Detection and memory of nonracemic molecules by a racemic host polymer film
ABSTRACT Robust syndiotactic polystyrene films, presenting a suitable nanoporous host crystalline phase, are able to transfer, amplify, and memorize the chirality of nonracemic low-molecular-mass molecules. In fact, after temporary exposure to volatile nonracemic guests, the polymer films present intense induced circular dichroism (ICD) phenomena. These ICD phenomena are associated with the temporary formation of polymer/guest cocrystalline phases.
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ABSTRACT: Thermal transitions of the three crystalline phases (γ, δ, and) of syndiotactic polystyrene (s-PS), presenting s(2/1)2 helices, have been compared by X-ray diffraction, differential scanning calorimetry (DSC), and dynamic-mechanical analyses. These analyses have been conducted on crystalline (δ and) films, obtained by similar solvent sorption and desorption procedures, starting from a same γ-form film. The Fourier transform Infrared (FTIR) spectra of the three films have also been compared. The obtained results indicate that the recently discovered -phase, as the already known δ-phase, is transformed in γ-phase by heating above 100 °C. However, the f γ transition occurs directly without the formation, for intermediate temperatures, of a helical mesomorphic phase, as instead observed for the δ f γ transition. DSC studies and FTIR measurements also suggest that the crystalline packing of the -form could be rather similar to that one of the γ-form.Macromolecules 12/2007; 40(26). DOI:10.1021/ma071640q · 5.93 Impact Factor
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ABSTRACT: Guest-induced transitions from α and γ phases of syndiotactic polystyrene (s-PS) toward cocrystalline and nanoporous phases, and related guest-induced orientation phenomena, have been investigated by X-ray diffraction. Guests, being able to induce cocrystal formation in amorphous s-PS samples, are able to induce room-temperature cocrystal formation from γ and α form films, only if their vapor pressure is higher than 20 and 60 Torr, respectively. Guest-induced recrystallizations of unoriented γ form films generally lead to unoriented cocrystalline and δ form films, while chloroform-induced recrystallization leads to cocrystalline and ε form films with perpendicular orientation of chain axes. On the other hand, guest-induced recrystallizations of unoriented α form films generally lead to oriented cocrystalline and derived δ form films. In particular, recrystallizations of unoriented α form films by room-temperature sorption of trichloroethylene and CHCl3 lead to films with (002) uniplanar and (2̅10) uniplanar orientations, i.e., with chain axes perpendicular and parallel to the film plane, respectively. The new procedures to prepare nanoporous films with different uniplanar orientations present substantial advantages with respect to the procedures already described in the literature.Macromolecules 04/2008; 41(7). DOI:10.1021/ma7026275 · 5.93 Impact Factor
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ABSTRACT: Thorough analyses of X-ray diffraction patterns of syndiotactic polystyrene (s-PS) films, exhibiting different crystalline and co-crystalline phases, and related evaluations of degrees of orientation have allowed to give a more accurate as well as simpler description of the three known uniplanar orientations. This new description involves the three simplest orientations of the high density ac layers (i.e. of the layers of close-packed alternated enantiomorphous s-PS helices) with respect to the film plane. On this basis it is proposed that the three uniplanar orientations should be named ac, ac and ac, i.e., by a nomenclature which also presents the advantage to be independent of the helical crystalline or co-crystalline s-PS phase.Macromolecules 10/2008; 41(22). DOI:10.1021/ma801180b · 5.93 Impact Factor