphors in thermoluminescence dosimetry

Organic materials in general and polymers in particular have traditionally been considered as to be phosphors and have been ruled out as materials which could be useful in dosimetry of ionizing radiations by thermoluminescence. Some results reported during the past decade suggested possibilities of organic phosphors with good thermoluminescence characteristics. Experiments were undertaken to exploit the various possibilities. The results show that “crystalline polymers” can have adequate thermoluminescence properties to be useful in dosimetry. It is suggested that further studies on thermoluminesence in crystalline polymers and highly drawn fibers of high polymers will prove fruitful.     

Asymptotic behavior of the primitive function of different “symmetry-adapted” perturbation schemes for the H ground state

The leading terms in the asymptotic 1/R expansion of the wave functions and energies of various “symmetry-adapted” perturbation schemes for intermolecular forces, as well as for the “polarization approximation” (PA ) are derived for the H ground state, both exactly (i.e., to infinite order in λ) and in the first two orders of the λ expansion. It is pointed out that only in the PA and the Hirschfelder–Silbey scheme is the formal primitive function Φ genuinely primitive, whereas Φ in the other schemes is asymmetric in a rather strange way. In this lack of genuine primitivity lies the reason why in these schemes the leading term of the 1/R expansion is only recovered to infinite order in λ and requires knowledge of the R^?4 term of the wave function, provided that one uses the “internal” energy expression. Four different energy expressions are compared that behave differently in the different schemes. The results obtained here are basis independent, but the implications of the basis completeness problem are discussed as well.     

Silica Scaffold with Shifted “Plumber's Nightmare” Networks and their Interconversion into Diamond Networks

Bicontinuous structures with hyperbolic surfaces have been found in a variety of natural and synthetic systems. Herein, we present the synthesis and structural study of the shifted double‐primitive networks, which is known as the rare “plumber's nightmare”, and its interconversion into diamond networks. The scaffold was prepared by self‐assembly of an amphiphilic triblock terpolymer and silica precursors. Electron crystallography indicates that the structure consists of two sets of hollow primitive networks shifted along 0.75b and 0.25c axes ( 2pcu (38 63), space group Cmcm ). The “side‐by‐side” epitaxial relationship of the primitive and diamond networks with unit cell ratio of about 1.30 has been directly observed with the intermediate surface related to the rPD family. These results bring new insights to previous theoretical studies.