²H NMR Study of Aromatic Guest Dynamics in Clathrate Phases of Syndiotactic Polystyrene

Abstract

Summary: 2H NMR solid‐state spectra of aromatic molecules (benzene, toluene, chlorobenzene, naphthalene) included in clathrate phases of syndiotactic polystyrene (s‐PS) or absorbed in the amorphous phase of s‐PS, have been recorded and analyzed for a broad range of temperature (230–360 K). The dynamic processes accessible to aromatic molecules absorbed in s‐PS clathrate phases are essentially temperature independent for the whole temperature range under investigation. Moreover, the molecular re‐orientations reflected in the NMR line‐shapes are similar to those accessible to the same molecules when absorbed in polystyrene amorphous phase at temperatures substantially lower than the polymer glass transition temperature. A simulation procedure for 2H NMR line‐shape analysis has been used to establish models for the dynamic processes of the different aromatic guest molecules.Solid‐state 2H NMR spectrum of naphtalene‐d8 in the amorphous phase of a semi‐crystalline s‐PS film (A), in the s‐PS clathrate phase (B) and the simulated spectrum for a static CD bond (C).magnified imageSolid‐state 2H NMR spectrum of naphtalene‐d8 in the amorphous phase of a semi‐crystalline s‐PS film (A), in the s‐PS clathrate phase (B) and the simulated spectrum for a static CD bond (C).

Understanding at molecular level of nanoporous and co-crystalline materials based on syndiotactic polystyrene

“…Particularly informative are solid state 2 H NMR spectra of deuterated molecules being guest of cocrystalline s-PS phases [94,96], which have been compared (over a broad temperature range, 233-333 K) to the spectra of the same molecules absorbed in the amorphous s-PS phase. Motional models, suggested also on the basis of 2 H NMR line-shape simulation procedures, indicate a generally more restricted mobility for the considered aromatic molecules in the co-crystalline phases as opposed to the amorphous phase.…”

“…Also the spectra of chlorobenzene-d 5 guest molecules can be described in terms of superposition of two Pake patterns indicating that about 10% of the rings undergo an ill-defined 180°flip motions about the C-Cl axis [96]. The spectra of naphthalene-d 8 guest molecules present a static Pake pattern with a splitting of 142 Hz, indicating the absence of motion of the naphthalene guest molecule, at least on a time scale for which the NMR line-shape is sensitive (s << 10 ls) [96].…”

“…Mobility of guest molecules confined in the crystalline cavity and resultant effects on the reorientational dynamics of the guests have been investigated in detail by means of different experimental [94][95][96] and molecular modeling techniques [83,[97][98][99].…”

“…The spectra of toluene-d 8 guest molecules can be described in terms of superposition of two Pake patterns indicating that the motion of the toluene guest molecule is restricted to rotation of the methyl group about its C 3 symmetry axis [94,96]. Also the spectra of chlorobenzene-d 5 guest molecules can be described in terms of superposition of two Pake patterns indicating that about 10% of the rings undergo an ill-defined 180°flip motions about the C-Cl axis [96]. The spectra of naphthalene-d 8 guest molecules present a static Pake pattern with a splitting of 142 Hz, indicating the absence of motion of the naphthalene guest molecule, at least on a time scale for which the NMR line-shape is sensitive (s << 10 ls) [96].…”

Polymer co-crystalline films for photonics

“…Unlike all the traditional procedures that lead to the formation of amorphous phases which display optoelectronic properties and are characterized by a disordered distribution of the photoactive groups, chromophore guest molecules of sPS cocrystals, although with some mobility with respect their minimum energy positions [17,18], present well defined threedimensional order with respect to the crystalline axes [3]- [6]. Moreover, since depending on their preparation procedure sPS co-crystals can assume different kinds of uniplanar orientation [19]- [21], it is possible to control the orientation of the guest molecules not only in the microscopic crystalline phase but also in macroscopic films.…”