Intercrystalline links in polyethylene crystallized from the melt

Intercrystalline links in polyethylene have been revealed by crystallizing from the melt mixtures of fractionated polymer and the linear hydrocarbon n-C₃₂H₆₆, the latter constituent being removed later by washing at room temperature in an organic solvent. These fibrous links measure up to 15,000 A. in length and are 30–300 A. in thickness. Molecular chains are oriented parallel to the lengths of the links, and apparently nucleate on tie molecules formed by the simultaneous crystallization of different parts of the same molecule on the surfaces of different, and often widely separated, crystals. The maximum length of the links found in a given polymer varies as the square root of molecular weight, and there are indications that molecules in the melt are much more extended than is predicted by conventional configurational statistics. The links are under tension and presumably exert a significant influence on physical properties.     

On the theory of electron correlation in atoms and molecules. II. General cluster expansion theory and the general correlated wave functions method

An exact cluster expansion of many electron wave functions is derived, beginning with a finite linear combination of Slater determinants rather than the more usual single determinant. This general cluster expansion is found to apply both in the case where all possible Slater determinants from a finite set of spin orbitals are included in the linear combination, and in the case where the number of determinants is restricted. The special properties of that finite linear combination of determinants closest to the exact wave function in the least squares sense are studied. These properties lead to the derivation of a general correlated wave functions method, illustrating again the close relationship between methods of this type and cluster expansion theory. Additional approximations, necessary for practical calculations, are set out.     

The magnetic susceptibilities of cobaltocene and chromocene

The magnetic susceptibilities of cobaltocene and chromocene have been measured between 83 and 293 K; for cobaltocene the results suggest an appreciable orthorhombic splitting of the ²∏(σ²πδ⁴ ground state, whilst for chromocene the data provide further support for the ³Δ(σδ³) ground state previously deduced.     

Mechanism of oxidation at a copper–polyethylene interface. II. Penetration of copper ions in the polyethylene matrix

Two surface analysis techniques (Rutherford backscattering and surface composition by analysis of neutral and ion impact radiation) have been applied to the study of interfacial copper transport in the oxidation of polyethylene films over copper surfaces. Analysis of films oxidized several thousand hours at 40, 57, and 87°C shows maximum concentrations of copper species in the polymer matrix of ～0.1M extending to depths of several thousand angstroms. These results, together with previous infrared spectroscopic studies, allow some significant conclusions and hypotheses to be drawn as regards the roles of heterogeneous and homogeneous catalytic processes which occur in the thermal-oxidative degradation of polyethylene–copper systems.     

SCF-π-electron calculations using orthogonalised atomic orbitals

Modifications of the SCF-LCAO-π-MO method analysed in the previous paper are described in which provision is made for the incorporation of Variable Bond Order and Variable Electronegativity procedures. A comparison is made with the results of other π-electron calculations and values are reported for twenty hydrocarbon systems.     

Steady-state electrolysis at a grooved or ridged plane

This study concerns an infinite plane whose smoothness is marred by a single defect: either a groove or a ridge. The blemished plane serves as an electrode supporting a diffusion-controlled steady-state process. By using a convenient coordinate transformation, the local current density at all points on the surface is determined exactly. The results are found to confirm intuitive expectations. Thus, compared with normal values on the plane remote from a groove, the electron transfer rate is diminished within the groove but enhanced along its margins. Similarly, an abnormally large transfer rate is encountered high on the ridge but the rate is subnormal on its lower flanks. The total current is demonstrated to be unchanged by the presence of the blemish. Received: 27 September 1996 / Accepted: 11 March 1997     

Modelling the Chemistry of Zeolites by Computer Graphics

The unique structural, adsorptive, and catalytic properties of zeolites are particularly amenable to illustration by computer (especially color) graphics. The siting of cations, the accommodation of guest reactant or product species, as well as the occurrence of various kinds of intergrowths (e.g. twin planes and coincidence boundaries) within these microporous solids can all be effectively portrayed by graphical means in such a manner as to emphasize the shape-selective character of the host zeolite. The dynamics of translational and angular motion of guest species (for example benzene) in a channel of molecular dimensions within a typical zeolitic solid (for example silicalite) can also be probed interactively using appropriate potential functions.     

Application of tandem analyser to SIMS studies of hydrocarbon polymers

The fragmentation of ions sputtered from the surface of low-density poly(ethylene) (LDPE) has been investigated by studying their collisionally activated dissociation (CAD) when incident upon a variety of target gases in the collision cell of a triple quadrupole SIMS instrument. It was found that heavier targets resulted in more extensive CAD than was observed with lighter targets but that sulphur hexafluoride is inefficient target because of the amount opf energy that is transferred to its vibrational modes of motion (rather than being available to induce fragmentation in the parent ion.) The behaviour observed for an oxygen target was quite different to that observed for other targets (at higher pressures). In general oxygen induced markedly greater fragmentation for the small parent ions but xenon was the preferred target for the larger parent ions. Fragmentation patterns could readily be assembled for all of the parent ions observed in the SIMS spectrum of LDPE using the CAD data. There are good indications that the data obtained may assist in indentification of ion structures and in elucidation of general rules governing the fragmentation of organic materials during SIMS. For example, LDPE fragment ions were found to obey quite strictly the Even Electron Rule, a well-known rule in mass spectrometry.     

Practical version of the Asymptotic Linearity Theorem with applications to the additivity problems of thermodynamic quantities

By using fundamental notions and theorems of the Lesbesgue integral, a practical version of the Asymptotic Linearity Theorem has been derived. From this new version of the theorem, it easily follows that the theorem is also applicable to the additivity problems of thermodynamic quantities of molecules having many identical moieties, as well as to those of the zero-point vibrational energy of hydrocarbons and the total pi electron energies of altemant hydrocarbons.On leave from: Institute for Fundamental Chemistry, 34-4 Nishihiraki-cho, Takano, Sakyo-ku, Kyoto 606, Japan.