Self-nucleation and recrystallization of isotactic polypropylene (α phase) investigated by differential scanning calorimetry

The crystallization behavior after partial or complete melting of the α phase of iPP is examined by combined differential scanning calorimetry (DSC) and optical microscopy: calorimetric results are directly correlated with corresponding morphologies of microtome sections of DSC samples. On partial melting at various temperatures (hereafter referred to as T_s) located in a narrow range (4°C) below and near T_m, the number of nuclei increases (as in classical self-nucleation experiments), by several orders of magnitude; on subsequent cooling, the crystallization peak is shifted by up to 25°C. After partial melting in the lower part of the T_s range and recrystallization, the polymers display a prominent morphology “memory effect” whereby a phantom pattern of the initial spherulite morphology is maintained. After partial melting in the upper part of the T_s range the initial morphology is erased and self-nucleation affects only the total number of nuclei. The present experimental procedures make it possible to define, under “standard” conditions, the crystallization range of the polymer and in particular, the maximum crystallization temperature achievable when “ideally” nucleated. © John Wiley & Sons, Inc.     

Basic modes of three-dimensional polymer crystal associations: Interlocked single crystals and crystal halves

Tridimensional associations of lamellar polymer single crystals, grown from dilute solutions, are described as derived from their sedimentation patterns. These associations include interlocked crystals and decorating crystal halves. The origin of these crystals and their mutual orientation are discussed and tentatively interpreted by specific interactions between the fold surface and the crystallizing chains.     

Über Chalkogenolate. 162. Umsetzungen von Hydrazin mit Kohlenstoffdisulfid. 1. Darstellung und Eigenschaften von 1,2-Hydrazin-bis(dithioformiaten)

On Chalcogenolates. 162. Reactions of Hydrazine with Carbon Disulfide. 1. Synthesis and Properties of 1,2-Hydrazine-bis (dithioformates) The prepared 1,2-hydrazine-bis(dithioformates) have been characterized with chemical methods as well as by means of electron absorption, infrared, nuclear magnetic resonance (¹H and ¹³C), and mass spectra.     

Embeddings ofC(Δ) andL 1[0, 1] in Banach lattices

It is proved that ifE is a separable Banach lattice withE′ weakly sequentially complete,F is a Banach space andT:E→F is a bounded linear operator withT′F′ non-separable, then there is a subspaceG ofE, isomorphic toC(Δ), such thatT _G is an isomorphism, whereC(Δ) denotes the space of continuous real valued functions on the Cantor discontinuum. This generalizes an earlier result of the second-named author. A number of conditions are proved equivalent for a Banach latticeE to contain a subspace order isomorphic toC(Δ). Among them are the following:L ¹ is lattice isomorphic to a sublattice ofE′;C(Δ)′ is lattice isomorphic to a sublattice ofE′; E contains an order bounded sequence with no weak Cauchy subsequence;E has a separable closed sublatticeF such thatF′ does not have a weak order unit. The research of both authors was partially supported by the National Science Foundation, NSF Grant No MPS 71-02839 A04.     

Disjunkte Folgen in Banachverbänden und Kegel-absolutsummierende Operatoren

Ohne ZusammenfassungDie Autoren wurden unterstützt von der Alexander von Humboldt-Stiftung (Cartwright) sowie von der United States National Science Foundation (Lotz).     

Electron-impact ionization cross-sections for atoms up to Z=108

Using the formula recently proposed, electron-impact ionization cross-sections for single ionization from the ground state of free atoms up toZ=108 are given for energies of the impact electron between threshold and 1 keV. The probable error is estimated to be approximately \(_{ - 30}^{ + 40} \% \) , but near threshold the error is larger and no fine structures are accounted for.     

Electron-impact ionization cross-sections and ionization rate coefficients for atoms and ions from hydrogen to calcium

Using the empirical formula recently proposed, electron-impact ionization cross-sections for single ionization from the ground state are given for free atoms and for all ionization stages from hydrogen to calcium (Z=20). Ionization rate coefficients are given for these species on the assumption of a Maxwellian distribution of the impacting electrons. Multiple ionization, lowering of ionization potential, or collision limit are not taken into account.     

Liquid-crystalline textures in binary and ternary block copolymer–solvent systems

A number of characteristic liquid-crystalline textures can be obtained in binary and ternary systems (i.e., including one or two solvents) based on polystyrene-poly(ethylene oxide) (PS-PEO) and polystyrene-polyisoprene block copolymers. These textures include oily streaks, myelinic figures, and vesicles, all characteristic of a lamellar structure; fan-shaped textures of cylindrical structure; and isotropic domains indicative of a cubic structure. Experimental conditions used to systematically produce the mesomorphic textures are described, and the rather critical solubility conditions which the solvents must meet are indicated. The rules and described procedures should be quite general and applicable to other copolymers as well. Finally, highly unusual examples of “pseudomorphosis” typical of liquid-crystalline textures occurring in bulk upon melting and crystallization of the PEO sequences in PEO-PS copolymers are also reported.     

Quantitative analysis of electron diffraction data from epitaxially grown crystals

Epitaxial growth produces oriented crystal projections where a long unit cell axis is parallel to the major crystal face rather than perpendicular to it and thus provides a favorable condition for electron diffraction data collection which minimizes perturbations due to elastic crystal bending. Even though the crystals are not so perfect as those produced by solution growth, the intensity data from them have been useful for the quantitative crystal structure analysis of several molecular organic compounds and linear polymers as discussed in this review.