1,721,283 research outputs found
Conformational equilibria and transport processes of chlorinated compounds into different crystalline forms of yndiotactic polystyrene
No full textSpectroscopic investigation of host-guest interactions into clathrate phases of syndiotactic polystyrene containing chlorinated compounds
No full textInfluenza della struttura indotta dalla orientazione in flusso di polimeri cristallizzabili sulle proprietà di trasporto di sostanze a basso peso molecolare.
No full textClathrate phase in syndiotactic polystyrene gels
No full textGels and semicrystalline clathrate samples formed by syndiotactic polystyrene (sPS) with 1,2-dichloroethane (DCE) and 1-chloropropane (CP) have been investigated, for the entire composition range from pure solvent to pure polymer, by wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR). WAXD measurements show that, at least for gels with polymer concentration higher than 0.1 g/g, peaks typical of sPS/DCE and sPS/CP clathrate structures are present. FTIR
measurements show the occurrence of the same kind of formational selectivity for DCE (in favor of the trans conformer) and the absence of conformational selectivity for CP for both gel and clathrate samples. Moreover, the molar ratio between styrenic units and DCE in the crystalline phase of the gels, as evaluated from FTIR data, is nearly constant (3.6 ( 0.3) for the entire composition range; that is close to the 4/1 styrenic unit/guest molecule ratio, which has been observed for the clathrate crystal structure.
The whole set of results indicates that the polymer-rich phase forming the cross-link domains of these sPS gels is a crystalline clathrate phase. Both WAXD and FTIR measurements indicate that this clathrate crystalline phase, when present in the gels, would be characterized by coherent lengths being much higher
along the chain axes than perpendicular to them
Isothermal guest desorption from crystalline and amorphous phases of syndiotactic polystyrene
No full textMAKROMOL.CHEM.PHYS., MAKROMOL.SYMP
Guest desorption from crystalline and amorphous phases of syndiotactic polystyrene films
No full text
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
Evaluation of the amount and composition of the polymer-rich and polymer-poor phases of syndiotactic polystyrene gels with bynary solvent mixtures
No full textGels of syndiotactic polystyrene (sPS) in a binary mixture of 1,2-dichloroethane (DCE) and 1-chlorotetradecane (CTD) have been investigated by attenuated total reflectance-Fourier transform
infrared spectroscopy. Host-guest interactions into the clathrate phase induce not only the well-known selectivity in favor of the trans conformer but also a well-defined shift of the CH2 wagging mode of such conformer. Independent evaluations of the DCE content in the polymer-rich and polymer-poor phases,based on DCE conformer equilibrium and peak shift, give essentially identical results. As a consequence, an accurate evaluation of the amount and composition of the polymer-poor and polymer-rich phases of these gels from binary solvent mixtures can be achieved
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