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Two different kinds of uniplanar–axial orientations, exhibiting the polymer chain axis parallel to the main draw direction (cax)and the ac plane parallel or perpendicular with respect to the film plane (a∥caxand a⊥cax, respectively) have been achieved for several cocrystalline s-PS phases. The preparation procedures involve an unbalanced biaxial stretching, leading to mesomorphic trans-planar phases, followed by cocrystallization procedures induced by suitable guest molecules. In particular, cocrystalline films with a∥caxand a⊥caxorientations have been obtained by using more (e.g., carbon disulfide) and less volatile (e.g., 1,4-dimethylnaphthalene) guest molecules. These uniplanar–axial orientations can be maintained after guest removal procedures leading to the δ phase (i.e., the crystalline phase exhibiting nanoporous cavities), after thermal treatments, leading to the orthorhombic dense γ phase. These uniplanar–axial orientations after chloroform sorption–desorption procedures lead to a⊥caxand b⊥caxorientations of the orthorhombic nanoporous ε phase (i.e., the crystalline phase exhibiting channel-shaped porosity). High degrees of uniplanar–axial orientations can lead to a complete 3-D orientational order among the crystallites and as a consequence maximize the anisotropy of the physical properties. [ABSTRACT FROM AUTHOR]

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 aclayers (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 a?c?, a?c?and a?c?, i.e., by a nomenclature which also presents the advantage to be independent of the helical crystalline or co-crystalline s-PS phase. [ABSTRACT FROM AUTHOR]

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 CHCl 3lead 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. [ABSTRACT FROM AUTHOR]

The reorientational dynamics of benzene-d6molecules hosted into the cavity of a cavitand-based, self-assembled capsule was investigated by Molecular Dynamics (MD) simulations and temperature-dependent solid-state 2H NMR spectroscopy. MD simulations were preliminarily performed to assess the motional models of the guest molecules inside the capsules. An in-plane fast reorientation of the benzene guest around the C6symmetry axis (B1 motion), characterized by correlation times of the order of picoseconds, was predicted with an activation barrier (∼8 kJ/mol) very similar to that found for neat benzene in the liquid state. An out-of-plane reorientation corresponding to a nutation of the C6symmetry axis in a cone angle of 39° (B2 motion, 373 K) with an activation barrier (∼39 kJ/mol) definitely larger than that of liquid benzene was also anticipated. In the temperature range 293−373 K correlation times of the order of a nanosecond have been calculated and a transition from fast to slow regime in the 2H NMR scale has been predicted between 293 and 173 K. 2H NMR spectroscopic analysis, carried out in the temperature range 173−373 K on the solid capsules containing the perdeuterated guest (two benzene molecules/capsule), confirmed the occurrence of the B1 and B2 motions found in slow exchange in the 2H NMR time scale. Line shape simulation of the 2H NMR spectral lines permitted defining a cone angle value of 39° at 373 K and 35° at 173 K for the nutation axis. The T1values measured for the 2H nuclei of the encapsulated aromatic guest gave correlation times and energetic barrier for the in-plane motion B1 in fine agreement with theoretical calculation. The experimental correlation time for B2 as well as the corresponding energetic barrier are in the same range found for B1. A molecular mechanism for the encapsulated guest accounting for the B1 and B2 motions was also provided. [ABSTRACT FROM AUTHOR]

The paper compares X-ray diffraction patterns of δ-clathrates of s-PS with a large number of guests, having molecular volume in the range 0.058−0.195 nm3, mainly focusing on the distance between the aclayers of enantiomorphous polymer helices (d010), as precisely evaluated by measurements on films exhibiting the a∥c∥uniplanar orientation. The reported data and the crystal structure determination of the δ-clathrates with dinitrobenzene and dibenzofuran allow concluding that beside the already known large number of δ-clathrates of s-PS with monoclinic unit cells there is also a large number δ-clathrates of s-PS with triclinic unit cells. In particular, monoclinic or triclinic δ-clathrates are generally obtained with guests whose molecular volume is lower or higher with respect to the cavity of the δ nanoporous crystalline form (≈ 0.125 nm3). Small guests are easily accommodated in the cavities of the δ phase, thus maintaining its monoclinic unit cell and P21/asymmetry. Bulky guests, on the contrary, can be accommodated by substantial changes of the structural organization of the starting δ nanoporous form, leading to the occupation of only half of the cavities initially present while the other half is lost. This new kind of structural organization of the triclinic δ clathrates allows the inclusion of guest molecules definitely bigger than until now expected, although it halves the maximum guest/styrenic-unit molar ratio, which is reduced from the usual 1/4 to 1/8. [ABSTRACT FROM AUTHOR]

The full vibrational spectra of the γ, δ, and ε crystalline phases of syndiotactic polystyrene (sPS), i.e., phases presenting the s(2/1)2 helical conformation, have been experimentally determined and compared with that calculated at the B3LYP/6-31G(d,p) level of theory for an infinite helix. The assignment of the different modes was highly facilitated and validated by the experimental evaluation of the direction of the transition moment vector of most IR peaks, which was made possible for the first time by measurements on sPS films with different uniplanar orientations of the crystalline phase. The normal vibration analysis of most representative modes of the periodic model allowed for a general description of each one to be obtained, which was further confirmed by the direct inspection of mode animations. [ABSTRACT FROM AUTHOR]

The full vibrational spectra of and crystalline phases of syndiotactic polystyrene (sPS), that is, phases presenting the trans-planar conformation, have been experimentally determined and compared with that calculated at the B3LYP/6-31G(d,p) level of theory for an infinite trans-planar chain. The normal vibrational analysis of most representative modes of the periodic model allowed us to give a general description of each one, which was further confirmed by the direct inspection of mode animations. An assignment of the different modes was performed in terms of frequency, relative intensity, and direction of the transition-moment vector of the observed IR peaks as well as Raman vibrational frequencies. [ABSTRACT FROM AUTHOR]