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Polymeric sensing films absorbing organic guests into a nanoporous host crystalline phase
No full textPolymeric sensing films absorbing organic guests into a nanoporous host crystalline phase
No full textCrystal-structure of the Form I of Syndiotactic Poly(1-butene)
No full textThe crystal structure of the form I of syndiotactic poly(1-butene) is presented. According to the present analysis, chains having s (2/1)2 helical conformation are packed in an orthorhombic unit cell with a = 16,81 angstrom, b = 6,06 angstrom and c = 7,73 angstrom. The density is 0,96 g/cm3 with two chains in the cell (8 monomeric units), the space group is C222(1). Disorder, corresponding to the statistical presence of right- and left-handed helices in each site of the lattice, could be present. The space group for the completely disordered structure is Cmcm
Gas sorption and transport in syndiotactic polystyrene with nanoporous crystalline phase.
No full textIn this contribution we analyze sorption and transport of several gases in semicryst. syndiotactic polystyrene with nanoporous cryst. d form. Investigation was performed on amorphous samples and on samples characterized by different degrees of crystallinity. Sorption isotherms of carbon dioxide, nitrogen and oxygen in the cryst. phase have been detd. starting from exptl. results obtained for semicryst. and amorphous samples. Corresponding isosteric heats of sorption were evaluated for the cryst. and amorphous phase. Permeation tests were also performed to gather information on mass transport properties of semicryst. samples, evaluating av. diffusivities of carbon dioxide and oxygen, in the limit of small concns. as function of degree of crystallinity
Crystalline structures of intercalate molecular complexes of syndiotactic polystyrene with two fluorescent guests: 1,3,5-trimethyl-benzene and 1,4-dimethyl-naphthalene
No full textX-ray-diffraction, Conformational-analysis and Stereoregularity of A Crystalline Poly(3-methyl-1,3-pentadiene)
No full textX-ray diffraction patterns of unoriented samples of a recently synthesized highly crystalline poly(3-methyl-1,3-pentadiene) show the presence of two polymorphic forms. For one of these forms a fibre pattern is presented and the identity period of the chain is determined. To obtain information on the type of tacticity of the polymer, geometric and energy analyses and Fourier transform calculations on isolated chain models have been performed. It is suggested that the experimentally observed chain axis repeat value is more easily accounted for by a 1,4-cis-syndiotactic structure
Crystal-structure of Form III and the Polymorphism of Isotactic Poly(4-methylpentene-1)
No full textA preliminary model for the crystal structure of form III of isotactic poly(4-methylpentene-1) is suggested on the basis of structure factor calculations. Chains in 4(1) helical conformations are packed in a tetragonal unit cell with axes a = 19.38 angstrom and c = 6.98 angstrom; the space group is I4(1). The polymorphic behavior of poly(4-methylpentene-1) is discussed on the basis of conformational energy calculations on the isolated chain. The presence of different modifications is in accordance with energy minima present in the conformational energy map
Chain Conformation and Unit-cell In the Crystalline Phase of Syndiotactic Poly(4-methyl-1-pentene)
No full textA preliminary characterization of the crystalline structure of syndiotactic poly(4-methy-1-1-pentene) is presented. X-ray diffraction patterns of powder and fiber samples are reported. On the basis of X-ray diffraction data as well as conformational energy calculations, a helical chain conformation with a sequence of dihedral angles of the kind almost-equal-to (TTGG)n having symmetry s(12/7)2 and chain repetition c = 46.91 angstrom is suggested. A tetragonal unit cell with axis a = 18.03 angstrom is proposed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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